Variation within and between birds in corticosterone responses of great tits (Parus major)

The present study investigated inter- and intraindividual variation of the stress response (in terms of plasma levels of corticosterone) to handling in birds. Individual captive great tits (Parus major) were exposed to a standardised capture and handling protocol three times at about 2-week intervals. Mean plasma corticosterone levels were low (<5 ng/ml) when the birds were first sampled and increased in all birds 10 min after handling (mean levels on each sampling occasion 14 to 22 ng/ml). Levels in some birds then continued to increase, whereas in other birds levels remained relatively constant or had declined 30 min after handling began. Corticosterone responses were measured three times in each bird so that variation in plasma corticosterone levels could be defined. The area under the corticosterone response curve was defined as the integrated corticosterone response and was calculated for each response curve. Variation between birds was quantified by comparing mean values of corticosterone levels and integrated corticosterone responses between birds, then calculating a coefficient of variation for the mean of the individual bird means for each corticosterone parameter. Variation within birds was quantified by calculating the mean of the coefficients of variation for each bird for each corticosterone parameter. Variation in corticosterone levels in the first blood samples at 0 min (coefficient of variation (CV) 84.0%) was greater than variation in peak levels at 10 min (CV 35.1%) and in integrated corticosterone responses (CV 31.9%), indicating that corticosterone responses were more consistent between birds than were basal corticosterone levels. This study has demonstrated that corticosterone responses to a stressor tend to be repeatable in individual great tits, and has provided a method for quantifying variation in corticosterone responses for comparison with other birds in the future.

Sight of a predator can stimulate a corticosterone response in the great tit (Parus major)

The corticosterone response to the sight of a natural predator was investigated in free-living and captive great tits (Parus major). Free-living great tits responded to the sight of a stuffed, slowly moving Tengmalm's owl, a major predator of great tits, with warning calls and a change in behaviour around a feeder. Great tits returned to the feeder within a few minutes and began to approach the owl, and there was no increase in plasma corticosterone levels in birds sampled 30-50 min after they first saw the owl. Captive great tits in an aviary were exposed for 30 min to a stuffed Tengmalm's owl, to a stuffed brambling, and to a cardboard box. All three stimulus objects were slowly rotated during the exposure period. Great tits exposed to the owl changed their behaviour immediately, and spent most of the time when the owl was visible flying around the aviary and hanging from the roof, with very few visits to a feeder. Great tits exposed to the brambling and to the moving box also changed their behaviour and made fewer visits to the feeder. The great tits responded to the sight of the owl with a marked increase in plasma corticosterone levels, whereas there was no change in corticosterone levels (mean levels < 11 ng/ml) in birds exposed to the brambling or to the moving box. Mean corticosterone levels were high (37.1 +/- 4.9 ng/ml) 0.5 h after exposure to the owl, remained high (38.9 +/- 6.0 ng/ml) 1 h after exposure, and had returned to basal (5.3 plus minus 1.3 ng/ml) 3 h after exposure to the owl. This is the first demonstration for any bird of a complete corticosterone response to a predator. The sight of a predator initiated a corticosterone response in great tits that could not move more than 3 m away, whereas free-living great tits that could choose how far to fly away from the predator either did not initiate a corticosterone response, or had a small corticosterone response in which corticosterone levels were not significantly different from basal 30-50 min later. The results indicate that the initiation of a corticosterone response in birds depends on whether or not a bird perceives that a stimulus is a threat. Furthermore, they illustrate the importance of not making generalised conclusions based on laboratory experiments.

The effects of testosterone on a viral infection in greenfinches (Carduelis chloris): an experimental test of the immunocompetence-handicap hypothesis

The immunocompetence-handicap hypothesis suggests that the honesty of quality signals could be guaranteed if testosterone (T) suppresses immune function while enhancing male ornaments. In addition, it has been proposed that the cost of enhancing ornaments should be highest for males with small ornaments. Recently, the assertion that T causes obligate immunosuppression has been questioned. In this study, we tested whether elevated T levels would increase susceptibility to a viral infection, and whether this hypothesized effect would be most pronounced in males with small ornaments. We surgically inserted T implants into 15 male greenfinches (Carduelis chloris) and control implants into a further 15 males. All birds were then infected with a naturally occurring virus (Sindbis virus, Alphavirus genus), and each bird's daily viraemia (blood virus concentration) was measured for seven days. The specific antibody response was measured for eight weeks. T-implanted males did not exhibit increased viraemia or decreased antibody response, and males with small and large ornaments did not respond differently to T implantation. We did, however, find that T implantation decreased viraemia early in the course of the infection and increased viraemia late in the infection. Thus, our results demonstrate that T may act both to increase and to decrease viraemia.

Testosterone, ticks and travels: a test of the immunocompetence-handicap hypothesis in free-ranging male sand lizards

The immunocompetence-handicap hypothesis suggests that androgen-dependent male characters constitute honest signals of mate and/or rival quality because of the imposed costs through immune suppression associated with elevated testosterone levels. We demonstrate in a field experiment that male sand lizards (Lacerta agilis) exposed to elevated testosterone suffered from increased mass loss and tick load compared to control males. Although the first of these two results could be due to an elevated basal metabolic rate from increased plasma testosterone levels, the increased parasite load was statistically independent of the loss in body condition and is likely to be due to compromised immune function. Testosterone-treated males showed greater mobility than control males, and greater mobility resulted in higher mating success. Our experiment thus lends support to the immunocompetence-handicap hypothesis, suggesting that male testosterone levels have been moderated by balancing selection for reproductive success and sustained immune function.

Distribution of aromatase activity in the brain and peripheral tissues of passerine and nonpasserine avian species

Many behavioral effects of testosterone on hypothalamic and limbic brain areas are mediated by the action, at the cellular level, of estrogens derived from local testosterone aromatization. Aromatase activity and cells containing the aromatase protein and mRNA have accordingly been identified in the brain areas involved in the control of behavior. The presence of an unusually high level of aromatase activity has been detected in the telencephalon of one songbird species, the zebra finch (Taeniopygia guttata), and it is suspected that this high telencephalic aromatase may be a specific feature of songbirds but this idea is supported only by few experimental data. The distribution of aromatase activity in the brain of zebra finches and of one nonsongbird species, the Japanese quail (Coturnix japonica), was compared with the distribution of aromatase activity in the brain of four species of free-living European songbirds, the chaffinch (Fringilla coelebs, Fringillidae), willow warbler (Phylloscopus trochilus, Sylviidae), great tit (Parus major, Paridae), and pied flycatcher (Ficedula hypoleuca, Muscicapidae). High levels of enzyme activity were observed in the diencephalon of all species. The high levels of aromatase activity that had been observed in the zebra finch telencephalon and were thought to be typical of songbirds were also present in the four wild oscine species but not in quail. None of these songbird species had, however, a telencephalic aromatase activity as high as that in the zebra finch, which may represent an extreme as far as the activity of this enzyme in the telencephalon is concerned. Measurable levels of aromatase activity were also detected in all songbird species in the liver and in the three other brain areas that were assayed, the optic lobes, cerebellum, and brain stem, with the exception of the cerebellum in willow warblers and quail, but no detectable activity was observed in the testes, muscle, and adrenals of all species. Additional studies will be needed to identify the functional significance of estrogen synthesis in areas that are not classically known to be implicated in the control of reproduction. Within a given species, the birds that had the highest plasma testosterone levels also displayed the highest levels of diencephalic aromatase activity and the interspecies differences in the two variables were positively related. This raises the possibility that the absolute level of diencephalic aromatase represents a species-specific characteristic under the control of plasma testosterone levels. There was, in contrast, no correlation between the aromatase activity in the telencephalon and the plasma testosterone levels but the enzyme activity was correlated with the plasma levels of luteinizing hormone. These data bring additional support to the idea that the diencephalic and telencephalic aromatases are controlled by independent mechanisms.

Effect of season and photoperiod on FSH in male great tits

The present study investigated (1) the photoperiodic threshold for an increase in FSH and LH secretion in male great tits (Parus major) from south Sweden and (2) seasonal changes in FSH secretion patterns in short day (SD; 8 L:16 D) and long day (LD; 20 L:4 D) exposed great tits. When fully photosensitive great tits were exposed to a simulated vernal increase in day lengths plasma levels of FSH started to rise at a shorter day length (10.5 h) than did LH (11 h). Once the photoperiodic threshold was exceeded FSH levels increased slowly, but continuously, and reached maximum levels when day lengths had reached 13-14 h, whereas LH levels rose to maximum levels more or less immediately. Great tits break photorefractoriness in September. Exposing sham-operated and castrated great tits to SD or LD in October and February resulted in clear seasonal differences in their FSH cycles. At both times the great tits responded to castration and exposure to long days. However, castration and photoperiodic FSH responses were not only more rapid in February, but also of a higher magnitude.

Territorial behaviour and hormones of pied flycatchers in optimal and suboptimal habitats

Since pied flycatchers, Ficedula hypoleuca, breed at higher densities in deciduous forests than in coniferous forests, competition for territories is likely to be greater in the former, optimal habitat. I tested the hypotheses that males in a deciduous forest defend their newly established territories more intensely and have higher plasma levels of testosterone than males in a suboptimal coniferous forest. In the deciduous forest, breeding density was higher, egg laying started earlier and more fledglings were produced. Morphological characters such as wing length, plumage colour and the size of the white forehead patch did not differ consistently between males establishing territories in deciduous and coniferous forests. Before the nest-building period, males in the deciduous forest were heavier, and had significantly larger furcula fat depots. I tested territorial aggressiveness by exposing unmated territorial males to simulated territorial intrusions. A significantly higher proportion of territorial males in the deciduous forest physically attacked the intruder; those that did attack also attacked more frequently than did males in the coniferous forest. Furthermore, males in the deciduous forest stayed closer to the decoy, and were more restless during the simulated territorial intrusion. Males in the deciduous forest had higher plasma levels of testosterone and corticosterone than did males in the coniferous forest, but there was no difference in dihydrotestosterone levels. These hormonal differences are most likely to be the result of a higher intrusion rate and a higher population density in the deciduous forest. I conclude that prior ownership is a crucial factor in maintaining a territory, and that differences in aggressive motivation between unmated males in the deciduous and coniferous forests reflect the value of the nestboxes defended. The high testosterone levels observed in males from the deciduous forest are likely to be the physiological factor increasing their aggressive motivation and persistency. Copyright 1998 The Association for the Study of Animal Behaviour.

Neuroanatomical distribution and variations across the reproductive cycle of aromatase activity and aromatase-immunoreactive cells in the pied flycatcher (Ficedula hypoleuca)

The anatomical distribution and seasonal variations in aromatase activity and in the number of aromatase-immunoreactive cells were studied in the brain of free-living male pied flycatchers (Ficedula hypoleuca). A high aromatase activity was detected in the telencephalon and diencephalon but low to negligible levels were present in the optic lobes, cerebellum, and brain stem. In the diencephalon, most aromatase-immunoreactive cells were confined to three nuclei implicated in the control of reproductive behaviors: the medial preoptic nucleus, the nucleus of the stria terminalis, and the ventromedial nucleus of the hypothalamus. In the telencephalon, the immunopositive cells were clustered in the medial part of the neostriatum and in the hippocampus as previously described in another songbird species, the zebra finch. No immunoreactive cells could be observed in the song control nuclei. A marked drop in aromatase activity was detected in the anterior and posterior diencephalon in the early summer when the behavior of the birds had switched from defending a territory to helping the female in feeding the nestlings. This enzymatic change is presumably controlled by the drop in plasma testosterone levels observed at that stage of the reproductive cycle. No change in enzyme activity, however, was seen at that time in other brain areas. The number of aromatase-immunoreactive cells also decreased at that time in the caudal part of the medial preoptic nucleus but not in the ventromedial nucleus of the hypothalamus (an increase was even observed), suggesting that differential mechanisms control the enzyme concentration and enzyme activity in the hypothalamus. Taken together, these data suggest that changes in diencephalic aromatase activity contribute to the control of seasonal variations in reproductive behavior of male pied flycatchers but the role of the telencephalic aromatase in the control of behavior remains unclear at present.

Behavioural and hormonal responses of the pied flycatcher to environmental stressors

I investigated the effects of high plasma levels of corticosterone in male pied flycatchers, Ficedula hypoleuca, during the period of territorial establishment and the nestling period. In a second experiment males were exposed to a territorial intruder, a great spotted woodpecker model and a weasel model during the nest-building and nestling periods and their behavioural and hormonal reactions studied. Males were also exposed to handling stress (hormonal study) during these periods. During the period of territorial establishment, corticosterone-treated males, as well as control males, abandoned the territory in which they were captured; however, males in both groups very soon established new territories. During the nestling period, corticosterone-treated males, but not control males, abandoned their nests. During the nest-building period, intact males frequently attacked the territorial intruder but corticosterone-treated males never did; the woodpecker was only rarely attacked by intact males, and the weasel never. During the nestling period, the weasel was not attacked and territorial intruders only rarely; but woodpeckers were frequently attacked. With the progress of the breeding season, male flycatchers significantly reduced their sensitivity, in terms of the adrenocortical response, to all stressors tested. During the nest-building period, corticosterone levels were significantly higher in males exposed to handling, a weasel and a territorial intruder than in unmanipulated males; corticosterone levels in males exposed to a woodpecker did not differ from those in unmanipulated males; and testosterone levels were significantly elevated in males exposed to a woodpecker and to an intruder, but were reduced in males exposed to a weasel. Handling did not affect the testosterone level. During the nestling period, all groups showed low testosterone levels, and only exposure to a weasel and to handling increased corticosterone levels significantly. The results indicate that environmentally induced changes in testosterone and corticosterone secretion can be affected independently from one another, and that there are ecological bases for the differentiated hormonal responses to stress. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Seasonal changes in follicle-stimulating hormone in free-living great tits

We describe the annual cycle in plasma levels of FSH in free-living male and female great tits from southwest Sweden. Both juvenile (here defined as first-time breeders or birds <1 year old) and adult great tits, of both sexes, showed clear annual cycles with three periods of elevated FSH levels: period from territorial establishment till end of breeding (mid-March to June), October (a time when the birds break photorefractoriness), and winter (January-February). Significant differences between ages and between sexes occurred only during March and April (period of territorial establishment and gonadal recrudescens). Male FSH levels increased significantly as early as between early February and early March. Levels continued to increase until mid-April when maximal values had been reached in paired males. Territorial, but unpaired, males had significantly lower plasma levels of FSH in mid-April than did territorial and paired males. After this, FSH levels did not change until levels had decreased to basal in early July. On average, females did not show a vernal increase in FSH levels until early/mid April. However, just as in males, female FSH levels were dependent upon whether she was paired or unpaired. Females having a mate in mid-April had significantly higher FSH levels than did single females. Contrary to the males, females showed a transitory FSH peak during egg-laying. Females showed no differences between other breeding stages, until basal levels were reached during incubation of the second clutch in July. Adult birds (of both sexes) had significantly higher plasma levels of FSH than juvenile birds of the same sex during the period March-April. Furthermore, during this period adult males continually had higher FSH levels than did adult females, and juvenile males continually had higher levels than did juvenile females. In all groups a second period of elevated FSH levels occurred during early October, a time when the great tits break photorefractoriness. All groups showed basal levels during November and December. By January all four groups had increased their circulating levels of FSH to moderately high. This elevated level was maintained during February and was at the same level as that observed in October.

Natural and photoperiodically induced changes in plasma prolactin levels in male great tits

Plasma levels of prolactin showed a pronounced annual cycle in free-living male great tits (Parus major). During the period from August to April, levels were very low. Prolactin levels started to increase in mid-April, and maximal levels were reached in June. By mid-July prolactin levels had decreased to near basal levels. The exact breeding stage was known for all males captured during the breeding period, and prolactin levels increased continuously from the period of territorial defense to the nestling period. Males were exposed to different light regimes at three different times of the year (late August, late November, and early March). Males exposed to 14L:10D (14 h light:10 h darkness) and 20L:4D showed pronounced prolactin cycles at all times of the year, but the patterns differed markedly with the season. In November the 20L:4D and the 14L:10D prolactin patterns differed markedly from each other. In the 20L:4D group prolactin levels started to increase before testes had reached maximal size, whereas in the 14L:10D group prolactin levels did not start to increase until testes were almost completely regressed. In early March the prolactin pattern of change over time was the same for great tits kept on 20L:4D and 14L:10D. In both cases prolactin levels increased during the testicular growth period, and prolactin levels were maximal during the period of spermatogenesis. Prolactin levels did not change over time in males kept on 8L:16D in August and November. Males exposed to short days in early March showed a significant increase in prolactin levels about 3 weeks after the onset of the experiment. Plasma levels of prolactin in males castrated in late November and exposed to a 20L:4D light regime did not differ from those in intact males. In castrated males given a testosterone implant prolactin levels immediately increased to significantly higher levels than those observed in intact or castrated males. Prolactin levels remained significantly higher in the testosterone implanted males for about a month. In one group of castrated birds the testosterone implant was removed 13 days after the onset of the experiment. This removal resulted in a significant decrease in circulating levels of prolactin.

Thyroid hormones in nestling great tits (Parus major)

Plasma concentrations of thyroid hormones (T4 and T3) were examined in nestlings of the altricial great tit (Parus major), from hatching to when young birds left the nest at 16 days of age. T4 levels were approximately 1-2 ng/ml during the first 2 days after hatching and increased to reach maximal levels (9-10 ng/ml) 12 days after hatching, a time at which nestlings reach maximum body weight. Both sexes showed the same pattern. T3 levels showed a quite different pattern. Levels were at all times low (1-3 ng/ml). Both sexes showed a transitory, but significant, increase in circulating levels of T3 during the early nestling period.

The development of the hypothalamic-pituitary-gonadal axis in juvenile great tits

The development of the hypolamic-pituitary-gonadal axis in free-living nestling great tits (Parus major) was studied from the day of hatching until about 40 days of age. The hypothalamic content of GnRH was low during the entire nestling period, although a significant increase was noted between 6 and 9 days of age. Thereafter there was no further increase. The pituitary content of LH was low in 1- to 6-day-old nestlings, but increased significantly at 9 days of age; this increase was only temporary, and levels decreased in 12-day-old nestlings. Injections of chicken GnRH increased plasma levels of LH in newly hatched great tits. The high plasma levels of LH in newly hatched great tits of both sexes decreased to basal by 9 days of age. Circulating levels of testosterone and estradiol showed more or less the same pattern as LH. Both steroids showed very high levels in newly hatched birds of both sexes. Testosterone levels were down to basal in 3-day-old nestlings, and estradiol levels were basal in 2-day-old nestlings. The only sex difference was observed in 1- and 2-day-old nestlings. During this period males had significantly higher plasma levels of testosterone than females. Gonads showed a more or less linear growth during the entire nestling period, and did not increase further after fledging. Histological and ultrastructural examinations of the testis showed that mature Leydig cells appeared for the first time in 6-day-old birds and become common in 9-day-old nestlings. The development of the seminiferous tubules, the interstitial tissue, and the tunica albuginea reached a "plateau" when the nestlings had reached an age of 9 days. At no age had the germinal epithelium developed beyond the stage of spermatogonia. GnRH treatment did not change male testosterone or female estradiol levels until the nestlings were 9 days of age. The response decreased in older nestlings. Castration of 9-day-old male nestlings showed that neither was there a negative feedback of testosterone on LH in older nestlings.

Influence of the opposite sex on photoperiodically induced LH and gonadal cycles in willow tit (Parus montanus)

In early January photosensitive willow tits (Parus montanus) were transferred from natural to long days (20L;4D). The study included three groups of birds: one group consisted of pairs (one male and one female kept together in a cage), a second group consisted of males, and a third group included only females. Birds from the separate groups could neither see nor hear each other. Gonadal and LH cycles were followed over a 2-month period. The reproductive systems of male and female willow tits were activated by the long day exposure. This response was, however, affected by the presence/absence of a mate. Ovarian follicles in females caged together with a male grew faster than did follicles in females kept alone in their cages. Ovarian regression started at the same time in both female groups. Contrary to females, gonads in males caged together with females grew slower and also regressed much earlier than did tests in males kept alone. LH cycles differed only slightly between the two groups of females. In both groups maximum LH levels were reached already after 3 days of long day exposure. Maximum LH level was attained earlier in paired males (Day 3) than in single male (Day 7). Males without female company however maintained high plasma levels of LH for a much longer period of time (about 4-5 weeks) than did paired males. The observed differences are discussed in relation to the ecology of the willow tit.

Low temperatures affect the photoperiodically induced LH and testicular cycles differently in closely related species of tits (Parus spp.)

Photosensitive great tits (Parus major) and willow tits (P. montanus) were exposed to long days (20L:4D) under three different temperature conditions (4+, +10, and +20 degrees C) in early winter. The two species showed significant differences in their LH and testicular reaction patterns to low temperatures. Testes showed pronounced growth cycles under all temperature regimes. For the willow tit, testes in birds kept at +20 degrees C reached maximum size about 2 weeks earlier than testes in birds living under the two lower temperature regimes, whereas in the great tit testes reached maximum size at about the same time in all three groups. Low temperatures delayed the onset of testicular regression in both species. Plasma levels of LH did change with time in both species. However, the patterns of the induced LH-cycles in the three great tit groups differed significantly from each other, whereas this was not the case for the willow tits. The LH cycle was especially pronounced in great tits kept at +20 degrees C. The initial LH peak in great tits kept at +4 and +10 degrees C was about 50% lower than in great tits kept at +20 degrees C. These results are discussed in relation to species differences in winter ecology and establishment of breeding territories.

Photoperiodic adaptation to breeding at different latitudes in great tits

The photoperiodic responses in testicular growth and plasma levels of LH in nonmigratory great tits from Tromsö, Norway (69 degrees 40'N), Göteborg, Sweden (57 degrees 42'N), and Milano, Italy (45 degrees 26'N) were compared under the same lighting conditions. Male great tits, collected during midwinter, were transferred to Göteborg, and shifted from an 8-hr day in early January to a lighting regime in which day length was increased by 1/2 hr per week for 16 weeks. Control birds (only from Sweden) were kept on a 8L:16D light regime during the entire study. Blood samples were collected weekly, and laparotomies were performed every other week. Initially testicular size (approximately 1.6 mm) and plasma levels of LH (approximately 0.45 ng/ml) were similar among the four groups. Between 4 and 8 weeks after the onset of the experiment testes gradually, but significantly, increased to about 2 mm in length in the control group. This slow growth was also observed in the experimental groups. The control bird testes did not increase in size any further. The onset of the rapid testicular growth phase differed among the three experimental groups. In great tits from Milano it began when day length exceeded 11 hr; in birds from Tromsö, when day length was greater than 12 hr; and in great tits from Göteborg, when day length was between 11 and 12 hr. Once the rapid gonadal growth phase had begun it took about 6 weeks for the testes to reach maximal size (approximately 6.8 mm) in all three populations.(ABSTRACT TRUNCATED AT 250 WORDS)

Territorial aggressiveness and its relation to the endocrine system in the pied flycatcher

Behavioral and endocrine responses were studied following simulated territorial intrusions performed at two different stages in the breeding cycle (pre-nest-building and nestling period) of the pied flycatcher (Ficedula hypoleuca). Only 45% of the unpaired territorial males from the pre-nest-building period defended their territories by attacking the decoy. After the experimental intrusion unpaired males attacking the decoy had significantly higher plasma testosterone levels than nonattacking unpaired males. Plasma corticosterone levels were significantly higher in both attacking and nonattacking unpaired males than in control males. There were no differences in body size between attacking and nonattacking males. The attacking paired males and paired control males, however, had significantly lower fat depots than other males. The endocrine system of the male pied flycatcher responded within 1 day to the settlement of a female in the territory in that plasma testosterone levels of paired control males were significantly higher than those in unpaired territorial control males. The proportions of attacking males increased significantly (up to 80%) once a female had settled. Unlike in unpaired territorial males, testosterone levels in paired males that attacked the decoy were similar to those in non-attacking males and to those in paired control males after a simulated territorial intrusion. Data suggest that the high testosterone levels are related to territorial aggressiveness and not to sexually related events such as mate-guarding or singing. Forty-five percent of the males from the nestling period did attack the decoy. Despite the strong behavioral response these attacks had no effects on plasma testosterone or corticosterone levels.(ABSTRACT TRUNCATED AT 250 WORDS)

The abnormal conduct of capercaillies Tetrao urogallus

The frequency, behavior, and testosterone levels of deviant capercaillies were studied in southern Finland. Roughly 1% of the population was estimated to behave abnormally. Deviant males display and show threatening behavior toward not only humans, but also attacked stuffed capercaillie males and without hesitation copulated with a stuffed female. Deviant females appear tame and crouch in front of humans, but avoid males. The testosterone level in deviant males was about five times higher than that of normal displaying males. The origin of this striking phenomenon is still unclear, although it must be connected with display. Two, though not mutually exclusive, proximate mechanisms for the development of this abnormal behavior are presented: anomalous sex hormone concentrations and incorrect sexual imprinting. The ultimate reason for the apparent increase in numbers of deviant capercaillies is probably logging which diminishes populations and, thereby, favors the spreading of abnormal behavior.

The ovarian cycle in the natterjack toad, Bufo calamita, and its relation to breeding behaviour

Abstract

The ovarian cycle in natterjack toads Bufo calamita from an island population with unpredictable breeding conditions was studied in an archipelago off the Swedish west coast. About 80% of the female population bred during spring and early summer, and the rest later in summer and early autumn. Time of breeding and female size (age) were not correlated. It was found that first growth phase (FGP) oocytes were recruited from oogonia mainly during early spring and late autumn, but that recruitment could occur at any time of the year. The FGP oocytes grew rapidly immediately after recruitment, and when transferred into second growth phase (SGP) oocytes. In between these two periods the FGP oocytes seemed to be in a resting stage. Females showed an asynchrony in ovarian developed. We found females with fully developed SGP oocytes, ready for ovulation, as well as females with ovaries in only an early vitellogenic growth phase at all times of the year. Females did not neccessarily ovulate as soon as the vitellogenic oocytes had reached full size. There were strong indications that some females only ovulated and laid a fraction of the egg mass in their first batch, and that they laid a second batch later in the season. This second batch was thought to originate from the same recruitment of oocytes as the first batch. There was a tendency for SGP oocytes to grow faster during summer than during spring. It was also concluded that SGP oocytes coulde be recruited all year around. Bimodal size frequency distribution patterns were found both among the FGP and the SGP oocytes; they were most pronounced among the latter, where they were found throughout the year.

Annual changes in plasma levels of LH, and prolactin in free-living female great tits (Parus major)

Plasma levels of LH and prolactin were measured in free-living female great tits throughout the year. Plasma concentrations of LH increased at the onset of winter (January), onset of spring (March), nest-building period, (for both the first and the second clutch), last part of the incubation period, (for both the first and the second clutch), and early autumn (August). Plasma prolactin increased between March and April. A further increase occurred during the nest-building period, which continued during the early part of the egg-laying period. Prolactin levels increased further once incubation had started. During nest-building and egg-laying of the second clutch, prolactin levels were low, but not basal. Prolactin levels increased again during incubation of the second clutch. Between July and March prolactin levels usually were below the limit of detection of the assay.

Behavioral, hormonal, and morphological responses of free-living male pied flycatchers to estradiol treatment of their mates

A field experiment was performed implanting female pied flycatchers (Ficedula hypoleuca) during the nest-building period with silastic tubes containing 17 beta-estradiol. Control females were given empty silastic tubes. The pied flycatcher is a polygamous and polyterritorial bird species. During two successive breeding seasons effects on reproductive behavior and the reproductive systems of males were studied. Reproductive success was not affected by the treatment. Estradiol treatment of females caused marked changes in the behavior of males, increasing aggressive and mate-guarding behavior. The results of the present study also support the idea that cuckoldry is a problem for the territory holder. Fewer males paired with estradiol-treated females established secondary territories, and significantly more of the polyterritorial males from the experimental population showed up in the home-territory when a simulated territorial intrusion was performed there. Control males were much more successful in getting a second female to breed. Spermatogenesis and hormonal cycles (DHT, LH, and testosterone) in males were not prolonged as a result of estradiol treatment of the females.

Biochemical characterization and seasonal changes in the concentration of testosterone-metabolizing enzymes in the European great tit (Parus major) brain

Homogenates of diencephala obtained from brains of European great tits (Parus major) were incubated in the presence of tritiated testosterone (T) as precursor, and four metabolites produced from this steroid were formally identified and quantified. Conversion into 5 beta-dihydrotestosterone (5 beta-DHT) constituted the major metabolic pathway of T. Smaller amounts of 5 alpha-dihydrotestosterone (5 alpha-DHT), 5 beta-androstane-3 alpha, 17 beta-diol (5 beta-DIOL), and estradiol (E2) were also produced. The metabolism of T was time-dependent, and it varied as a function of the initial precursor concentration. The kinetics of 5 beta- and 5 alpha-reductases, as well as aromatase, followed the Michaelis-Menten model. It was found that 5 beta-reductase has a low apparent affinity for T, but is present in large concentrations. In contrast, the apparent affinity for T and the concentration of aromatase were approximately 3.9 times higher and 130 times smaller, respectively, than those of 5 beta-reductase. Intermediate values were found for 5 alpha-reductase. The validated assay was used to measure seasonal changes in the in vitro metabolism of T in the anterior (AH) and posterior (PH) hypothalamus and the cerebellum (CER) of free-living juvenile and adult male great tits. The production of 5 beta-DHT was low during the winter period in the PH of adult males, whereas the 5 beta-DIOL production was low in both parts of the hypothalamus at this time of the year. During autumn the production of these metabolites showed a transitory decrease in both parts of the hypothalamus of the juveniles. The production of 5 beta-reduced metabolites by the CER was high at all times of the year. In juveniles, the CER production of 5 beta-DHT did not change seasonally, whereas 5 beta-DIOL production peaked during summer. In the CER of adults, maximum production of both metabolites occurred during summer. Generally, less T was converted into 5 beta-reduced metabolites by the PH than by either the AH or the CER. E2 production was observed only in the AH and PH. With one exception (summer; AH), E2 production was high in both parts of the hypothalamus of adults throughout the year. In both AH and PH of juveniles, E2 production was low during summer. In these birds, it increased between summer and autumn in both parts of the hypothalamus, and also between autumn and winter in the PH. The production of 5 alpha-DHT did not change as a function of the season, the age of the birds, or the brain region.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of environmental events immediately after birth on postnatal testosterone secretion and adult sexual behavior in the male rat

A rise in plasma testosterone (T) levels occurs in male rats during the first 2 hr after birth which is of importance for the process of sexual differentiation. To study the influence of environmental factors on the postnatal T surge and sexual development, newborn male rats were subjected to various treatments immediately after cesarean delivery including cooling, ether anesthesia, and mother-infant separation. In adulthood, the animals were observed for masculine and feminine sexual behavior. Males anesthetized at 0 hr showed elevated levels of feminine sexual behavior and impaired masculine sexual behavior. Pups subjected to cooling or mother-infant separation showed slightly prolonged intromission latencies, but otherwise normal levels of feminine sexual behavior. Significantly elevated plasma T levels were found in intact pups 2 hr after birth but not in pups subjected to cooling or ether anesthesia. Significantly higher levels of T were observed in pups subjected to cooling 4 hr after birth, suggesting a delay of the T surge. The most pronounced impairing effects were seen in the defeminization process, but the masculinization process also is affected by ether anesthesia. It was concluded that ether anesthesia immediately after birth may permanently interfere with the sexual development by suppressing the neonatal T surge.

Plasma prolactin concentrations in breeding pied flycatchers (Ficedula hypoleuca) with an experimentally prolonged brooding period

This experiment explored the stimulatory effect of brooding newly hatched young on plasma prolactin concentration in male and female pied flycatchers, Ficedula hypoleuca. By exchanging offspring between nestboxes, one group of parents was exposed to 1- to 3-day-old nestlings for 12 days. Females in this group continued night-time brooding during these 12 days. The females, but not the males (who do not participate in brooding nestlings), after 6 days had higher plasma prolactin concentrations than control birds which had shown a 50% reduction in night-time brooding at this stage. By Day 12, however, prolactin concentration had decreased to the same level as in control birds, even though these females were still brooding 3-day-old nestlings. Female flycatchers given 3-day-old nestlings on the day their own eggs hatched showed an earlier reduction in night-time brooding and an earlier decrease in plasma prolactin than did control birds. An early decrease in prolactin was also seen in the males of this experimental group.

Hormonal correlates of migration and territorial behavior in juvenile willow tits during autumn

This study compared plasma levels of dihydrotestosterone, testosterone, corticosterone, luteinizing hormone, growth hormone, and prolactin in migrating juvenile willow tits with those in territorial juveniles. Both categories of birds were caught in late September. Migrating juveniles had higher plasma levels of corticosterone than territorial juveniles. Only corticosterone secretion was affected by "handling stress" in both migrating and territorial juveniles. However, territorial birds showed a much stronger relationship between these two variables. It is suggested that high corticosterone levels are involved in the emigration of juveniles out of the coniferous forest. Only juveniles were found among the migrating willow tits, and these birds were not well adapted for migration. Migrating juvenile males had less fat stored than did territorial ones. Furthermore, migrating juvenile males had higher liver/somatic index and higher plasma levels of growth hormone than did territorial males. These results indicate that migrating males had been, or were, exposed to food restrictions. The same proportion of migrating and territorial juveniles, males as well as females, had high plasma levels of testosterone. We suggest that these high levels were caused by recent aggressive interactions. To test the hypothesis that high plasma levels of testosterone are important for a juvenile to become a member of a territorial winter group, we performed a field experiment in which juveniles were given testosterone implants (controls were given empty silastic tubes) at the beginning of the territorial establishment period. The same proportion of testosterone-implanted birds and control birds succeeded in becoming members of territorial winter groups. Thus, testosterone does not seem to play an essential role in autumn territoriality, and it does not prevent autumn migration.

Hormonal correlates of male attractiveness during mate selection in the mallard duck (Anas platyrhynchos)

The aims of the present study were (1) to examine if feeding condition prior to mating influences male hormone levels and behavior, (2) to evaluate the effect of age on male hormone levels, (3) to examine a possible association between male social display activity and four steroid hormones (testosterone, dihydrotestosterone, estrogen, and corticosterone), and (4) to examine if female behavior influences male hormone levels. Thirty male and fifteen female mallards were used in this study. Observations were made on a mixed flock of mallards for 10 consecutive days in autumn. Five weeks before the observations, males were randomly assigned to a feeding regime with either an unlimited food supply (UL group) or a limited food supply (L group). Males in the UL group showed significantly greater social display activity compared to the L group males. Females never incited (courted) males from the L group. Dihydrotestosterone levels were significantly higher in males showing social display activity as compared to males not showing these behavior patterns. Testosterone levels were significantly higher in males incited by females compared to males not incited by females.

Seasonal changes in body weight, fat depots, and plasma levels of thyroxine and growth hormone in free-living great tits (Parus major) and willow tits (P. montanus)

Annual changes in body weight, fat depots, and plasma levels of thyroxine (T4) and growth hormone (GH) were studied in free-living great tits and willow tits. Birds were collected during six ecologically well-defined periods of the year. Special attention was given to the nonreproductive part of the year. T4 showed simple unimodal cycles in both species and both sexes, with high levels during the warmer part of the year, and low levels during the winter and spring periods. Although increasing levels were temporarily separated between the two species, they were in both cases correlated with the onset of gonadal regression and moult. Plasma levels of GH fluctuated in a much more complex pattern, and no obvious and consistent correlation to any extrinsic or intrinsic factor was found. Body weights and fat depots both showed seasonal variations that varied slightly between the two species. Values, with the exception for breeding females, were generally the highest during the autumn, winter, and spring periods.

Effects of corticosterone on territorial behavior of free-living male song sparrows Melospiza melodia

A group of 10 territorial male song sparrows, Melospiza melodia, were given subcutaneous implants of corticosterone in Silastic tubing. A second group of 10 territorial males were given empty implants as controls. After 18-24 hr all males were then subjected to a simulated territorial intrusion (STI) by placing a caged male song sparrow in the center of the subject's territory, and playing tape recorded songs through a speaker placed alongside. Significantly fewer males with corticosterone implants responded to STI than to controls, and the latency to respond was longer. Of the 3 experimental males that did respond to STI, all had a lower frequency of songs and did not approach the simulated intruder as closely as controls. Many males were captured 2-7 days after implantation and blood samples collected for measurement of circulating hormone levels. As expected, plasma levels of corticosterone were high in the group given corticosterone implants. However, plasma levels of luteinizing hormone (LH) were not affected by treatment with corticosterone, and although circulating levels of testosterone were depressed slightly compared with controls, they were within the normal range for territorial and breeding males. There were no differences in body mass despite greatly increased fat depots in males treated with corticosterone. These data suggest that high levels of corticosterone, similar to those measured during stressful episodes both in the laboratory and field, may suppress territorial behavior independently of the adenohypophysial-gonad axis. Since plasma levels of LH and testosterone are not depressed markedly, thus maintaining the gonads in a near functional state, renesting can begin as soon as environmental conditions ameliorate. Such mechanisms could potentially increase the probability of raising viable young after unpredictable, severe weather resulted in failure of the previous breeding attempt.

Corticosterone-binding proteins and behavioral effects of high plasma levels of corticosterone during the breeding period in the pied flycatcher

In the pied flycatcher there exists an anomaly in the relationship between cortical histology and plasma levels of corticosterone during the breeding period. In an attempt to study this anomaly, binding capacity and binding affinity of plasma corticosterone-binding proteins (CBP) were studied in free-living pied flycatchers during the early and late parts of the breeding period. Binding capacity of CBP showed a significant decrease with the progress of the breeding season in both males and females. During the early parts of the breeding season binding capacity was significantly higher in males than in females. No difference between sexes was observed during the nestling period. In males there also was a seasonal decrease in the binding affinity of CBP. The results show that there is a good relationship between periods with high plasma levels of corticosterone and its binding capacity in the blood. A second study showed that an experimentally increased plasma level of corticosterone during the nestling period drastically reduced reproductive success. Parents given silastic implants containing corticosterone fed their nestlings less frequently and produced significantly fewer fledglings than did controls. Unlike the control birds, the body weight of the corticosterone-implanted birds did not decrease during the nestling period. Birds given corticosterone implants in which one small hole had been punched, in order to facilitate diffusion of corticosterone, all abandoned their territories and, consequently, these parents produced no fledglings. Thus, the results show that an elevation of plasma levels of corticosterone in adult pied flycatchers during the nestling period affects parental as well as territorial behavior.

Plasma levels of luteinizing hormone and steroid hormones in free-living winter groups of willow tits (Parus montanus)

Plasma levels of LH, DHT, testosterone, and corticosterone were measured for all members in free-living winter flocks of willow tits, Parus montanus. Hormonal data were related to (1) flock size and (2) age/sex differences. The winter flock defends a large winter territory and shows a well-established social hierarchy in which adults consistently dominate first-year birds. One winter group normally consists of four individuals, two adults and two juveniles. In flocks containing four or five members juvenile willow tits had significantly higher corticosterone values than adults. In small-sized groups, containing three members, all individuals had high plasma levels of corticosterone. No other effects of flock size was found. When data were treated on an age/sex basis, i.e., flock size was not considered, juvenile females were found to have significantly higher plasma levels of testosterone than adult birds, and also significantly higher levels of DHT than juvenile males and adult females. Also, juvenile willow tits had significantly higher plasma levels of corticosterone than adult birds.

The effects of modifying incubation on prolactin secretion in free-living pied flycatchers

Plasma prolactin concentrations in female pied flycatchers are high during incubation, but fall from 156 +/- 27 to 67 +/- 6 ng/ml (P less than 0.01) between 2 and 4 days after the young hatch. The timing of the fall in prolactin could be determined by factors associated with the hatching of the eggs and growth of the offspring; alternatively, prolactin may remain high for a fixed period (16 days) after the onset of incubation. To distinguish between these possibilities, eggs were exchanged between nest boxes to ensure incubation periods of either 10, 14, or 19 days by different females. The results showed that the period of high prolactin secretion was shortened by 2-4 days where the eggs hatched early, but, conversely, was not lengthened in those females with extended incubation periods, the levels actually falling in these birds before the eggs hatched. There was, however, a secondary rise in prolactin 3 days after hatching, when the level of 114 +/- 11 ng/ml 22 days after the onset of incubation was much higher than that (30 +/- 4 ng/ml) at a comparable stage in the control females. Thus, high prolactin secretion cannot be maintained for longer than 16-17 days in incubating birds, but newly hatched, naked young can stimulate prolactin release in female flycatchers over a flexible period.

Effects of prolactin on the gonad and body weight of the male pied flycatcher during the breeding period

In the studies concerning the regulation of testicular regression in the pied flycatcher, the antigonadal effect of ovine prolactin has been examined. The species is a migratory, hole-nesting bird. Males were given daily injections of 200 microgram prolactin for 14 days. No antigonadal effects were observed. The body weight of the prolactin treated males was significantly higher than that of the control group.