Hormonal patterns in breeding and nonbreeding kestrels, Falco tinnunculus: field and laboratory studies

Does the Stress of Laboratory Life and Experimentation on Animals Adversely Affect Research Data? A Critical Review

Recurrent acute and/or chronic stress can affect all vertebrate species, and can have serious consequences. It is increasingly and widely appreciated that laboratory animals experience significant and repeated stress, which is unavoidable and is caused by many aspects of laboratory life, such as captivity, transport, noise, handling, restraint and other procedures, as well as the experimental procedures applied to them. Such stress is difficult to mitigate, and lack of significant desensitisation/habituation can result in considerable psychological and physiological welfare problems, which are mediated by the activation of various neuroendocrine networks that have numerous and pervasive effects. Psychological damage can be reflected in stereotypical behaviours, including repetitive pacing and circling, and even self-harm. Physical consequences include adverse effects on immune function, inflammatory responses, metabolism, and disease susceptibility and progression. Further, some of these effects are epigenetic, and are therefore potentially transgenerational: the biology of animals whose parents/grandparents were wild-caught and/or have experienced chronic stress in laboratories could be altered, as compared to free-living individuals. It is argued that these effects must have consequences for the reliability of experimental data and their extrapolation to humans, and this may not be recognised sufficiently among those who use animals in experiments.

Effects of temperature on the timing of breeding and molt transitions in house finches

Temperature-correlated shifts in reproductive timing are now well documented in numerous bird species. However, whether temperature directly influences reproductive timing or whether its effects are mediated by an intermediate environmental cue, such as plant phenology, remains poorly understood. In this study, we investigated the direct effects of temperature on reproductive timing in house finches (Haemorhous mexicanus), which have a range and breeding diet not well represented in previous studies of temperature and reproductive timing. We conducted experiments with captive male house finches in which temperature was elevated within realistic ranges and the effects on the timing of preparations for reproduction, as well as on the termination of reproduction and the onset of prebasic feather molt, were examined. We found no adjustments in the timing of reproductive preparations of males in direct response to temperature. However, elevated temperature did advance the breeding-molt transition. Our results suggest that elevated temperatures in the range tested here do not directly impact physiological preparations for reproduction in male house finches, but may constrain the timing of the breeding-molt transition in this species.

Feather corticosterone content in predatory birds in relation to body condition and hepatic metal concentration

This study investigated the feasibility of measuring corticosterone in feathers from cryo-archived raptor specimens, in order to provide a retrospective assessment of the activity of the stress axis in relation to contaminant burden. Feather samples were taken from sparrowhawk Accipiter nisus, kestrel Falco tinnunculus, buzzard Buteo buteo, barn owl Tyto alba, and tawny owl Strix aluco and the variation in feather CORT concentrations with respect to species, age, sex, feather position, and body condition was assessed. In sparrowhawks only, variation in feather CORT content was compared with hepatic metal concentrations. For individuals, CORT concentration (pgmm(-1)) in adjacent primary flight feathers (P5 and P6), and left and right wing primaries (P5), was statistically indistinguishable. The lowest concentrations of CORT were found in sparrowhawk feathers and CORT concentrations did not vary systematically with age or sex for any species. Significant relationships between feather CORT content and condition were observed in only tawny owl and kestrel. In sparrowhawks, feather CORT concentration was found to be positively related to the hepatic concentrations of five metals (Cd, Mn, Co, Cu, Mo) and the metalloid As. There was also a negative relationship between measures of condition and total hepatic metal concentration in males. The results suggest that some factors affecting CORT uptake by feathers remain to be resolved but feather CORT content from archived specimens has the potential to provide a simple effects biomarker for exposure to environmental contaminants.

At the crossroads of physiology and ecology: food supply and the timing of avian reproduction

This article is part of a Special Issue “Energy Balance”. The decision of when to breed is crucial to the reproductive success and fitness of seasonally breeding birds. The availability of food for adults prior to breeding has long been thought to play a critical role in timing the initiation of seasonal reproductive events, in particular laying. However, unequivocal evidence for such a role remains limited and the physiological mechanisms by which an increase in food availability results in seasonal activation of the reproductive system are largely speculative. This lack of mechanistic information partly reflects a lack of integration of ecological and physiological approaches to study seasonal reproduction. Indeed, most work pertaining to the role of food availability for adults on the timing of avian reproduction has been ecological and has focused almost exclusively on female traits associated with reproductive timing (e.g., lay date and clutch size). By contrast, most work on the physiological bases of the relationship between food availability and the timing of reproduction has investigated male traits associated with reproductive development (e.g., reproductive hormones and gonadal development). To advance our understanding of these topics, we review the role of proximate factors including food availability, social factors, and ambient temperature in the control of breeding decisions, and discuss the role of three potential candidates (leptin, glucocorticoids, and GnIH-neuropeptide Y) that may mediate the effects of food availability on these decisions. We emphasize that future progress in this area is heavily contingent upon the use of physiology-based approaches and their integration into current ecological frameworks.

Avian ecologists and physiologists have different sexual preferences

Seasonal timing is studied by ecologists and physiologists alike and it is now widely recognized that further integration of these fields is needed for a full understanding of phenology. This is especially true in the light of the impact of global climate change on living organisms. In studies of avian reproduction, one obstacle to this integration is that ecologists and physiologists do not allocate their research efforts equally to males and females. The physiological orchestration of breeding stages has been studied almost exclusively in males, while in avian ecology and evolutionary biology females are more often considered. This sex bias has severe implications: sexes differ in the way they use external cues to organize their life cycles, but often cue in on each other's physiology and behavior. The simultaneous investigation of both males and females within single studies is thus essential. In this review, I begin by illustrating the sex-bias in studies and attempt to explain its origin. I then provide a number of examples in which focusing on a single sex would have resulted in misleading conclusions. Finally, I review some classical studies of female reproductive physiology that have promoted and developed research on the "forgotten-sex".

Reproductive endocrinology of wild, long-lived raptors

The last decades have witnessed a surge of studies analyzing the role of sex hormones on the behavior and ecology of wild bird populations, allowing a more integrated view of the evolution of avian physiology and life histories. Despite a marked progress, field studies show a considerable bias towards research on specific phylogenetic groups, neglecting a significant fraction of the class Aves. Here we analysed changes in the circulating levels of sex steroids in relation to reproductive behaviour in wild black kites (Milvus migrans), a long-lived and socially monogamous Accipitridae raptor. Males and females displayed a single seasonal peak of circulating testosterone (males) and estradiol (females) during pre-laying and laying. Absolute male testosterone levels were low even at the seasonal maximum and remained below detection limits in females. The latter results supports the idea that avian species establishing long-term pair bonds require lower amounts of circulating androgens for reproduction. Circulating progesterone showed a single seasonal peak in females and males, but their timing (during Incubation and Post-brooding respectively) did not overlap. The fact that females black kites perform the majority of incubation and males provide the majority of care to fledglings suggests that progesterone is involved in the expression of parental behaviors.

Proximate and ultimate factors explaining floating behavior in long-lived birds

Avian populations are composed of reproductive individuals coexisting in space and time with young, non-breeding conspecifics or "floaters". Despite the fact that first breeding can be delayed for years and can exert profound effects on fitness, many aspects of the behavior, ecology and physiology of young floaters remain poorly understood. By means of combining endocrine, behavioral and life history information from a population of black kites (Milvus migrans) monitored long-term, we tested several hypotheses suggesting endocrine function as a determinant of floating status. Sexual function in non-breeding males, estimated through determination of systemic testosterone and progesterone levels, was similar to that in reproductively active conspecifics. Floating females, on the contrary, displayed an endocrine pattern of circulating estrogens and progesterone that was parallel in timing but reduced in magnitude as compared to breeders. Our results suggest that floaters are not physiologically constrained to reproduce, but the cost-benefit balance of attaining complete gonadal function is sexually dependent. While young, unmated males could increase their breeding prospects by attaining sexual maturity regardless of their social environment, natural selection would favor females relying on social cues to mature. Consistent with the sexual roles of socially monogamous species, gonadal recrudescence and testosterone production would allow unmated males to access breeding resources (e.g. through male-male competition and extra-pair fertilizations). Unmated females, on the contrary, would reduce physiological costs by means of delaying ovarian maturation until establishing pair bonds with a male providing access to breeding resources.

Lab and field experiments: are they the same animal?

To advance our understanding of biological processes we often plan our experiments based on published data. This can be confusing though, as data from experiments performed in a laboratory environment are sometimes different from, or completely opposite to, findings from similar experiments performed in the "real world". In this mini-review, we discuss instances where results from laboratory experiments differ as a result of laboratory housing conditions, and where they differ from results gathered in the field environment. Experiments involving endocrinology and behavior appear to be particularly susceptible to influence from the environment in which they are performed. As such, we have attempted to promote discussion of the influence of housing environment on the reproductive axis, circadian biology and behavior, immune function, stress biology, neuroplasticity and photoperiodism. For example, why should a rodent species be diurnal in one housing environment yet nocturnal in another? Are data that are gathered from experiments in the laboratory applicable to the field environment, and vice-versa? We hope not only to highlight the need for experiments in both lab and field when looking at complex biological systems, but also to promote frank discussion of discordant data. Perhaps, just as study of individual variation has been gaining momentum in recent years, data from variation between experimental arenas can provide us with novel lines of research.

Testosterone treatment diminishes sickness behavior in male songbirds

Males of many vertebrate species are typically more prone to disease and infection than female conspecifics, and this sexual difference is partially influenced by the immunosuppressive properties of testosterone (T) in males. T-induced immunosuppression has traditionally been viewed as a pleiotropic handicap, rather than an adaptation. Recently, it has been hypothesized that suppression of sickness behavior, or the symptoms of infection, may have adaptive value if sickness interferes with the expression of T-mediated behaviors important for male reproductive success. We conduct a classic hormone replacement experiment to examine if T suppresses sickness behavior in a seasonally-breeding songbird, Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii). Triggered experimentally by bacterial lipopolysaccharide (LPS), sickness behavior includes decreased activity, anorexia, and weight loss. Gonadectomized (GDX) males that were treated with silastic implants filled with T exhibited suppression of behavioral and physiological responses to LPS compared to GDX and sham-GDX controls given empty implants. Sickness responses of control groups were statistically indistinguishable. T-implanted birds had significantly higher plasma T than control groups and levels were within the range associated with aggressive interactions during male-to-male contests. These findings imply that suppression of sickness behavior could occur when T is elevated to socially-modulated levels. Alternatively, it is possible that this suppressive effect is mediated through a stress-induced mechanism, as corticosterone levels were elevated in T-implanted subjects compared to controls. We propose that males wounded and infected during contests may gain a brief selective advantage by suppressing sickness responses that would otherwise impair competitive performance. The cost of immunosuppression would be manifested in males through an increased susceptibility to disease, which is presumably offset by capitalizing upon limited reproductive opportunities.

Fecal steroid monitoring for assessing gonadal and adrenal activity in the golden eagle and peregrine falcon

We examined the efficacy of noninvasive monitoring of endocrine function via fecal steroid immunoassays in the golden eagle and peregrine falcon. High-pressure liquid chromatography analyses of fecal glucocorticoid metabolites (fGCM) revealed that minor percentages of immunoreactive fGCM co-eluted with [(3)H]corticosterone in both sexes of the eagle (2.5-2.7%) and falcon (7.5-11.9%). In contrast, most fecal estrogen metabolites in eagle and falcon females co-eluted with radiolabeled estradiol-17beta ([(3)H]; 57.6, 64.6%, respectively) or estrone ([(3)H]; 26.9, 4.1%, respectively). Most fecal progestin metabolite immunoreactivity in the female eagle (24.8%) and falcon (21.7%) co-eluted with progesterone ([(14)C]). Most fecal androgen metabolite immunoreactivity in eagle (55.8%) and falcon (63.7%) males co-eluted with testosterone ([(14)C]). Exogenous adrenocorticotropin hormone induced increased fGCM excretion above pre-treatment in both species, but only significantly (P < 0.05) in the eagle. Both species showed increased fGCM after saline administration, suggesting the detection of 'handling stress.' Both species exhibited enterohepatic and renal recirculation of administered steroids as demonstrated by biphasic and triphasic excretion patterns. Thus, noninvasive fecal hormone monitoring is a valid and promising tool for assessing gonadal and adrenal status in rare and threatened birds-of-prey.

Prior experience with photostimulation enhances photo-induced reproductive development in female European starlings: a possible basis for the age-related increase in avian reproductive performance

Reproductive performance in female birds improves with age, and this is generally attributed to experiences obtained during breeding. In temperate-zone species, experience with photostimulation during the first breeding year may prime the hypothalamo-pituitary-gonadal axis to respond to photic cues more rapidly or robustly in subsequent years. To test this idea, we captured 32 photorefractory juvenile (hence naive to photostimulation) female European starlings (Sturnus vulgaris) and held half of them (naive group) on a photoperiod of 8L:16D for 32 wk and the other half (experienced group) on 8L:16D for 12 wk, 16L:8D for 12 wk, and then 8L:16D for 8 wk. When we subsequently transferred all birds to 16L:8D, the increase in body mass, which may presage egg laying in the wild, was more robust in experienced than in naive females. Experienced females also showed a more robust elevation in plasma concentrations of the yolk-precursor protein vitellogenin, although naive females showed an initial rapid but transient rise in vitellogenin that we attribute to their extended exposure to short-day photoperiods prior to photostimulation. Finally, the photo-induced increase in diameter of the largest ovarian follicle, in plasma concentrations of luteinizing hormone, and in the number of septo-preoptic fibers relative to the number of cell bodies immunoreactive to GnRH was greater in experienced than in naive females. Thus, prior experience with photostimulation enhances some initial phases of photo-induced reproductive development and may explain, in part, why reproductive performance improves with age in temperate-zone birds.

Comparative analysis of male androgen responsiveness to social environment in birds: the effects of mating system and paternal incubation

Male androgen responses to social challenges have been predicted to vary with mating system, male-male aggressiveness, and the degree of paternal investment in birds ("challenge hypothesis," Am. Nat. 136 (1990), 829). This study focused on the interspecific predictions of the challenge hypothesis. Comparative methods were used to control for effects of the phylogenetic relatedness among the sampled species. Male androgen data of 84 bird species were collected from literature records on seasonal androgen patterns. From these, the androgen responsiveness (AR) was calculated as described in the original challenge hypothesis (i.e., maximum physiological level/breeding baseline). Scatterplots of AR versus mating strategy, male-male aggressiveness, and the degree of paternal care confirmed the expected interspecific patterns. When phylogenetic analyses were performed among all of the sampled species, the effects of paternal investment disappeared while the AR remained covarying to a high degree with mating system and male-male aggressiveness. Although these mechanisms may be different at the intraspecific level, this suggests that interspecific differences of AR in male birds may have evolved in response to changes of mating strategies, rather than in response to altered paternal duties. However, control for phylogeny among the subsample of 32 passerine species revealed that if any paternal investment contributed to the observed variance in AR, then the change from "no male incubation" to "male shares incubation duties" represented the most effective, whereas the male's contribution to feeding offspring did not explain the observed variation of AR.

A long photoperiod overrides non-photoperiodic factors in blue tits' timing of reproduction

Endocrinological studies have contributed considerably to the development of theory concerning the proximate aspects of the timing of reproduction. In non-domesticated, avian species, the relative importance of the photoperiodic and non-photoperiodic factors influencing later stages of the breeding cycle, such as the onset of egg laying, remains unclear because egg laying is difficult to obtain with captive populations and laboratory experiments of breeding are rarely carried out in the framework of long-term field studies. We set up a special experimental design such that captive Mediterranean blue tits (Parus caeruleus) can breed with success in large outdoor aviaries at similar latitudes and altitudes to their wild counterparts. Here we demonstrate experimentally that the non-photoperiodic factors responsible for large and consistent differences in the expression of natural breeding responses between three captive outdoor blue tit populations are ignored during long-day treatment. Based on these findings, an evolutionary explanation is provided for why the relative importance of the non-photoperiodic factors decreases with the progress of the season. The hypothesis can explain observed maladapted breeding dates in free-living populations and could possibly be used to increase the success of breeding programmes with some endangered, captive, non-domesticated, photoperiodic species.

Copulatory behaviour and paternity in the American kestrel: the adaptive significance of frequent copulations

The adaptive significance of repeated withinpair copulations is not well understood. We analysed the copulatory behaviour of 16 pairs of solitary-nesting American kestrels, Falco sparverius, in southern Quebec (Canada), and the achieved reproductive success (paternity) of 21 kestrel families determined by DNA fingerprinting, in terms of four hypotheses. (1) The paternity assurance hypothesis, which suggests that males copulate frequently to avoid being cuckolded, was rejected because there were few extrapair copulation attempts (<1% of all copulations observed), withinpair copulations were not timed during the fertile period and mate attendance did not increase as the fertile period approached. (2) The immediate material benefits hypothesis, which suggests that females trade copulations for food, was refuted because copulations most often occurred without food transfers, especially outside the fertile period. (3) The female mate guarding of males hypothesis, which suggests that females distract their mates from other mating opportunities by copulating frequently, was rejected because extrapair copulation attempts were infrequent, male and female solicitation frequencies were similar and females did not differ in the timing or frequency of solicitations. (4) The mate assessment hypothesis, which suggests that assessment of mate quality is mediated via copulation, most closely predicted the behaviour observed since withinpair copulations were frequent outside the fertile period and at pair formation, males and females solicited similar numbers of copulations and pairs did not differ significantly in solicitation or copulation frequency. In line with this hypothesis we found that only one brood was extrapair, probably the result of mate replacement.Copyright 1998 The Association for the Study of Animal Behaviour

Plasma levels of luteinizing hormone and androgens in relation to age and breeding status among cooperatively breeding Australian magpies (Gymnorhina tibicen Latham)

Plasma levels of luteinizing hormone (LH), testosterone (T), and 5 alpha-dihydrotestosterone (DHT) were measured in relation to age and social/breeding status among free-living male Australian magpies. Magpies live in territorial groups of up to 20 individuals and due to a largely age-related dominance hierarchy among males, many individuals are prevented from breeding. Adult plumage is not attained until the fourth year, but males can produce motile sperm in their first year. Plasma levels of LH and T peaked just prior to egg-laying among breeding males, but DHT levels remained steady or declined slightly during the breeding period. Adults (greater than 3.5 years) had significantly higher levels of both LH and androgens than did subadults (less than 3.5 years) during the breeding season. Nonbreeding adults had similar levels to those found among the breeding adults, but breeding subadults had higher levels of both LH and androgens than the nonbreeding subadults. These results are interpreted in terms of the opportunities for each of these classes to obtain copulations and are discussed in relation to age-related hormonal secretion in other species.

Photoperiodic control of reproduction and molt in the kestrel, Falco tinnunculus

An adaptive decline in average clutch size with progressive date of laying is characteristic of most bird species with a single clutch of variable size per year. The effect of photoperiod on timing of laying, clutch size, and subsequent molt was investigated in kestrel pairs breeding and raising their young in captivity. In natural daylight (nLD), clutch size, under ad libitum feeding, showed the same decline with date as in nature. Birds breeding later also started molt later and molted faster (more feathers simultaneously), so that all birds completed molt more or less at the same time. Constant long days (LD 17.5:6.5 and LD 13:11) from December 1 onward advanced both reproduction and molt. The LD 17.5:6.5 group developed the reproductive system faster, had a shorter courtship period, and laid eggs earlier than the LD 13:11 group. In both photoperiods there was a decrease in clutch size with progressive laying date, similar to that in nLD. Molt started in both groups at about the end of the laying period and slowed down in the longer photoperiod, especially in males. Plasma luteinizing hormone (LH) changes in the two photoperiods were different for males and females. Males showed the expected slower LH response in the shorter photoperiod, but the initial LH response by females was the same in both photoperiods. Data on LH, reproductive behavior, and body mass suggest that females have a wider annual reproductive window than males. Data on time of laying and number of eggs suggest that clutch size in the kestrel is determined by laying date itself, following an endogenous rhythm that is phase-locked to the reproductive cycle.