Effects of zinc sulphate-induced anosmia on homing behaviour of pigeons

Volatile organic compounds in preen oil and feathers - a review

For a long time birds were assumed to be anosmic or at best microsmatic, with olfaction a poorly understood and seldom investigated part of avian physiology. The full viability of avian olfaction was first discovered through its functions in navigation and foraging. Subsequently, researchers have investigated the role of olfaction in different social and non-social contexts, including reproduction, kin recognition, predator avoidance, navigation and foraging. In parallel to the recognition of the importance of olfaction for avian social behaviour, there have been advances in the techniques and methods available for the sampling and analysis of trace volatiles and odourants, leading to insights into the chemistry underlying chemical communication in birds. This review provides (i) an overview of the current state of knowledge regarding the volatile chemical composition of preen oil and feathers, its phylogenetic coverage, chemical signatures and their potential functions, and (ii) a discussion of current methods used for the isolation and detection of volatiles. Finally, lines for future research are proposed.

Pigeon navigation: exposure to environmental odours prior to release is sufficient for homeward orientation, but not for homing

The role of environmental olfactory information in pigeon navigation has been extensively studied by analysing vanishing bearing distributions and homing performances of homing pigeons subjected to manipulation of their olfactory perception and/or the olfactory information they were exposed to during transportation and at the release site. However, their behaviour during the homing flight remains undocumented. In this experiment we report the analysis of tracks of birds made anosmic at the release site by washing their olfactory mucosa with zinc sulfate. We thus can assess the role of local odours at the release site as well as the role of environmental odours perceived on the way, far from the release site. We observed that pigeons transported and kept at the release site in purified air and made anosmic at the release site were unable to orient towards home and were impaired at homing. By contrast, pigeons allowed to smell environmental odours during transportation and at the release site, although made anosmic prior to release, displayed unimpaired homeward orientation, but nevertheless showed impaired homing performance. These results are consistent with the view that local odours at the release site are critical for determining the direction of displacement (olfactory map) and suggest that pigeons consult the olfactory map also during their homing flight in order to be able to find their way home.

Sublethal toxicity of untreated and treated stormwater Zn concentrations on the foraging behaviour of Paratya australiensis (Decapoda: Atyidae)

Aquatic organisms use chemical cues to perform key ecological behaviours such as locating food. Anthropogenic pollutants have the potential to disrupt these behaviours by down-regulating chemoreception. Urban stormwater runoff is a major source of metal pollution, particularly Zn, and is a leading contributor to the degradation of receiving waters. Consequently, significant remedial efforts have focused on using constructed stormwater wetlands to reduce pollutant loads. However, no studies have examined the efficacy of water quality improvements on ecologically relevant behaviours in aquatic biota. We conducted controlled laboratory experiments to test whether untreated (100 and 400 µg L(-1)) and treated (40 µg L(-1)) stormwater Zn concentrations observed in constructed wetlands interfere with the foraging behaviour of the glass shrimp (Paratya australiensis). The ability of shrimp to perceive, approach and search for a chemoattractant source was used to assess foraging behaviour. Abnormal foraging behaviour was observed in shrimp exposed to Zn at untreated stormwater concentrations. The strongest change relative to the control was observed for perception, which decreased by more than 80 and 60 % in the 400 µg Zn L(-1) and 100 µg Zn L(-1) groups, respectively. The behaviour of shrimp exposed to Zn concentrations measured in treated stormwater did not differ from the controls. The results suggest that the reduction of stormwater Zn concentrations via wetland treatment can prevent abnormal contamination-induced behaviours in shrimp, leading to improved aquatic ecosystem health. This study also highlights the subtle, but biologically significant impacts arising from sublethal exposures of Zn, and emphasise the utility of behavioural toxicology. The behavioural test used here is a simple and effective approach that could be incorporated into studies assessing the efficacy of stormwater treatment.

Back home at night or out until morning? Nycthemeral variations in homing of anosmic Cory's shearwaters in a diurnal colony

Olfactory cues have been shown to be important to homing petrels at night, but apparently those procellariiform species that also come back to the colony during the day are not impaired by smell deprivation. However, the nycthemeral distribution of homing, i.e. whether displaced birds released at night return to their burrow by night or during daylight, has never been investigated. To explore this question, we studied the homing behaviour of Cory's shearwater (Calonectris borealis) in the only known population where these birds are active at the colony both during the day and the night. Here, we compared the nocturnal versus diurnal homing schedule of birds treated with zinc sulphate to induce a reversible but complete anosmia, to that of controls. Our results show that anosmic shearwaters were unable to home in the dark and were constrained to wait for the daylight to find their burrow again. Our results confirm that olfaction is the basic sensory input for homing by night even in a petrel species that is diurnally active at the colony.

Testing the role of sensory systems in the migratory heading of a songbird

The identification of the sensory cues and mechanisms by which migratory birds are able to reach the same breeding and wintering grounds year after year has eluded biologists despite more than 50 years of intensive study. While a number of environmental cues have been proposed to play a role in the navigation of birds, arguments still persist about which cues are essential for the experience based navigation shown by adult migrants. To date, few studies have tested the sensory basis of navigational cues used during actual migration in the wild: mainly laboratory based studies or homing during the non-migratory season have been used to investigate this behaviour. Here we tested the role of olfactory and magnetic cues in the migration of the catbird (Dumetella carolinensis) by radio tracking the migration of birds with sensory manipulations during their actual migratory flights. Our data suggest that adult birds treated with zinc sulphate to produce anosmia were unable to show the same orientation as control adults, and instead reverted to a direction similar to that shown by juveniles making their first migration. The magnetic manipulation had no effect on the orientation of either adults or juveniles. These results allow us to propose that the olfactory sense may play a role in experience based migration in adult catbirds. While the olfactory sense has been shown to play a role in the homing of pigeons and other birds, this is the first time it has been implicated in migratory orientation.

The role of uropygial gland on sexual behavior in domestic chicken Gallus gallus domesticus

Recent studies have indicated that avian social behavior is influenced by olfactory cues. During the reproductive season a change in the chemical composition of uropygial gland secretion has been reported in some species and the hypothesis that olfactory signals may be produced by this gland has been proposed. To examine this hypothesis we performed two behavioral experiments to determine whether a female's uropygial gland produces chemical signals that stimulate mating behaviors in domestic chickens. In Experiment 1 the role of the female's uropygial gland in male mating behavior was examined by removing and examining the female's uropygial gland. The frequency of mounts and copulations of intact male birds with sham-operated female birds was significantly higher than with uropygial glandectomized female birds. With respect to the number of waltzing that is one of the courtship displays intact males showed no significant difference between sham-operated female birds and uropygial glandectomized female birds. In Experiment 2 the relationship between male olfaction and the female's uropygial gland was investigated using olfactory bulbectomized male birds. The number of mounts and copulations of sham-operated male birds with sham-operated female bird was significantly higher than with uropygial glandectomized female birds. In contrast olfactory bulbectomized male birds showed no significant differences in the number of mounts and copulations between sham-operated female birds and uropygial glandectomized female birds. These results indicate that intact and sham-operated male birds prefer to mate with female birds with the uropygial gland. The number of courtship waltzing of sham-operated male birds showed no significant difference. However olfactory bulbectomized male birds significantly courted to uropygial glandectomized female birds. Summarizing our results show that while anosmic males did not have any preference, both intact and sham-operated male birds chose to mate with female birds having an intact uropygial gland, suggesting that mate preference involves in male olfaction and that the female's uropygial gland acts as a source of social odor cues in domestic chickens.

Sensitivity to dimethyl sulphide suggests a mechanism for olfactory navigation by seabirds

Petrels, albatrosses and other procellariiform seabirds have an excellent sense of smell, and routinely navigate over the world's oceans by mechanisms that are not well understood. These birds travel thousands of kilometres to forage on ephemeral prey patches at variable locations, yet they can quickly and efficiently find their way back to their nests on remote islands to provision chicks, even with magnetic senses experimentally disrupted. Over the seemingly featureless ocean environment, local emissions of scents released by phytoplankton reflect bathymetric features such as shelf breaks and seamounts. These features suggest an odour landscape that may provide birds with orientation cues. We have previously shown that concentrated experimental deployments of one such compound, dimethyl sulphide (DMS), attracts procellariiforms at sea, suggesting that some species can use it as a foraging cue. Here we present the first physiological demonstration that an Antarctic seabird can detect DMS at biogenic levels. We further show that birds can use DMS as an orientation cue in a non-foraging context within a concentration range that they might naturally encounter over the ocean.

Olfaction and the homing ability of pigeons raised in a tropical area in Brazil

Several workers have investigated the effect of anosmia on pigeon navigation in different geographical locations because it has been suggested that homing behavior is based on different cues, such as olfactory cues, the Earth's magnetic field or infrasound, and that in the absence of one cue another would be used. In this situation, no cue is universally indispensable, including olfactory ones. In order to extend such observations to a novel biome, we observed the behaviour of 192 young inexperienced birds raised in southeastern Brazil, a tropical area where olfactory tests had never been run before. The birds were released from eight symmetrically distributed sites 17 to 44 km from the loft. Half of these birds (experimentals) had been made temporarily anosmic by washing their olfactory mucosae with 4% solution of ZnSO4 the day before release, while controls were treated with Ringer solution. The results of release tests showed that anosmia totally impaired the navigational performance of experimental birds, which were unable to home from sites at relatively short distances from home (34-44 km) and whose pooled initial bearings produced a (negative) homeward component not significantly different from 0. Homing performance of controls was significantly better, and their pooled vanishing bearings had a significant homeward component, in spite of much scatter in individual releases. We conclude that pigeon homing in the study area depends on olfactory information, even though local environmental conditions in the interior of the State of Sao Paulo, as in several other parts of the world, do not appear to be as favorable as Italy for the development of efficient olfactory navigation.

Factors reducing the expected deflection in initial orientation in clock-shifted homing pigeons

To orient from familiar sites, homing pigeons can rely on both an olfactory map and visual familiar landmarks. The latter can in principle be used in two different ways: either within a topographical map exploited for piloting or in a so-called mosaic map associated with a compass bearing. One way to investigate the matter is to put the compass and the topographical information in conflict by releasing clock-shifted pigeons from familiar locations. Although the compass orientation is in general dominant over a piloting strategy, a stronger or weaker tendency to correct towards the home direction by clock-shifted pigeons released from very familiar sites has often been observed. To investigate which factors are involved in the reduction of the deviation due to clock-shift, we performed a series of releases with intact and anosmic pigeons from familiar sites in unshifted and clock-shifted conditions and a series of releases from the same sites with naive clock-shifted birds. Our data suggest that the following factors have a role in reducing deviation due to the clock-shift: familiarity with the release site, the lack of olfactory information and some unknown site-dependent features.

Smelling home: a good solution for burrow-finding in nocturnal petrels?

Many burrowing petrels are able to return to their nests in complete darkness. The well-developed anatomy of their olfactory system and the attraction that food-related odour cues have for some petrel species suggest that olfaction may be used to recognize the burrow. In contrast,surface-nesting petrels may rely on visual cues to recognise their nest. We performed experiments on nine species of petrel (with different nesting habits) rendered anosmic either by plugging the nostrils or by injecting zinc sulphate onto the nasal epithelium. Compared with shamtreated control birds,we found that anosmia impaired nest recognition only in species that nest in burrows and that return home in darkness. Therefore, petrels showing nocturnal activity on land may rely on their sense of smell to find their burrows, while petrels showing diurnal activity or surface nesters may disregard olfactory cues in favour of visual guidance.

Relevance of visual cues for orientation at familiar sites by homing pigeons: an experiment in a circular arena

Whether pigeons use visual landmarks for orientation from familiar locations has been a subject of debate. By recording the directional choices of both anosmic and control pigeons while exiting from a circular arena we were able to assess the relevance of olfactory and visual cues for orientation from familiar sites. When the birds could see the surroundings, both anosmic and control pigeons were homeward oriented. When the view of the landscape was prevented by screens that surrounded the arena, the control pigeons exited from the arena approximately in the home direction, while the anosmic pigeons' distribution was not different from random. Our data suggest that olfactory and visual cues play a critical, but interchangeable, role for orientation at familiar sites.

Could osmotaxis explain the ability of blue petrels to return to their burrows at night?

Like many other species of petrel, blue petrel (Halobaena caerulea) are able to return to their nest burrows at night in complete darkness. Since petrels have a well-developed olfactory system, we carried out an experiment to test whether blue petrels use olfaction to localise their nest burrows. Incubating birds were injected intranasally with a zinc sulphate solution, which reversibly impairs the sensitivity of the olfactory mucosa; control birds were treated with physiological saline solution. None of the anosmic birds returned to their burrows, whereas all the birds treated with saline solution did. Our results suggest that olfactory cues are necessary for blue petrels to find their burrows.

The ontogeny of the homing pigeon navigational map: evidence for a sensitive learning period

Homing pigeons can learn a navigational map by relying on the heterogeneous distribution of atmospheric odours in the environment. To test whether there might be a sensitive period for learning an olfactory-based navigational map, we maintained a group of young pigeons in an aviary screened from the winds until the age of three to four months post-fledging. Subsequently, the screens were removed and the pigeons were exposed to the winds and the environmental odours they carry for three months. One control group of pigeons was held in a similar aviary but exposed to the winds immediately upon Hedging, while another control group of pigeons was allowed free-flight. When the pigeons from the three groups were released from two distant release sites at about six months of age post-fledging, the two control groups were found to be equally good at orientating and returning home, while the experimental pigeons held in the shielded aviary for the first three months post-fledging were unable to orientate homeward and they were generally unsuccessful in returning home. This result supports the hypothesis that environmental experience during the first three months post-fledging is critical for some aspect of navigational map learning and that navigational map learning displays sensitive period-like properties.

Hippocampal participation in navigational map learning in young homing pigeons is dependent on training experience

The homing pigeon navigational map is perhaps one of the most striking examples of a naturally occurring spatial representation of the environment used to guide navigation. In a previous study, it was found that hippocampal lesions thoroughly disrupt the ability of young homing pigeons held in an outdoor aviary to learn a navigational map. However, since that study an accumulation of anecdotal data has hinted that hippocampal-lesioned young pigeons allowed to fly during their first summer could learn a navigational map. In the present study, young control and hippocampal-lesioned homing pigeons were either held in an outdoor aviary or allowed to fly during the time of navigational map learning. At the end of their first summer, the birds were experimentally released to test for navigational map learning. Independent of training experience, control pigeons oriented homeward during the experimental releases demonstrating that they learned a navigational map. Surprisingly, while the aviary-held hippocampal-lesioned pigeons failed to learn a navigational map as reported previously, hippocampal-lesioned birds allowed flight experience learned a navigational map indistinguishable from the two control groups. A subsequent experiment revealed that the navigational map learned by the three groups was based on atmospheric odours. The results demonstrate that hippocampal participation in navigational map learning depends on the type of experience a young bird pigeon has, and presumably, the type of navigational map learned.

The effects of lesions to the caudolateral neostriatum on sun compass based spatial learning in homing pigeons

To better define the role of the avian caudolateral neostriatum (NCL) in spatial behavior, we used homing pigeons to explore the effects of NCL lesions on a sun compass based spatial learning task. Although NCL lesioned birds learned the task, they required more sessions to reach criterion than controls. NCL lesioned pigeons were also able to acquire a color discrimination task that was procedurally similar to the sun compass spatial learning task, but they made more errors than controls. Both the deficits observed in sun compass based spatial learning and color discrimination were correlated with the volume of lesion damage to dorsal rather than ventral portions of NCL. Overall, these findings suggest that the role of NCL in homing pigeon navigation from distant unfamiliar locations is not related to a bird's ability to learn stimulus-direction associations using a sun compass. However NCL does appear involved in a pigeon's ability to perform at least some behaviors common to both the color discrimination and the sun compass based spatial learning tasks.

Olfaction and the homing ability of pigeons in the southeastern United States

The importance of atmospheric odors for homing pigeon navigation was tested using birds from a loft located in Savannah, GA, in the southeastern United States. When released from a familiar training site, control pigeons and pigeons given intranasal injections of zinc sulfate to produce anosmia both displayed good homeward orientation and homed quickly. When released from three unfamiliar release sites, in contrast, control birds tended to orient southeast, while zinc sulfate-treated birds were more likely to fly northwest. More importantly, while the majority of control pigeons returned to the home loft, few of the zinc sulfate-treated birds returned. The good performance of both groups from the familiar site indicates that zinc sulfate treatment does not impair the general motor ability or motivation of homing pigeons. Therefore, the observed impairment in homing success of the zinc sulfate-treated pigeons from the unfamiliar locations presumably reflects an impaired ability to use atmospheric odors to navigate home. As such, the data support the hypothesis that successful homing pigeon navigation is based on the perception of atmospheric odors and that olfactory navigation is the primary mechanism used by pigeons over a broad range of geographic areas to approximate their relative position with respect to home from unfamiliar locations.