Spontaneous egg or chick abandonment in energy-depleted king penguins: a role for corticosterone and prolactin?

Various exogenous or endogenous factors may induce an emergency response in birds, redirecting current activity towards survival. In fasting, breeding penguins, the achievement of a critical energy depletion was suggested to induce egg abandonment and departure to sea for re-feeding. How such a behavioral shift is hormonally controlled remains unknown. The possible involvement of corticosterone and prolactin was examined by characterizing the nutritional and hormonal states of king penguins at egg abandonment. Further, we tested if these states differ according to whether an egg or a chick is abandoned, and according to the timing of breeding. In every case of abandonment, birds were in phase III fasting characterized by accelerated protein catabolism. However, body condition at egg abandonment was lower in early than in late breeders, suggesting that king penguins are willing to tolerate a larger energy depletion when their potential breeding success is high. At egg and chick abandonment, plasma corticosterone levels were, respectively, increased by 2- and 4-fold, whereas plasma prolactin levels were, respectively, depressed by 3- and 1.4-fold. The increase in plasma corticosterone and the decrease in plasma prolactin could be involved in the control of abandonment by, respectively, stimulating the drive to re-feed and diminishing the drive to incubate or brood. The smaller decrease in prolactin levels and the greater increase in corticosterone levels observed at chick vs egg abandonment suggest that, in addition to nutritionally-related stimuli, tactile or audible stimuli from the egg or chick could intervene in the endocrine control of abandonment.     

Impact of season and social challenge on testosterone and corticosterone levels in a year-round territorial bird

Plasma testosterone increases during breeding in many male vertebrates and has long been implicated in the promotion of aggressive behaviors relating to territory and mate defense. Males of some species also defend territories outside of the breeding period. For example, the European nuthatch (Sitta europaea) defends an all-purpose territory throughout the year. To contribute to the growing literature regarding the hormonal correlates of non-breeding territoriality, we investigated the seasonal testosterone and corticosterone profile of male (and female) nuthatches and determined how observed hormone patterns relate to expression of territorial aggression. Given that non-breeding territoriality in the nuthatch relates to the reproductive context (i.e., defense of a future breeding site), we predicted that males would exhibit surges in plasma testosterone throughout the year. However, we found that males showed elevated testosterone levels only during breeding. Thus, testosterone of gonadal origin does not appear to be involved in the expression of non-breeding territoriality. Interestingly, territorial behaviors of male nuthatches were stronger in spring than in autumn, suggesting that in year-round territorial species, breeding-related testosterone elevations may upregulate male-male aggression above non-breeding levels. In females, plasma testosterone was largely undetectable. We also examined effects of simulated territorial intrusions (STIs) on testosterone and corticosterone levels of breeding males. We found that STIs did not elicit a testosterone response, but caused a dramatic increase in plasma corticosterone. These data support the hypothesis that corticosterone rather than testosterone may play a role in the support of behavior and/or physiology during acute territorial encounters in single-brooded species.     

Changes in pituitary and adrenal sensitivities allow the snow bunting (Plectrophenax nivalis), an Arctic-breeding song bird, to modulate corticosterone release seasonally

Several free-living avian species have recently been shown to seasonally modulate corticosterone release in response to capture and restraint. We examined possible mechanisms underlying seasonal adrenocortical modulation in snow buntings (Plectrophenax nivalis), a species that breeds and molts (the energetically costly replacement of feathers) in the Alaskan Arctic. Snow buntings dramatically reduced baseline and maximal corticosterone titers during molt compared to the breeding season. This effect is not explained by changes in either corticosterone binding protein capacity or the overall condition of the bird (assessed by weight and fat storage). Although the adrenal's capacity to secrete corticosterone is reduced during molt, adrenal insensitivity does not fully explain reduced maximal output since exogenous adrenocorticotropic-hormone enhanced corticosterone release during both seasons. In contrast, no exogenous adrenocorticotropic hormone releasing factor (corticotrophin-releasing factor, arginine vasotocin or mesotocin) enhanced corticosterone secretion during molt. This suggests that the pituitary's endogenous adrenocorticotropic secretion was maximal in response to capture and handling, making the pituitary an important site regulating corticosterone levels. Taken together, these results indicate that seasonal modulation of corticosterone release in this species is controlled at both the adrenal and pituitary glands. Accepted: 16 February 1998     

Stress hormones in relation to breeding status and territory location in colonial king penguin: a role for social density?

Because glucocorticoid (stress) hormones fundamentally affect various aspects of the behaviour, life history and fitness of free-living vertebrates, there is a need to understand the environmental factors shaping their variation in natural populations. Here, we examined whether spatial heterogeneity in breeding territory quality affected the stress of colonial king penguin (Aptenodytes patagonicus). We assessed the effects of local climate (wind, sun and ambient temperature) and social conditions (number of neighbours, distance to neighbours) on the baseline levels of plasma total corticosterone (CORT) in 77 incubating and 42 chick-brooding birds, breeding on territories of central or peripheral colony location. We also assessed the oxidative stress status of a sub-sample of central vs. peripheral chick-brooders to determine whether chronic stress arose from breeding on specific territories. On average, we found that brooders had 55 % higher CORT levels than incubators. Regardless of breeding status, central birds experienced greater social density (higher number of neighbours, shorter distance between territories) and had higher CORT levels than peripheral birds. Increasing social density positively explained 40 % of the variation in CORT levels of both incubators and brooders, but the effect was more pronounced in brooders. In contrast, climate was similar among breeding territories and did not significantly affect the CORT levels of breeding birds. In brooders, oxidative stress status was not affected by local density or weather conditions. These results highlight that local heterogeneity in breeding (including social) conditions may strongly affect the stress levels of breeding seabirds. The fitness consequences of such variation remain to be investigated.     

Carry‐over effects provide linkages across the annual cycle of a Neotropical migratory bird,the Louisiana Waterthrush Parkesia motacilla

Population limitation models of migratory birds have sought to include impacts from events across the full annual cycle. Previous work has shown that events occurring in winter result in some individuals transitioning to the breeding grounds earlier or in better physical condition than others, thereby affecting reproductive success (carry‐over effects). However, evidence for carry‐over effects from breeding to wintering grounds has been shown less often. We used feather corticosterone (CORT_f) levels of the migratory Louisiana Waterthrush Parkesia motacilla as a measure of the physiological state of birds at the time of moult on the breeding territory to investigate whether carry‐over effects provide linkages across the annual cycle of this stream‐obligate bird. We show that birds arriving on wintering grounds with lower CORT_f scores, indicating reduced energetic challenges or stressors at the time of moult, occupied higher quality territories, and that these birds then achieved a better body condition during the overwinter period. Body condition, in turn, was important in determining whether adult birds returned the following winter, with birds in better condition returning at higher rates. Together these data suggest a carry‐over effect from the breeding grounds to the wintering grounds that is further extended with respect to annual return rates. Very few other studies have linked conditions during the previous breeding season with latent effects during the subsequent overwintering period or with annual survival. This study shows that the effects of variation in energetic challenges or stressors can potentially carry over from the natal stream and accumulate over more than one life‐history period before being manifested in reduced survival. This is of particular relevance to models of population limitation in migratory birds.     

Corticosterone,testosterone and life-history strategies of birds

Steroid hormones have similar functions across vertebrates, but circulating concentrations can vary dramatically among species. We examined the hypothesis that variation in titres of corticosterone (Cort) and testosterone (T) is related to life-history traits of avian species. We predicted that Cort would reach higher levels under stress in species with higher annual adult survival rates since Cort is thought to promote physiological and behavioural responses that reduce risk to the individual. Conversely, we predicted that peak T during the breeding season would be higher in short-lived species with high mating effort as this hormone is known to promote male fecundity traits. We quantified circulating hormone concentrations and key life-history traits (annual adult survival rate, breeding season length, body mass) in males of free-living bird species during the breeding season at a temperate site (northern USA) and a tropical site (central Panama). We analysed our original data by themselves, and also combined with published data on passerine birds to enhance sample size. In both approaches, variation in baseline Cort (Cort0) among species was inversely related to breeding season length and body mass. Stress-induced corticosterone (MaxCort) also varied inversely with body mass and, as predicted, also varied positively with annual adult survival rates. Furthermore, species from drier and colder environments exhibited lower MaxCort than mesic and tropical species; T was lowest in species from tropical environments. These findings suggest that Cort0, MaxCort and T modulate key vertebrate life-history responses to the environment, with Cort0 supporting energetically demanding processes, MaxCort promoting survival and T being related to mating success.     

Breeding territory fidelity in a partial migrant, the American dipper Cinclus mexicanus

American dipper Cinclus mexicanus populations are frequently composed of resident individuals that occupy permanent territories year round and migratory individuals that overwinter with residents but migrate to breeding territories on higher elevation creeks each spring. Between 1999 and 2004 we examined how migratory strategy (resident/migratory) and sex differences influence breeding territory fidelity of American dippers occupying the Chilliwack River watershed, British Columbia, Canada. Counter to expectation we found that the migratory strategy of American dippers did not influence whether birds breeding in one year were found on their former breeding territory in the next. Migratory strategy also did not affect the probability that known surviving dippers occupied the same breeding territory in the following year. Males and females were equally likely to be found on their former territory in the following year (females 43%, males 41%) and known survivors had similar levels of breeding territory fidelity (females 74%, males 68%). However, breeding territory fidelity of males and females varied in response to different factors. Surviving female dippers were more likely to be found on their former breeding territory in the subsequent year following a successful breeding attempt than an unsuccessful breeding attempt. Prior reproductive performance did not influence whether surviving male dippers were found on their former breeding territory. Male dippers were more likely to be found on their former territory and, if they survived, have higher breeding territory fidelity when their mate also returned to that same territory. Mate retention also influenced whether females were found on their former territory in the following year but had no effect on the breeding territory fidelity of known survivors. We argue that sex‐specific dispersal decision rules in American dippers are driven by sex differences in the predictability of breeding performance between years and sex differences in how mate retention influences subsequent reproductive success.     

Corticosterone responses of grey-faced petrels (Pterodroma macroptera gouldi) are higher during incubation than during other breeding stages

We report the results of the first field study examining seasonal changes in corticosterone responses of typically long-lived birds of the order Procellariiformes. In particular, we examined whether grey-faced petrels Pterodroma macroptera gouldi showed changes in circulating baseline corticosterone concentrations and corticosterone responses to a standardized handling protocol across the breeding season. Such changes have been associated with changes in body condition and variations in energy demands on adult birds through the breeding season. During early incubation, males were in significantly better condition than females that had just completed laying, whereas during late incubation, males were in significantly poorer condition than females. In spite of these differences, there was no significant difference in baseline corticosterone concentrations between sexes or among birds at different reproductive stages. However, we detected significant differences in corticosterone responses associated with a standardized handling protocol at different stages through the breeding season. Responses were significantly greater during incubation compared with the prelay period and late chick rearing. Body condition was weakly and negatively correlated with maximum and total integrated corticosterone level, indicating that some of the individual variability in stress corticosterone responses could be explained by variation in body condition. However, the largest stress response occurred during late incubation and was independent of sex, although males were in relatively poor condition and females in relatively good condition. This period coincided with the breeding stage in which energy constraints on individual adults were higher than at other periods of the reproductive cycle and birds may be physiologically primed for extended fasts.     

The breeding season duration hypothesis: acute handling stress and total plasma concentrations of corticosterone and androgens in male and female striped plateau lizards (Sceloporus virgatus)

Acute glucocorticoid elevations can be adaptations to short-term stressors. The breeding season hypothesis predicts reduced glucocorticoid responsiveness to acute stressors in populations or species with short breeding seasons. The striped plateau lizard (Sceloporus virgatus) has a short breeding season in Arizona. We measured plasma corticosterone and total androgen levels (dihydrotestosterone and testosterone) following one of the four stress-handling treatments (0, 10, 60, or 180 min). In both sexes, longer handling stress yielded higher corticosterone; females had higher corticosterone than males at all time points. Androgens did not vary with handling duration, in either sex. Combining treatments, plasma androgens correlated positively with corticosterone (CORT) in females but not in males; plasma CORT and body mass residuals were negatively correlated in both sexes, suggesting lizards in poor body condition and/or not investing heavily in reproduction (follicle mass) have higher acute corticosterone. Total plasma androgens and body mass residuals were positively associated in males, but showed no association in females. The maximal CORT elevation after handling stress in this single-clutching species was of comparable magnitude to responses in related multi-clutching lizard species with longer breeding seasons. Using data from studies of multiple populations of three Sceloporus species, we found no relationship between the relative magnitude of the CORT increase and either latitude or elevation, two variables in the literature correlated with duration of the breeding season, and only weak relationships with geographic elevation and actual (not relative) stress-elevated CORT values in this multi-population comparison.     

Space‐use strategies of wintering Ovenbirds in Belize: causes and consequences

For long‐distance migrants, territoriality and prey biomass during the non‐breeding season have been linked to body condition that can carry over to affect spring migration and breeding events. For Ovenbirds (Seiurus aurocapilla), studies in Jamaica showed that body condition in mid‐season depended on leaf litter prey biomass and declined seasonally as conditions became drier, and that individuals with sedentary (territorial) and wandering space‐use strategies did not differ in age or body condition. During October and November 2010–2011, we radio‐tracked Ovenbirds in Belize to determine if space‐use patterns differed with age and sex, if space‐use strategy influenced foraging behavior or body condition, and if areas used by wanderers and territory owners differed in food abundance or habitat characteristics. Most Ovenbirds (41 of 51, 80.4%) possessed small (1‐ha) territories with largely non‐overlapping cores, but 22.5% (10 of 51) of birds were wanderers (～7‐ha home range). Early season space use was predicted by age class, with most wanderers (90%, 9 of 10) being first‐year birds and most territory owners (63%) being older birds. Sex ratios of wanderers and territory owners did not differ. We found that wanderers may have been at a disadvantage because they had significantly lower foraging rates and lower relative body masses than territorial birds, although baseline corticosterone levels did not differ. Habitat characteristics of areas used by wanderers and territory owners did not differ nor did biomass of ground‐surface arthropods, likely because ranges of most wanderers overlapped those of territory owners. Using stable hydrogen isotopes in feathers, we found that first‐year Ovenbirds that were wanderers tended to have a more northern natal origins than sedentary birds, though the difference was not significant. Longer migration distances could delay arrival and reduce competitive ability. Our results suggest that wandering may not be an alternative and equally successful strategy, at least early in the season, and instead young birds may be competitively excluded from territory ownership.     

Ecological factors affecting the adrenocortical response to stress in chestnut-collared and McCown's longspurs (Calcarius ornatus, Calcarius mccownii)

Secretion of the steroid hormone corticosterone (CORT) in response to perturbations results in behavior patterns that can maximize survival. Three commonly cited hypotheses suggest that during breeding, there are advantages associated with suppressed (CORT) secretion in (1) the sex that is most important for parental care, (2) individuals in good body condition, and (3) species with a short breeding season and limited renesting opportunities. We addressed these hypotheses in two midlatitude breeders, chestnut-collared and McCown's longspurs, by assessing CORT secretion over a 1-h period of handling. These species have congeners that are exclusively arctic breeders, and this provides a unique opportunity to assess adrenocortical responsiveness both within a phylogenetic framework and across environmental variables. In both species, males and females showed similar CORT secretion patterns in response to handling, and body condition was unrelated to CORT secretion. Additionally, although these midlatitude breeders have more opportunities to attempt a renest than their arctic congeners, their hormonal response to stress was similar to that reported for their arctic congeners. We suggest that an attenuated stress response may relate to the severity of the breeding environment and a low likelihood of successful renesting, since these variables are common to both arctic and grassland habitats.     

Seasonal stress physiology and body condition differ among co-occurring tropical finch species

Seasonal changes in avian hormonal stress responses and condition are well known for common species found at temperate and arctic latitudes, but declining and tropical species are poorly studied. This study compares stress and condition measures of co-occurring declining and non-declining tropical grass finch species in Australia. We monitored declining Gouldian finches (Erythrura gouldiae) and non-declining long-tailed and masked finches (Poepila acuticauda and P. personata) during two seasons that are potentially stressful: peak breeding (early dry season when food is plentiful) and moult (late dry to early wet season when food may be scarce). We measured body condition (muscle and fat), haematocrit, and stress response to capture using plasma corticosterone and binding globulin concentrations. All species had higher muscle and lower fat indices during breeding than moult. Haematocrit did not consistently differ between seasons. Long-tailed finches had higher stress responses during breeding than moult, similar to other passerines studied. Masked finches showed no seasonal changes in stress response. Gouldian finches had stress response patterns opposite to those of long-tailed finches, with higher stress responses during moult. However, seasonal trends in Gouldian and long-tailed finch stress responses sometimes differed between years or sites. The differences in stress response patterns between species suggest that the declining Gouldian finch is more sensitive to recent environmental changes which are thought to further reduce grass seed food resources during the late dry to early wet season. Retention of stress responsiveness during a protracted moult could increase the survival potential of Gouldian finches. This study highlights the utility of stress and condition indices to determine the sensitivity of co-occurring species to environmental conditions.     

Dispersal, migration, and offspring retention in saturated habitats

We examine the evolutionary stability of year-round residency in territorial populations, where breeding sites are a limiting resource. The model links individual life histories to the population-wide competition for territories and includes spatial variation in habitat quality as well as a potential parent-offspring conflict over territory ownership. The general form of the model makes it applicable to the evolution of dispersal, migration, partial migration, and delayed dispersal (offspring retention). We show that migration can be evolutionarily stable only if year-round residency in a given area would produce a sink population, where mortality exceeds reproduction. If this applies to a fraction of the breeding habitat only, partial migration is expected to evolve. In the context of delayed dispersal, habitat saturation has been argued to form an ecological constraint on independent breeding, which favors offspring retention and cooperative breeding. We show that habitat saturation must be considered as a dynamic outcome of birth, death, and dispersal rates in the population, rather than an externally determined constraint. Although delayed dispersal often associates with intense competition for territories, life-history traits have direct effects on stable dispersal strategies, which can often override the effect of habitat saturation. As an example, high survival of floaters selects against delayed dispersal, even though it increases the number of competitors for each breeding vacancy (the "habitat saturation factor"). High survival of territory owners, by contrast, generally favors natal philopatry. We also conclude that spatial variation in habitat quality only rarely selects for delayed dispersal. Within a population, however, offspring retention is more likely in high-quality territories.     

Complex effects of habitat loss on Golden Eagles Aquila chrysaetos

The development of commercial forests presents potential threats to large raptors that rely on prey caught in open country. We examined the effect of afforestation of breeding habitat used by a population of Golden Eagles Aquila chrysaetos in Scotland where, over the last 50 years, extensive stands of exotic conifers have been planted. Using data for 31 years on territory occupancy and breeding success, together with spatiotemporally dynamic mapping of forest cover and predicted areas of territory‐use in a Geographical Information System, we examined relationships between forest cover and Eagle ecology at landscape and individual territory scales. Several territories were abandoned during the earliest phases of forest planting, but relatively few were apparently lost to later plantings. Territories with poorer breeding productivity appeared to be more vulnerable to abandonment than territories with better breeding productivity. At the landscape scale, temporal differences in breeding productivity were negatively related to the extent of forest cover, although productivity of individual territories showed no clear relationship with forest cover. Several territories with less than a 5% increase in forest cover experienced reduced productivity; however, territories least constrained by neighbouring pairs of Eagles showed an increase in productivity. Territories experiencing the greatest increases in forest cover showed a greater use of spatially separated nest‐sites by occupying pairs. Hence, pairs that were less constrained by neighbours appeared to compensate for loss of open habitat by shifting their territory‐use, whereas pairs that were more constrained could not compensate for open habitat loss and suffered reduced productivity (and, probably in some cases, abandoned the territory). We suggest that simple guidelines based on the extent and locations of habitat loss are inadequate when predicting effects on large territorial raptors such as Golden Eagles. Consideration should also be given to the ‘quality’ of a territory or occupying pair, as well as the extent to which territory‐use is constrained by neighbouring pairs or other ‘unsuitable habitat’ which may have been affected by previous episodes of open habitat loss.     

Steroid hormone interrelationships with territorial aggression in an Arctic-breeding songbird,Gambel's white-crowned sparrow,Zonotrichia leucophrys gambelii

The breeding season is very brief for arctic-breeding passerines, and any interruptions of parental care by aggressive interactions over territory may reduce reproductive success. We tested both the "testosterone insensitivity" and "corticosterone insensitivity" hypotheses in the arctic-breeding Gambel's white-crowned sparrow, Zonotrichia leucophrys gambelii. Additionally, we tested whether simulated territorial intrusions (STIs), known to stimulate increases in luteinizing hormone (LH) and testosterone (T) in mid-latitude breeding Z. l. pugetensis, would also be effective in either the early or late phases of the brief breeding season of Z. l. gambelii. Plasma levels of T and LH were high early in the breeding season and declined as egg laying began. Exposure of free-living males to 10 min of STI significantly increased LH but not T secretion. Nonetheless, the pituitary-gonadal axis is sensitive as jugular injection of gonadotrophin-releasing hormone increased plasma T at 10 min relative to saline-challenged controls. T implants failed to increase territorial aggression following STI during incubation. These data are consistent with the T insensitivity hypothesis and contrast sharply with the response of the southerly breeding subspecies, Z. l. pugetensis, in which the territorial response to T administration is retained throughout its relatively long breeding season. However, corticosterone implants during the incubation period decreased territorial aggression during STI. This responsiveness to corticosterone is not consistent with the corticosterone insensitivity hypothesis of stress modulation. Z. l. gambelii retain sensitivity to corticosterone levels that may occur naturally in response to environmental perturbations resulting in suppression of territorial behavior.     

Dynamics of food availability, body condition and physiological stress response in breeding Black-legged Kittiwakes

1. The seasonal dynamics of body condition (BC), circulating corticosterone levels (baseline, BL) and the adrenocortical response to acute stress (SR) were examined in long-lived Black-legged Kittiwakes, Rissa tridactyla , breeding at Duck (food-poor colony) and Gull (food-rich colony) Islands in lower Cook Inlet, Alaska. It was tested whether the dynamics of corticosterone levels reflect a seasonal change in bird physiological condition due to reproduction and/or variation in foraging conditions.
2. BC declined seasonally, and the decline was more pronounced in birds at the food-poor colony. BL and SR levels of corticosterone rose steadily through the reproductive season, and BL levels were significantly higher in birds on Duck Island compared with those on Gull Island. During the egg-laying and chick-rearing stages, birds had lower SR on Duck Island than on Gull Island.
3. The results suggest that, in addition to a seasonal change in bird physiology during reproduction, local ecological factors such as food availability affect circulating levels of corticosterone and adrenal response to acute stress.     

Modulation of prolactin but not corticosterone responses to stress in relation to parental effort in a long-lived bird

We tested the hypothesis that parental effort modulates the magnitude of corticosterone and prolactin responses to stress in a long-lived bird, the Black-legged kittiwake (Rissa tridactyla). To do so, we compared corticosterone and prolactin responses to capture/restraint stress between chick-rearing birds and failed breeders (no parental effort). We predicted that (1) the increase in plasma corticosterone levels in response to stress should be lower in chick-rearing birds, (2) the decrease in plasma prolactin levels in response to stress should be lower in chick-rearing birds, and (3) as both sexes care for the chick, there should be no sex difference in the hormonal response to stress. Baseline plasma corticosterone and prolactin levels were higher in chick-rearing birds and were not influenced by body condition. Failed breeders were in better condition than chick-rearing individuals. Corticosterone response to stress was unaffected by parental effort as both chick-rearing and failed birds exhibited a robust corticosterone increase. Prolactin response to stress was however clearly influenced by parental effort: chick-rearing birds showed a modest 9% prolactin decrease whereas in failed birds prolactin concentrations fell by 41%. Body condition did not influence hormonal responses to stress. When facing stressful condition, breeding kittiwakes attenuate their prolactin response to stress while enhancing their secretion of corticosterone. Increasing corticosterone secretion triggers foraging efforts and diminishes nest attendance whereas an attenuation of prolactin response to stress maintains parental behavior. We suggest that this hormonal mechanism facilitates a flexible time-budget that has been interpreted as a buffer against environmental variability.     

Manipulating Individual Decisions and Environmental Conditions Reveal Individual Quality in Decision-Making and Non-Lethal Costs of Predation Risk

Habitat selection is a crucial decision for any organism. Selecting a high quality site will positively impact survival and reproductive output. Predation risk is an important component of habitat quality that is known to impact reproductive success and individual condition. However, separating the breeding consequences of decision-making of wild animals from individual quality is difficult. Individuals face reproductive decisions that often vary with quality such that low quality individuals invest less. This reduced reproductive performance could appear a cost of increased risk but may simply reflect lower quality. Thus, teasing apart the effects of individual quality and the effect of predation risk is vital to understand the physiological and reproductive costs of predation risk alone on breeding animals. In this study we alter the actual territory location decisions of pied flycatchers by moving active nests relative to breeding sparrowhawks, the main predators of adult flycatchers. We experimentally measure the non-lethal effects of predation on adults and offspring while controlling for effects of parental quality, individual territory choice and initiation of breeding. We found that chicks from high predation risk nests (<50 m of hawk) were significantly smaller than chicks from low risk nests (>200 m from hawk). However, in contrast to correlative results, females in manipulated high risk nests did not suffer decreased body condition or increased stress response (HSP60 and HSP70). Our results suggest that territory location decisions relative to breeding avian predators cause spatial gradients in individual quality. Small adjustments in territory location decisions have crucial consequences and our results confirm non-lethal costs of predation risk that were expressed in terms of smaller offspring produced. However, females did not show costs in physiological condition which suggests that part of the costs incurred by adults exposed to predation risk are quality determined.     

Determining habitat quality for the cooperatively breeding Rufous Treecreeper,Climacteris rufa

Abstract The theory of habitat selection predicts that organisms should use habitat that maximizes their fitness. The cooperatively breeding Rufous Treecreeper, Climacteris rufa, exhibits non‐random habitat use at a number of spatial scales. By assessing correlative relationships between nest‐site use and nest success, and territory use and reproductive success and survival, it was determined whether non‐random use of habitat yields fitness benefits. It was also determined whether breeding group size contributed significantly to fitness once differences in territory quality had been considered. Structural characteristics of nest sites that were positively correlated with the probability of a site being used had no relationship with nest success. This result probably reflects the relatively unrestricted access to an abundance of suitable nest sites in the study area. Habitat traits that predicted territory use by treecreepers were positively correlated with a number of fitness measures. They were also positively correlated with breeding group size and provisioning rate to nestlings, which in turn were correlated with fitness. However, group size was not significantly related to any measure of fitness, except primary male survival, once territory quality had been considered. The quality of territories occupied by Rufous Treecreepers appeared to be a significant factor for breeding group fitness.     

Interplay between plasma hormone profiles, sex and body condition in immature hawksbill turtles (Eretmochelys imbricata) subjected to a capture stress protocol

We investigated plasma hormone profiles of corticosterone and testosterone in immature hawksbill turtles (Eretmochelys imbricata) in response to a capture stress protocol. Further, we examined whether sex and body condition were covariates associated with variation in the adrenocortical response of immature turtles. Hawksbill turtles responded to the capture stress protocol by significantly increasing plasma levels of corticosterone over a 5 h period. There was no significant sex difference in the corticosterone stress response of immature turtles. Plasma testosterone profiles, while significantly different between the sexes, did not exhibit a significant change during the 5 h capture stress protocol. An index of body condition was not significantly associated with a turtle's capacity to produce plasma corticosterone both prior to and during exposure to the capture stress protocol. In summary, while immature hawksbill turtles exhibited an adrenocortical response to a capture stress protocol, neither their sex nor body condition was responsible for variation in endocrine responses. This lack of interaction between the adrenocortical response and these internal factors suggests that the inactive reproductive- and the current energetic- status of these immature turtles are important factors that could influence plasma hormone profiles during stress.