Sonia Cabezas

Physiological stress levels predict survival probabilities in wild rabbits

Among vertebrates, short-term elevations of glucocorticoid hormones (corticosterone or cortisol) facilitate a suite of physiological and behavioral changes aimed at overcoming environmental perturbations or other stressful events. However, chronically elevated glucocorticoids can have deleterious physiological consequences, and it is still unclear as to what constitutes an adaptive physiological response to long-term stress. In this study, we experimentally exposed European wild rabbits Oryctolagus cuniculus to a source of long-term stress (simulated through a 2- to 4-week period of captivity) and tested whether glucocorticoid physiology predicted two major components of rabbit fitness: body condition and survival probability. Following exposure to long-term stress, moderately elevated serum corticosterone and fecal glucocorticoid metabolites levels in the wild rabbits were negatively associated with body condition, but positively associated with subsequent survival upon release. Our results suggest that the cost of maintaining elevated corticosterone levels in terms of decreased body condition is balanced by the increased chance of survival upon release.

Tracking stress: localisation, deposition and stability of corticosterone in feathers.

SUMMARY How animals cope with stressors is an important determinant of their well being and fitness. Understanding what environmental perturbations are perceived as stressors, and quantifying how they are responded to, how often they occur and the negative consequences of exposure to glucocorticoids, has been problematic and limited to short-term physiological measures. By contrast, the quantification of corticosterone (CORT) in feathers represents a long-term, integrated measure of hypothalamic–pituitary–adrenal activity. In the present study, we show that by understanding how the hormone is deposited in feathers, in combination with specific sampling protocols, one can identify localised patterns of CORT deposition that reveal different temporal patterns of a birds response to stressors. CORT in feathers appears to be stable over time, is resistant to heat exposure and is useful in determining both the overall exposure of the bird to the hormone over days or weeks, as well as identifying discrete, punctuated, stressful events. Variation in feather CORT can also be examined among individuals of a population at one point in time, as well as over years by using museum specimens. The ability to track stress over time allows for new questions to be asked about the health and ecology of birds and their environment.

Long-term decline of the European wild rabbit (Oryctolagus cuniculus) in south-western Spain

The European wild rabbit (Oryctolagus cuniculus) is a species native to the Iberian Peninsula, where it was once extremely abundant. It is considered the most important prey item for the peninsulas assemblage of Mediterranean vertebrate predators, which includes two endangered specialist rabbit feeders, the Spanish imperial eagle (Aquila adalberti) and the Iberian lynx (Lynx pardinus). However, rabbit population trends in Spain have not been accurately documented. In the present study, we analysed trends in a population of European rabbits monitored over 23 years in the Donana National Park, home to one of the most diverse and densest predator communities in Europe. Rabbit abundance and population trends were estimated using roadside counts. Results show that the rabbit population declined sharply by ~60% during the first wave of epizootic rabbit hemorrhagic disease (RHD) in 1990. Since then, rabbit numbers have declined at a relatively constant rate and the species has become progressively scarcer in the area. The current population is less than 10% of that before the arrival of RHD. However, after the RHD epizootic we observed increasing intra-annual population recruitment. We hypothesise that density-dependent factors caused by enzootic viral diseases (myxomatosis, RHD) and higher predation of rabbits are the main factors preventing recovery of rabbit numbers. The effects of a decline in the prey species on the ecology of sympatric rabbit predators are discussed, and measures to improve ongoing rabbit conservation efforts are suggested.

Links between fear of humans, stress and survival support a non-random distribution of birds among urban and rural habitats

Urban endocrine ecology aims to understand how organisms cope with new sources of stress and maintain allostatic load to thrive in an increasingly urbanized world. Recent research efforts have yielded controversial results based on short-term measures of stress, without exploring its fitness effects. We measured feather corticosterone (CORTf, reflecting the duration and amplitude of glucocorticoid secretion over several weeks) and subsequent annual survival in urban and rural burrowing owls. This species shows high individual consistency in fear of humans (i.e., flight initiation distance, FID), allowing us to hypothesize that individuals distribute among habitats according to their tolerance to human disturbance. FIDs were shorter in urban than in rural birds, but CORTf levels did not differ, nor were correlated to FIDs. Survival was twice as high in urban as in rural birds and links with CORTf varied between habitats: while a quadratic relationship supports stabilizing selection in urban birds, high predation rates may have masked CORTf-survival relationship in rural ones. These results evidence that urban life does not constitute an additional source of stress for urban individuals, as shown by their near identical CORTf values compared with rural conspecifics supporting the non-random distribution of individuals among habitats according to their behavioural phenotypes.

Vaccination Success and Body Condition in the European Wild Rabbit: Applications for Conservation Strategies

Abstract The European wild rabbit (Oryctolagus cuniculus) is the main prey for several endangered species and an important game species in the Iberian Peninsula. However, over the last several decades 2 diseases, myxomatosis and rabbit hemorrhagic disease (RHD), have contributed to a decline in rabbit populations. In Spain, vaccination campaigns against both diseases and the translocation of vaccinated rabbits are frequently used in projects aimed at stimulating the recovery of wild populations. We estimated which factors related to body condition were associated with successful immunization by vaccination. In 191 adult wild rabbits, we calculated a body-mass index and analyzed a number of biochemical parameters and antibody concentrations before and after vaccination. Results showed that, respectively, 81 and 84% of initially seronegative rabbits seroconverted after vaccination against myxomatosis and RHD. We also found that RHD antibody concentrations after vaccination were positively associated with total protein concentrations at the moment of vaccination in all rabbits, whereas RHD antibody concentrations were negatively related to the creatinine concentration at the end of our study for initially seronegative rabbits. Our results suggested that in wild rabbits vaccination was an effective way of increasing antibody concentrations and, thus, of fighting myxomatosis and RHD, although the intensity of the immune response was conditioned by the body condition of individual rabbits. Consequently, rabbit translocations could be improved by avoiding the translocation of individuals with poor body condition and by improving vaccination protocols. In addition, success rates in mass vaccination programs carried out in free-living wild populations may be increased if the body condition of individuals is evaluated before vaccination campaigns are carried out.

Carotenoids and Skin Coloration in a Social Raptor

Abstract The outcome of social and sexual competition in animals is typically mediated through the expression of body traits. Conspicuous characters such as yellow, orange, and red colorations in skin, scales, and feathers are often posited as quality-dependent signals, because such colors are made of dietary carotenoids and their use for signaling conflicts with health functions. Raptors often lack brightly colored feathers but most diurnal species display intense orange and yellow hues in the cere and legs. Here we test the hypothesis that integument coloration functions as a signal of status in wild raptors, revealing availability of carotenoid pigments. As study model we used the Black Kite (Milvus migrans), a highly social, long-lived, and sexually monogamous Accipitriform. Regular trapping of adults throughout the breeding season revealed that circulating carotenoid levels were highest in breeding males, whereas breeding females and floaters showed moderate and statistically similar carotenoid titer...

Ambient temperature, body condition and sibling rivalry explain feather corticosterone levels in developing black kites

Summary In birds, the steroid hormone corticosterone (CORT) is considered a major mediator in a number of physiological mechanisms and behaviours critical for the regulation of an organisms energy balance. However, the question of whether the way in which circulating plasma CORT is incorporated into feathers actually reflects this regulation, and consequently whether feather CORT (CORT-F) measures allow to make inferences on past levels of energetic demands (also known as the allostatic load), remains unclear. While previous studies have yielded promising results, the technique still wants further study and validation in a wider range of bird species, across life-history stages and under different ecological situations. Here, we tested whether CORT-F levels in a sample of 427 nestling black kites (Milvus migrans) reflected interindividual variation in a number of environmental, social and physiological variables known to elevate allostatic load during development. We found that nestlings exposed to low ambient temperatures exhibited high CORT-F, suggesting that feathers registered the expected rise in circulating CORT levels inducing thermogenesis in response to cold stress. CORT-F was also negatively related to body condition, supporting the notion that allostasis becomes less affordable as energy stores become depleted. Finally, CORT-F also reflected brood hierarchy rank, with subordinate chicks exhibiting the highest levels, followed by first-hatched (dominant) chicks and lastly singleton nestlings. Moreover, CORT-F levels in nestlings from multiple-chick broods (but not in singletons) declined with age, mirroring the dynamics of establishment and stabilization of sibling hierarchies in black kites. Altogether, our results underscore the potential of using CORT-F to infer allostatic load in wild avian populations and their potential power as indicator tools in conservation biology.

Effects of Ontogeny, Diel Rhythms, and Environmental Variation on the Adrenocortical Physiology of Semialtricial Black Kites (Milvus migrans)

We examined whether hypothalamic-pituitary-adrenal axis activity in the nestlings of a semialtricial raptor, the black kite (Milvus migrans), varied with advancing age, throughout the day, and in response to a number of socioecological factors presumed to affect allostatic load. Both baseline corticosterone (CORT) titers and maximum CORT levels during 30 min of handling and restraint augmented across all sampled ages, suggesting that nestlings’ energetic demands and capacity to respond to perturbations increase progressively throughout development. CORT secretion also peaked in the early morning, reached minimum levels in the central hours of the day, and increased again before dusk, suggesting a possible role of CORT in the regulation of activity-inactivity patterns. Finally, nestlings raised in a year of low marsh inundation, implying lower food availability and heightened allostatic loads, exhibited higher adrenocortical responsiveness to stress than nestlings raised in years of intermediate or high flooding. The nondetectable effect of other socioecological variables, such as territory quality, temperature, or brood order, suggests that parents may be able to buffer their nestlings from adverse environmental conditions or that the effect of such factors may have been obscured by selective mortality operating before sampling. We propose that future studies increase the simultaneous use of complementary techniques (fecal sampling, feather analysis) to reach firmer and more comprehensive conclusions, especially for planning the management and conservation of sensitive species.

Is the rufous axillary patch of the screaming cowbird a secondary sexual character

Summary. The screaming cowbird Molothrus rufoaxillaris is described as being sexually monochromatic, although it has a rufous axillary patch that shows inter-individual size variation. We investigated potential sex differences in patch size in 82 molecularly-sexed adults. All males exhibited large patches and 23 females had small patches; however, seven females lacked a patch and nine had large patches. Patch size was associated with sex and independent of body condition, location or date of sampling. We discuss several hypotheses that may explain the incidence of this male character in some females.