Oxytocin is involved in a broad array of social behaviours. While saliva has been used regularly to investigate the role of oxytocin in social behaviour of mammal species, so far, to our knowledge, ...no-one has tried to measure its homolog, mesotocin, in birds' saliva. Therefore, in this study we measured salivary mesotocin in common ravens (Corvus corax), and subsequently explored its link to three aspects of raven sociality. We trained ravens (n = 13) to voluntarily provide saliva samples and analysed salivary mesotocin with a commercial oxytocin enzyme-immunoassay kit, also suitable for mesotocin. After testing parallelism and recovery, we investigated the effect of bonding status, sex and season on mesotocin levels. We found that mesotocin was significantly more likely to be detected in samples taken during the breeding season (spring) than during the mating season (winter). In those samples in which mesotocin was detected, concentrations were also significantly higher during the breeding than during the mating season. In contrast, bonding status and sex were not found to relate to mesotocin detectability and concentrations. The seasonal differences in mesotocin correspond to behavioral patterns known to be associated with mesotocin/oxytocin, with ravens showing much more aggression during the mating season while being more tolerant of conspecifics in the breeding season. We show for the first time that saliva samples can be useful for the non-invasive determination of hormone levels in birds. However, the rate of successfully analysed samples was very low, and collection and analysis methods will benefit from further improvements.
•Ravens were trained to provide saliva samples voluntarily.•Salivary mesotocin levels were determined with an enzyme-immunoassay (EIA).•Mesotocin was more likely to be detected in the breeding than in the mating season.•Ravens' mesotocin levels were higher in the breeding than in the mating season.
Corticosterone (Cort) is involved in multiple physiological processes during bird migration, complicating its interpretation in a stress context. We investigated whether the leukocyte coping capacity ...(LCC) provides useful complementary information on the stress response in migratory Garden Warblers (
Sylvia borin
) and how it relates to Cort and energetic condition. Contrary to Cort levels, LCC significantly decreased, implying high-stress levels and a diminished capacity to recover after a stressful event. The absence of significant effects of body conditions on the stress parameters shows no simple relationship between these traits and highlights the need for additional stress metrics to measure stress in life-history contexts.
In many birds and mammals, male territorial aggression is modulated by elevated circulating concentrations of the steroid hormone testosterone (T) during the breeding season. However, many species ...are territorial also during the non-breeding season, when plasma T levels are basal. The endocrine control of non-breeding territorial aggression differs considerably between species, and previous studies on wintering birds suggest differences between migratory and resident species. We investigated the endocrine modulation of territorial aggression during the breeding and non-breeding season in a resident population of European stonechats (Saxicola torquata rubicola). We recorded the aggressive response to a simulated territorial intrusion in spring and winter. Then, we compared the territorial aggression between seasons and in an experiment in which we blocked the androgenic and estrogenic action of T. We found no difference in the aggressive response between the breeding and the non-breeding season. However, similarly to what is found in migratory stonechats, the hormonal treatment decreased aggressive behaviors in resident males in the breeding season, whereas no effects were recorded in the non-breeding season. When we compared the aggressive responses of untreated birds with those obtained from migratory populations in a previous study, we found that territorial aggression of resident males was lower than that of migratory males during the breeding season. Our results show that in a resident population of stonechats T and/or its metabolites control territorial aggression in the breeding but not in the non-breeding season. In addition, our study supports the hypothesis that migratory status does modulate the intensity of aggressive behavior.
► Territoriality in sedentary stonechats is similar in breeding and non-breeding season. ► However the hormonal control of territorial behavior changes seasonally. ► Territorial aggression was lower compared to breeding migratory stonechats. ► Life-history changes modulate the intensity of territorial aggression.
In birds, territorial aggression during the breeding season is regulated by testosterone (T). However, many bird species also express aggressive behavior during the nonbreeding season, when plasma ...levels of T are low. It has been suggested that during this period estrogens might play a major role in regulating territorial aggression. In the present study we compared the effects of simultaneous blockage of androgenic and estrogenic actions on territorial aggression during the breeding and nonbreeding seasons in free-living male European stonechats (Saxicola torquata rubicola). European stonechats are of particular interest since they establish territories and form pairs during both the breeding and the nonbreeding seasons. Thus territorial aggression and its endocrine control can be compared between reproductive and nonreproductive contexts. Inhibition of androgenic and estrogenic actions by simultaneous application of Flutamide and ATD reduced territorial aggression during the breeding season, but not during the nonbreeding season. Our results show that androgens and/or estrogens are involved in the endocrine control of territorial aggression in stonechats only in a reproductive context, but not in a nonreproductive one.
In most bird species, male courtship behavior is controlled by testosterone (T) and its metabolites. In species breeding in temperate and arctic regions T circulates at high levels during a ...relatively short courtship period because high levels of T can be costly in terms of immunocompetence and parental care. Few studies have investigated androgen modulation of courtship behavior in tropical birds. Male golden-collared manakins (
Manacus vitellinus) aggregate in leks for several months and perform spectacular, acrobatic courtship displays. Here we examined whether T is elevated in golden-collared manakins during the displaying period and if courtship behavior is modulated by androgen action on androgen receptors. We measured T levels in displaying males at the beginning of the breeding season and again, one month later. In addition, both wild and captive males were treated with the anti-androgen, flutamide, and their courtship behavior was recorded for several weeks. T levels were relatively high shortly after leks were established but decreased substantially a month later, even though the amount of courtship did not change. Flutamide reduced male courtship activity for one week, but display behavior then increased after two weeks of flutamide treatment. Our studies show that androgens modulate male manakin courtship, but the amount of courtship is not directly correlated with the concentration of circulating T. These results suggest that the relationships between androgen and courtship might differ between tropical and temperate birds.
The ability of individual animals to defend a territory as well as various phenotypic and behavioral traits may be targets of sexual selection used by males to evaluate their competitors or by ...females to choose males. A frequent question in animal behavior is whether male traits and characteristics of their territory are correlated and what are the mechanisms that may mediate such associations when they exist. Because hormones link phenotype to behavior, by studying the role of testosterone in territoriality one may come closer to understanding the mechanisms mediating correlations or lack thereof between characteristics of territories and of males. We evaluated whether variation in characteristics of territories (size and quality) are correlated with variation in morphology, coloration, testosterone, heterozygosity, and calls in two species of poison frogs. The Amazonian frog Allobates aff. trilineatus exhibits male care and defends territories only during the breeding season, while the endangered frog Oophaga lehmanni displays maternal care and defends territories throughout the year. We found that morphological traits (body length, weight, thigh size), call activity, and testosterone levels correlated with size and various indicators of quality of the territory. However, the direction of these correlations (whether positive or negative) and which specific morphological, acoustic traits or testosterone level variables covaried depended on the species. Our findings highlight an endocrine pathway as part of the physiological machinery that may underlie the interplay between male traits and territorial behavior. We were able to identify some male traits related to territory attributes, but whether females choose males based on these traits requires further research.
•Morphology, calls, and testosterone correlate with territory features in poison frogs.•Involved traits and the type of correlation depended on the species.•Testosterone could be the mechanism underlying these correlations.•Leaf litter is a key resource for a cryptic, male care and seasonal breeding frog.•Bromeliads are essentials for an aposematic, maternal care and extended breeding frog.
Hormones play a fundamental role in mediating social behaviors of animals. However, it is less well understood to what extent behavioral variation between individuals can be attributed to variation ...in underlying hormonal profiles. The goal of the present study was to infer if individual androgen levels, and/or the modulation thereof, can explain among-individual variation in aggressiveness, boldness and exploration. We used as a model the dart-poison frog Allobates femoralis and took repeated non-invasive water-borne hormonal samples of individual males before (baseline) and after (experimental) a series of behavioral tests for assessing aggression, boldness, and exploratory tendency. Our results show that androgen levels in A. femoralis are quite stable across the reproductive season. Repeatability in
T baseline levels was high, while time of day, age of the frog, and trial order did not show any significant impact on measured
T levels. In general, experimental
T levels after behavioral tests were lower compared to the respective baseline levels. However, we identified two different patterns with regard to androgen modulation in response to behavioral testing: individuals with low baseline
T tended to have increased
T levels after the behavioral testing, while individuals with comparatively high baseline
T levels rather showed a decrease in hormonal levels after testing. Our results also suggest that baseline
T levels are linked to the personality trait exploration, and that androgen modulation is linked to boldness in A. femoralis males. These results show that differences in hormonal profiles and/or hormonal modulation in response to social challenges can indeed explain among-individual differences in behavioral traits.
Stress is a collective term for certain conditions and sequences of physiological events enabling living organisms to overcome unpredictable and uncontrollable situations. The context-dependent ...nature, multidimensional course and large individual variability make stress responses difficult to measure. In avian species, a plethora of studies on short-term stress responses have been conducted by measuring the corticosteroid response to a standardized stress protocol. Here we aimed to test the viability of the leukocyte coping capacity (LCC), measuring oxygen radical production by leukocytes, to assess short-term stress in birds. We collected blood samples from captive house sparrows (Passer domesticus) in the two seasons of winter and spring, right after capture and 30min thereafter. In order to assess the overall physiological stress response to a standardized stressor, i.e. handling and temporary constraint, we measured LCC and additionally combined it with measures of total circulating glucocorticoids (GCs) and oxidative stress. All three methodologies detected significant changes due to the stressor albeit they were not correlated with each other and revealed different information. There was no significant change in oxidative stress levels between the two time points although the amount of relative oxidative damage as well as the anti-oxidative capacity changed significantly. We observed a significant seasonal difference in GC stress response with no difference between sexes. On the contrary, LCC measures revealed with a high individual consistency, that individuals experienced a similar magnitude of stress in both seasons with a significant difference between sexes. Total GC-levels have to be interpreted with caution regarding the assessment of short-term stress reactions. We therefore suggest to supplementary combine classical approaches for measuring stress with the immunological tool of LCC. Our results reveal LCC as a strong and reliable tool to assess short-term stress in captive house sparrows and as promising for other bird species. Collectively the study highlights the necessity to incorporate a range of physiological systems and their endpoints to measure and to assess stress reactions effectively.
•Leukocyte Coping Capacity is a strong proxy for stress.•LCC reveals pronounced sexual differences in stress response.•Short term stress is changing redox physiology but not overall oxidative stress.
The hormone melatonin, a main component of the avian circadian system, plays an important role in the physiological transitions that accompany activation of the migratory phenotype in passerine ...birds. Most small passerines migrate at night when circulating concentrations of melatonin are elevated. Previous work measured nocturnal melatonin levels of migratory birds only in captive animals, because free-living individuals are usually caught in the daytime. In this study, we compared nocturnal melatonin levels of European robins (
) caught during the day and held in cages overnight with those of birds that were caught at night and sampled immediately. We found that circulating melatonin at night was lower in birds held in cages compared with birds that were actively migrating. This result suggests that temporary caging affects the melatonin system and that, in nature, melatonin levels could be generally higher than those previously described by studies on captive birds.
Stopover territoriality, i.e., the defense and broadcast of an ephemeral home range during avian migration, is rare or perhaps overlooked. However, settling on a territory may allow for easier access ...to resources and therefore promote faster refueling despite the added costs of territory defense. We examined the occurrence of stopover territoriality and its relationship to body condition and refueling rates. We color-ringed Western Subalpine Warblers (
Curruca iberiae
) mapped their home ranges and measured associated habitat characteristics during a spring stopover in the Sahara. We simulated territory intrusions via song playback to quantify territorial behavior. Males aggressively defended and broadcasted their stopover territories in response to intruders. Initial body condition in males was negatively related to home range vegetation density, suggesting that males in higher condition are selective for certain territory features. Low vegetation density does not support habitat selection for foraging, but perhaps does support social monitoring or predator vigilance as its functions. Fuel deposition rates in recaptured males were unrelated to home range habitat characteristics. Female Subalpine Warblers did not use repeated home ranges yet had similar refueling rates, body conditions, and stopover durations as territorial males. Therefore, while stopover territories were selected based on body condition, territory characteristics did not influence refueling rates. Subalpine Warblers expressed reduced migratory characteristics, making prolonged stopovers of up to 27 days with low refueling rates but maintaining body condition while defending territories. These results suggest that some individuals are staging for non-energetic reasons, such as pre-breeding preparations, or transitioning between a migratory and a breeding life history stage.
Significance statement
Territoriality in birds is commonly associated with breeding activities, less so with the wintering period and rarely with migratory periods. However, territoriality during migration may be energetically beneficial. During a trans-Saharan stopover, male warblers establish and defend temporary territories by singing and engaging in physical defense of home ranges, and those in better condition occupied territories with sparser vegetation. Females were not territorial but refueled at similar rates as males. Stopover territoriality did not increase access to food-rich patches, but perhaps aided in efficient social monitoring and preparations for the approaching breeding season. This is the first detailed documentation of birds defending ephemeral territories during migration, and its potential functions, costs and benefits may inform studies of full-annual cycles and life histories of many migratory species.
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