Didone Frigerio

Spatial proximity among adult siblings in greylag geese (Anser anser): evidence for female bonding?

Abstract By staying close to allies, individuals may enjoy benefits through social support. In the socially monogamous greylag goose (Anser anser), pair-partners, parents, and even human foster parents may provide social support, facilitating access to resources or reducing agonistic pressure. In the present work, we analysed the spatial distribution of individuals within a semi-feral flock of 120 greylag geese, which contained 23 adult sibling groups of 2–4 individuals from 2 to 12 years old. During resting periods we scored dyadic distances between 28 focal individuals of different social categories, their siblings and unrelated control individuals of the same age. Adult female siblings (i.e. those hatched in the same year and raised together) rested significantly closer to each other than to either their brothers or unrelated control individuals. We attribute this to social attraction rather than to just a common preference for the same resting site. Thus, kinship bonds as expressed by cohesion might persist into adulthood, at least in the females. We discuss the potential benefits of proximity between related individuals with regard to reduced social stress via social support.

Experimentally elevated testosterone increases status signalling in male Greylag geese (Anser anser)

Testosterone modulates male vertebrates’ sexual and social behaviour. We experimentally investigated the testosterone-sensitive behaviours in male greylag geese (Anser anser) by implanting silastic tubes containing crystalline testosterone during the mating season (February; 5 implanted and 5 control males) and in the early winter (November; 7 and 7). Focal animals were part of a semi-tame, unrestrained flock with fully intact social relationships. Excreted testosterone and corticosterone immunoreactive metabolites (TM, BM) were determined by enzyme immunoassay. Individual faecal samples and behavioural protocols were collected daily over a period of 5 weeks, including 1 control week before implantation. In February, no significant behavioural effects of the supplemental testosterone were observed, which may be due to the naturally occurring high systemic androgen levels in spring. In November, however, implanted males had higher TM excretion rates and performed status signalling behaviour (“beak up”) more frequently than control males. No differences between implanted and control males were found with respect to BM, agonistic interactions or vigilance behaviour. Furthermore, during the second week after implantation, TM positively correlated with the frequency of “beak up” of implanted males, whilst their female partners were attacked with lower latency by other members of the flock than the females of control males. Hence, status signalling in greylag ganders seems to be testosterone-sensitive year-long and “inappropriate” status signalling of males may draw attacks towards their females.

Seasonal differences of corticosterone metabolite concentrations and parasite burden in northern bald ibis ( Geronticus eremita ): The role of affiliative interactions

The reproductive season is energetically costly as revealed by elevated glucocorticoid concentrations, constrained immune functions and an increased risk of infections. Social allies and affiliative interactions may buffer physiological stress responses and thereby alleviate associated effects. In the present study, we investigated the seasonal differences of immune reactive corticosterone metabolite concentrations, endoparasite burden (nematode eggs and coccidian oocysts) and affiliative interactions in northern bald ibis (Geronticus eremita), a critically endangered bird. In total, 43 individually marked focal animals from a free-ranging colony were investigated. The analyses included a description of initiated and received affiliative interactions, pair bond status as well as seasonal patterns of hormone and endoparasite levels. During the reproductive season, droppings contained parasite eggs more often and corticosterone metabolite levels were higher as compared to the period after reproduction. The excretion rate of endoparasite products was lower in paired individuals than in unpaired ones, but paired animals exhibited higher corticosterone metabolite concentrations than unpaired individuals. Furthermore, paired individuals initiated affiliative behaviour more frequently than unpaired ones. This suggests that the reproductive season influences the excretion patterns of endoparasite products and corticosterone metabolites and that affiliative interactions between pair partners may positively affect endoparasite burden during periods of elevated glucocorticoid levels. Being embedded in a pair bond may have a positive impact on individual immune system and parasite resistance.

Social and environmental factors modulate leucocyte profiles in free-living Greylag geese (Anser anser)

Background Blood parameters such as haematocrit or leucocyte counts are indicators of immune status and health, which can be affected, in a complex way, by exogenous as well as endogenous factors. Additionally, social context is known to be among the most potent stressors in group living individuals, therefore potentially influencing haematological parameters. However, with few exceptions, this potential causal relationship received only moderate scientific attention. Methods In a free-living and individually marked population of the highly social and long-lived Greylag goose, Anser anser, we relate variation in haematocrit (HCT), heterophils to lymphocytes ratio (H/L) and blood leucocyte counts to the following factors: intrinsic (sex, age, raising condition, i.e. goose- or hand-raised), social (pair-bond status, pair-bond duration and parental experience) and environmental (biologically relevant periods, ambient temperature) factors. Blood samples were collected repeatedly from a total of 105 focal birds during three biologically relevant seasons (winter flock, mating season, summer). Results We found significant relationships between haematological parameters and social as well as environmental factors. During the mating season, unpaired individuals had higher HCT compared to paired and family individuals and this pattern reversed in fall. Similarly, H/L ratio was positively related to pair-bond status in a seasonally dependent way, with highest values during mating and successful pairs had higher H/L ratio than unsuccessful ones. Also, absolute number of leucocytes tended to vary depending on raising condition in a seasonally dependent way. Discussion Haematology bears a great potential in ecological and behavioural studies on wild vertebrates. In sum, we found that HTC, H/L ratio and absolute number of leucocytes are modulated by social factors and conclude that they may be considered valid indicators of individual stress load.

Excretion patterns of coccidian oocysts and nematode eggs during the reproductive season in Northern Bald Ibis (Geronticus eremita).

AbstractIndividual reproductive success largely depends on the ability to optimize behaviour, immune function and the physiological stress response. We have investigated correlations between behaviour, faecal steroid metabolites, immune parameters, parasite excretion patterns and reproductive output in a critically endangered avian species, the Northern Bald Ibis (Geronticus eremita). In particular, we related haematocrit, heterophil/lymphocyte ratio, excreted immune-reactive corticosterone metabolites and social behaviour with parasite excretion and two individual fitness parameters, namely, number of eggs laid and number of fledglings. We found that the frequency of excretion of parasites’ oocysts and eggs tended to increase with ambient temperature. Paired individuals excreted significantly more samples containing nematode eggs than unpaired ones. The excretion of nematode eggs was also significantly more frequent in females than in males. Individuals with a high proportion of droppings containing coccidian oocysts were more often preened by their partners than individuals with lower excretion rates. We observed that the more eggs an individual incubated and the fewer offspring fledged, the higher the rates of excreted samples containing coccidian oocysts. Our results confirm that social behaviour, physiology and parasite burden are linked in a complex and context-dependent manner. They also contribute background information supporting future conservation programmes dealing with this critically endangered species.ZusammenfassungAusscheidungsmuster von Kokzidienoozysten und Nematodeneiern während der Fortpflanzungsperiode bei Waldrappen (Geronticus eremita) Individueller Fortpflanzungserfolg hängt weitgehend von der Fähigkeit ab, Verhalten, Immunfunktion und die physiologische Reaktion auf Stress zu optimieren. In der vorliegenden Studie untersuchten wir Zusammenhänge zwischen Verhalten, fäkalen Steroidmetaboliten, hämatologischen Parametern, Parasitenausscheidungsmustern und Fortpflanzungserfolg in einer vom Aussterben bedrohten Vogelart, dem Waldrapp (Geronticus eremita). Insbesondere untersuchten wir Zusammenhänge zwischen ausgeschiedenen immunoreaktiven Corticosteronmetaboliten, dem Verhältnis von Heterophilen zu Lymphozyten, Hämatokrit und dem Sozialverhalten mit der Menge ausgeschiedener Parasiten und mit Fitness-Parametern, wie der Anzahl der gelegten Eier und der flügge gewordenen Jungvögel. Die Anzahl der Kotausscheidungen, die Parasiteneier enthalten, steigt tendenziell mit der Umgebungstemperatur. Verpaarte Vögel schieden deutlich öfter Kot mit Nematodeneiern aus, als Unverpaarte. Zudem enthielt der Kot der Weibchen signifikant öfter Nematodeneier, als der der Männchen. Individuen mit einem hohen Anteil an Kokzidienoozysten im Kot wurden häufiger von ihren Partnern gekrault, als Individuen mit geringeren Ausscheidungsraten. Je mehr Eier ein Individuum während der Brutzeit ausbrütete, und je weniger Nachwuchs flügge wurde, desto höher war die Rate von mit Kokzidienoozysten befallenen Proben. Unsere Ergebnisse bestätigen, dass Sozialverhalten, Physiologie und Parasitenbelastung in einer komplexen Weise miteinander verbunden sind. Darüber hinaus unterstützt die vorliegende Studie das Management dieser vom Aussterben bedrohten Vogelart.

Differential responses to gosling distress calls in parental and non-parental Greylag Geese

The pre-fledging survival of Greylag goslings (Anser anser) is known to be influenced by parenting style and particularly parental vigilance. Visual and acoustic cues may be important in parental vigilance: if vision is blocked, for example in a highly structured habitat, acoustic recognition of the goslings by their parents would be beneficial. We confronted parental and non-parental Greylag Geese with playbacks of gosling distress calls and analyzed their behavioral responses. Parental geese showed a significant increase in their vigilance behavior during and after playbacks while geese without offspring showed increased comfort behavior. In a permutated discriminant function analysis, we found no family-specific vocal cues in gosling calls, and potential call familiarity did not have any effect on parental behavioral responses. Vigilance in families was further influenced by the number of goslings and gosling age, with increased vigilance when the number of goslings was high, and when goslings were younger. Parental females were more vigilant than parental males, suggesting differences in parental investment between males and females. We conclude that visual cues may be more important in offspring-related vigilance than calls, which elicited different behavioral responses depending on the social class of the geese.ZusammenfassungReaktionsunterschiede auf Weinlaute in Grauganspaaren mit und ohne Nachwuchs Das Überleben von Gösseln der Graugans (Anser anser) vor dem Flüggewerden wird bekanntermaßen beeinflusst vom Erziehungsverhalten der Eltern, und im Besonderen von ihrer Wachsamkeit. Visuelle und akustische Hinweise können von Bedeutung sein für die elterliche Wachsamkeit: wenn die Sicht behindert ist, beispielsweise in einem dicht bewachsenen Lebensraum, wäre die akustische Erkennung der Gössel durch die Eltern von Vorteil. Graugänse mit und ohne Nachwuchs wurden mit Weinlauten von Gösseln konfrontiert und ihre Verhaltensantworten wurden analysiert. Graugänse mit Gösseln zeigten einen signifikanten Anstieg in ihrer Wachsamkeit während und nach dem Abspielen der Weinlaute, wohingegen Graugänse ohne Gössel verstärkt Komfortverhalten zeigten. In einer permutierten Diskriminanzfunktionsanalyse fanden wir keine akustischen Hinweise auf Familienzugehörigkeit in den Rufen der Gössel, und eine potentielle Bekanntheit der Rufe hatte keinen Einfluss auf die Verhaltensantworten der Eltern. Die Wachsamkeit in den Familien wurde außerdem von der Anzahl und dem Alter der Gössel beeinflusst, sie waren wachsamer wenn sie mehr und jüngere Gössel hatten. Innerhalb der Familien waren die Weibchen wachsamer als die Männchen, was auf Unterschiede im Aufwand zwischen den Geschlechtern hindeutet. Wir schlussfolgern, dass für die Wachsamkeit in Bezug auf den Nachwuchs visuelle Signale von größerer Bedeutung sein könnten als Rufe, die je nach sozialer Klasse unterschiedliche Verhaltensantworten bewirkten.