Interplay of hormones and behaviour in Arctic-breeding geese

The daily or seasonal release of hormones is essential for synchronising biochemical, physiological or behavioural processes. Different hormones interact with each other at various levels; therefore, examining only one hormone separately will lead to an incomplete picture. No single hormone has a one-to-one relationship with any particular behaviour, and neither is any behaviour regulated by only one hormone. One main goal here is to gain a more complete understanding of the relationships between three rhythmic hormones and their influence on daily and seasonal activity at the individual level. This is highly relevant as mistimed biological clocks or deviations of a bodys own rhythm may cause health problems. The Kongsfjorden barnacle goose (Branta leucopsis) colony, one of the best studied bird colonies worldwide, will serve as a model system. These geese have been investigated comprehensively for decades, therefore 2/3 of them are individually ringed. In the summer, they breed in the High Arctic (Spitzbergen, Norway, 7855N, 1215E), overwinter in a well-defined area in Scotland, and their spring and fall migration routes are known. Furthermore, all necessary technology and laboratory analyses to be applied are at hand. As the major product of avian clocks, melatonin controls the sleep-wake cycle and other daily activities (feeding, rest) along with seasonal activities (e.g. hibernation, moult, migration and reproduction). The release of melatonin is controlled by daily changes of light and darkness: light causes an inhibition, but darkness triggers secretion, resulting in increased levels. Finally, melatonin triggers the regulation of other rhythmic hormones, such as prolactin and corticosterone. Besides other functions, all three hormones are released during the stress response, an elemental physiological task. The relationship between melatonin and the light-dark cycle is clearly defined in temperate latitudes, but above the Arctic and below the Antarctic circle (66N/S), where 24-hours of daylight prevail in the summer, but 24-hours of darkness in the winter, this relationship is less clear, but it is fascinating for studying the effects of time and rhythmical phenomena of life processes. Indeed, the results so far are ambivalent: in some species the rhythm of melatonin secretion and associated physiological and behavioral processes are lost whereas other species retain them. we have recently demonstrated the presence of an intact, but phase-shifted circadian pattern in corticosterone excretion in Arctic barnacle goslings, I will for the first time examine, how the three hormones behave under polar summer light conditions in individual geese, and if and how they are associated with activity. It is also new to continue data collection by tracking those geese throughout the year to assess seasonal adaptations and relationships of the three hormones and biologically relevant events, such as during migration when on the wintering grounds

Endogenous biological clocks coordinate physiological, and behavioural processes that are rhythmic and limited to specific times of the day or season. Day length serves as the primary Zeitgeber to synchronize these processes. The polar regions pose a challenge, however, as they are characterized by continuous daylight in summer and continuous darkness in winter. Whereas some species maintain intact diurnal rhythms in the polar summer, other do not. We set out to investigate the interplay between behaviour and hormones of individual barnacle geese over the course of the year. Our main goals were to investigate the interactions between activity patterns and physiological rhythms of three hormones with typical release patterns (1) over the course of the reproductive period under arctic summer conditions and (2) at times when these individuals experience defined dark-light-cycles in winter, and during migration in autumn and spring. We were unable to examine (2) due to the COVID-19 pandemic. Weekly changes in travel regulations made organization of short notice trips to Norway to collect data from migrating geese just as unfeasible as trips to the UK. Going along with the latter was a lack of regulations for planned animal experiments due to Brexit and a ban to visit the wintering area after an avian influenza outbreak. We, however, succeeded in visiting Svalbard in the summer months 2020 and 2021 despite immense unplanned costs and enormous logistical effort. Here, we investigated potential rhythmicity of activity during incubation, chick rearing and moult. Using camera traps and accelerometers, we found that geese take about five 20-minute breeding breaks daily, following a circadian pattern, i.e. a naturally repeating rhythm in a 24-hour cycle, and that they are more active during conventional day time. During the flightless period of moult, geese without young showed strong rhythmic activity over a 12-hour cycle, whereas geese with offspring show no rhythmic activity until young fledge. This indicates that parental geese adjust to the changing needs of goslings over development. We also examined hormonal rhythmicity. We extracted corticosterone, melatonin and prolactin metabolites (2020: 350 samples from 26 individuals; 2021: 334 samples from 52 individuals distributed evenly over 24 hours and the entire breeding season). In both years we found daily rhythms in corticosterone and prolactin. Unfortunately, we could not complete the analyses of melatonin as the additional costs caused by the pandemic exceeded our budget In conclusion, despite the lack of a clear day-night-cycle, barnacle geese, which breed in the high Arctic, maintain diurnal and seasonal rhythmicity in physiological and behavioural processes. In a next step we intend to complete the analyses of melatonin, to collect the missing autumn, winter and spring data, and to determine, among other things, which other Zeitgebers coordinate these rhythms.