Diel rhythmicity of activity and corticosterone metabolites in Arctic barnacle geese during breeding

Abstract

Birds that migrate from temperate areas to the Arctic to breed lose their strongest Zeitgeber of circadian organization when they cross the Arctic circle in spring - the 24h light-dark cycle. Under continuous daylight, diverse behavioral and physiological patterns have been detected in both free-ranging and laboratory animals. To better understand the evolution of plasticity in circadian clocks, it is essential to study behavioral and physiological rhythmicity in the context of a species' ecology. Employing a multifaceted approach, which included wildlife cameras, accelerometers, and noninvasive sampling of hormone metabolites, we investigated activity patterns and corticosterone rhythmicity in a migratory herbivore, the barnacle goose (Branta leucopsis), during its Arctic breeding season on Svalbard. We found that females showed a combination of both ultradian and diel rhythmicity in nest recesses and sleep during incubation. In both parents, these rhythms in activity continued also during the gosling rearing phase. During molt, many geese aligned activity with the prevailing tidal rhythm. Barnacle geese showed weak diel rhythmicity in excreted corticosterone metabolites (CORTm). This suggests that while Arctic geese may adopt an alternative Zeitgeber during the Arctic summer to maintain a diel rhythm, ultradian rhythmicity remains essential, allowing the geese to flexibly adjust their rhythms to environmental conditions.

Keywords: GPS transmitter; camera trap; circadian rhythmicity; fecal glucocorticoid metabolites; hormones; polar.

Fig. 1.

Rhythmicity of females during incubation recesses [panels (A) and (B)] and ‘sleep’ [panels (C) and (D)] based on wildlife camera pictures. Double plotted actograms of female ID CA41113 as an example show in black when she is away from the nest during incubation recesses (A) or when she is on the nest in the sleeping posture (C), while transparency indicates inactivity on the nest in (A) or any behavior other than sleep in (C). The height of the bars indicates how often the specific behaviors are observed during that time. The x-axis displays two consecutive days, and these consecutive days are also shown from top to bottom on the y-axis. On the y-axis t = 0 is the day the first pictures were taken by the wildlife camera on 2021-06-18 from 03:22:20 onwards. Population level (N = 11) graphs show the fraction of time, averaged over 24 h, spent on incubation recesses (B) and in sleep posture (D) in percentages (y-axis). The x-axis displays time over 24 h, and the black line represents the mean, while in gray bootstrapped 95% confidence intervals are displayed.

Fig. 2.

Percentages of rhythmicity types based on transmitter accelerometer data for 18 individual geese over the course of two summer seasons. Over the three breeding stages either ultradian or diel rhythmicity alone, a combination of ultradian and diel rhythmicity, or no rhythm were observed. Numbers above the stacked bars indicate sample size per breeding stage.

Fig. 3.

Diel and ultradian average peak periodicity during different breeding stages based on transmitter accelerometer data. The values of the peak period are for rhythmic geese only, ie a peak above the significance threshold at α = 0.05. Individual geese are shown as dots. The size of the dots represents the power of the peak period; a representation of the strength of the signal. The error bars are 95% bootstrap confidence intervals on the population mean.

Fig. 4.

Population level graphs, based on transmitter accelerometer data, showing the fraction of time active, averaged over 24 hrs., during nesting (A), when geese had goslings (B), and during molt (C) in percentages (y-axis). Females (f) and males (m) are indicated in different colors. The x-axis displays time over 24 h, and the solid lines represent the mean, while in transparent color bootstrapped 95% confidence intervals are displayed.

Fig. 5.

Daily rhythmicity in log-transformed corticosterone metabolite (CORTm) concentration measured in barnacle goose droppings in 2 yr. The dots represent individual measurements, and the solid line represents the predicted values from the model. 2020: n = 349 droppings, 26 individuals. 2021: n = 333 droppings, 52 individuals.