Ecophysiological response of Adélie penguins facing an experimental increase in breeding constraints

Abstract

SUMMARYForaging strategies play a key role in breeding effort. Little is known, however, about their connection with hormonal and nutritional states, especially when breeding constraints vary. Here, we experimentally increased foraging costs and thus breeding constraints by handicapping Adélie penguins (Pygoscelis adeliae) with dummy devices representing 3-4% of the penguins' crosssectional area. We examined food-related stress (via plasma corticosterone concentration) and nutritional state (via metabolite levels). Concurrently, we investigated the use of ecological niches via the isotopic signature of red blood cells indicating the trophic position ( 15 N) and the spatial distribution ( 13 C) of penguins. Handicapped birds performed ~70% longer foraging trips and lost ~60% more body mass than controls and their partners. However, corticosterone levels and the nutritional state were unchanged. The isotopic signature revealed that males and females differed in their foraging behaviour: upper trophic levels contributed more in the males' diet, who foraged in more pelagic areas. Handicapped and partner birds adopted the same strategy at sea: a shift towards higher  13C values suggested that they foraged in more coastal areas than controls. This change in foraging decisions may optimize feeding time by decreasing travelling time. This may partly compensate for the presumed lower foraging efficiency of handicapped birds and for the energetic debt of their partners who had to fast ~70% longer on the nest. We propose that this flexible use of ecological niches may allow birds facing increased breeding constraints to avoid chronic stress and to minimize the impact on their body condition.

King penguins adjust their diving behaviour with age

“…For example, Wilson noted how old feathers reduced the maximum speed of African penguins, Spheniscus demersus, by almost a third (Wilson, 1985), and drastic alterations in diving behaviour have been noted following an artificial increase in the drag in several other penguin species. For example, handicapped Adélie penguins, Pygoscelis adeliae, feed in inshore areas in comparison with non-handicapped ones that can travel further offshore (Beaulieu et al, 2010); little penguins, Eudyptula minor, increase the number of dives and the time allocated to prey pursuit with increasing hydrodynamic drag . Feather age is unlikely to account for drag differences in king penguins as moulting in early breeders is relatively synchronous, i.e.…”

Sex-specific foraging behaviour and a field sexing technique for Endangered African penguins

“…nonbreeding rockhopper penguins Eudyptes chrysocome chrysocome, Dehnhard et al 2011), but such differences could also be attributed to different prey caught within the same foraging area. To our knowledge, Adélie penguins are the only studied species that share equal parental duty during chick-rearing but exhibit large sexual differences in diet, foraging location and trip duration, suggesting potential niche partitioning between sexes with a consequent reduction in intra-specific competition (Clarke et al 1998, Beaulieu et al 2010). …”

Evaluating the Impact of Handling and Logger Attachment on Foraging Parameters and Physiology in Southern Rockhopper Penguins

“…Besides alterations of foraging and diving behaviour, handling and logger attachments can have effects on physiological parameters [15], [19]–[21], [63]. Even birds that seem to be calm can be stressed while being handled or disturbed [4], [64], [65] and the pure presence of a human close to a bird can cause alterations in stress hormones [66].…”

“…More recently, technologies allow measuring physiological parameters during foraging (see [17] for review), and several studies have tried to assess physiological changes that occur due to logger attachments (e.g. [15], [18], [19]). …”