Is the transition from biparental to male-only care in a monogamous seabird related to changes in body mass and stress level?

Abstract

In a number of species with biparental care, the parents of one sex desert the mate and brood before the chick is independent. The reasons for this desertion are poorly understood. In the study reported here we investigated whether sex-specific changes in body mass corrected for size (in short body mass) and the stress-related heterophil to lymphocyte ratio (H:L) during the late incubation and chick-rearing period are related to female brood desertion in a small Arctic seabird, the Little Auk (Alle alle). The body mass of both sexes did not change during the study periods, although females were significantly lighter than males. No sex differences were found in the pattern of changes in the H:L ratio. In both sexes, the H:L ratio, and thus the stress level, increased significantly just after hatching and remained high until the last week of chick rearing when it fell back to the level recorded during incubation. These results support behavioural reports of an equal male and female contribution to parental care. The similar body condition of males and females undermines the hypothesis on the depletion of female body reserves as the main trigger of their earlier brood desertion. It is possible that a sex-specific role in parental care during and after fledging and/or an ancestral pattern of parental care are responsible for the transition to paternal care in Little Auks. Keywords

The effects of loggers on the foraging effort and chick-rearing ability of parent little auks

“…Chicks reach their peak body mass (120-124 g, max 150 g) at the age of 19-24 days, and fledge weighing 110-114 g on average (Stempniewicz 1980(Stempniewicz , 2001. Body mass recession preceding fledging may be associated with a reduction in feeding frequency (females cessate feeding before fledging, probably due to a sex-specific role in parental care during and after fledging and/or an ancestral pattern of parental care; Wojczulanis-Jakubas et al 2011), tissue maturation and/or might be an essential prerequisite for efficient flight (Ricklefts 1968;Gaston 1985;Taylor and Konarzewski 1989;Stempniewicz 1980Stempniewicz , 2001. The fledging age of chicks varies among individuals.…”

Trade‐offs between reproduction and self‐maintenance (immune function and body mass) in a small seabird, the little auk

“…Lack of sex differences in BKC, SMI and blood parameters (H/L ratio, numbers of heterophils, lymphocytes and all leucocytes per 10 000 RBC) throughout the breeding season deny the hypothesis that little auk females desert the brood earlier than the male because of body reserve depletion. Previous studies on temporal variation of body condition variables also do not support this hypothesis (Jakubas et al , Wojczulanis‐Jakubas and Jakubas , Wojczulanis‐Jakubas et al , ).…”

“…and ), reflecting carry‐over effects from previous phases of breeding (egg incubation, chick brooding and feeding). Previous studies have also reported lower SMI in adult little auks during chick rearing compared to earlier phases of the breeding cycle (Taylor , Wojczulanis‐Jakubas et al , but see Wojczulanis‐Jakubas et al ). Mass loss during breeding, also observed in other alcids [e.g.…”

“…If mass loss is stress‐induced, we would expect a decrease in body mass throughout the breeding phase with the most rapid decline during the phase with the highest energetic demands (usually chick rearing) and this was recorded in our study. In contrast, if mass loss is adaptive, we would expect an abrupt, or stepwise decline in mass at or just before the moment when mass loss becomes most adaptive, i.e., when flight demand increases (Harding et al , Wojczulanis‐Jakubas et al ).…”

“…At the end of the chick rearing phase, females abandon the brood and the male stays with the offspring during fledging (Harding et al , Wojczulanis‐Jakubas and Jakubas ). One hypothesis to explain this female brood desertion is that it is the result of her lowered body reserves (Wojczulanis‐Jakubas and Jakubas , Wojczulanis‐Jakubas et al ). Due to these life‐history traits and high energy demands, the little auk may serve as a good model species to investigate resource allocation in adults during the breeding, including sex differences.…”