Preservation of winter social dominance status in Brent Geese Branta bernicla bernicla within and across winters

Abstract

Dominant and subordinate individuals in a group may benefit from the stability of the social dominance organisation, avoiding excessive waste of time and energy in aggressive interactions and reducing injury risks. Nevertheless, the likely evolutionary incentive for individuals to become, and furthermore to stay, dominant may destabilise such dominance hierarchies. In this context, the relative importance of fixed (e.g. sex, morphological size) and fluctuating (e.g. body condition, mating status, reproductive success, social unit size) traits influencing the establishment and preservation of dominance relationships could play a key role in group structure. We investigated the relative role of fixed and fluctuating traits on social status in Dark-bellied Brent Geese Branta bernicla bernicla which form large fairly unstable groups both within and across winters. We compared individual dominance scores of ringed Brent Geese during four consecutive winters. Brent Geese conserved their dominance score within a given winter irrespective of their age but were generally unable to conserve it across consecutive winters. As winter dominance scores correlated best with social unit size, dominance status thus appeared to be mostly a by-product of a fluctuating trait: breeding success in the previous summer. When we considered only adults that had the same social unit size during two consecutive winters, we observed a significant preservation of dominance scores. This result suggests that a fixed trait such as sex or morphological size may still play a role in setting dominance status.

Mate fidelity improves survival and breeding propensity of a long‐lived bird

“…Mate fidelity in brent likely conveys social benefits to individuals throughout the annual cycle. This is because brent, like most geese, have a strong social hierarchy in their wintering flocks with family groups dominating pairs without offspring, and pairs dominating singletons (Black & Owen, 1989; Gregoire & Ankney, 1990; Poisbleau et al., 2006, 2010; Raveling, 1970). This social hierarchy is positively related to achieving access to habitats with superior forage during winter (Black, Carbone, Wells, & Owen, 1992; Stahl, Tolsma, Loonen, & Drent, 2001) and, as a result, improvements in survival and breeding probability (Sedinger et al., 2011).…”

“…An individual's position in the social hierarchy affects their ability to efficiently forage during winter and spring migration (Poisbleau et al., 2006). Nutrient acquisition advantages can influence reproductive investment during the next breeding season (Ankney, 1984; Ankney & MacInnes, 1978), which, in turn, affects the social status during the next winter (Poisbleau, Guillon, & Fritz, 2010). Though socially monogamous, brent adults participate in extra‐pair copulations (Welsh & Sedinger, 1990) and 8% of eggs at Tutakoke River are the product of extra‐pair copulations (Lemons et al., 2015).…”

Comparing dominance hierarchy methods using a data-splitting approach with real-world data

“…However, most behavioural studies assume that individual dominance rank is relatively stable over time (e.g. Poisbleau, Guillon & Fritz 2010). With this in mind, Sánchez-Tójar, Schroeder & Farine (2018) suggested a modification to the original Elo-rating based on randomizing the order in which interactions occurred: the randomized Elo-rating method (method 7).…”

A practical guide for inferring reliable dominance hierarchies and estimating their uncertainty

“…However, most behavioural studies assume that individual dominance rank is relatively stable over time (e.g. Poisbleau, Guillon, & Fritz, 2010). We propose an improvement of the original Elo-rating based on randomizing the order in which interactions occurred ( n = 1 000 randomizations throughout).…”