Age-specific nest-site preference and success in eiders

Abstract

Variation in nest concealment is puzzling given the expected strong selection for safe nest sites. Selecting a concealed nest may decrease the risk of clutch predation but hinder parents from escaping predators, providing a possible solution to this paradox. Because the relative value of current versus future reproduction may vary with breeder age or state, nest concealment may also vary as a function of these attributes. We tested four predictions of the female and clutch safety trade-off hypothesis in eiders (Somateria mollissima): (1) nest concealment is negatively related to escape possibilities, (2) our capture rate of females is higher in covered nests, (3) egg predation is higher in open nests, and (4) overall nest success is unrelated to nest habitat. We also analysed nest microhabitat preferences and nest success relative to breeder age and body condition, controlling for nest spatial centrality. As expected, nest concealment and potential escape angle were negatively related, and capture by us, indicating female predation vulnerability, increased with nest cover. Clutch size was smaller in open nests, suggesting higher partial clutch predation, while it was larger among experienced and good-condition breeders. The probability of successful hatching was unrelated to nest habitat, positively associated with breeder experience, and negatively associated with hatching date. Experienced females selected more concealed and centrally located nests without sacrificing potential escape angles. The age-specific spatial distribution of nests on islands was unrelated to nest initiation dates, indicating no apparent competition. The age-specific preference of eiders for concealed nests may reflect declining reproductive value with age or confidence in surviving despite selecting a concealed nest. The apparently positive relationship between female age and survival and fecundity in eiders refutes the former alternative. Individual improvement in choosing safe nest sites, coupled with differential survival of individuals performing well, most likely explains age-specific nest-site preference and success.

Indeterminate laying and flexible clutch size in a capital breeder, the common eider

“…Other diVerences in females with few developing follicles might also be expected, such as later laying start or smaller eggs, for which there was likewise no evidence. Still another possibility is that females which persisted laying after early egg predation were older and more experienced birds, with larger clutches (Öst and Stele 2010). However, experienced females also tend to lay earlier than others (Baillie and Milne 1982), but there was little diVerence in laying date between abandoned and other nests, casting doubt on this explanation.…”

The early birds and the rest: do first nesters represent the entire colony?

“…We hypothesize that first nest date represents only a handful of the fittest or most determined individuals, whereas the 50 % threshold at least awaits the arrival of half the population and may better represent the general public. An alternative hypothesis is to view common eiders as pioneers and followers, where such grouping of each individual could be determined by personality (Seltmann et al 2014), body condition (Parker and Holm 1990;Ö st and Steele 2010), affinity for public information (Valone 2007) or an interaction of these factors (Seltmann et al 2012). Our study colony of common eiders is somewhat unique in being densely occupied by nesters and also having high incidence of nest parasitism but probably is representative for other such colonies and also valuable in providing insights into a population that is healthy and stable, with high adult survival (Jónsson and Lúðvíksson 2013).…”

“…At least three individual traits can drive individual females to arrive early and try to obtain a favored nest site. One obvious candidate is body condition and its relationship with stress or nest initation date (Ö st and Steele 2010;Seltmann et al 2012) especially because body condition of individual eiders can vary from year to year (Ö st et al 2007). The choice or ability to compete for best nest sites each year could thus be positively related to body condition.…”

“…Early nesting individuals generally are in optimal physical condition, often lay large clutches or attain a high nesting success (Erikstad et al 1993;Arnold et al 2004;Bêty et al 2004). Clutch size commonly is inversely related to nest date and survival of subsequent young can be negatively related to hatch date (Traylor and Alisauskas 2006;Ö st and Steele 2010;Clark et al 2014;Westneat et al 2014). A potential drawback of very early nesting and subsequent early hatch is a temporary high exposure to predators, which can incur costs on the earliest individuals (Lepage et al 2000;Bêty et al 2004;Pálsdóttir 2016).…”

Causes and consequences of fine-scale breeding dispersal in a female-philopatric species

“…Forero et al 1999;Newton 2001;Serrano et al 2001). However, as young breeders often have poor breeding success (Blums et al 1997;Devries et al 2008;Ö st and Steele 2010), this fact alone could make them more prone to disperse. The few studies that have aimed at separating the effects of nest failure and parental experience on breeding dispersal have shown that the effect of one factor can overcome the effect of another (e.g.…”