Bill morphology reflects female independence from male parental help

Abstract

The study of territorial polygyny in birds has been in£uential in the development of the theory of social mating systems. Alternative female mating options have been studied within the framework of the polygyny-threshold model and later as the outcome of con£icts of interest between individuals. However, little attention has been given to variations between individual females, and how this a¡ects their mating behaviour. Here, we test the hypothesis that some females are better adapted to raise nestlings without male assistance, and thus to mate polygynously. Speci¢cally, we investigate whether intraspeci¢c variation in female bill morphology is related to mating behaviour. This hypothesis is derived from earlier studies showing that, in both intra-and interspeci¢c comparisons, uniparental care by females is correlated with the catching of larger prey items than when both parents provision the young. Using the polygynous dusky warbler (Phylloscopus fuscatus) as a model species, we found that, in accordance with our prediction, females with deep bills were more likely to mate as a secondary female. Moreover, regardless of mating status, females with deep bills settled in territories with more food and they received less male assistance in feeding their o¡spring. We argue that females with stronger bills are better adapted to exploit the abundance of large food items in rich territories and thus to raise young on their own. Our results demonstrate the importance of studying variations between individual females, and provide evidence for an extended version of the`constrained-female hypothesis'. As bill depth is a highly heritable trait, our study strongly suggests that variation in female mating behaviour is not only related to ecological factors and female condition (as shown elsewhere) but also to heritable morphological traits.

Factors affecting the survival of founding individuals in translocated New Zealand Saddlebacks Philesturnus carunculatus

“…Wider bills in female Saddlebacks were associated with increased survival and may indicate superior foraging ability (e.g. Forstmeier et al . 2001) but this result should be substantiated by future studies with larger sample sizes.…”

Inferences of genetic architecture of bill morphology in house sparrow using a high‐density SNP array point to a polygenic basis

“…Bill form and function varies both between and within species in response to a range of ecological factors, including the availability of differing food sources and interspecific competition (Abzhanov et al., ; Riyahi et al., ; Soons et al., ). Subtle differences in bill morphology can have important consequences for variation in individual fitness by affecting relative foraging efficiency (Temeles, Koulouris, Sander, & Kress, ), defining diet (Soons et al., ), altering survival probability (Boag & Grant, ; Grant & Grant, ) or affecting nestling provisioning rate (Forstmeier, Leisler, & Kempenaers, ; Ringsby, Berge, Sæther, & Jensen, ).…”

Lazy males and hardworking females? Sexual conflict over parental care in a brood parasite host and its consequences for chick growth

“…Statistical significance (P<0.05) is indicated by different letters above the bars 2002). In this respect, some females are better suited to raising their progeny without male assistance than others and polygynous males then adjust their paternal effort to the female's ability (Forstmeier et al 2001b). While none of the female great reed warbler social status categories differ in body mass and intensity of egg shell coloration (Honza et al 2011;Trnka and Prokop 2011), they may still differ in other traits (not measured by us) or parenting quality.…”

“…If so, then adjustment of male care in response to female traits might explain the decreased investments of polygynous males in our study. We expected that the females of polygynous males (especially secondary females) would provide more food to nestlings in response to lower male investment (Sejberg et al 2000;Forstmeier et al 2001b;Redpath et al 2006).…”

“…As a result, the parents may disagree on the amount of parental care that males should provide, with females usually becoming the losers in this game. To compensate for low male investment, the females are expected to increase their own workload (Sejberg et al 2000;Forstmeier et al 2001b;Redpath et al 2006), though this is often not completely within their power. As a consequence, fewer or lower quality young usually fledge from nests with reduced or no male assistance compared with fully male-assisted nests (Pinxten and Eens 1990;Kermott 1993, but see Bensch 1996).…”