Male-built nest volume varies with colony and the timing of the breeding
season but not with the nesting-substrate quality and egg production in
whiskered terns
Abstract
Nest building can represent an energetically-costly activity for a
variety of animal taxa. Besides, the determinants of within-species
variation in the design of nests, notably with respect to natural and
sexual selection, are still poorly known although the situation has been
partly remedied recently. Based on an observational study, we examined
the influence of nesting conditions (nesting-substrate quality, colony,
laying date, and year) on the volume of male-built nests and its
potential role as a post-mating sexually-selected display in the
whiskered tern Chlidonias hybrida, a monogamous species with obligate
bi-parental care breeding on unstable aquatic vegetation beds. No
relationship was found between the nest volume and the nesting-substrate
quality (i.e. nest stability) indicating that the density of white
waterlily leaves was large enough when whiskered terns breed. In
contrast, building a large nest likely constitutes a selective advantage
since nests were larger in less densely populated colonies and for early
breeders whatever the year. Since being influenced by nesting
conditions, the volume of male-built nests was unlikely to be a sexually
selected trait in whiskered terns. The reproductive effort by females
(the probability of laying one, two or three eggs, and variation in mean
egg volume per clutch) was indeed not correlated with the volume of
male-built nests. The fitness consequences of building a large nest are
yet to be studied and additional investigations are recommended to
better depict the participation of males early during breeding
(including notably courtship feeding) and later to chick provisioning.