Abstract
AbstractAimNest building is widespread among animals. Nests may provide receptacles for eggs, developing offspring and the parents, and protect them from adverse environmental conditions. Nests may also indicate the quality of the territory and its owner and can be considered as an extended phenotype of its builder(s). Nests may, thus, function as a sexual and social signal. Here, we examined ecological and abiotic factors—temperature, nest predation and interspecific information utilization—shaping geographical variation in a specific nest structure—hair and feather cover of eggs—and its function as an extended phenotype before incubation in great (Parus major) and blue tits (Cyanistes caeruleus) across Europe. We also tested whether egg covering is associated with reproductive success of great tits.LocationFourteen different study sites and 28 populations across Europe.TaxonParus major, Cyanistes caeruleus.MethodsWe recorded clutch coverage estimates and collected egg covering nest material from the tit nests. We also measured nest specific breeding parameters and phenotypic measurements on adults. We tested whether mean spring temperatures, nest predation rates and flycatcher (Ficedula spp) densities in the study areas explain the large‐scale geographical variation of clutch coverage and reproductive success of tits.ResultsThe degree of egg coverage of great tits increased with lower mean spring temperature, higher nest predation rate and higher flycatcher density. We did not find egg covering of blue tits to be associated with any of the ecological or abiotic factors. Moreover, egg covering of great tits was not associated with reproductive success in our cross‐sectional data, yet a rigorous assessment of fitness effects would require long‐term data.Main conclusionsOur findings suggest that, in great tits, egg covering may simultaneously provide thermal insulation against cold temperatures during egg‐laying in spring and also represent a counter‐adaptation to reduce information parasitism by flycatchers and nest predation. Hence, geographical variation in interspecific interactions, and consequently in co‐evolutionary processes, may affect the evolution of nest characteristics besides environmental conditions.
Highlights
In the animal kingdom, nest building is a common behaviour
Egg covering most likely serves multiple functions in great tits. It provides thermal insulation against cold temperatures and hides the eggs from the nest predators looking for an egg meal and from information parasites searching for clutch-size information
The interactions among the nest predators, information parasites and tits are expected to result in a series of adaptations and counteradaptations, egg covering having a function in hiding the eggs
Summary
Nest building is a common behaviour. The basic functions of nest building are thought to be protection against elements of abiotic (e.g. low temperatures, humidity) and biotic (e.g. nest predators, parasites) risks for offspring until they hatch or become independent from parental care (Hansell, 2007). Some species invest a considerable amount of time and resources in building complex and decorated nest structures while, in others, just a few pieces of rock or plant material are enough (Hansell, 2007). This implies that nests may have functions other than offering security to offspring during development. A perceptible nest can be considered an extended phenotype of its builder(s) (Dawkins, 2016), because the placement, structure, materials and size of the nest affects the probability that the genes of the builder(s) are transmitted to the generation by affecting mate selection and offspring survival probability
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