The roles of temperature, nest predators and information parasites for geographical variation in egg covering behaviour of tits (Paridae)

Abstract

AimNest 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.

No evidence for cross-contextual consistency in spatial learning and behavioural flexibility in a passerine

“…The great tit (Parus major) is a model species for ecological and behavioural studies (e.g. Aplin et al, 2015;Cole et al, 2011;Dutour et al, 2020;Loukola et al, 2020;Morand-Ferron et al, 2011). Great tits adapt well to temporary captivity, allowing for their use in controlled experiments on individual differences.…”

No evidence that nest site choice in Pied Flycatchers is mediated by assessing the clutch size of a heterospecific, the Great Tit

“…During egg-laying, Great Tits often cover their eggs with lining materials (Loukola et al 2020a). Each year during 2016-19, when visiting tit nest boxes during egg-laying at Daeli, we removed the lid and first counted the eggs seen from above and then lifted away any covering materials to record the total number of eggs actually present.…”

“…Fourth, because we found no relationship between these indirect cues and clutch size (see results), we tested whether final tit clutch size itself can be assessed by prospecting Pied Flycatchers during the egg-laying period when clutch size is incomplete and when the tits spend much time outside the nest cavity and when flycatchers have been observed to inspect their nest (Forsman et al 2018). This is not obvious because at this stage of nesting, the tits often cover the eggs when leaving the nest (Haftorn and Slagsvold 1995;Loukola et al 2020a). Fifth, we documented the extent of variation in Great Tit clutch size among females and study years to assess whether many tit nests need to be visited by prospecting Pied Flycatchers to obtain a reliable assessment of the relative quality of a local demonstrator tit in the population.…”

The correlates of intraspecific variation in nest height and nest building duration in the Eurasian blue titCyanistes caeruleus

“…For example, Lombardo et al (1995) found that fewer chicks fledge from nests which contain fewer feathers, and Podkowa and Surmacki (2017) found that nests in cavities with lower levels of illumination tend to be taller, in order to increase the eggs' exposure to light, which increases embryonic metabolic rates (Cooper et al 2011). The materials used and the structure of the nest allows for adjustment of the microclimate (Lombardo et al 1995, Hilton et al 2004, Podkowa and Surmacki 2017, de Zwaan and Martin 2018) and defensive camouflage (Westmoreland and Kiltie 2007), as well as providing structural support to the eggs and potentially decreasing the risk of ectoparasitism (Quiroga et al 2012, Tomás et al 2012), predation (Møller 1987, Lovell et al 2013) and bacterial infection (Gwinner and Berger 2005, Mennerat et al 2009, Peralta‐Sanchez et al 2010, Álvarez et al 2013, Loukola et al 2020).…”

“…Although the nest cup lining is likely to be the primary insulator (Mainwaring and Hartley 2008), the nest base may also provide some thermal benefits (Kaliński et al 2014). Furthermore, nest sites may be selected to be more thermally favourable (Ardia et al 2006, Maziarz and Wesołowski 2013), and certain behaviours during incubation, like egg covering, are likely to aid in maintaining a steady nest microclimate (Loukola et al 2020). Several studies have found that nest insulation materials and nest mass and height correlate with environmental factors like elevation, latitude and spring temperature over time and space (McGowan et al 2004, Mainwaring and Hartley 2008, Mainwaring et al 2012, 2014, Álvarez et al 2013), while others have found no relationship between nest structure and these same variables (Suárez et al 2005, Tomás et al 2006, Schöll and Hille 2014).…”