Exploring Biotic and Abiotic Determinants of Nest Size in Mediterranean Great Tits (Parus major) and Blue Tits (Cyanistes caeruleus)

Abstract

Standardized long-term multi-plot investigations of variation in nest size in free-ranging model species are rare, despite their value for understanding how the environment influences plastic traits such as nest size. Here, we report the results of an 18-yr descriptive study of nest size in first clutches produced by secondary-cavity nesting great tits (Parus major) and blue tits (Cyanistes caeruleus) in the Mediterranean, whilst also taking individual (lay-date, clutch size, age, species) and environmental characteristics (e.g. weather, oak habitat, region) into account. Nests of both species were built in relatively small standardized boxes erected in habitat patches that differed in the presence of the dominant oak species which was either summergreen deciduous or evergreen sclerophyllous. Nest size showed strong differences between species, and also in relation to environmental factors. Great tits built smaller nests than blue tits, Corsican birds had larger nests than mainland ones, nests tended to be larger in evergreen oak-habitat, and larger nests were built during drier weather. None of the individual-specific traits most often considered in long-term studies (lay-date, clutch size, and female age) were related to nest size in either species. Experimental approaches will be required to identify the underlying mechanisms that caused the observed phenotypic diversity for nest size in our study system.

Experimental manipulation of photoperiod and temperature does not influence nest size in Blue and Great tits

“…Nest-size measures were taken in the aviaries from 1997 to 2005, following protocols described by Lambrechts et al (2016). Birds nested in cylindrical, wood-and-concrete Schwegler B1 boxes (Schorndorf, Germany) or in concrete boxes, all of which had approximately the same nestchamber size (floor area~113 cm 2 , distance between entrance and bottom about 13-14 cm).…”

“…After removing the front door of the box (cf. Lambrechts et al 2012Lambrechts et al , 2016, we quantified nest building by measuring the vertical height of the external nest wall at 60.5 cm (measured from the bottom of the nest box to the top of the nest rim on the frontal part of the nest), also called ''nest depth'' (Hansell 2000), ''nest height'' (Lambrechts et al 2012), or ''nest thickness '' (Hurtrez-Boussès et al 1999). Thus, nest volume as a proxy of nest size was estimated by multiplying nest height with the inner surface of the standardized box floor (cf.…”

“…Birds have been predicted to build larger, more insulated, nests at more northern latitudes, at higher altitudes, during colder years, or earlier in the season (Nager and van Noordwijk 1992, Hansell 2000, Britt and Deeming 2011, Crossman et al 2011, Heenan et al 2015, Lambrechts et al 2016. Longer days provide more opportunities to find the resources needed to build larger nests and have been shown to increase nest-building rates (Hinde et al 1974).…”

“…Several correlative studies have shown a negative or no significant relationship between temperature and nest size (e.g., Deeming et al 2012, Mainwaring et al 2014. A recent study, using a long-term dataset, found no relationship with temperature but a negative one with rainfall (Lambrechts et al 2016). However, direct evidence that investment in nest size is causally adjusted to changes in environmental factors is lacking because of the logistical difficulties of (1) experimentally inducing non-domesticated outdoor breeders to build nests outside their normal breeding window or (2) exposing nest-builders to an experimental change in climate-associated factors in wild conditions (e.g., Lambrechts et al 1997Lambrechts et al , 1999; but for a brief discussion of a few case studies, see Deeming and Mainwaring 2015).…”

“…We thus also considered first-egg date and clutch size in our analyses. In our study, we focused on the proxies of nest size (nest volume, nest mass) that were investigated in all correlative field studies of cavity nests throughout Europe (e.g., Deeming et al 2012, Deeming and Mainwaring 2015, Bueno-Enciso et al 2016, Lambrechts et al 2016.…”