Effects of interspecific coexistence on laying date and clutch size in two closely related species of hole‐nesting birds

Abstract

Coexistence between great tits Parus major and blue tits Cyanistes caeruleus, but also other hole-nesting taxa, constitutes a classic example of species co-occurrence resulting in potential interference and exploitation competition for food and for breeding and roosting sites. However, the spatial and temporal variations in coexistence and its consequences for competition remain poorly understood. We used an extensive database on reproduction in nest boxes by great and blue tits based on 87 study plots across Europe and Northern Africa during 1957-2012 for a total of 19,075 great tit and 16,729 blue tit clutches to assess correlative evidence for a relationship between laying date and clutch size, respectively, and density consistent with effects of intraspecific and interspecific competition. In an initial set of analyses, we statistically controlled for a suite of site-specific variables. We found evidence for an effect of intraspecific competition on blue tit laying date (later laying at higher density) and clutch size (smaller clutch size at higher density), but no evidence of significant effects of intraspecific competition in great tits, nor effects of interspecific competition for either species. To further control for site-specific variation caused by a range of potentially confounding variables, we compared means and variances in laying date and clutch size of great and blue tits among three categories of difference in density between the two species. We exploited the fact that means and variances are generally positively correlated. If interspecific competition occurs, we predicted a reduction in mean and an increase in variance in clutch size in great tit and blue tit when density of heterospecifics is higher than the density of conspecifics, and for intraspecific competition, this reduction would occur when density of conspecifics is higher than the density of heterospecifics. Such comparisons of temporal patterns of means and variances revealed evidence, for both species, consistent with intraspecific competition and to a smaller extent with interspecific competition. These findings suggest that competition associated with reproductive behaviour between blue and great tits is widespread, but also varies across large spatial and temporal scales.

Nesting outcomes under anthropogenic change – effects of changing climate and nestbox provision on the reproduction of Great TitsParus major

“…This value is similar to changes from southern Sweden (Kallander et al 2017) and more southerly UK and Dutch populations (Visser et al 2012). This advance was also clearly independent of the number of nesting conspecifics, with the number of nestboxes provided (a strong proxy for the number of nesting attempts) and previous year's productivity (a proxy for local changes in population size), both uninformative explanatory variables, as also recently found in a broader continental study (Møller et al 2018).…”

Accounting for interspecific competition and age structure in demographic analyses of density dependence improves predictions of fluctuations in population size

“…Great tits and blue tits (Cyanistes caeruleus) are hole-nesting bird species that compete for cavities and food. Competition intensity varies across Europe (Møller et al 2018) and between habitats (Dhondt 2011). Long-term, individualbased monitoring of these two species have been performed across Europe and two complementary approaches have been adopted to understand how they compete.…”

Interaction of climate change with effects of conspecific and heterospecific density on reproduction

“…Information on latitude, longitude and altitude was provided by the authors of earlier studies or found in publications (for details see Møller et al 2014a, b2014b, 2018, Vaugoyeau et al 2016). Tree species vary significantly in timing and amount of invertebrates available for raising offspring in tits (Kennedy and Southwood 1984, Lambrechts et al 2008).…”

“…clutch size). Intra‐ and interspecific competition are known to affect laying date and clutch size in hole‐nesting birds (Dhondt 2010, 2012, Stenseth et al 2015, Møller et al 2018). However, some studies suggest that such effects of competition are significant only in specific plots or specific periods, raising questions about the generality of these phenomena, but also about their underlying causes (Alatalo and Lundberg 1984, Török and Tóth 1988, Dhondt et al 1992).…”

“…Recently, Møller et al (2018) published extensive analyses of effects of competition on laying date and clutch size in great and blue tit across Europe and North Africa. Here we expand these analyses by testing for the first time whether the effects of climate change during the last 50 years significantly influenced intra‐ and interspecific competition by measuring their presumed effect on lay date and clutch size while controlling statistically for a number of variables that are known to predict lay date and clutch size in blue and great tit (Møller et al 2014a).…”