Temperature synchronizes temporal variation in laying dates across European hole-nesting passerines

Abstract

Identifying the environmental drivers of variation in fitness-related traits is a central objective in ecology and evolutionary biology. Temporal fluctuations of these environmental drivers are often synchronized at large spatial scales. Yet, whether synchronous environmental conditions can generate spatial synchrony in fitness-related trait values (i.e., correlated temporal trait fluctuations across populations) is poorly understood. Using data from long-term monitored populations of blue tits (Cyanistes caeruleus, n = 31), great tits (Parus major, n = 35), and pied flycatchers (Ficedula hypoleuca, n = 20) across Europe, we assessed the influence of two local climatic variables (mean temperature and mean precipitation in February-May) on spatial synchrony in three fitness-related traits: laying date, clutch size, and fledgling number. We found a high degree of spatial synchrony in laying date but a lower degree in clutch size and fledgling number for each species. Temperature strongly influenced spatial synchrony in laying date for resident blue tits and great tits but not for migratory pied flycatchers. This is a relevant finding in the context of environmental impacts on populations because spatial synchrony in fitness-related trait values among populations may influence fluctuations in vital rates or population abundances. If environmentally induced spatial synchrony in fitness-related traits increases the spatial synchrony in vital rates or population abundances, this will ultimately increase the risk of extinction for populations and species. Assessing how environmental conditions influence spatiotemporal variation in trait values improves our mechanistic understanding of environmental impacts on populations.

Keywords: birds; climate; clutch size; comparative analysis; fitness-related traits; fledgling number; phenology; spatial synchrony; timing of breeding; weather.

FIGURE 1

Map of the 86 studied populations of blue tit (B), great tit (G), and pied flycatcher (P) at 44 locations in (a) Europe, with insets of the (b) United Kingdom and (c) the Netherlands and Belgium.

FIGURE 2

Temporal variation in (a–c) laying dates (1 = April 1), (d–f) clutch size, and (g–i) fledgling number of blue tit (a, d, g), great tit (b, e, h), and pied flycatcher (c, f, i) populations. Lines and points correspond to population time series of annual average trait values (median laying dates, mean clutch sizes, and mean fledgling numbers), allowing years with missing data. Histograms show annual data density, that is, the relative frequency of populations available per year. The analysis of spatial synchrony was carried out over the detrended and normalized annual average trait values (Appendix S1: Figure S5). Bird drawings reproduced with permission of Mike Langman, RSPB (rspb‐images.com).

FIGURE 3

Spatial synchrony in (a–c) laying date, (d–f) clutch size, and (g–i) fledgling number of blue tit (a, d, g), great tit (b, e, h), and pied flycatcher (c, f, i) populations in relation to the distance (in kilometers) between populations. Blue solid lines are the median and blue ribbons the 95% confidence interval based on 2000 bootstrap replicates. Gray points are correlations between the time series of pairs of sites whose size is proportional to the number of overlapping years between them. Spatial synchrony parameters (${\widehat{\mathrm{\rho }}}_0$, ${\widehat{\mathrm{\rho }}}_{\infty }$, and $\widehat{l}$) were restricted to positive values. Bird drawings reproduced with permission of Mike Langman, RSPB (rspb‐images.com).

FIGURE 4

Spatial synchrony in (a–c) laying date, (d–f) clutch size, and (g–i) fledgling number of blue tit (a, d, g), great tit (b, e, h), and pied flycatcher (c, f, i) populations in relation to the distance (in kilometers) between populations. Blue dashed lines are the spatial synchrony in the traits without accounting for the effects of climatic variables (Figure 3), teal lines are the spatial synchrony in the residuals after accounting for the effects of mean temperature in February–May, and yellow lines are the spatial synchrony in the residuals after accounting for the effects of mean precipitation in February–May. Lines are the median and ribbons the 95% confidence interval based on 2000 bootstrap replicates. Spatial synchrony parameters (${\widehat{\mathrm{\rho }}}_0$, ${\widehat{\mathrm{\rho }}}_{\infty }$, and $\widehat{l}$) were restricted to positive values. Bird drawings reproduced with permission of Mike Langman, RSPB (rspb‐images.com).