Scale-Dependent Phenological Synchrony between Songbirds and Their Caterpillar Food Source

Abstract

In seasonal environments, the timing of reproduction has important fitness consequences. Our current understanding of the determinants of reproductive phenology in natural systems is limited because studies often ignore the spatial scale on which animals interact with their environment. When animals use a restricted amount of space and the phenology of resources is spatially variable, selection may favor sensitivity to small-scale environmental variation. Population-level studies of how songbirds track the changing phenology of their food source have been influential in explaining how populations adjust to changing climates but have largely ignored the spatial scale at which phenology varies. We explored whether individual great tits (Parus major) synchronize their breeding with phenological events in their local environment and investigated the spatial scale at which this occurs. We demonstrate marked variation in the timing of food availability, at a spatial scale relevant to individual birds, and that such local variation predicts the breeding phenology of individuals. Using a 45-year data set, we show that measures of vegetation phenology at very local scales are the most important predictors of timing of breeding within years, suggesting that birds can fine-tune their phenology to that of other trophic levels. Knowledge of the determinants of variation in reproductive behavior at different spatial scales is likely to be critical in understanding how selection operates on breeding phenology in natural populations.

Hatching asynchrony vs. foraging efficiency: the response to food availability in specialist vs. generalist tit species

“…In the face of current climate change, breeding mismatches across trophic levels are arising in all ecosystem types, from terrestrial to marine habitats, threatening hundreds of well-established trophic interactions4. As individuals make decisions about breeding timing well before their offspring needs are at their highest, and because the optimal reproduction window is usually narrow1256, species belonging to higher trophic levels must employ mechanisms to reduce mistiming. One of these mechanisms is the adjustment of breeding onset to prevailing environmental conditions, a strategy that can be fine-tuned.…”

“…One of these mechanisms is the adjustment of breeding onset to prevailing environmental conditions, a strategy that can be fine-tuned. It has been shown, for instance, that laying date in great tits Parus major can be predicted by the phenology of the nearest oak to a nesting site6. Another mechanism is compensatory/delayed growth, as animals born late/early in the season can accelerate/delay their growth to correct their mistiming (reviewed for several taxa in ref.…”

Application of High Resolution Satellite Imagery to Characterize Individual-Based Environmental Heterogeneity in a Wild Blue Tit Population

“…By validating the assumption that there is consistent covariation between data collected on the ground and recorded from space at the same spatial scale, we now have the possibility to move beyond data available from the ground and use filters centered around each nestbox of a radius that is relevant to any particular ecological process of interest. The question of scale has been recently emphasized by Hinks et al [23], who demonstrated that while spatial scales at which association between oak phenology and great tit Parus major breeding occurs is often limited to a 50 m radius around the nestbox, this value varies depending on life-history stage. For example, the scale of oak and tit associations differ when laying dates vs. hatching dates are compared, as well as depending on the type of biological information included in the models.…”

“…This finding is consistent with the general observation that blue tits reproduce later in evergreen-rich areas of the woods (unpublished data). However, such analysis was only performed on one year of data (2013), while the detection of phenological matching between oak and bird timing of reproduction usually requires the use of long-term datasets [22,23]. Future analyses of the synchrony between animal and vegetation phenology would therefore benefit from multi-year or multi-site approaches, but also from deriving start of season statistics that are robust to both evergreen and deciduous oak phenology dynamics (see for example [22] where generalized additive models are used to infer the greatest rate of change in green-up).…”

“…While caterpillar peaks are triggered by spring temperatures [20], they also show substantial variation across deciduous and evergreen habitats [16]. Blue tit reproductive peaks are dependent on photoperiod and temperature [12,21], but also vegetation type [4] and/or vegetation phenology [22,23]. In Mediterranean habitats, the contrasted phenology of deciduous and evergreen oaks can in fact override the importance of temperature variation: thus, blue tit timing of breeding is strongly correlated with the phenology of the dominant vegetation, which was found to be a more robust predictor of the timing of breeding than temperature at the inter-population level [13].…”