Shifts in caterpillar biomass phenology due to climate change and its impact on the breeding biology of an insectivorous bird

Abstract

Timing of reproduction has major fitness consequences, which can only be understood when the phenology of the food for the offspring is quantified. For insectivorous birds, like great tits (Parus major), synchronisation of their offspring needs and abundance of caterpillars is the main selection pressure. We measured caterpillar biomass over a 20-year period and showed that the annual peak date is correlated with temperatures from 8 March to 17 May. Laying dates also correlate with temperatures, but over an earlier period (16 March-20 April). However, as we would predict from a reliable cue used by birds to time their reproduction, also the food peak correlates with these temperatures. Moreover, the slopes of the phenology of the birds and caterpillar biomass, when regressed against the temperatures in this earlier period, do not differ. The major difference is that due to climate change, the relationship between the timing of the food peak and the temperatures over the 16 March-20 April period is changing, while this is not so for great tit laying dates. As a consequence, the synchrony between offspring needs and the caterpillar biomass has been disrupted in the recent warm decades. This may have severe consequences as we show that both the number of fledglings as well as their fledging weight is affected by this synchrony. We use the descriptive models for both the caterpillar biomass peak as for the great tit laying dates to predict shifts in caterpillar and bird phenology 2005-2100, using an IPCC climate scenario. The birds will start breeding earlier and this advancement is predicted to be at the same rate as the advancement of the food peak, and hence they will not reduce the amount of the current mistiming of about 10 days.

Short-Term Alterations in Songbird Breeding Schedule Lead to Better Synchronization With Food Availability

“…Hence, selection is presumably strong for parents to time their reproduction to match the period of greatest food demand by the young (about 9-10 days of age). To assess the relative timing of each breeding pair (i.e., an estimate of the degree of mismatch with the food peak), we calculated the days elapsed between the day their chicks were 9 days old and the caterpillar peak date ("synchrony" sensu Visser et al 2006).…”

“…This idea has been supported by a large number of studies of the Paridae. For this family, fledgling condition, which largely determines postfledging survival (Naef-Daenzer et al 2001) and recruitment (Both et al 1999), depends mainly on food supply (Naef-Daenzer and Keller 1999, Visser et al 2006). However, for Great and Blue tits (Parus major and Cyanistes caeruleus, respectively), whose main food is lepidopteran larvae, the short period during which foraging conditions are optimal is very unpredictable because the development of caterpillars is temperature dependent (van Asch and Visser 2007 and references therein).…”

Temperate and boreal forest tree phenology: from organ-scale processes to terrestrial ecosystem models

“…There is ample evidence that year-to-year variations in leaf phenology modulate ecosystem carbon (Goulden et al 1996;Barr et al 2004;Delpierre et al 2009b), water, and energy balances (Wilson and Baldocchi 2000). At the community scale, the timing of leafing is known to condition the fitness of insect herbivores that feed on trees (Tikkanen and Julkunen-Tiitto 2003), with potential consequences at upper levels of the trophic web (Visser and Holleman 2001;Visser et al 2006;Donnelly et al 2011). Comparatively, considerably less effort has been focused on assessing the impact of phenology on the functioning of individual plants.…”

Interspecific variation in the relationship between clutch size, laying date and intensity of urbanization in four species of hole‐nesting birds

“…Synchrony between individual behavior and suitable timing of breeding is determined by environmental clues (Parmesan 2006; Visser et al. 2006; Sih et al. 2011) such as temperature (Both et al.…”