A higher incidence of moult–breeding overlap in great tits across time is linked to an increased frequency of second clutches: a possible effect of global warming?

I Solís,J J Sanz,E Álvarez,E Barba,L Imba

doi:10.32800/abc.2021.44.0303

Abstract

The rise of temperatures due to global warming is related to a lengthening of the breeding season in many bird species. This allows more pairs to attempt two clutches within the breeding season, thus finishing their breeding activity later in the season and therefore potentially overlapping these with post–breeding moult. We tested whether this occurred in two Spanish great tit Parus major populations. The proportion of pairs laying second clutches increased from 1 % to 32 % over the study period in one of the populations (Sagunto, 1995–2019), while it did not change in the other (Quintos, 2006–2019; mean 5 %). We did not find any temporal trend for moult start date of late–breeding birds in any population. The proportion of individuals of both sexes that overlapped moult and breeding increased in Sagunto. For this latter population, sex and age, but not clutch type, contributed to the variability in the probability of overlapping in late–breeding individuals, this being higher for first–year males and lower for older females.

Highlights

The rise in temperatures due to global warming has affected ecosystems in various ways in recent decades (Walther et al, 2002), and is predicted to have dramatic effects in the near future (Trisos et al, 2020)
We aimed to answer the following specific questions for each population: (1) is there a temporal trend in the proportion of pairs attempting replacement or second clutches? (2) is there atemporal trend in the date of moulting of late–breeding pairs? (3) what proportion of the breeding population shows overlaps in breeding and moult? (4) is there a temporal trend in the proportion of individuals showing overlapping of breeding and moult? (5) which individual traits are related to the probability of overlapping? (6) does the probability of overlapping differ between birds attempting replacement clutches and those involved in second clutchew?
The study was conducted in two wild great tit populations breeding in nestboxes in Spain One was located within an extensive orange Citrus aurantium monoculture near Sagunto (Valencia, eastern Spain; 39o 42' N, 0o 15' W, 30 m a.s.l.), and data relevant for the present study are available between 1995 and 2019 (Álvarez and Barba, 2014; Rodríguez et al, 2016)

Summary

Introduction

The rise in temperatures due to global warming has affected ecosystems in various ways in recent decades (Walther et al, 2002), and is predicted to have dramatic effects in the near future (Trisos et al, 2020). For example, the timing of reproduction (Both et al, 2004; Källander et al, 2017), moult (Morrison et al, 2015) and, for migratory species, migration (Charmantier and Gienapp, 2014; Tomotani et al, 2017) are all being affected by global warming. For moult, birds must replace (partially or completely) their feathers to adequately maintain the main functions of the plumage, such as thermal insulation, flight, and appearance (Payne, 1972; Jenni and Winkler, 2020) Small birds, such as passerines, have the highest cost of moult per body mass (Hoye and Buttermer, 2011), and BMR could be up to 2.11 times higher than that during the moulting period (Lindström et al, 1993)

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Conclusion