Temperature sensitivity of breeding phenology and reproductive output of the Common Redstart (Phoenicurus phoenicurus)

Author(s): Lonero, I., Eddowes, M.J., Burgess, M.D., Pearce-Higgins, J.W. & Phillimore, A.B.

Published: November 2024

Journal: Ibis

Digital Identifier No. (DOI): 10.1111/ibi.13376

One of the most obvious ways in which birds have responded to climate change is by shifting the timing of their breeding and migration. In spring, many long-distance migratory species are now arriving earlier than in the past, and most species are also nesting earlier than then used to, particularly in warmer years. But has this led to a mismatch in the timing of the breeding season and the peak availability of key food resources for breeding birds and their young, leading to a reduction in breeding success and eventual population declines?

Although in general there is not a strong signal that climate change is causing a sufficient mismatch between avian predators and their insect prey, such as caterpillars, flies and other insects, to be driving population declines, this can be difficult to study. The Redstart is one long-distance migratory species that is potentially sensitive to the impacts of this so-called phenological mismatch. This species has experienced significant population fluctuations in the UK over the last 25 years, and is currently on the Birds of Conservation Concern Amber List.

This study takes advantage of the efforts of volunteers participating in our Nest Record Scheme to investigate the impacts of changes in temperature upon the breeding success of this woodland bird. After analysing data from over 4,000 Redstart nests alongside spring temperature data from 1974 to 2020, Redstart laying date was shown to move forward by 1–2 days for every 1°C rise between mid April and late May. Over the study period, laying date advanced by more than 11 days, which is more than expected from the temperature effect on phenology alone through the mechanism of plasticity (the same individuals nesting earlier or later in response to warm or cold temperatures). This could be due to evolutionary adaptation or factors other than temperature also affecting nesting phenology. Increasing spring temperature had a weak positive effect on clutch size, but a negative effect on brood reduction from hatching to fledging. Taken together, these two effects meant the study found no net effect of rising spring temperatures on fledging success.

This study provides the most detailed assessment of the impacts of warmer spring temperatures upon one of the UK’s declining long-distance migratory bird species. In so doing, it demonstrates the value of our long-running monitoring schemes, which underpin such work.

Abstract

Over the past four decades, rising temperatures have impacted the breeding phenology of many bird species, in some cases with consequences for their reproductive success. Migratory birds face particular challenges in shifting breeding phenology to track warmer springs, and understanding the impacts of rising spring temperatures on migratory birds’ breeding is urgent. Here, we use over 4000 UK observations of Common Redstart nests, and spring temperature data from 1974 to 2020, to examine the effect of spring temperatures on laying date, clutch size and brood size. We use a sliding window approach to detect periods over which traits are most sensitive to temperature, and compare phenotypic responses to temperature over space and time with the aim of identifying causal effects of temperature and inferring the contributions of plasticity and local adaptation. We found that redstart laying date was sensitive to spring temperature from mid-April to late May, with a relatively shallow response of 1–2 days/°C that was similar across space and time, but shallower than the phenological response of many of the resource species. Over the study period, laying date has advanced by more than 11 days, which is substantially more than can be explained based on the temperature plasticity estimates we obtained. Spring temperature had a weak, but positive, impact on clutch size, but with no evidence of an effect of spatial variation in temperature. The rate of brood size reduction from hatching to fledging became more negative at higher temperatures, but after taking into account a non-significant but positive effect of temperature on brood size at hatching, there was no net effect of temperature on fledging success. Taken together, we found little evidence that higher temperatures in the UK lead to lower reproductive output.

Notes

The authors sincerely thank all the volunteer recorders whose passion and dedication to contributing data to the British Trust for Ornithology (BTO) were vital to the success of this study.

Staff Author(s)

James Pearce-Higgins

Director, Science

Publication Topics

Climate change in a warming world

BTO science contributes to our understanding of future scenarios, and informing policies and conservation management strategies to help species adapt.