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News article28 September 2022Directorate-General for Environment4 min read

Temperature-driven changes in traits of European birds are also influenced by other factors

Issue 584: Studies that observe physical and behavioural changes in wild species over periods of rising temperature rarely evaluate the role of climate change in relation to simultaneous changes of other environmental factors.

Temperature-driven changes in traits of European birds are also influenced by other factors
Photo by: matushaban, Shutterstock

This study applied a novel approach to long-term datasets on European birds to quantify the contribution of other factors to observed changes over past decades. The researchers say that just over half of observed effect was due to rising temperatures, with other factors mostly accentuating these impacts.

The impact of climate change on physical and behavioural traits of animal species around the world has been widely reported in scientific literature. These findings are often used to inform conservation planning policies and actions. However, global biodiversity is also affected by a wide range of other factors, many of them anthropogenic and progressive, such as habitat loss, overexploitation and invasive exotic species. Few studies on the effects of climate change quantitatively assess the potential influence of these non-climatic factors on changes in species traits over time. This study uses two long-term datasets to evaluate the relative contribution of climatic and non-climatic factors on changing traits in European bird species.

The study used data collected by the British Trust for Ornithology’s Nest Record scheme on 36 bird species over a period 54 years, and from the Dutch Constant Effort Site Programme on 47 species over 21 years. The researchers considered three traits recorded in these datasets: timing of egg laying, number of offspring per brood and body condition. They focused their analysis on the species and specific time windows in which rising temperature was mostly closely related to changes in these traits. Using a statistical model, the researchers calculated separately the degree to which each trait changed over time and the degree to which it changed across the temperature gradient. From these figures they determined the degree of change over time due to non-temperature effects.

The researchers report that across all three traits, 52% of the observed change was due to temperature, ranging from 57% for egg laying to 44% for body condition. In most cases the change due to other non-temperature climatic factors, operated in the same direction, reinforcing the effects of rising temperature, they say; although in some cases it operated in the opposite direction – counteracting the temperature-related effect.

The researchers say that the proportion of overall trait change due to warming temperatures varied widely according to species, from 13% to 82%. However, they say that differences between species in overall trait change were mostly due to differences in the effect of non-temperature factors. They suggest that this was probably because responses to temperature did not vary as much between species as responses to other factors.

The researchers highlight that although on average more than half of the trait change effect was due to temperature increase, a substantial contribution came from other factors. These other effects were mostly in the same direction as the warming effect, they say, thus exaggerating the scale of this effect. They suggest that the assumption, made by some scientific reviews, that recent trait changes are predominantly driven by rising temperatures may over-emphasise the contribution of temperature to the observed changes. The researchers also point out that when examining the relationship between temperature and trait changes, it is important to recognise that other factors may also be involved. Temperature may be only one factor affecting such behaviour changes.

However, they note that in a minority of cases (32% for laying time and less than 20% for the other two traits) the effects were in the opposite direction and could conceal the impacts of rising temperature.

The researchers argue that studies comparing the relative sensitivity of different species to climate change need to pay particular attention to the influence of different factors. They note that the results presented here suggest that such disparities in sensitivity are likely to be influenced more by responses to non-temperature factors than by responses to temperature change.

The study highlights the importance of conducting further work to identify which specific non-temperature factors are contributing to the observed effects, and to what degree. The researchers note that these could include non-temperature climatic factors, such as rainfall, as well as non-climatic factors, such as land-use change. They also suggest that the statistical approach used in this study could form the basis of future studies in this area. They argue that such work is important to guide accurate and relevant conservation priority setting.


McLean, N., Kruuk L. E. B., van der Jeugd, H. P., Leech, D., van Turnhout C. A. M., and van de Pol, M. (2022) Warming temperatures drive at least half of the magnitude of long-term trait changes in European birds. PNAS 119(10): e2105416119.

To cite this article/service:

Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

Notes on content:

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.


Publication date
28 September 2022
Directorate-General for Environment

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