#StoryBehindThePaper

Earlier fledging phenology in warmer years depends on local environmental conditions and species.

This blog post is provided by Paul Cuchot and tells the #StoryBehindThePaper for the paper “How interacting anthropogenic pressures alter the plasticity of breeding time in two common songbirds” which was recently published in the Journal of Animal Ecology. The authors study the breeding phenology in tits using citizen science and mist netting.
Context:

Phenological adjustment is the first line of adaptive response of vertebrates to disruption of seasonality by climate change. For instance, in response to increasing spring warmth, many bird species advance their migration and breeding time. This ability for birds (and other organisms) to adjust such phenological events with varying environmental conditions is called ‘phenological plasticity’ and varies between species, according to ecological preferences and life history traits.

A recent study showed important variations in phenological plasticity of laying dates between tits populations (Parus major and Cyanistes caeruleus; Bailey et al., 2022) and suggested that local environment (forest type and climate change exposure) may be the cause. Their study highlighted the importance of studying variations between populations, as it could explain the current decline in some populations and the future of others. However, studying phenological changes through space and time can be difficult to address with classical intensive monitoring of bird reproduction with nest boxes.

Challenge: Inferring phenological data from “Constant Effort Site” monitoring program.

In contrast to intensive nest box monitoring programs, citizen science provides data that generally cover a greater variety of habitats, as larger scale sampling is possible thanks to the involvement of many volunteers. One of the most important observable indexes of breeding phenology is the increasing appearance of juveniles in the population during the breeding season (Figure 1). Unfortunately, age status (newly fledged, i.e., juveniles, or adults) is rarely reported in occurrence/observation data. Therefore, we decided to use mist net (Figure 2) capture data, which allows an accurate and systematic estimation of the age status (Figure 3 and 4), from the French Constant Effort Site monitoring program.

Figure 1: Proportion of juveniles increases throughout the breeding season. At the beginning, chicks are not born yet, only adults are captured. At the end, nearly all juveniles have fledged and can be captured.
Figure 2:  Mist net capture sessions start at dawn. © Pierre-Yves Henry

Our first objective in this analysis was to devise a method capable of estimating breeding phenology through capture data. To achieve this, we used hierarchical non-linear models, exploiting the curve shape parameters associated with fledging phenology (see Figure 1) and modelled their response to temperature variation (i.e., plasticity).

Figure 3: Capture of an adult Blue Tit Cyanistes caeruleus during a mist net capture session. Birds are identified at the species level, measured (wing and tarsus length, weight), aged and sexed (when possible). © Simon Benateau.
Figure 4: Handling an adult Great tit Parus major during a mist net capture session. © Christophe de Franceschi.
Investigating environmental drivers of variation in phenological plasticity

Once phenology was inferred across a large number of sampling sites, we investigated potential drivers of variation in phenological plasticity: the quantity of available forest (inversely proportional to the proportion of farmland area) and the proportion of impervious surface area, which relates to any road or build-up. Our results suggest that phenological plasticity is highly variable between tit populations and that these differences are explained by forest cover and urbanisation, but only for the blue tit. Overall, the main result is that a decrease in blue tit phenological plasticity, the breeding response to local spring temperature, was associated with a decrease in forest cover and therefore, with an increase in agricultural land. This suggests that habitat quality, and/or their level of disturbance can alter breeding phenology, with differing sensitivity across species.

This study was only possible thanks to the long-term commitment of many French licensed ringers over the last 30 years alongside with the CRBPO (Centre de Recherches sur la Biologie des Populations d’Oiseaux) and the French national museum of natural history (MNHN) that host and coordinate the program. This is a good example of how small-scale studies/participation can generate knowledge at national and species level.

References

Bailey, L. D., van de Pol, M., Adriaensen, F., Arct, A., Barba, E., Bellamy, P. E., … & Visser, M. E. (2022). Bird populations most exposed to climate change are less sensitive to climatic variation. Nature Communications, 13(1), 2112.

Read the paper

Cuchot, P., Bonnet, T., Dehorter, O., Henry, P.-Y., & Teplitsky, C. (2024). How interacting anthropogenic pressures alter the plasticity of breeding time in two common songbirds. Journal of Animal Ecology, 00, 1–14. https://doi.org/10.1111/1365-2656.14113

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