Jacopo G. Cecere, Simona Imperio
This indicator provides an overview of the health status of common migratory passerine bird populations in Europe by assessing the resilience of migratory species to climate change. Rising spring temperatures due to global warming lead to an earlier onset of vegetation growth and, consequently, an earlier peak in insect abundance. As a result, if migratory birds do not arrive at their breeding sites earlier by the same degree, they will not find an abundance of prey when they need to feed their chicks. Failure to bring forward the migration date results in low resilience of migratory populations to climate change, with negative effects on their survival. We therefore analyzed the temporal variation in the arrival dates of migratory passerines at stopover sites used after crossing the Sahara and the Mediterranean Sea during their spring journey from Africa to European breeding grounds. Based on an analysis of the migration dates of 10 bird species recorded at 26 banding stations participating in ISPRA’s Small Islands Project during the period 1988–2025 (38 years), it was found that 80% of the species considered show a shift in migration dates that is too slow (approximately 1 day every 7+ years) to be considered sufficient to counteract the effects of climate change.
The indicator is based on data collected as part of the Small Islands Project, coordinated by ISPRA and operating continuously since 1988 with the aim of studying and monitoring the migration phenology of passerine birds that spend the winter south of the Sahara, using the bird-banding technique. The Small Islands Project involves the application of standardized bird banding protocols at strategic sites where passerines stopover during spring migration (small islands as well as coastal sites), from April 16 to May 15 of each year. The indicator considers 10 species of passerines: Common Redstart, Nightingale, Spotted Flycatcher, Black Redstart, Common Reed Warbler, Reed Bunting, Great Reed Warbler, Stonechat, Green Sandpiper, and Oriole. For each species, the temporal variation in the median date of passage at the sampling sites was analyzed over the period from 1988 to 2025, taking into account possible site-specific variations in the passage of migrants at the 26 stations that have participated in the project over the years.
To assess the resilience of small migratory birds to climate change by analyzing changes in the spring migration dates of 10 bird species.
Birds Directive (2009/147/EC).
Objective: to maintain bird species in a satisfactory conservation status.
Bonn Convention – CMS – Convention on the Conservation of Migratory Species of Wild Animals.
Objective: to ensure a good conservation status for migratory species.
Law 157/92 – Regulations for the protection of homeothermic wild fauna and hunting activities. Objective: to maintain bird species in a satisfactory conservation status.
Both, C., & Visser, M. E. (2001). Adjustment to climate change is constrained by arrival date in a long-distance migrant bird. Nature, 411(6835), 296-298.
Jonzén, N., Lindén, A., Ergon, T., Knudsen, E., Vik, J. O., Rubolini, D.,... & Stervander, M. (2006). Rapid advance of spring arrival dates in long-distance migratory birds. Science, 312(5782), 1959-1961.
Møller, A. P., Rubolini, D., & Lehikoinen, E. (2008). Populations of migratory bird species that did not show a phenological response to climate change are declining. Proceedings of the National Academy of Sciences, 105(42), 16195-16200.
The sampling period (April 16 – May 15) exhaustively covers the migration period for a large proportion of the species (including the 10 analyzed), but not for all those sampled during the Small Islands Project.
None are expected
ISPRA (Italian Institute for Environmental Protection and Research)
Bird ringing database, managed by the ISPRA Bird Ringing Office [see the ISPRA National Biodiversity Network map viewer to consult the data: http://geoviewer. nnb. isprambiente. it/mapreacter/#/]
National
1988-2025
Median capture date for each species at one of the Small Islands Project stations; capture station; year.
The indicator is calculated across 10 passerine species: Common Redstart, Common Nightingale, Whinchat, European Pied Flycatcher, Eurasian Reed Warbler, Sedge Warbler, Icterine Warbler, Garden Warbler, Wood Warbler, and Eurasian Golden Oriole. For each species, the median capture date (thus representing passage and migration) was calculated for each year at every ringing site participating in the Small Islands Project (Progetto Piccole Isole). A linear mixed-effects model was then constructed for each species, using the median capture date per year and site as the dependent variable and the year as the independent variable. The median date was calculated only for instances where at least 3 individuals were captured at a site during a single season (April 16 – May 15); typically, the number of birds captured per station and season is orders of magnitude higher than 3. Finally, capture site was included as a random factor in the model to account for site-intrinsic effects, such as geographic location (e.g., birds arriving from Africa reach low-latitude sites earlier than higher-latitude ones) and the fact that different sites may host distinct populations—and thus exhibit different phenologies—of the same species.
In 2025, the indicator shows a seemingly favorable picture for only 20% of the migratory species analyzed. The remaining 80% do not significantly advance their spring migration date, thus demonstrating a low degree of resilience to climate change.
The trend is negative, as analysis of the available historical series (Figure 1) shows that the Garden Warbler advances its median migration date by 1 day every 8.9 years, the Common Nightingale by 1 day / 13.9 years, the Icterine Warbler by 1 day / 13.2 years, the Eurasian Golden Oriole by 1 day / 8 years, the Sedge Warbler by 1 day / 9 years, the Eurasian Reed Warbler by 1 day / 12.8 years, the European Pied Flycatcher by 1 day / 12.9 years, and the Wood Warbler by 1 day / 7.7 years.
Conversely, an advancement greater than 1 day every 7 years can be considered favorable for a species, as it is likely sufficient to counteract the disadvantages arising from rising spring temperatures, net of other threat factors (e.g., habitat modification). This more favorable situation was observed only for the Common Redstart and the Whinchat, which show an advancement of the median migration date of 1 day every 7.1 and 6.8 years, respectively.
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Figure 1: Trend in the median passage date at the ringing stations of the Progetto Piccole Isole (Small Islands Project) during the 1988–2025 period for 10 common trans-Saharan migratory passerine species in Europe during spring migration. Fonte
ISPRA (Italian Institute for Environmental Protection and Research) Legenda
On the y-axis, the value 100 corresponds to April 10th, while the value 140 corresponds to May 20th. The number of active ringing stations varies from year to year (min 2 in 1989, max 15 in 2012), and not all stations record the 10 target species every year. |
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Trend in the median passage date at the ringing stations of the Progetto Piccole Isole (Small Islands Project) during the 1988–2025 period for the Eastern Olivaceous Warbler (Iduna pallida) during spring migration. Fonte
ISPRA (Italian Institute for Environmental Protection and Research) |
Resilience to climate change is a factor that directly and indirectly impacts the conservation status of migratory bird species. The relationship between the temporal variation of migration dates and the conservation status of migratory birds in Europe has been demonstrated in several scientific studies: species that have failed to adapt to global warming by significantly advancing their migration date are now in a poor conservation status.
The analysis of the 10 species considered shows a biologically significant advancement of the spring migration date only for the Common Redstart and the Whinchat; these species appear to demonstrate a certain degree of resilience to global warming. Conversely, the Garden Warbler, Common Nightingale, Icterine Warbler, Eurasian Golden Oriole, Sedge Warbler, Wood Warbler, European Pied Flycatcher, and Eurasian Reed Warbler show a spring migration advancement that is too slow (1 day every 7+ years), likely failing to respond adequately to the environmental changes driven by rising spring temperatures (Figure 1).