Study concludes that migratory birds may not be able to help plants escape climate change

A study published today in the journal Nature, with the participation of researchers from 13 European institutions, including the University of Coimbra (UC) and the University of Porto (UP), concluded that migratory birds disperse seeds mainly in the opposite direction to what would be necessary. to help plants escape climate change.

A juvenile blackbird (Turdus merula) eating the fruits of the Hedgehog (Rhamnus alaternus). Non-migrating or resident birds tend to disperse seeds over shorter distances, usually less than 1km from the parent plant, which will probably not be enough to keep up with the speed at which the climate is changing (Credit: Juan P. González-Varo)

Migratory birds can help plants adapt to climate change by eating their fruits and dispersing their seeds to more favourable locations. However, this new study shows that the vast majority of European forest seed species are dispersed by birds during their migration towards warmer southern latitudes, and only a minority to colder northern latitudes – on the contrary of what plants would need to adapt to global warming.

The results of this research are fundamental to understanding, halting and mitigating the effects of climate change on biodiversity.

As a result of global warming, ideal climatic conditions for species are shifting to cooler latitudes, leading to a redistribution of biodiversity globally. In Europe, this movement takes place in the South-North direction. However, while animals can move independently, plants depend to a large extent on frugivorous animals, and especially migratory birds, to disperse their seeds to places with more favourable conditions.

“We know the climate is, and will continue to warm, and as a result, many species in Europe are moving from areas that are becoming too arid and hot – to the south – and expanding into new areas. where conditions are becoming more favourable – to the north. For animals, including us, this movement is easier, but many plants need the help of animals, which, when consuming their fruits, end up depositing the seeds in new places where the plants can grow. Migratory birds, many of them travelling hundreds of kilometres in a few hours, play a very important role in providing this free ride service on a global scale», explains Ruben Heleno, a researcher at the Functional Ecology Center (CFE) of the Faculty of Sciences and Technology at the University of Coimbra (FCTUC), co-author of the study.

A Common Thrush (Turdus philomelos) eating a holly berry (Ilex aquifolium). The long period of fruiting of the holly, from autumn to the end of winter, overlaps with the migration of the common thrush to the north, and therefore this bird may have an important effect in dispersing the holly seeds to cooler latitudes to the north (Credits: David Chapman).

The research was based on the study of interactions between frugivorous plants and birds in 13 forests in 6 European countries, including a forest in Souselas – Coimbra, where for 6 years Portuguese researchers studied which species of birds disperse each species of plant and at what stage of the migration. In total, the study involved 949 interactions between 46 species of birds and 81 species of fruit-bearing plants.

The study shows that only 35% of plant species are dispersed by birds when they are migrating northwards, while 86%, the vast majority of species, are dispersed when birds that consume their fruit are flying northwards. towards warmer southern latitudes.

“Migratory birds are the perfect vehicle for taking berry-producing plants to new places and can help them change their distribution in the face of current climate change. However, we have shown that only a third of the plants can count on migratory birds to expand northwards, in order to maintain their current ecological niches», stresses Luís da Silva, a researcher at the Center for Research in Biodiversity and Genetic Resources (CIBIO -InBIO) of the University of Porto, co-author of the study.

A Blackcap’s Warbler (Sylvia atricapilla) eating the fruits of the Legitimate Sanguinho (Cornus sanguinea). This plant has a short fruiting period during the autumn when Blackcap Warblers are migrating south. Therefore, the warblers that eat their fruit will have a high probability of taking these seeds south, where they will face warmer temperatures in the future (Credits: Luis Ojembarrena).

Some birds are especially important to disperse plants to the north.

In Europe, birds migrate from south to north in spring, and from north to south in autumn. This study shows that birds that winter in southern Europe and northern Africa are especially important in helping plants move to more favourable northern latitudes.

This important service is provided by a few species, including the Red-breasted Robin, the Blackhead Warbler and several species of thrush, all of which are still relatively common in Europe. However, some of them are hunted legally and illegally in several countries in the Mediterranean basin, despite their important ecological role.

The study authors suggest that this difficulty in finding suitable dispersers may affect the specific composition of European forests in the future, as many plants may be left behind. Plant species that cannot keep up with the shift in their preferred survival conditions will have to face more arid, drier and hotter climates in the south.

The scientific article is available here.

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