Some species of plants are capable of colonising new habitats thanks to birds that transport their seeds in their plumage or digestive tract. Until recently it was known that birds could do this over short distances, but a new study shows that they are also capable of dispersing them over more than 300 kilometres. For researchers, this function could be key in the face of climate change, allowing the survival of many species.
Birds can act as dispersers of seeds and other propagules -buds, bulbs, tubers or spores- over short distances which, in many cases, do not exceed a kilometre and a half. However, it had not been demonstrated whether or not they were capable of doing so over longer distances.
A team led by scientists at the Doñana Biological Station-CSIC (Spanish Council for Scientific Research) in Seville (Spain) confirmed this hypothesis due to the seeds found in the digestive tract of various species of birds hunted in the Canaries by Eleonoras falcons (Falco eleonorae) during their migration towards Africa.
“This mechanism of long-distance dispersion had not been confirmed until now, mainly due to the difficulty involved in sampling propagules transported by birds during their migratory flight. We were able to analyse it thanks to the hunting behaviour of Eleonoras falcons,” Duarte Viana, researcher in the Doñana Biological Station and co-author of the study, explained.
The data, published in the journal Proceedings of the Royal Society B, reveal for the first time that there are species that may be excellent dispersers of propagules over long distances of more than 300km. These birds were flying over the sea in an area located between the Canaries and Africa, and scientists found in them seeds that belonged to a plant that was not native to the Canary Islands, which demonstrates that they are capable of promoting colonisation of distant and remote areas.
In total, researchers sampled 408 specimens of 21 species. Five birds from three different species stored 45 seeds inside them: the European pied flycatcher (Ficedula hypoleuca), the common redstart (Phoenicurus phoenicurus) and the common quail (Coturnix coturnix). The first two transported seeds of fleshy fruits (two species of the Rhamnus genus), while the common quail transported up to three different species (Rubus, Genisteae and Persicaria)..
“The best dispersers would be frugivorous birds, which eat fruit; granivorous birds, which eat seeds, such as the quail; and water birds, many of which eat the sediment of ponds. We could be talking about thousands of species of birds around the world, many of which are migratory,” said Viana.
According to researchers, faced with a situation of global change, long-distance dispersers will allow many species of plants and organisms to reach new habitats that offer them optimal conditions for their survival.
The seeds transported by migratory birds are defecated and deposited in the place where the birds arrive. If the new habitat is favourable to germination and the subsequent establishment of a viable population, the species of plant dispersed may successfully colonise this area, grow and reproduce.
The study was focussed on three islands to the northeast of the archipelago of the Canaries: Alegranza -from which a large part of the samples were obtained-, Montaña Clara and Roque del Este, places where Eleonoras falcon nests and towards which the trade winds usually drag the migratory birds that go from Europe to Africa. Here they are hunted, particularly in October, when there is large-scale migration.
After examining the stomach and intestine contents of the prey stored in the falcon nests, the experts demonstrate that most of the species to which the seeds belong grow more than 100 or 200km from the islands studies, and one of them, Persicaria, is not even a Canary Island.
“In the particular case of Alegranza, the likelihood of colonisation is slim since this islet has an extremely arid climate, which is unsuitable for the life of most plant species. However, other islands of the Canary archipelago may have been colonised through seeds that come from further afield, continental Africa or, more likely, the Iberian Peninsula,” concluded Viana.
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It took a while to confirm this long-distance dispersion mechanism, mostly because it was challenging to sample propagules carried by migratory birds during their flight. The hunting behavior of Eleonoras falcons allowed us to analyze it,” said Duarte Viana, co-author of the study and researcher at the Doñana Biological Station.
The findings, which were published in the Proceedings of the Royal Society B journal, show for the first time that certain species may be highly effective propagule dispersers over distances greater than 300 km. Scientists discovered seeds from a plant not native to the Canary Islands in these birds while they were flying over the sea in an area between the Canaries and Africa. This shows that these birds have the ability to encourage the colonization of far-off places.
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In total, researchers sampled 408 specimens of 21 species. 45 seeds were stored inside the bodies of five birds, belonging to three distinct species: the common quail (Coturnix coturnix), the European pied flycatcher (Ficedula hypoleuca), and the common redstart (Phoenicurus phoenicurus). Two species of Rhamnus seeds were carried by the first two, whereas up to three distinct species were carried by the common quail (Rubus, Genisteae, and Persicaria).
This theory was verified by a group of researchers at the Doñana Biological Station-CSIC (Spanish Council for Scientific Research) in Seville, Spain, thanks to seeds discovered in the stomachs of several bird species that Eleonoras falcons (Falco eleonorae) hunted in the Canaries as they migrated towards Africa.
According to the University of Nevada, Las Vegas, the seeds of the mistletoe plant are covered in a sticky substance – birds wipe their beaks on a branch to rid themselves of the seeds, allowing mistletoe to reach the environment it prefers.
Plants use vibrant, high-energy fruits or large nuts as food to attract birds to their seeds. Bird cherry and other plants have developed together to the point where the seeds of these plants need to pass through the digestive tract of birds in order to germinate. Mutualism is the term for a relationship in which both organisms gain from one another. ?.
In some cases, birds do not digest and receive energy from the seeds they consume. Instead, they seek the nutritious fruits and berries surrounding the seeds, and the seeds come along with the bargain, notes Cornell Universitys Naturalist Outreach. Examples of plants that use this seed dispersal method include raspberries, blackberries and blueberries.
Birds may also partially crack or nick the seed coat trying to open a seed, allowing it to more easily germinate. According to The Seed Site, other plants depend on birds and other animals to forget where they have hidden or buried seeds, effectively distributing the seeds and allowing them to colonize a new area. The acorns of oak trees are often dispersed in this way.
Birds may use their beaks or claws to transport seeds to a new area. A bird may take off carrying a seed or fruit to a safe location while preparing to eat or construct a nest. The bird may drop seeds or entire fruits along the route, enabling them to reach new locations far from the parent plants where there are enough resources for them to flourish.
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