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Cormorants confirm Darwin’s theory of secondary dispersal of seeds and invertebrates via predation of fish

Published: 04 October 2017

Charles Darwin noted the potential of birds to spread plant seeds and invertebrates through their fish prey. His theory has now been studied and proved to occur in Great cormorants. Secondary dispersal may provide critical connectivity for plant and invertebrate populations inhabiting different water bodies, and allow movement of species facing anthropogenic stressors such as climate change.

It is well known that fish and birds are important dispersal vectors for seeds and invertebrates, but it is now shown that secondary dispersal may additionally play an important role for several species. Plant seeds or small aquatic invertebrates are often eaten by fish, which in turn are eaten by birds such as cormorants. After a day of hunting for fish, cormorants vomit pellets with indigestible remains of their prey in the evening, often in suitable habitat for the establishment of plants and invertebrates.

-We found viable seeds of three plant species and one bryozoan statoblast in vomited pellets, says Dr Maria Ovegård, researcher at Department of Aquatic Resources at Swedish University of Agricultural Sciences, one of the coauthors to the article published in Biology Letters.

Cormorants eat around 500 grams of fish per day. They do not digest ingested hard material of their prey, but instead vomit this in a mucus coated pellet that often ends up below colonies or roosting areas. This new study collected pellets from several cormorant colonies in Europe. Seeds were found in one third of the pellets from in total 21 species, from 16 different plant families. One in five pellets contained intact invertebrates of in total seven different taxa, including the first record of bird-mediated dispersal of fresh water sponges.

- Secondary dispersal via fish-eating birds can provide essential connectivity over tens of kilometers between otherwise separated aquatic habitats, and contribute to plant and invertebrate diversity.

Link to article:

Great Cormorants reveal overlooked secondary dispersal of plants and invertebrates by piscivorous birds


Maria Ovegård SLU, Department of Aquatic Resources, Division of Coastal Research, SLU, , +46(0)10 - 478 41 19

Casper H. A. van Leeuwen Department of Aquatic Ecology, Netherlands Institute of Ecology,

Maria Ovegård, Environmental Monitoring and Assessment Analyst
Department of Aquatic Resources, Integrerad resurs- och miljöanalys, 010-4784119, 076-126 80 59

Maria Ovegård, researcher, environmental monitoring and assessment analyst, Department of Aquatic Resources, Institute of Marine Research, SLU, +46 (0)10-478 41 19

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