95% of the seeds are transported within the city itself over distances of around 700 meters
The remaining 5% can be moved up to 35 kilometers beyond the city limits
the seagulls disperse about 30% of plant seedsautochthonous and also invasive, in urban green areas, according to a study led by the Institute of Marine Sciences (ICM-CSIC) and the Doñana Biological Station (EBD-CSIC).
The study, whose results have implications for the management of urban green spaces, has been carried out in the city of Barcelona analyzing the GPS-tagged seagull movements and the detection of seeds found in their diet.
“Birds can play a fundamental role in the dispersal of plants, including exotic species”, has summed up the EBD-CSIC researcher, explains Víctor Martín, who has detailed that birds can ingest the seeds directly or ingest other smaller birds that have previously ingested them, and then those seeds are deposited elsewhere as they pass through the digestive tract.
“If this dispersion occurs in the cities, it can cause ecological and economic problems related to the management of green urban areas, especially when the plants that are dispersed are invasive species, which affects the local biodiversity of urban ecosystems”, the researcher warned.
Different types of seed
Most of the seeds found in the study did not have fleshy fruits and were small in size, which indicates that seagulls acquire them through the consumption of other species of smaller size, such as pigeons and Argentine parrots, which are mainly granivorous.
They also found other species of plants with larger seeds Y fleshy fruit that they would be consumed directly by the seagulls.
The study, published in the journal ‘Science of the Total Environment’, focused on the yellow-legged gull (Larus michahellis), an opportunistic seabird that has stable populations in Barcelona and is adapted to exploit urban resources.
In the research, in which researchers from the Barcelona Public Health Agency (ASPB), the Catalan Institute of Ornithology (ICO) and the Hungarian Center for Ecological Studies have also collaborated, the biologists analyzed the movements made between 2018 and 2019 by 20 yellow-legged gulls tagged with GPS devices.
“Understanding dispersion and spatial patterns can help the knowledge of exotic species within urban green areas”, highlighted Tomás Montalvo, ASPB researcher.
A thousand seeds a day dispersed
In the study they have identified seven exotic species that are dispersed by seagulls: fig, toothgrass, nightshade, trompillo, kiwi, Mexican fan palm, and dodder.
According to the work, more than 1,000 seeds a day are dispersed by seagulls inside and outside the limits of the city of Barcelona.
The 95% of the seeds are transported within the city itself at distances of around 700 meters, and the remaining 5% can move up to 35 kilometers beyond the city limits.
Of the seeds that are dispersed within the city, about 30% are deposited in urban green areas, suitable for seeds to establish (shrub areas, green parks and urban pastures).
Important for green areas
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In this sense, Raül Aymí, a researcher at the ICO, pointed out that “the results of the study suggest that the seagulls would be important dispersal vectors between urban green areas and open the door to other studies on how birds can contribute to the expansion of exotic species in cities”.
The ICM-CSIC researcher Joan Navarro has concluded that “this work contributes very valuable information to understand urban marine ecologyespecially the interactions with human interests and the possible ecosystem services of the population of seagulls residing in Barcelona”.