Gulls are coastal birds. Most of the gull species are closely linked to coastal areas . They nest on the ground, near the shore, generally in areas protected by natural structures, such as cliffs or cliffs, forming very large groups. They fly to the beaches or to the intertidal region where they hunt for crabs, small fish, molluscs, small mammals, other birds, their eggs, or scavenge carcasses of stranded animals or hunted by other animals. Of course, thanks to the fact that humans have colonized the coasts, they take advantage of our waste to look for food.
However, it is not uncommon to find tens or even hundreds of thousands of seagulls flying through the skies of Madrid every winter. An inland city, hundreds of kilometers from the nearest coast, turns out to meet each and every one of the prototypical features of inland cities except one: seagulls.
Madrid destination where seagulls winter
The usual thing for seagulls is to stay all their lives near the coast. However, when the winter is particularly harsh, it is not uncommon for some groups of seagulls to decide to migrate inland, looking for a place to spend the winter, to return to the coast in spring. Just find a place that has enough food and water.
In principle, the area represented by Madrid would not have to be attractive for these animals . Its river has little volume and little food, its winter is cold and its fauna is not very abundant. But there are two aspects that make Madrid the perfect destination for a seagull looking for a place to spend the winter. On the one hand, the city and its inhabitants, with their vehicles and their heaters, create what is known as the heat island effect, a more tolerable microclimate that tempers the rigors of winter. And, on the other hand, the garbage . The same rubbish that invites the storks to stay and not migrate to Africa, invites the seagulls to migrate to the capital.
At first, few seagulls arrived. However, those who hibernated in Madrid discovered a paradise in which to settle, and returned the following winter. Year after year, more seagulls found themselves in Madrid’s landfills. Family groups were added, generation after generation, until counting in these years more than 200,000 seagulls each winter. It is common to find them in landfills devouring leftover food discarded by restaurants and by citizens.
It has been observed that these animals learn certain patterns of human behavior and use them as a signal to find food, adapting their schedules to these patterns.
Problems that seagulls can cause to Madrid
Like many other wildlife, seagulls can cause a number of problems when they enter urban environments. One of the most important is the possibility of transmitting diseases . This is particularly dangerous in areas where food is handled.
In the case of Madrid, areas such as Mercamadrid can be a risk . The amount of food that is handled in the largest food market in Spain is enormous, and proportional to the amount of waste that is discarded. The seagulls, called by the meat and fish waste, have an all-you-can-eat buffet in Mercamadrid. For this reason, specific plans have been launched in Madrid to scare away the seagulls from Mercamadrid, using trained birds of prey and acoustic signals.
But seagulls rarely eat where they get their food. The normal thing is that they go with the food to nearby places, but more protected, such as the roofs of buildings. That is where a good amount of garbage ends up, such as what is not eaten: bones, mollusk shells or feathers, and seagull droppings. Not only is all that expensive to clean, but if it gets washed away in the rain, it can clog gutters and cause structural damage.
When they go to rest, they look for bodies of water, and since they don’t find enough volume in the capital, they end up traveling to reservoirs and other nearby wetlands , where the seagulls can cause a new ecological problem. In those places of rest they not only defecate, they also expel their pellets, boluses of undigested food remains that they regurgitate: food remains, plastic and other contaminants.
In this way, seagulls act as a vector that displaces anthropogenic waste from urban environments to wetlands.
These problems do not usually occur in such an accentuated way in coastal cities, because they prefer to get their food and rest in natural enclaves near the sea.
Problems that Madrid can cause to seagulls
Of course, the presence of seagulls in Madrid is not only a risk for the people of Madrid, it is also a risk for the seagulls . Apart from the intrinsic risks of a wild animal in a city – for example, being run over by a vehicle – feeding exclusively on food scraps can cause problems for seagulls.
On the one hand, a change in their behaviors ; they cease to be facultative hunters and scavengers, to become exclusively scavengers. When they return to the coastal areas where they nest and spend the summer, they will retain these behaviors. This obviously affects the ecosystem, which loses a predator, with its functions in controlling prey populations, and only obtains a scavenger .
But perhaps the most relevant impact is on your health. In many cases, the food in landfills is in a very advanced state of decomposition, or mixed with other garbage , with the risk of diseases in seagulls, which can be lethal.
REFERENCES:
Goumas, M., Boogert, NJ, et al. 2020. Urban herring gulls use human behavioral cues to locate food. Royal Society Open Science, 7(2), 191959. DOI: 10.1098/rsos.191959
Moreno Díaz, FJ 2019. Contract for bird population control services in the Mercamadrid food unit and in the Mercamadrid expansion (Assessment report PC-MER/2019/00027-ORD; p. 8). Mercamadrid. https://contrataciondelestado.es/wps/wcm/connect/97a8ccf9-fdb2-4f7f-af5a-c38d1e919e8f/DOC20191126203829INFORME+DE+VALORACION+SOBR E+B+PC+MER+2019+00027+ORD.pdf?MOD=AJPERES
Spelt, A., Soutar, O., et al. 2021. Urban gulls adapt foraging schedule to human-activity patterns. Ibis, 163(1), 274-282. DOI: 10.1111/ibi.12892
Stewart LG, Lavers JL, et al. 2020. Seasonal ingestion of anthropogenic debris in an urban population of gulls. Marine Pollution Bulletin, 160, 111549. DOI: 10.1016/j.marpolbul.2020.111549
