Gulls are taking over our European cities

Coastal cities in Europe are swarmed with gulls, to the annoyance of many of those cities’ inhabitants. Gulls (Larus spp.) are naturally cliff-nesting species, but are able to thrive in urban areas because of the high food availability, the suitable climate, the similarity of nest substrate, lesser risk of predation and the presence of conspecifics like other gulls (Mainwaring et al., 2014). In addition to these five factors, climate change and human behaviour is adding to the reasons we see ever-growing populations of gulls in our European coastal urban areas. In particular, the Lesser black-backed gull (Larus fuscus) and the Herring gull (Larus argentatus) are represented in large numbers. See the maps below for their current distribution (BirdLife International, 2018; BirdLife International, 2021).

Fish populations, which are the gulls’ natural food source, are decreasing in the Celtic sea, North sea, and Norwegian sea. One of the reasons for this decrease is the increase in sea temperatures because of climate change: fish distributions are shifting towards the colder, more oceanic waters, and away from the gulls’ territory. The second main reason for the decline is overfishing, especially of cod, herring, and whiting (OSPAR, 2017).

And so, the gulls are drawn towards the mainland and the cities. Within the cities they can find consumable trash strewn all around. Half-eaten snacks, bags of chips, all this litter laying around unguarded, ready to grab for the gulls. Trashcans are often not sealed well enough or don’t even have a lid, collections are not frequent enough. This is a problem that should be tackled at the source, for example with proper waste management (Belant, 1997).

It appears that gulls’ behavioural patterns are actually changing as they adapt to the urban environment. Since they started appearing in our cities about a 100 years ago, researchers have found that both Lesser black-backed gulls and Herring gulls show behaviours that suggest greater boldness and aggression in urban areas. Along an urban-to-rural gradient, city gulls had a shorter flight initiation distance, a shorter flight distance, a reduced escape speed, and increased numbers of agonistic interactions compared to their non-urban counterparts (Pavlova & Wronski, 2020). Gulls are kleptoparasitic, which means they take food from other gulls, but since they now live alongside humans and have become more aggressive, we have apparently become a target of this behaviour as well (Holloway, 2023).

The abundance of gulls in cities may represent a growing public health risk as well. Gulls are known to be carriers and spreaders of bacteria like Salmonella, transmitting it to humans and other animals, especially in highly populated areas like cities. They also contaminate public water supply with their feces (Belant, 1997).

But to end on a positive note, in defence of the gulls: they are great seed dispersers within and outside urban environments! Seeds get dispersed at distances as far as 35 km, of which 95% end up in urban environments and 30% were even deposited into urban green spaces (Martín-Vélez et al., 2022).

 

Sources

Belant, J. L. (1997). Gulls in urban environments: landscape-level management to reduce conflict. Landscape and Urban Planning, 38(3-4), 245–258. doi:10.1016/s0169-2046(97)00037-6

BirdLife International. 2019. Larus fuscus (errata version published in 2022). The IUCN Red List of Threatened Species 2019: e.T22694373A211737029. Accessed on 13 June 2024.

BirdLife International. 2021. Larus argentatus. The IUCN Red List of Threatened Species 2021: e.T62030608A206585142. https://dx.doi.org/10.2305/IUCN.UK.2021-3.RLTS.T62030608A206585142.en. Accessed on 13 June 2024.

Holloway, P. (2023). Why we see so many gulls in our cities and towns. University College Cork. https://www.ucc.ie/en/eri/news/why-we-see-so-many-gulls-in-our-cities-and-towns.html?

Mainwaring, M. C., Hartley, I. R., Lambrechts, M. M., & Deeming, D. C. (2014). The design and function of birds’ nests. Ecology and Evolution, 4(20), 3909–3928. doi:10.1002/ece3.1054

Martín-Vélez, Víctor, Tomás Montalvo, Isabel Afán, Antoni Sánchez-Márquez, Raül Aymí, Jordi Figuerola, Ádám Lovas-Kiss, and Joan Navarro. (2022). Gulls Living in Cities as Overlooked Seed Dispersers Within and Outside Urban Environments.” Science of the Total Environment 823: 153535. https://doi.org/10.1016/j.scitotenv.2022.153535.

OSPAR (2017). Marine birds in trouble. https://oap.ospar.org/en/ospar-assessments/intermediate-assessment-2017/key-messages-and-highlights/marine-birds-trouble/

Pavlova, O. and Wronski, T. (2020). City gulls and their rural neighbours: Changes in escape and agonistic behaviour along a rural-to-urban gradient. In: Daniels, JA, (ed.) Advances in Environmental Research. Nova Science Publishers, Inc., New York, pp. 33-62. ISBN 978-1-53618-000-8