A concrete hunting ground: a new environment for raptors

Within cities, the number of trophic levels present in the community can change when animals migrate there. Smaller predators can end up at the top of the trophic chain or a different species, like the domestic cat, becomes the apex predator of the city. How are apex predators like raptors thriving or at least surviving in cities? In the natural environment, raptors, also known as birds of prey, can play an essential role as apex predators by keeping populations of smaller animals in check. They can fill the same role in the urban environment if they are able to find an appropriate habitat. Suitable nest sites and prey availability are typically considered to be the key determinants of successful raptor populations. In the urban habitat, they can help humans by keeping rodent populations down, but it is questionable if the socio-ecological systems in urban areas can actually create the right habitats for raptors.

Raptors do use urban resources 

They can nest in trees in urban greenspaces, but sometimes also nest in anthropogenic structures, such as rooftops and cavities in buildings. Hawks take residence in trees with open nests, owls usually reside in cavities of anthropogenic structures, and peregrines live in open nests on anthropogenic structures. This does happen naturally, but sometimes raptors have to be encouraged to nest in urban areas. Some raptor nests are taken over by other urban birds, but human activity can create many other nesting opportunities. For instance, we can create nest boxes and preserve historical buildings (e.g., churches) and window planters. Raptors are still seen as unusual in cities, therefore positive human interactions are important. In densely populated urban areas, the nests are especially vulnerable to human disturbances, but these disturbances have been generally tolerated.

Urban birds are smaller, generalists

When it comes to the bird species present in urban centres, almost all species are smaller and habitat-generalists. These types of raptors do well with a variety of vegetation and terrain types for both foraging and breeding. Because urban areas have this variety, it provides them a larger chance for survival. Small raptors do well in cities if elements from the nearby woodland are present for nesting. There is not yet a clear answer on why mainly small raptors are found in cities, but it may be because they are more common in general or they have advantages such as reduced metabolic needs with the urban heat island. Interestingly, the trend for small generalist species is not due to a phylogenetic signal, like a monophyletic clade of small, generalist raptors. While there are some bigger specialist species who live in the city, they are not common. This means that bigger raptors who are specialists may be at greater risk and likely cannot settle in urban areas. Also, migratory species are rarely found in urban areas.

The gradient form natural areas to highly urban areas shows where the filtering of raptor species takes place. At highly conserved areas, the highest variety of raptor species can be found. At high impervious surfaces in urban centres, the number of species can decrease more than half. The higher the percentage of impervious surface, the less species are found.

Raptors are present in the city where they can have an important impact on the food web. But more conservation efforts are needed in order to attract them to urban city centres. The large bodied, specialist raptors will probably not be seen anytime soon in cities, but we can create more suitable habitat for a few more species in the green outskirts of urban areas.

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References

Cooper, D. S., Shultz, A. J., Şekercioğlu, Ç. H., Osborn, F. M., & Blumstein, D. T. (2022). Community science data suggest the most common raptors (Accipitridae) in urban centres are smaller, habitat‐generalist species. Ibis, 164(3), 771–784. https://doi.org/10.1111/ibi.13047

Mak, B., Francis, R. A., & Chadwick, M. A. (2021). Living in the concrete jungle: a review and socio-ecological perspective of urban raptor habitat quality in Europe. Urban Ecosystems, 24(6), 1179–1199. https://doi.org/10.1007/s11252-021-01106-6

Martín-Cruz, M. A. S., Villegas-Patraca, R., Martínez-Gómez, J. E., & Inzunza, E. R. (2024). Raptors of a Neotropical city: diversity and habitat relationships along an urbanization gradient. Urban Ecosystems. https://doi.org/10.1007/s11252-023-01495-w