Poor success of birds breeding in urbanized areas
21 January 2017
South African Jacques de Satgé wins the second Ornithology prize 'Wim Dings – De Wielewaal'.
Great tits breeding in urban areas raise fewer offspring, and this applies not only to large cities but also to parks and gardens in small towns. The reason appears to be lack of natural food such as large caterpillar populations in indigenous trees. This was found by Jacques de Satgé, winner of the bi-annual Ornithology prize ‘Wim Dings – De Wielewaal’ of the University of Antwerp.
We often hear about success stories of nature in cities: exotic parakeets in the heart of Brussels, foxes in the suburbs, and an increasing number of plant and animal species that manage to adapt to life in urban environments. The much acclaimed BBC-series Planet Earth devoted an entire episode to animals in cities.
Many popular garden birds appear to thrive in our cities and towns. But is their presence also sustainable? Jacques de Satgé, Master student at the University of Antwerp, studied the breeding success of great tits in nest boxes in a large number of Flemish cities and towns. In his Master’s thesis he reports that the number of fledged young per nest is up to 30% lower in the most urbanized areas compared to forests in rural areas.
South African student Jacques de Satgé
“In addition the fledged young weigh about 10% less which further reduces their survival chances”, says de Satgé. “Great tits also start laying earlier and produce fewer eggs, but still the success per egg is lower.”
Caterpillars in short supply
Previous studies had already shown that great tits and other songbirds raise fewer young in urban areas. What is new in this study is that the effect is not limited to major cities. Birds breeding in a park in the middle of a small town have equally poor success. What seems to be most important is the degree of urbanization within a few hundred meters around the nest.
“Video registrations show that parents provision their young with significantly fewer caterpillars in urbanized areas compared to rural areas. This is probably due to the lower abundance of indigenous trees such as oaks. These trees can harbour huge caterpillar populations exactly when the nestlings are growing.”
The good news is that great tits are still abundant in Flanders without sign of a negative trend: the large productivity in forested areas probably compensates for the low success in cities. De Satgé: “City parks and gardens may function as an ‘ecological trap’ that attracts new breeders in every successive generation thanks to its seemingly attractive vegetation with safe nesting sites. But in the end these birds fail to produce enough young to maintain their numbers.”
South African student Jacques de Satgé did his research as part of the international Master in Biodiversity at the University of Antwerp. His Master’s thesis is awarded with the Ornithology prize ‘Wim Dings – De Wielewaal’ worth 2000 euros. This prize is awarded every two years in remembrance of the Flemish field ornithologist Wim Dings (1927-2012), active member of the 'De Wielewaal' society. The prize aims to encourage and support research in the field of ornithology.
“This year’s submissions were of very high quality”, says Prof Erik Matthysen (University of Antwerp), chairman of the jury. “The winning thesis has high societal relevance allowing policy makers to optimize decisions on planning and management of urban greenspaces. With a South African winner the prize now also reaches an international dimension.”