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How much do cities affect bird lives?

You have probably already noticed the decline of insects in nature, either through the media or even from your own experience. Now, an international European research group has investigated how disappearing insects can affect bird populations. Professor Jiří Reif, from the Faculty of Science at Charles University, was involved in this research too, particularly in the planning of the project. According to the authors, insectivorous birds could be negatively affected by the depletion of insect communities.

Pesticide use, loss of natural habitat, climate change, and invasive organisms could all be behind the decline in the number of invertebrate species. But some factors might not immediately come to one's mind, such as elements of urbanization, which are also responsible for light and noise pollution.

Illustrative photo of a young Eurasian blue tit
author: Tereza Žirovnická

Data collection for the research took place in 14 European cities, including Prague. The study divided a total of 126 bird species observed for comparison into three groups: granivorous, insectivorous, and omnivorous. Data were collected in 2018 during the breeding season of each species. Observation points were marked in each city, from which birds were subsequently counted by experienced ornithologists. Based on the information collected, species richness and distribution into feeding categories were determined. Finally, the level of artificial light and noise pollution was included in the analysis.

City light and attracted insect
source: pexels.com

Meanwhile, you may be asking: How can artificial night lighting harm insects? There are several answers to that. While individual light sources are attractive to insects, more extensive light pollution is harmful to insects for several reasons. Regular daily movements on a small scale can amount to large-scale migrations and thus exhaust the insects, with some disruption to natural movement patterns and changes in the distribution of insects in the landscape. Concentrations below light sources also make insects more susceptible to predation. Night lighting can also build up diurnal insects to activity, but they are not specialized for foraging at night or for activity in cooler temperatures. Finally, juvenile development and reproductive instincts are also affected. Exhaustion, disruption of diurnal rhythms, and reproduction all result in the necessary decline of insects. With increasing light, the heterogeneity of the insect population also decreases, despite the fact that there is a certain amount of green space in the city.

Dusk over Prague,
author: Tereza Žirovnická

Both urban and rural (field, forest) bird species were affected by this finding, and this points to the fact that the degree of influence of night lighting on a bird community depends on its food type, not its abundance. As expected, insectivorous and omnivorous birds were particularly affected. The research also speaks to the influence of noise but does not present new findings, and therefore further observations are needed. According to previous studies, birds can adapt to high levels of noise pollution by simply modifying their vocal expressions and staying in populated areas. Thus, the impact of noise on bird communities may have little or no impact. Finally, the researchers add that urban greenery alone does not increase species richness; the key to species richness is heterogeneity. Although the recommendation is directed at urban planners and architects, you too can make a small contribution to the recovery of nature by consciously laying out your garden or by regulating outdoor lighting.

Morelli, F., Tryjanowski, P., Ibáñez-Álamo, J. D., Díaz, M., Suhonen, J., Møller, A. P., Prosek, J., Moravec, D., Bussière, R., Mägi, M., Kominos, T., Galanaki, A., Bukas, N., Markó, G., Pruscini, F., Reif, J., & Benedetti, Y. (2023). Effects of light and noise pollution on avian communities of European cities are correlated with the species’ diet.

Tereza Žirovnická

Published: Aug 13, 2023 08:45 AM

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