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Nestling birds in the city clearly affected by air pollution and which trees surround them

Baby birds in a hand. Photo.
Newly hatched baby birds - the study investigated how they were affected by various effects of the urban environment. Photo: Caroline Isaksson, Lund University.

Life in the city is tough – if you are a baby bird you are markedly affected by a certain type of air pollution and by which trees are close to the nest, new research from Lund, Sweden shows. Underlying the study is a new more detailed way of investigating what factors in an urban environment impact birds and animals.

Cities are generally a harsh environment for birds and other animals to live in, but researchers do not know much about the reasons for this. The city is such a different and altered environment compared to natural habitats that it is difficult to single out what is affecting the animals most – is it pollution in the air? Is it artificial light at night? Or is it which plants exist, or rather are absent, in the city?

In a new study, Johan Kjellberg Jensen, doctoral student at the Centre for Environmental and Climate Science (CEC) at Lund University, has investigated how birds’ physiology is affected by a life in the city and what parts of the urban environment are most significant for their well-being. He has been aided by a more detailed method than the one normally used, which has provided interesting results. 

- We can show that the physiology of baby birds is affected by the local environment and urban aspects that exist there. What we see affecting the nestlings most is what kind of trees there are in the vicinity of the nest, along with a particular type of pollution (PM 2.5 airborne particles smaller than 2.5 micrometres), he says.

Aspects of the urban environment, such as air pollution and tree species, has a direct effect on birds

One of the study’s aims was to test a new method of measurement. Traditionally, when investigating the effect of the city on birds and animals, something known as urbanisation gradients have been used. This basically means generalising the environment being studied as “more urbanised” or “less urbanised”. In this study, the researchers instead chose a more detailed approach in which they looked at several specific aspects of the urban environment: two different kinds of air pollution, temperature, artificial light, how many trees and of what species there are in the vicinity of the nests studied. Specific elements of the environment were then linked to the birds’ physiology, primarily nutrition (nutrients in the body) and antioxidants (which protect against air pollution).

What researchers saw was that air pollution reduced the antioxidant capacity of the birds, and that nestlings were larger when there were more oaks in the vicinity.
Johan Kjellberg Jensen underlines that the study has not investigated whether the impact on the young birds is negative in the long term, even if there are reasons to assume that this is the case.

- The most important result of the study is actually that we can show that it is possible to isolate parts of the urban environment and link them to effects on animals and nature. It shows that we must be cautious about generalising urban environments, that there is great variation in nature here, and that in time we will be able to point to specific parts of the city as particularly important or particularly harmful to the ecosystem. This has great significance for urban planning and nature stewardship, he says.

Importance for future physical planning of cities

Even if methodology is mainly interesting to researchers at this point, Johan Kjellberg Jensen believes that ultimately the results could be significant for the physical planning of our cities. 

- I hope that this kind of concrete results can lead to efficient, focused measures to build better cities for both people and animals. Having a functioning ecosystem in the city is not just important from a biological point of view, it also plays a big role in the well--being of us humans.

Johan Kjellberg Jensen had expected to see a greater interaction between the various environmental factors being investigated – that certain effects would only be seen when several different parts of the environment interact. But that was not the case.

- One must of course be humble about the fact that this is just a single study, using a pretty innovative method, so more research is needed before we can draw any unequivocal conclusions.
The study is published in the scientific journal Science of The Total Environment

Footnote: Physiology is the study of how living organisms, their organs and tissues work.