Are city or country tits healthier?

Year of the Great Tit science news conveyed by Marko Mägi UT Bird Ecology researcher
Photo Arne Ader
Translation Liis
Rivalling great tits
Great tit     Rasvatihane      Parus major    
In  cities they often feed on what is easily available and don’t seem to care about the quality of the food at all. But the food should contain, in addition to the macro nutrients (for instance proteins, carbohydrates), vitamins, minerals and different fatty acids. The necessary amount and composition of energy-rich fatty acids for the normal functions of the organism depends largely on the food and the environmental conditions. Scientists at the University of Lund, Sweden, studied the fatty acids in the bodies of great tits in the city of Malmö and its surroundings, and linked the results to the diet of the birds in summer and in winter. As  far as is known, this is the first time that the impact of urbanisation on birds has been studied from the perspective of fatty acids.
In winter great tits feed basically on seeds, in summer however on insects. Since the city and forest landscapes differ with respect to temperature and food objects – in the city food (including junk food) is easier obtainable than in the forest – it was assumed that the composition of fatty acids in the organisms of birds living in the city and the forest would differ.
With respect to body mass and measures, great tits in the city were in a better state in winter but in summer the birds living in the forest during the breeding period fared better. The difference is due to the richer food table in winter in the city (also from extra feeding) versus the higher quality food in the forest in the breeding period. The blood of wintering and breeding birds also differed with respect to the content of fatty acids – the level of Omega-3 fatty acids was 30 times lower in winter than in the breeding period. There is plenty of Omega-3 fatty acid in the basic summer food of great tits – caterpillars. But for instance the oleic and linoleic acids that occur abundantly in seeds and nuts were found in greater amount in winter when the birds are largely herbivorous, independent of the environment.
The content of several fatty acids varied significantly too for urban and forest great tits. For instance arachidonic acid (Omega-6 fatty acid), which is linked to thermoregulation and occurs in the organism in connection with  he inception of inflammations  is present in greater amounts in great tits wintering in the city. In contrast the great tits living in the forest have more of Omega-3 fatty acids that suppress inflammations. The differences between the great tits in the city and forest with respect to fatty acids point to the negative aspects of urban life due to pollutants, which results in more intense inflammatory processes in the organism. Physiologically such processes are energy-demanding and impair the normal functions of the organism.
At a first glance it might be assumed that the life of a great tit in the city is simpler, but the price to be paid for this is quite high.
Andersson MN, Wang H-L, Nord A, Salmón P, Isaksson C. (2015) Composition of physiologically important fatty acids in great tits differs between urban and rural populations on a seasonal basis. Frontiers in Ecology and Evolution 3:93. doi: 10.3389/fevo.2015.00093




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