From 1975 to 2017 Finnish breeding birds decreased by 1.7 days. According to ornithologists, this is a reaction to global climate change, through which birds begin to breed early, and the incubation of eggs and growth of Chicks they occur faster. The most dramatic changes in the timing of breeding is typical for sedentary species and near migrants. As noted in an article in the journal Proceedings of the National Academy of Sciences, the study will help to understand what is the fate of various species of Northern birds further climate change.
Living organisms around the world are forced to adapt to climate change. Some of them move habitats toward the poles or higher on the mountain slopes, others refuse old habits, and still others are switching to new types of food. The strongest pressure experienced by the inhabitants of the high latitudes with a seasonal climate.
In Finland over the past half century the average temperature rose by 0.8-1.6 degrees Celsius. A team of ornithologists headed by Hallfors Mary (Maria H. Hällfors) from the University of Helsinki decided to find out how this affected the reproduction of local birds.
The researchers analyzed data about the beginning and the end of the breeding season in 73 species for 43 years, from 1975 to 2017. These figures are calculated on the basis of records of banded. To mark a young bird ring only after it reaches a certain size, so knowing the date of banding, it is possible to calculate the time of egg laying.
It turned out that four decades of Finnish birds in different climatic zones have started to lay eggs at a rate of 4.6 days earlier. The end of the breeding season also has moved to the beginning of the year, and even more — by 6.3 days. As a result the overall duration of the breeding period decreased by 1.7 days. However, this effect was provided by a relatively small group of species: with the reduction of the breeding season encountered 23 species. Have five kinds instead, he lengthened, and the rest showed no significant trends.
The hardest time of reproduction has changed from the sedentary birds and near migrants. These included 20 of the 23 species in which the breeding period is shorter. Thus the birds that feed during the season more than one brood, the end date of reproduction shifted faster than average. The researchers also noted that closely related species respond to climate change in a similar way. For example, owls and thrushes actively pushed start, and gulls, corvids and Tits the end of the breeding season.
Conclusion on the reduction of the breeding season, contrary to previous studies indicating that global warming should increase the duration of the period during which birds can breed. According to the authors, the explanation of this paradox lies in the fact that due to the higher temperatures faster innumerous eggs, and Chicks grow faster.
At the same time, faster response sedentary birds and near migrants were not for ornithologists by surprise. Taking the decision to start breeding, these types rely on the weather, which allows them more flexibility to change the time of breeding in response to climate change. This allows you to synchronize the start of reproduction with the peak of the resources, for example, insects that as climate warming also occurs earlier.
It is assumed that migrants are far worse cope with climate change, because it’s harder for them to move the beginning of spring migration and to synchronize return home and start breeding with the changing peak of food availability. But a new study of six species of birds that breed in Europe and winter in tropical Africa, puts this view into question. It turned out that these birds are flexible to adjust the timing of the return, focusing on the weather at stopovers.