Az élőhely-urbanizáció ökológiai és viselkedési következményeinek vizsgálata házi verebeken = Ecological and behavioral consequences of urbanization for a worldwide urban exploiter, the house sparrow

A projekt során azt vizsgáltuk, hogy (i) az élőhely-urbanizációval miként változik a táplálékkompetíció és a predációs nyomás intenzitása, (ii) a madarak viselkedése, stressz-élettana, kondíciója és szaporodási sikere, és hogy (iii) az élőhelyi különbségek környezeti hatások vagy alkalmazkodás következményeként alakultak-e ki. Kimutattuk, hogy a felnőtt városi verebek erősebb ragadozóelkerülő reakciót mutatnak, mint a vidéki egyedek, ami intenzívebb városi predációs nyomásra utal. Ugyanakkor nem találtunk élőhelyi különbséget a madarak kompetitív képességeiben. Szintén nem volt különbség a sterssz-élettani és fizikai kondíciót jellemző tulajdonságokban. A vidéki populációk madarai több és nagyobb méretű fiókát neveltek, mint a szuburbán párok. Fogságban, azonos körülmények között szaporodó madarak esetében ugyanakkor nem volt élőhelyi különbség sem a szaporodási sikerben, sem a fiókák méretében. Vizsgálataink összességében a fiókakori környezeti hatások jelentőségét erősítették meg az urbanizációs gradiens mentén tapasztalható szaporodási és morfológiai különbségek kialakulásában. Úgy véljük, hogy különösen jelentős hatású a megfelelő rovartáplálék mennyiségének és/vagy összetételének kedvezőtlenné válása a városi területeken, ami a házi verebek mellett más rovarevő állatok számára is megnehezítheti az urbanizált helyeken való megtelepedést és fennmaradást. | Our aim was (i) to test the effects of habitat urbanization on the intensity of food competition and predation risk in bird populations, (ii) to study its effects on the sterss-physiology, condition and behavior of birds, and (iii) to test whether the morphological differences we found in house sparrows along the urbanization gradient represent environmental effects or adaptation. We found stronger predatory risk avoidance in adult urban sparrows than rural ones, suggesting higher predation risk in urban habitats of the species. There was no habitat difference in the competitive ability of sparrows. We also did not find any consistent difference in the birds’ stress response and multiple estimates of body condition between differently urbanized populations. Rural birds in wild populations had higher reproductive success and reared heavier nestlings than pairs in a suburban population. On the other hand, in captivity there was no habitat-related difference in either reproductive success or nestling mass. We concluded that environmental factors, particularly nestling food may play a key role in generating reproductive and morphological differences along the urban gradient. Reduced arthropod densities in urban habitats may negatively affect the reproduction and survival of other insectivorous animals that still persist in urbanized environments

Changing Migratory Behaviors and Climatic Responsiveness in Birds

Change of avian migratory behavior is one of the best-studied phenomena presumably associated with contemporary climate change, yet to what degree these behavioral changes represent responses to climate warming is still controversial. We investigated interspecific variation in migratory behavior over three decades at a Central-European site, testing whether the type and extent of behavioral change are predicted by species' responsiveness to short-term variation in large-scale climatic indices. We found that species with earlier arrivals at the breeding grounds after winters with higher North-Atlantic Oscillation indices were more likely to overwinter at the study site. This behavior was more frequent in the second half than in the first half of the study, although the extent of this change was not predicted quantitatively by short-term climatic responsiveness. Overwintering was more prevalent in short-distance migrants with more complex diets and larger population sizes. Furthermore, species arriving earlier after summers with higher Sahel rainfall indices increasingly advanced their first arrival date, whereas species that do not molt in the pre-breeding season increased their frequency of overwintering in more recent years. Our results demonstrate that interspecific variation in short-term climatic responsiveness predicts long-term changes in migratory behaviors, supporting that the latter are responses to climate change. Furthermore, the type of response (advancing arrivals or overwintering near the breeding grounds) depends on life history. Finally, we found that overwintering behavior during the study period predicted subsequent trends in population size, suggesting that information on temporal changes in migratory strategy may help conservation planning and risk assessment

Experimental evidence for beneficial effects of projected climate change on hibernating amphibians

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Latitudinal distribution, migration, and testosterone levels in birds

Tropical bird species usually have lower testosterone (T) levels during breeding than temperate species. However, the potential mechanisms behind the positive interspecific correlation between T and latitude remain unexplored. In a comparative study of more than 100 bird species, we examined whether social constraints during male-male competition arising from migration and breeding synchrony are responsible for the latitude effects. Species that breed at higher latitudes are more likely to migrate and experience more intense intrasexual competition upon spring arrival than nonmigrant species from lower atitudes. Additionally, species from higher latitudes cope with shorter breeding seasons and thus with more synchronous breeding, which selects for high T titers via increased male-male conflicts. Accordingly, peak T levels were associated with migration and the duration of the egg laying period that reflects breeding synchrony. Because migration and breeding synchrony were related to latitudinal distribution, they appear to be important components of the latitude effects on T. A multivariate model controlling for covariation of predictor variables revealed that latitude remained the strongest predictor of peak T. Therefore, selection due to migration and breeding synchrony may partially cause the latitude effect, but other geographically varying factors may also play a role in mediating peak T levels at different latitudes

Experimental evidence for beneficial effects of projected climate change on hibernating amphibians

Amphibians are the most threatened vertebrates today, experiencing worldwide declines. In recent years considerable effort was invested in exposing the causes of these declines. Climate change has been identified as such a cause; however, the expectable effects of predicted milder, shorter winters on hibernation success of temperate-zone Amphibians have remained controversial, mainly due to a lack of controlled experimental studies. Here we present a laboratory experiment, testing the effects of simulated climate change on hibernating juvenile common toads (Bufo bufo). We simulated hibernation conditions by exposing toadlets to current (1.5 °C) or elevated (4.5 °C) hibernation temperatures in combination with current (91 days) or shortened (61 days) hibernation length. We found that a shorter winter and milder hibernation temperature increased survival of toads during hibernation. Furthermore, the increase in temperature and shortening of the cold period had a synergistic positive effect on body mass change during hibernation. Consequently, while climate change may pose severe challenges for amphibians of the temperate zone during their activity period, the negative effects may be dampened by shorter and milder winters experienced during hibernation

Endocrine disruptors in breeding ponds and reproductive health of toads in agricultural, urban and natural landscapes

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