Habitat urbanization and its effects on birds

By transforming landscapes, human activity creates new types of habitats with altered environmental characteristics that never existed before. As the process of habitat urbanization bears impact on more and more natural habitats, it is essential for us to understand the changes we bring forth in the ecological forces shaping urban animal communities. Birds are perhaps the most frequently studied model organisms by urban ecologists. It is a well known general pattern that urban avian communities have typically reduced species richness, while the density of a few successful species is often higher in cities than in adjacent more natural habitats. But it is less understood which mechanisms generate and uphold these community-level changes. In this review we discuss the most important components of the urban environment influencing birds’ physiology, behaviour or morphology, and compile several recent studies to illustrate their effects. To understand urban food webs we also review the results of bottom-up and top-down approach which suggest that altered food availability and predation may play key roles in forming recent urban bird communities. We encourage future research to focus more on experimental, manipulative studies, that would help us not just to realize general patterns but shed more light on the mechanisms, the underlying processes prompting changes in urban bird communities

Éghajlatváltozás erdőn, mezőn: a vadon élő állatok kutatásának tanulságai

Az élőlények környezetének klimatikus viszonyai a legfontosabb ökológiai tényezők közé tartoznak, amelyek meghatározzák az állatok és növények éves életciklusát, befolyásolják a populációkat alkotó egyedek szaporodási és túlélési sikerét, és hosszútávon az életmódban, viselkedési és morfológiai tulajdonságokban megfigyelhető evolúciós változásokat indukálhatnak

Éghajlatváltozás erdőn, mezőn: a vadon élő állatok kutatásának tanulságai

Az élőlények környezetének klimatikus viszonyai a legfontosabb ökológiai tényezők közé tartoznak, amelyek meghatározzák az állatok és növények éves életciklusát, befolyásolják a populációkat alkotó egyedek szaporodási és túlélési sikerét, és hosszútávon az életmódban, viselkedési és morfológiai tulajdonságokban megfigyelhető evolúciós változásokat indukálhatnak

Obtaining accurate measurements of the size and volume of insects fed to nestlings from video-recordings

Video-recordings are commonly used to study the types, amount, and size of food items provided to nestling birds. However, the accuracy and repeatability of estimates of the size of food items from video-recordings has not been examined. We assessed three aspects of the reliability of measuring prey size from video-recordings of Great Tits (Parus major) provisioning nestlings. To test the accuracy of measurements of prey size (length and width) used to determine prey volume, we molded artificial plasticine caterpillars and compared their size and volume as determined using measurements of length and width on screenshots of video-recordings (using the vertical diameter of nest-box entrance holes as a size reference) to their actual size and volume. We also examined within- and among-observer repeatability of measurements of the size and volume of actual prey items delivered to nestlings by adult Great Tits. We found that observers were able to accurately measure prey size and determine volume, with high agreement between the actual size and volume of plasticine caterpillars and the size and volume as determined from measurements made on screenshots from video-recordings (rICC = 0.99), and, in addition, within- and among-observer repeatability were also high (rICC = 0.98 and 0.93, respectively). Overall, our results suggest that the size of prey items delivered to nestlings by adults in video-recordings can be accurately measured and those measurements, in turn, can be used to accurately determine the volume of those insect prey

The effect of artificial light at night on the biomass of caterpillars feeding in urban tree canopies

Alternation of day and night is the oldest cycle on Earth, which is increasingly disturbed by the accelerating rate of urbanization and technological development. Despite the ubiquity of light pollution in cities, many aspects of its influence on urban ecosystems are still poorly understood. Here we studied the effect of artificial light at night (ALAN) on the biomass of arboreal caterpillar populations, which are a major component of the diet of many insectivorous animals. We predicted that increasing ALAN intensity is associated with reduced caterpillar biomass, because ALAN may increase predation risk for both caterpillars and adult lepidopterans (i.e. moths), and can also hinder the moths' reproductive rate. We estimated caterpillar biomass from frass samples (n= 3061) collected from 36 focal trees in two cities in Hungary during four consecutive years. To quantify ALAN we measured light intensity during night at each focal tree (range of illumination: 0.69 – 3.18 lux). We found that caterpillar biomass of individual trees was repeatable over the four years. This temporal consistency in prey biomass production may be important for birds because it can help predict territory quality, especially in cities where caterpillar abundance is generally low. Our results did not support the negative effect of ALAN on urban caterpillar populations, because ALAN intensity was not related to caterpillar biomass, and this lack of effect was consistent between study sites and tree species. We suggest that the effect of ALAN on urban caterpillar biomass is either weak and thus can be masked by other, local environmental factors, or light pollution may have antagonistic effects acting during different stages of the lepidopteran life cycle. Another explanation could be that even the lower levels of our sites' public lighting are strong enough to cause serious detrimental effects for caterpillars, resulting in their uniformly low biomass