Migrating birds avoid flying through fog and low clouds.

Different weather conditions are known to affect bird migration, yet the influence of fog and low clouds on migrating birds has been rarely examined so far, and hence, their impact on bird movement is not well understood. Fog avoidance could be a consequence of visual limitations within the fog or may be the outcome of deteriorated soaring conditions due to the obstruction of the sun. We carried out a radar study at the Strait of Messina, which is a bottleneck for migrating birds traversing the Central Mediterranean Sea, to determine if the intensity of diurnal soaring bird migration was influenced by fog and other weather variables. We recorded bird movements using an X-band radar, which can detect birds flying within the fog, and recorded weather conditions using local meteorological observations. We examined if bird passage rate (number of tracks/hour) at the radar site was influenced by fog, wind speed and direction, air temperature and the time of day. Our findings suggest that fog was the most important factor affecting bird migration intensity as recorded by the radar, indicating that birds actively avoided flying into fog. In addition, wind direction affected bird migration intensity, with lower numbers recorded with southerly tailwinds and higher numbers recorded with westerly crosswinds. Our findings highlight a consequence of widespread meteorological conditions, and of fog in particular, on migrating birds, with implications for bird migration navigation, path length and flight energetics.

Interactions between commercial fishing vessels and a pelagic seabird in the southern Mediterranean Sea.

BACKGROUND: Fishing activities can influence foraging behaviour of many seabird species worldwide. Seabirds are attracted by fishing vessels which can facilitate access to demersal fish as a novel food resource that otherwise would be unavailable. On the other hand, intense fishing activities cause depletion of fish stocks with a reduction of natural prey available for seabirds. Moreover, fisheries discards can have lower nutritional value than natural prey. However, the importance of fisheries discard for seabirds and the possible implications on their foraging ecology is still poorly understood. In this study, we analysed the interactions of Scopoli's shearwaters (Calonectris diomedea) during their foraging trips with fishing vessels. We combined the GPS and accelerometer data of shearwaters with the GPS data gathered during the same period from fishing vessels. Accelerometers allowed us to identify the main behaviours of birds. RESULTS: The presence of fishing vessels significantly affected the individual behaviour of Scopoli's shearwaters. Birds increased the time spent sitting on the water within 1.28 ± 0.13 km of fishing vessels likely feeding or waiting for discards. Approaches towards vessels within the interaction distance were therefore classified as an interaction and were recorded in about 40% of individuals. Birds interacting with fisheries had longer flight time during their foraging trips and covered longer distances to reach more distant foraging areas compared with individuals not approaching vessels. CONCLUSIONS: Our results suggested that fisheries discard consumption might not be a profitable source of food for Scopoli's shearwaters. Despite the high density of fishing vessels in the home range of Scopoli's shearwater, most individuals did not interact with them. Accordingly, scavenging individuals showed a lower foraging efficiency than their conspecifics. Intraspecific competition for foraging areas might play an important role for the foraging decision of birds to consume fisheries discards.

Dietary flavonoids enhance conspicuousness of a melanin-based trait in male blackcaps but not of the female homologous trait or of sexually monochromatic traits.

Signalling theory predicts that signals should fulfil three fundamental requirements: high detectability, discriminability and, most importantly, reliability. Melanins are the most common pigments in animals. Correlations between genotypic and phenotypic qualities of the sender and size and morph of melanin-based traits are known, but it is contentious whether melanin-based colouration may signal any quality. We examined the effect of supplementing blackcaps (Sylvia atricapilla) with flavonoids, potent plant antioxidants, on plumage colouration. We demonstrate that melanin-based colour can fulfil all requirements of signals of phenotypic condition. As predicted by sexual selection theory, flavonoid supplementation influenced only the sexually dichromatic black cap of males, whereas the female homologous trait and the sexually monochromatic back colouration remained unaffected. Using avian vision models we show that birds can estimate male flavonoid intake from colouration of males' black cap. Because flavonoid ingestion can increase immune responsiveness in blackcaps, melanin head colouration may signal environmentally determined immune condition.