New hosts for the mite Ornithonyssus bursa in Argentina

The mite Ornithonyssus bursa (Berlese) (Mesostigmata: Macronyssidae) is considered a poultry pest causing important infestations in chickens and it is considered a potential vector of arbovirus. Despite being considered a common parasite in wild birds, there is scarce published information about its potential hosts and effects on them. Here we present new bird hosts for O. bursa, assess the presence of Alphavirus, Flavivirus and Bunyavirus in mites from three host species, and discuss its potential impact on wild bird populations. We found O. bursa infecting five raptor and six passerine wild bird species. For nine of these species, this is the first record of infection by O. bursa. Although all analysed mites were negative for the examined arboviruses, the small sample size of mites does not allow further conclusions at the present moment. Because of the general nature of this ectoparasite, its presence in migratory long dispersal and endangered bird species, and the seropositivity for arboviruses in some of the species studied here, we consider it critical to assess the role of O. bursa and other ectoparasites as vectors and reservoirs of pathogens and as potential deleterious agents in wild bird populations.

Hunting success of wintering Swainson's hawks: environmental effects on timing and choice of foraging method

We examined the predatory behavior of Swainson's hawks (Buteo swainsoni Bonaparte, 1838) wintering in the Argentine pampas. Aerial and ground foraging were the main hunting methods employed by hawks in this region. The overall hunting success of hawks preying on insects was 50% and age-related differences in hunting success were not significant. The Swainson's hawks, however, hunted more successfully in the air (65% of prey capture attempts) than on the ground (42%). Aerial hunting while soaring was the most successful hunting method based on the number of prey captured per energy unit. Based on the analysis of prey consumed by hawks during the study period, grasshopper species with poor flight capabilities were available in the air as a consequence of the vertical air motion. With regards to daily activity patterns, the time that a hawk spent using each hunting method was not proportional to the cost ratio associated with each method. Hawks foraged in the air only during midday hours when weather conditions permitted the formation of thermals. Thus, the use of soaring flights and the availability of prey in the air were constrained by the physical environment, and hawks could only exploit airborne food sources during limited periods of the day.