engleski

Seagulls, Laridae, as a model for research of wild birds´ diseases

Gulls are one of the most common birds in human surroundings. They are present in most aquatic habitats (from sea coasts and ports to lakes and rivers). In the last few decades, whenever there is no separation of the organic component of household garbage, they have found an endless source of food on open rubbish tips. They are especially numerous during the colder part of the year (Nov – Feb), when tens of thousands of gulls can be found feeding on rubbish tips. We have been studying gulls on Zagreb’s city rubbish tip since 1999. After the first ecological research we obtained new data about their movements and dynamics on the tip, with most attention paid to reading rings to determine their origin. There were 9 species of gulls recorded on the tip ; Black-headed Gull, Larus ridibundus, Yellow-legged Gull, L. michahellis, Common Gull, L. canus, Caspian Gull, L. cachinnans, Lesser Black-backed Gull, L. fuscus, Greater Black-backed Gull, L. marinus, Ring- billed Gull, L. delawarensis, Mediteranean Gull, L. melanocephalus, and Pallas’s Gull, L. ichthyaetus. In the winter of 2006/2007 we started catching and ringing gulls on the tip. Our results show that gulls feeding on Zagreb city rubbish tip originate from all over Europe: from central Russia in the east, the UK in the west, Finland in the north, while southernmost recovery was from Tunisia. As gulls are capable of crossing great distances in short periods, and tend to form huge flocks of individuals from different populations and age groups on adequate feeding sites, they can easily transmit and spread viruses and bacteria across a huge area, and therefore can potentially pose a serious threat to both humans and farm animals. Also, environmental conditions during these months are the most suitable for transmission of bacterial and viral pathogens, due to both low temperatures and huge aggregating flocks while feeding or roosting. In the winter of 2006 we started taking biological samples from captured gulls, mostly swabs, but also blood samples. We tested swabs for the presence of 2 viral (avian influenza and avian paramyxovirus) and 2 bacterial (Salmonella and Campylobacter) pathogens. Blood samples and smears were tested for the presence of avian haemosporidian parasites of the genera Haemoproteus, Plasmodium and Leucocytozoon, using a combination of molecular and microscopic approaches. During the past 11 years we have isolated the first H13 and H16 subtypes of avian influenza virus in Croatia. The vast majority of avian paramyxoviruses isolated from gulls belong to serotype 1. During our research we detected more than 10 different serovars of Salmonella. Also we found the first Campylobacter lari in Croatia. Most of the Campylobacter isolated from the gulls showed multiple resistance to antimicrobial drugs which contributes to the thesis of gulls as an important reservoir of these bacteria. In total, we screened 173 individual Blackheaded Gulls (Chroicocephalus ridibundus) and 97 blood samples of large gulls (Larus sp.) for haemosporidian parasites over two consecutive years (2015 and 2016). The preliminary results showed higher parasite prevalence in the large gulls (37.2% and 22.2% for the two years, respectively) compared to 2.7% in 2015 and 3.3% in 2016 in the Black-headed gulls. The predominant infections were by Haemoproteus spp. while haemosporidians of the genus Leucocytozoon were not detected. Plasmodium parasites, the causative agents of malaria, were recorded in one sample of Larus cachinnans, one sample of Larus michahellis and three samples of Black-headed gulls. The latter two species represent new host records for Plasmodium spp. among gulls.

gulls, diseases

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