Prevalence of Listeria monocytogenes and other Listeria spp. in gulls feeding on Zagreb landfill site, Croatia

Gulls, as migratory wild birds are known that can spread different pathogens over long distances. Aim of this study was to access prevalence of different Listeria species in their population fed at the Zagreb landfill site. Altogether, 390 gulls of three species were sampled: Yellow-legged Gull, Larus michahellis; Black-headed Gull, L. ridibundus and Common Gull, L. canus. Most prevalent species was L. innocua (14.4%), while L. monocytogenes was found in 11.3 % of tested samples. The presence of other species was found in a smaller percentage, namely L. welshimeri (1.3%), L. ivanovii (0.5%) and L. seeligeri (0.3%). Serotyping of L. monocytogenes isolates was performed using both molecular and conventional methods, and most isolates belonged to serotypes 1/2a and 1/2b. To the best of our knowledge, this study reports the first results of research on the presence of L. monocytogenes and other Listeria spp. in wild birds in Croatia.

The abundance of yellow-legged gulls Larus michahellis breeding in the historic centre of Venice, Italy and the initial effects of the new waste collection policy on the population

The yellow-legged gull Larus michahellis has undergone widespread colonization of the urban environment in the recent past. The first urban breeding gulls were recorded in the historical centre of Venice, Italy, in 2000, and by 2005 there were already 24 roof-nesting pairs, with this number increasing significantly over the last decade. In 2016, a new door-to-door garbage collection system was introduced in Venice to prevent the accumulation of rubbish in the streets and limit the trophic resources available for the species. This study provides an up-to-date estimate of the Venice yellow-legged gull urban population using distance sampling method. We also studied the effect of the new waste collection system on the species by comparing the population estimate before (2017) and after (2018) the full implementation of this change and by analysing the trend of individuals collected in the old town by the wildlife recovery service during 2010–2018. Results estimated ca. 430 breeding pairs in June 2018 showing a 36% decrease with respect to 2017. We also found a decrease in the number of 1-year-old birds and pulli collected by the wildlife recovery service starting from 2016, when the policy implementation began. Our data did not show a significant decrease in the overall number of individuals, suggesting that the new policy has a stronger effect on the breeding success of the species than on adult survival. This study emphasizes the importance of preventing rubbish accumulation in the streets as factor for reducing the abundance of urban yellow-legged gulls.

Prenatal yolk corticosterone exposure promotes skeletal growth and induces oxidative imbalance in yellow-legged gull embryos

Maternally-derived hormones induce variation in offspring phenotype, with consequences that can carry-over into post-natal life and even into adulthood. In birds, maternal egg corticosterone (CORT) is known to exert contrasting effects on offspring morphology, physiology and behaviour after hatching. However, information on the effects of CORT exposure on pre-hatching embryonic development is limited. We experimentally increased yolk CORT levels in yellow-legged gull (Larus michahellis) eggs, and assessed the effects on embryo pre-hatching development and oxidative status of brain and liver. CORT-supplemented embryos reached a larger skeletal size and liver mass compared to controls. Embryos from CORT-injected last-laid eggs showed decreased activity of the hepatic antioxidant enzymes superoxide dismutase and catalase, while intermediate-laid eggs showed an increased levels of lipid peroxidation. However, elevated yolk CORT did not affect oxidative stress endpoints in the brain. Our results indicate that elevated yolk CORT levels affect prenatal embryo development by promoting skeletal growth, and induce laying sequence- and organ-specific oxidative imbalance, with potential adverse consequences during postnatal life especially for late-hatched offspring.

Survey on the Presence of Bacterial and Parasitic Zoonotic Agents in the Feces of Wild Birds

Wild avifauna may act as fecal source of bacterial and parasitic pathogens for other birds and mammals. Most of these pathogens have a relevant impact on human and livestock health which may cause severe disease and economic loss. In the present study, the fecal samples collected from 121 wild birds belonging to 15 species of the genera Anas, Tadorna, Fulica, Arddea, Larus, Falco, Athene, Accipiter, and Columba were submitted to bacteriological and molecular analyses to detect Brucella spp., Coxiella burnetii, Mycobacterium spp., Salmonella spp., Cryptosporidium spp., Giardia spp., and microsporidia. Four (3.3%) animals were positive for one pathogen: one Anas penelope for C. burnetii, one Larus michahellis for S. enterica serovar Coeln, and two Columba livia for Encephalitozoon hellem. Although the prevalence rates found in the present survey were quite low, the obtained results confirm that wild birds would be the a potential fecal source of bacterial and parasitic zoonotic pathogens which sometimes can also represent a severe threat for farm animals.

High philopatry rates of Yellow-legged Gulls in the southeastern part of the Bay of Biscay

Background Philopatry rate is one of the main factors shaping population dynamics in colonial seabirds. Low rates of philopatry are linked to populations with high dispersal, while high rates are linked to populations with a very high spatial structure pattern (i.e., metapopulations). The Cantabrian Yellow-legged Gull (Larus michahellis) population is considered to be resident, with relatively low dispersal rates. Precise estimations of its philopatry rates are however still lacking. Here, we aimed to estimate philopatry rates in the main Yellow-legged Gull colonies of the province of Gipuzkoa, in the southeastern part of the Bay of Biscay. Methods We analysed 734 resightings, during the breeding season at the colonies of Getaria, Santa Clara and Ulia, relative to a total of 3245 individuals ringed at birth in these same colonies during a period of 13 years. These data were analysed using Multi-State Recapture models in MARK. Results After controlling survival and resighting probability, the average dispersal rate among colonies was 4% (± SD = 2%) when individuals are immature, decreasing to 1 ± 1%) for adult breeding gulls (i.e., philopatry rate was 99%). Annual survival rates were assessed to be 0.27 ± 0.02 for birds in their first year of life and 0.87 ± 0.01 for older individuals. The probability of observing immature birds in the colonies was 0.08 ± 0.01, as compared to 0.21 ± 0.02 in adult birds. Conclusions We obtained evidence of extremely high local philopatry rates, clearly within the upper limit found in gulls. A high philopatry favour a speciation in these species who are vulnerable to obtain the main food source (landfills and fishing discard) which are transforming under new ecological process.

Telomerase activity can mediate the effects of growth on telomeres during post-natal development in a wild bird

In wild animals, telomere attrition during early development has been linked with several fitness penalties throughout life. Telomerase enzyme can elongate telomeres, but it is generally assumed that its activity is suppressed in most somatic tissues upon birth. However, recent evidence suggests that this may not be the rule for long-lived bird species. We have therefore investigated whether telomerase activity is maintained during the postnatal growth period in a wild yellow-legged gull (Larus michahellis) population. Our results indicate that telomerase activity is not negligible in the blood cells, but activity levels sharply decline from hatching to fledging following a similar pattern to that observed in telomere length. Our results further suggest that the observed variation in telomere length may be the result of a negative effect of fast growth on telomerase activity, thus providing a new mechanism through which growth rates may affect telomere dynamics and potentially life-history trajectories.

Treatment of extremity fractures in 20 wild birds with a modified Meynard external fixator and clinical assessment of the results

The aim of this study is to evaluate the outcome of the treatment on twenty wild birds presenting with fractures that were stabilised with modified Meynard external fixators. The study material consisted of a total of twenty birds of eight different species, six white storks (Ciconia ciconia), one eastern imperial eagle (Aquila heliaca), one European honey buzzard (Pernis apivorus), one long-legged buzzard (Buteo rufinus), three common buzzard (Buteo buteo), one northern goshawk (Accipiter gentilis), one Armenian gull (Larus armenicus), and six yellow-legged gulls (Larus michahellis), which were diagnosed with fractures in their extremity bones following clinical and radiological examinations. The lesions of the twenty cases evaluated in the study were diagnosed as humerus fractures in nine cases, ulna fractures in three cases, tibiotarsus fractures in seven cases and a femur fracture in one case. The external fixators were removed between weeks five and nine postoperatively. While healing was seen in twelve of the twenty evaluated cases, the complete functional recovery occurred in six of these and they were released into nature. It was concluded that modified Meynard external fixator, which was made applicable for fractures in birds, could be an alternative method for fracture treatments in wild birds.