Migratory birds play an important role in the eco-epidemiology of tick-borne diseases due to their ability to carry ticks for long distances. The aim of the present study was to investigate the prevalence and factors influencing the intensity of tick infestation in migratory birds. The study was conducted in a locality situated in the Vistula River valley, eastern Poland, during autumn, when the high migratory activity of birds is registered in the region. The birds were captured using ornithological nets and identified at the species level. In the next step, they were carefully inspected for attached ticks. Tick infestation was observed in 4.43% of the captured birds. The highest mean intensity of tick infestation was observed in birds foraging on the ground or in low shrubs and by long- and medium-distance migrants, i.e., Turdus merula (2.73), T. philomelos (2.04), and Erithacus rubecula (1.58). Ixodes ricinus was found to infest the birds most frequently. However, other tick species, i.e., I. trianguliceps, I. crenulatus (synonym I. canisuga), and I. apronophorus, rarely found in eastern Poland, were also found parasitizing birds. The occurrence of I. persulcatus, I. frontalis, and I. acuminatus (synonym I. redikorzevi) was confirmed in the region for the first time. The results of the study suggest that captured bird species are susceptible to tick infestation and could play an important role in the circulation of some tick-borne pathogens. They also play a significant role in the spread of ticks. The ecology and ethology of birds, including their foraging styles and migratory habits, are factors determining the risk of exposure of birds to tick attacks.

Knowledge of the relationships between food habits and habitat is crucial for the assessment of habitat quality for birds. The present study investigated the diet and reproductive success of Little Bitterns Ixobrychus minutus nesting on cyprinid fish ponds, an important breeding habitat of this species in central and eastern Europe. Being subject to different management practices, fish ponds provide food resources of uneven availability for this small heron. Prey items regurgitated by nestlings were examined, and breeding success was estimated on monoculture ponds stocked either with small fish (of a size suitable for feeding nestlings) or large fish (unavailable to Little Bitterns and adversely affecting their non-fish prey), on abandoned ponds dominated by small fish but with large fish also present, and on angling ponds dominated by large sport fish but harbouring significant numbers of small fish as well. A total of 1356 prey items from 78 broods were identified. Although Little Bitterns exhibited dietary flexibility in response to the contrasting availability of prey on their nesting ponds, the bulk of the nestlings’ diet consisted of fish. The size of fish brought to the nest increased significantly with brood age, showing that parents adjusted the prey size to the gape constraints of their young. The chick production determined for 73 broods did not differ with respect to pond management, but the dietary composition indicated that to compensate for food shortages, birds nesting on ponds containing mainly large fish made foraging flights to food-richer ponds. The abundance of small-sized fish prey may be a factor limiting the breeding success of small- and medium-sized predatory waterbirds and should be taken into consideration in management strategies of habitats dominated by fish.

A key component of quantifying the threat of introduced exotic species and implementing their management is knowledge of whether their natural enemies counteract their invasion. Anti-predator defensive structures can help invaders by undermining biological control by native species. The invasive brown bullhead Ameiurus nebulosus has been highlighted as a potential driver of freshwater biodiversity loss in central and eastern Europe. The species is equipped with stout venomous spines in the pectoral fins, which may mitigate predatory pressure. We compared brown bullhead relative abundance in invaded water bodies in eastern Poland with its consumption, assessed through faecal analysis, by a top predator, the Eurasian otter Lutra lutra. The mean Jacobs’ index value for bullhead calculated from 14 study sites, tested against the neutral index value, indicated that otters showed a preference for this species. Also, otters displayed positive selectivity for littoral cyprinids and negative selectivity for open-water cyprinids. Bullhead was the otter’s main food source (on average 25.4% of fish prey by numbers and 23.6% by relative frequency of occurrence). Pectoral spines were among bullhead bones frequently recovered from otter faeces, indicating that otters had ingested them while eating the fish. Otters tended to take smaller bullheads than those caught by gillnetting or electrofishing at the study sites; smaller individuals may pose a lower risk of inflicting injury. Our results indicate that the brown bullhead’s defensive weapons provide no significant advantage over native fish species against otter predation, and that otters can contribute to the biotic resistance of the invaded community.