Abstract We analysed the mechanisms that, together with Mendelian inheritance, may be acting in the maintenance and evolution of colour polymorphism in the Booted Eagle ( Hieraaetus pennatus ), using observational data from successful breeding events of mixed pairs formed by light morph males and dark morph females, from a long-term study conducted in south-eastern Spain. Our results show that dark offspring produced in breeding events involving mixed-morph pairs far exceed the value expected in the Hardy–Weinberg equilibrium. Two-eaglet broods mostly resulted in one fledgling of each colour morph and in broods in which only one survived, it was predominantly the dark morph, with a ratio of 0.143:1 light/dark. In the two-egg clutches where only one hatched, the resulting eaglet was mostly dark morph with a ratio of 0.167:1 light/dark. Furthermore, three single-egg clutches produced a dark morph eaglet fledgling. However, these biases in embryo viability, chick survival and single clutches accounted for only seven (19.44%) of the 36 dark eaglets obtained. Of the remaining twenty-nine, six (16.67%) were expected according to Hardy–Weinberg equilibrium and twenty-three (63.89%) were produced by disassortative mating, a phenomenon described in previous studies, whereby heterozygous light males preferentially mate with dark females, likely based on the imprint of the colour morph of their mother. This long-term monitoring of breeding events has allowed us to understand the importance of each of the combined phenomena that contributes to the positive bias towards the dark morph in relation to the expected proportion according to the Hardy–Weinberg equilibrium.

Abstract In wild animal populations, the prevalence of vector-borne parasites can be a serious threat if derived in disease, but extreme environments can act as natural refuges by restricting the presence of vectors and, consequently, reducing the transmission of vector-borne parasites. The Andean Condor ( Vultur gryphus ), a key scavenger of ecological significance and flagship conservation status, inhabits high-altitude regions where abiotic factors may limit parasite transmission. Little is known about the prevalence of blood parasites in this species. In this study, we examined the presence of haemosporidian parasites ( Plasmodium, Haemoproteus, and Leucocytozoon ) in Andean Condors from both wild healthy and rehabilitating, and captive populations in Argentina. Blood samples were analyzed by blood smears examination and by using nested-PCR protocols targeting cyt b from parasite DNA. Of the 33 condors sampled, only two individuals tested positive for Plasmodium (Lineage ZEMAC01 and PADOM09), a wild adult male from Tucuman and a wild juvenile male from San Luis, sampled on the day of admission at Buenos Aires Zoo. These results may reflect the environmental conditions associated with high-altitude ecosystems, where low temperatures and other abiotic factors can limit the presence of vectors responsible for transmitting blood parasites. The detection of Plasmodium in wild condors raises concerns about potential pathogen introduction into recovery centers via admitted individuals, emphasizing the need for biosecurity protocols to prevent the spread of potential harmful pathogens in captive populations of endangered species. Given the increasing threats posed to this species, continuous monitoring of both wild and captive populations is recommended to detect emerging health risks and support effective conservation strategies.

Abstract Goose farming is gaining importance due to the economic value of meat and by-products; however, despite frequent reports of Plasmodium spp. infections in waterfowls, data on systemic biochemical responses in domestic geese remain limited. This study investigated biochemical alterations associated with natural Plasmodium spp. infection in Anser anser domesticus , focusing on acute phase proteins (APPs), thiol–disulfide homeostasis (TDH), and serum protein profiles. Blood samples were collected from geese with Plasmodium infection defined by combined microscopic examination and PCR (n = 35) and from uninfected geese (n = 20) Serum levels of APPs [Serum amyloid A (SAA), haptoglobin (Hp), total sialic acid (TSA)], TDH parameters [Native thiol (NT), total thiol (TT), disulfide (DS)], and serum proteins (total protein, albumin, globulin) were analyzed. Plasmodium -infected geese showed significantly higher levels of APPs than uninfected geese, indicating a strong acute phase response. Meanwhile, thiol components (TT, NT, DS) were significantly lower in Plasmodium -infected geese, reflecting infection-associated oxidative stress. However, redox ratios remained stable, suggesting preserved redox balance through compensatory antioxidant mechanisms. No significant differences were observed in serum protein concentrations. Correlation analysis revealed that Hp positively correlated with DS and negatively with NT/TT%, highlighting an interaction between inflammation and oxidative imbalance. Principal component analysis (PCA) showed that multivariate differentiation between infected and uninfected geese was mainly associated with protein-related and thiol-based redox parameters. In conclusion, Plasmodium infection triggers a distinct inflammatory and oxidative response in domestic geese, without affecting total serum protein levels. The combined use of APPs and TDH markers provides a promising non-invasive approach for monitoring infection-related physiological responses in avian malaria, supporting their potential utility in veterinary practice.

Abstract After expanding their range from the Netherlands to Germany, introduced Egyptian Geese ( Alopochen aegyptiaca , Tadornini) started to breed in Germany in 1981. Egyptian Geese are well-adapted to an aquatic lifestyle, which brings them into close contact with some of the vectors of avian malaria, such as biting insects in the order Diptera. As research on avian malaria in Anseriformes remains scarce in Europe, the prevalence and diversity of haemosporidians in Egyptian Geese were analyzed in 62 blood samples taken from 14 adult and 48 juvenile birds in Stuttgart, southwestern Germany. Blood was collected during the annual capture of family groups. The samples were tested for Plasmodium , Haemoproteus and Leucocytozoon using the nested PCR protocol developed by Hellgren et al. (2004). Surprisingly, none of the sampled geese tested positive for haemosporidian parasites, despite infections being observed in Egyptian Geese in their native range.

Abstract Avian malaria parasites and related haemosporidians include a highly diverse group of parasites infecting wild birds worldwide, with variable knowledge depending on bird taxa. Although comparatively less studied than terrestrial species, avian malaria infections in seabirds are generally rare, a pattern attributed to several non-mutually exclusive hypotheses, including limited exposure to vectors and differences in host life history traits. Here, we screened blood parasites by combining molecular detection and observation of blood smears in the highly endangered Bermuda Petrel (Cahow) Pterodroma cahow, sampled during the 2022 breeding season (January–April). In addition, we quantified the blood cell types to provide baseline information on the immunological status of this species. Furthermore, few blood samples of the White-tailed Tropicbird Phaethon lepturus catsbyii breeding in sympatry on the same archipelago were also analyzed for parasite presence. Our results support the absence of blood parasites of the genera Plasmodium , Haemoproteus , and Leucocytozoon as well as filaroid nematodes. The absence of blood parasite infections in both species may reflect low exposure to vectors in offshore marine and terrestrial environments, although other explanations, such as the absence of parasites able to infect these host species, are also possible. We found no significant differences in the relative abundance of monocytes among islets, although differences were observed, and a significantly higher total abundance of leucocytes in female Bermuda Petrels than males. Differential parasite exposure among islets and differential life history traits between sexes could account for these results. Negative records of parasite infections in wild birds, including endangered species, are essential for accurately characterizing global infection patterns and understanding host–parasite associations in avian communities.