Diversity and distribution of ectoparasites infesting Podiceps cristatus and Tachybaptus ruficollis (Aves, Podicipediformes) at a Ramsar site in northeast Algeria: new records.

Algeria hosts 55 Ramsar sites of international significance, serving as crucial habitats for a wide range of migratory, wintering, and breeding waterbird species. Despite this, research on the ectoparasites of aquatic avifauna in Algeria remains limited. This study aims to investigate the ectoparasite diversity infesting the Little Grebe ( Tachybaptus ruficollis Pallas, 1764) and the Great Crested Grebe ( Podiceps cristatus Linnaeus, 1758) in northeastern Algeria. To do so, we examined grebes of both species at Lake Tonga between 2022 and 2023. A total of 8,057 ectoparasites were collected, 24 of which belonged to Phthiraptera and 8,033 to Acari. Two lice species were identified: Aquanirmus podicipis Denny, 1842, belonging to the suborder Ischnocera, infesting the Great Crested Grebe and Pseudomenopon dolium Rudow, 1869, from the suborder Amblycera, infesting the Little Grebe. As for Acari, we identified two mite species belonging to the suborder Astigmata (Pterolichoidea; Ptiloxenidae): Ptiloxenus major Mégnin & Trouessart, 1884, and Ptiloxenus colymbi Canestrini, 1878 the latter of which had not been reported since its original description. This study reports a new host-parasite association in the global mite fauna (Great Crested Grebe - Ptiloxenus colymbi Canestrini, 1878). All the identified ectoparasite species are reported for the first time in Algeria. Feather mite infestation did not differ significantly between breeding and wintering seasons and showed only a weak correlation with host morphometric parameters. These findings suggest that neither season nor body size strongly influence feather mite dynamics in the studied grebes, while still providing valuable insights into their host–parasite relationships.