Chewing Lice (Phthiraptera: Amblycera, Ischnocera) of the Common Buzzards (Buteo buteo) in Romania: Host Age and Habitat Jointly Determine Lice Infestation

(1) Background: The common buzzard (<i>Buteo buteo</i>) is the most widespread raptor in Romania. This study aimed to assess the occurrence of chewing louse species and the factors influencing the epidemiology of louse infestation in the national bird populations. (2) Methods: Between 2012 and 2025, a total of 131 buzzards were collected from all over Romania, which were either roadkilled or died due to health issues. These birds were parasitologically examined, the gathered lice were identified, and epidemiological parameters were determined. (3) Results: The overall prevalence of louse infestation was 77.9%, with 4389 specimens collected. Five species were identified: <i>Degeeriella fulva</i> (55.7%), <i>Craspedorrhynchus platystomus</i> (37.4%), <i>Colpocephalum nanum</i> (42.0%), <i>Colpocephalum turbinatum</i> (7.6%), and <i>Laemobothrion maximum</i> (2.3%). Among the factors influencing the evolution of louse infestations, birds' age statistically significantly affected only the mean intensity (48.0 in subadults and 28.6 in adults, <i>p</i> < 0.001). Combined origin and season through temperatures and relative humidity also influenced the mean intensity of infestations. Sex-ratio and nymph-to-female ratio were, in the majority, female-biased and nymph-biased. (4) Conclusions: Lice infestation patterns of common buzzards are shaped more commonly by environmental and biogeographic context than by host sex, with temperature, humidity gradients, and region of origin primarily influencing mean intensity rather than prevalence. In addition, sex ratios were consistently female-biased across all lice species, and nymph-to-female ratios suggested contrasting demographic trajectories among taxa, with evidence of expanding infrapopulations in some species and more senescent structures in others.