The Influence of Biological Factors on Haematological Values in Wild Marsh Harrier (Circus aeruginosus) Nestlings

Marsh harrier (Circus aeruginosus) is a species with obligatory cainism, in which hatching asynchrony creates a pronounced size hierarchy in nestlings. The size-related competitive advantage of older nestlings means that they tend to dominate the younger ones, and brood reduction occurs in most nests. The aim of the study was to reference values and carry out a haematological examination in order to evaluate the physiological status and health of nestlings with respect to hatching order, brood size, and nest initiation date. To do so, we examined 19 nests with a total of 58 nestlings from a free-living population of this species located in fishpond complexes in the agricultural landscape of eastern Poland. Repeated blood samples (118 in all) were collected from nestlings. The following parameters were measured using fresh full blood: red blood cell count (RBC), haemoglobin level (Hb), white blood cell count (WBC), and plasma glucose level (Glu). The data were analysed using generalized linear mixed models and linear mixed models ((G)LMM). The study revealed that hatching order, but not brood size or nest initiation date, affected the physical condition of marsh harrier nestlings. Hb levels and RBC counts gradually decreased, whereas Glu levels and WBC counts increased from the first- to the last-hatched nestlings. This result points to the generally poorer condition of the youngest nestlings compared with their older siblings. The poor physiological condition of the youngest nestlings may consequently increase the likelihood of their perishing, and hence, of brood reduction.

Molecular identification of Sarcocystis halieti in the muscles of two species of birds of prey from Spain

Background Members of the genus Sarcocystis are protozoan parasites characterized by a prey–predator two-host life-cycle. Sarcocysts are formed in the muscles or central nervous system of the intermediate host (IH), while sporocysts develop in the small intestine of the definitive host (DH). Various birds of prey have been confirmed to be DH for Sarcocystis spp. Three Sarcocystis species, S. wobeseri, S. halieti and S. falcatula, have been identified in the muscles of birds of prey, of which the latter are known to be pathogenic and can cause encephalitis in various birds. The aim of this study was to identify Sarcocystis spp. in the muscles of birds of prey from Spain. Methods Between 2019 and 2020, muscle tissue samples taken from 59 birds of prey admitted to the Wildlife Recovery Centre in Ilundain (Navarra, Spain) were examined for the presence of Sarcocystis spp. Sarcocysts in fresh squashed samples were morphologically characterized under the light microscope (LM). Sarcocystis spp. were identified by means of 28S ribosomal RNA and internal transcribed spacer 1 sequence analysis. Results Microscopic examination of squashed tissue samples stained with methylene blue revealed the presence of sarcocysts in three of the 59 (5.1%) birds examined. Only one sarcocyst type was observed under the LM. Sarcocysts were thread-like (1050–2160 × 130–158 μm) and had a thin (0.7–1.4 μm) and smooth cyst wall. Septa divided the cysts into compartments filled with banana-shaped (5.9 × 1.7 μm) bradyzoites. On the basis of DNA sequence results, S. halieti was identified in the western marsh harrier (Circus aeruginosus) and the black kite (Milvus migrans) for the first time. Sarcocysts of S. halieti were shorter and wider compared to those observed in the great cormorant (Phalacrocorax carbo) and the herring gull (Larus argentatus). According to current knowledge, S. halieti may infect birds belonging to four different orders: Suliformes, Charadriiformes, Strigiformes and Accipitriformes. Conclusions This is the first report of S. halieti in the western marsh harrier and the black kite as IH. So far, little research has been conducted on birds of prey as IH for Sarcocystis spp. These results indicate that further studies combining morphological, histopathological, and molecular methods are required. Graphical abstract

Molecular Identification of Sarcocystis Halieti in Birds of Prey From Spain

Background: Members of the genus Sarcocystis are protozoan parasites characterized by a prey-predator two-host life cycle. Sarcocysts are formed in muscles or CNS of the intermediate host (IH), while sporocysts develop in the small intestine of the definitive host (DH). Various birds of prey were confirmed to be DH for Sarcocystis spp. By contrast, only two species, S. wobeseri and S. falcatula were identified in the muscles of birds of prey. The latter species is pathogenic and can cause encephalitis in various birds. The aim of the present study was to identify Sarcocystis species in the muscles of birds of prey from Spain. Methods: In the period between 2019 and 2020, muscle tissues of 59 birds collected from Spain were examined for the presence of Sarcocystis spp. Sarcocysts in fresh squashed samples were morphologically characterised under a light microscope (LM). Sarcocystis species were identified by means of 28S rRNA and ITS1 sequence analysis. Results: With the help of methylene blue-staining microscopic sarcocysts were detected in 3/59 (5.1%) birds of prey from Spain. Under LM, one type of sarcocysts was observed. Sarcocysts were thread-like (1050–2160 × 130–158 μm), had a thin (0.7–1.4 μm) and smooth cyst wall. Septa divided the cysts into compartments filled with banana-shaped (5.9 × 1.7 μm) bradyzoites. On the basis of DNA sequence results, S. halieti was identified in the western marsh harrier (Circus aeruginosus) and the black kite (Milvus migrans) for the first time. Sarcocysts of S. halieti detected in the black kite and the western marsh harrier were shorter and wider as compared to those observed in the great cormorant (Phalacrocorax carbo) and the herring gull (Larus argentatus). Hence, S. halieti might infect birds belonging to three different orders, Suliformes, Charadriiformes and Accipitriformes. Conclusions: This is the first report of S. halieti in birds of prey as IH. Due to the inconsistency of research on Sarcocystis spp. from birds of prey, further complex morphological, histopathological, and molecular studies are required.

Close to the Madding Crowd: How Resilient are Imperilled Mediterranean Urban Wetlands?

Investigating how Mediterranean wetlands respond to adjacent land use conversion, is an important first step in mitigating the impact of human encroachment and other environmental stressors. We monitored the composition and structure of waterbird assemblages, in a Mediterranean urban marsh, subjected to severe anthropogenic pressures. Remote sensing indicated that in the last two decades Boussedra Pond was subjected to landfill, resulting in a substantial reduction (~ 50%) of the marsh, while due to a lack of urban planning urban built-up and agriculture areas expanded considerably in its surroundings. Seasonal changes in the diversity of waterbirds, including the globally Endangered (EN) White-headed Duck Oxyura leucocephala and the Near-Threatened (NT) Ferruginous Duck Aythya nyroca, reflected the importance of the site as a staging and wintering area for many migratory species. The long-term study also suggested that breeding waterbirds species respond differentially to the loss and degradation of habitats, as highlighted by the resilience of the synanthropic Moorhen Gallinula chloropus and the disappearance of several breeding marsh specialists, like the Little Bittern Ixobrychus minutus and the Western Marsh Harrier Circus aeruginosus. The study points out the need for both a coordinated cross-sectorial land use planning and an immediate, affordable and sustainable wetland conservation action.

Diet composition, guild structure and trophic relationships of wintering birds of prey in an estuarine wetland (The Evros Delta National Park, Greece)

Seven species of birds of prey studied in the Evros Delta National Park belong to a common assemblage of a trophic guild. However, their diet study revealed different groups of feeding niches. A cluster analysis provided three groups with very similar diets: The eastern imperial eagle (Aquila heliaca) and greater spotted eagle (Clanga clanga) constituted a group feeding mainly on birds with their diets including 96% (13 bird species) and 98% (16 bird species), by number respectively, most bird prey being water birds. A second group, characterized by a considerable variety of prey types dominated by small mammals and birds, included the western marsh harrier (Circus aeruginosus) (67% mammals, 27% birds -at least 12 species ), black kite (Milvus migrans) (46% mammals, 39% birds -at least 11 species) and common buzzard (Buteo buteo) (birds 36% -at least 7 species, mammals 22%). In all three species, birds dominated by biomass, whereas other prey such as arthropods (mainly insects), amphibians and reptiles had a low contribution by mass where they occurred. A third group included the common barn owl (Tyto alba), feeding mainly on small mammals (97%, at least 12 species) and little owl (Athene noctua). The little owl’s diet consisted of mammals (29%, -at least 6 species), birds (5% -at least 7 species) and, though insects preponderated by number (64%), mammals were dominant by biomass in both owls. Diversity indices estimated on class level were low, ranked as B. buteo > M. migrans > A. noctua > C. aeruginosus > A. heliaca = T. alba > A. clanga. Dietary similarities may be partly due to common habitat preferences and the role of other potential factors to niche partitioning is discussed.

Effect of nest age and habitat variables on nest survival in Marsh Harrier (Circus aeruginosus) in a fishpond habitat

Background One important anti‐predator strategy adopted by birds involves nest site selection and timing of breeding. Nest-site selection by marsh-nesting birds often involves nest concealment and water depth as key features influencing nest survival. Marsh Harrier (Circus aeruginosus) is an obligate ground nester, which sets it apart from other raptors. The aim of the present study was to identify for the first time possible temporal and habitat factors affecting nest survival in Marsh Harrier. Understanding features which affect nest survival are essential for assessing relevant conservation strategies. Methods To understand the relative contributions of different temporal and habitat variables to brood losses, it is useful to determine the daily survival rate (DSR). We examined 82 Marsh Harrier nests located on fishponds in eastern Poland, where predation is the main cause of nest loss. Six habitat variables were measured for each active nest. DSR was calculated using known-fate models with the RMark package. Results The best-supported model predicted that DSR decreased with nest age and was positively affected by the water depth and the diameter of reed stems, but not by the height or density of vegetation at the nest site. The distances of nests to the fishpond dyke and to open water received no support in the models. The chances of nest survival were lower if a neighbouring nest had been depredated. This result suggests that the Marsh Harrier is more susceptible to mammalian than avian predation and confirms the high level of predator pressure in fishpond habitats.