Exogenous creatinine clearence indexed to body surface area allows estimation of GFR and across species comparison.

The assessment of renal function in birds is difficult because sensitive biomarkers are lacking. Previous studies have demonstrated the feasibility of measuring the exogenous creatinine clearance in pigeons, indicating the potential use of this technique for the assessment of renal function in birds. The aim of the study was to index the exogenous creatinine elimination rate by body surface area, enabling comparison between different species. Exploratory data on common buzzards (Buteo buteo), Eurasian eagle-owls (Bubo bubo), domestic goose (Anser anser domesticus) and racing pigeons (Columba livia) were collected and indexed by body surface area. A sterile creatinine solution was administered at a dose DM = 50 mg kg-1 i.m. into the deep pectoral muscle of 52 clinically healthy birds of the four species with different body masses. The time course of the plasma creatinine concentration was measured and analyzed by a parametric pharmacokinetic Bateman model, followed by indexing the exogenous creatinine clearance (ECC) by body surface area. The exploratory ECC values for birds with a mean body mass ranging from 0.42 kg (pigeon) to 8.2 kg (goose) were between 0.4261 mL min-1 dm-2 (CI 0.3882-0.4672) and 0.8717 mL min-1 dm-2 (CI 0.8091-0.9362). ECC indexed by body surface area turned out to be independent from body mass. Resulting exploratory data covering species with different body masses are comparable with published data from very complex studies of avian renal function.

Generalized Tuberculosis Due to Mycobacterium caprae in a Red Fox (Vulpes vulpes) in Austria.

Mycobacterium caprae subtype Lechtal was detected in a red fox (Vulpes vulpes) shot by a hunter in 2018 in the western part of Austria, where, among wildlife, tuberculosis is known to occur in red deer (Cervus elaphus). The red fox showed a generalized (disseminated) manifestation of the disease and a multibacillary distribution of mycobacteria in the inner organs.

THE EFFECTS OF MIGRATORY FLIGHT ON HEMATOLOGIC PARAMETERS IN NORTHERN BALD IBISES ( GERONTICUS EREMITA).

Under the project of "Human-Led Migration," the authors had the unique opportunity to accompany hand-raised northern bald Iibises (NBIs; Geronticus eremita) during migration, which occurred in stages from Bavaria, Germany, to southern Tuscany, Italy. The aim of this study was to investigate the immediate effects of flight, with respect to flight duration, and the more delayed recovery effects on hematologic variables. A total of 31 birds were sampled. Blood samples were taken immediately before takeoff, after landing, and 1 day after the flight. Hematocrit was determined and blood smears were prepared to estimate the total white blood count (tWBC) with leukocyte concentrations (absolute [abs.]) and differential blood cell count (%). Postflight, significant decreases in hematocrit, tWBC, lymphocytes (abs., %), heterophils (abs.), eosinophils (abs., %), and monocytes (abs.) were observed. In contrast, heterophils (%), basophils (%), and the heterophil/lymphocyte (H/L) ratio increased significantly. With increasing flight duration, the H/L ratio increased further. One day postflight, there were still significant decreases in tWBC, lymphocytes (abs.), and eosinophils (abs., %) and significant increases in heterophils (%) and the H/L ratio. The hematocrit dropped even further. These data show that the decrease of tWBC is mainly caused by the lymphocyte fraction and that NBIs need more than 1 day to reverse the postflight changes in some hematologic values. Hematocrit changes postflight and on the recovery day are most likely to be explained by hemodynamics and the metabolic and hormonal changes caused by flight. The hematologic changes postflight in NBIs were largely consistent with those of other birds, but they differed from humans and mammals postexercise mainly in the levels of tWBC, heterophils (matching neutrophils in mammals), and lymphocytes.

EXPLORATORY PLASMA BIOCHEMISTRY REFERENCE INTERVALS FOR URAL OWLS (STRIX URALENSIS, PALLAS 1771) FROM THE AUSTRIAN REINTRODUCTION PROJECT.

The Ural owl (Strix uralensis) is the biggest forest-living owl in Austria; however, it became extinct in Austria through poaching and habitat loss more than half a century ago. The birds examined in the present study were breeding pairs from the reintroduction project with the aim of determining exploratory plasma biochemistry reference intervals in Ural owls and evaluating the amount of biological variation between seasons, sexes, and ages. A total of 45 birds were sampled, including 13 adult males, 14 adult females, and 18 juvenile birds. Remarkably, almost all of the analytes showed significant differences between the subgroups, primarily between seasons, followed by age and sex. Only creatinkinase, glucose, lactatdehydrogenase, and triglycerides did not show any significant variations. Despite partitioning of reference values into subgroups according to biological variation diminishing the number of reference individuals in the respective groups, the resulting smaller reference intervals will improve medical assessment. The results of the present study once again demonstrate that significant seasonal fluctuations must be expected and considered in the interpretation. It can be assumed that these differences are probably even greater in free-range birds with considerable changes in food quantity and quality during and between years.

Energy Expenditure and Metabolic Changes of Free-Flying Migrating Northern Bald Ibis.

Many migrating birds undertake extraordinary long flights. How birds are able to perform such endurance flights of over 100-hour durations is still poorly understood. We examined energy expenditure and physiological changes in Northern Bald Ibis Geronticus eremite during natural flights using birds trained to follow an ultra-light aircraft. Because these birds were tame, with foster parents, we were able to bleed them immediately prior to and after each flight. Flight duration was experimentally designed ranging between one and almost four hours continuous flights. Energy expenditure during flight was estimated using doubly-labelled-water while physiological properties were assessed through blood chemistry including plasma metabolites, enzymes, electrolytes, blood gases, and reactive oxygen compounds. Instantaneous energy expenditure decreased with flight duration, and the birds appeared to balance aerobic and anaerobic metabolism, using fat, carbohydrate and protein as fuel. This made flight both economic and tolerable. The observed effects resemble classical exercise adaptations that can limit duration of exercise while reducing energetic output. There were also in-flight benefits that enable power output variation from cruising to manoeuvring. These adaptations share characteristics with physiological processes that have facilitated other athletic feats in nature and might enable the extraordinary long flights of migratory birds as well.