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A multisensor telemetry system for studying flight biology and energetics of free-flying Griffon Vultures
... The unit consisted of two distinct parts: an extracorporeal backpack and a smaller intra-abdominal implant. We also used a similar system for chamois (Rupicapra rupicapra) ( Bögel et al. 1998;Bögel et al. 1999;Walzer et al. 2000). While simple systems are available commercially (e.g. ...
Scavenging is a key process in the ecosystems. Studying foraging movements of obligate scavengers such as vultures can contribute to a better understanding of the scavenging-related patterns and processes. Here we review methods that can be used to track foraging vultures in the field. Yet, in order to track, vultures need to be trapped and tagged in manner that would ensure their health and normal survival and behavior. GPS telemetry is currently the best tool to track vultures for foraging studies. In a review of recent studies, we highlight the predominance of studies of species from Europe, North America and Southern Africa, and we deplore the lack of knowledge of species from the Tropics. Home ranges vary tremendously between sites, season and species (from a few km² to >300,000 km²) but also depending on the analysis method used. Daily distances travelled are more repeatable between species, with values ranging between 30 and 40 km. Yet the way that carrion distribution can affect scavenger distribution and foraging behavior is still poorly understood.
The diurnal cycle of metabolic rate (MR, J/g-h, based on VO2 and VCO2) was measured in 14 Griffon Vultures (Gyps fulvus), two Hooded Vultures (Necrosyrtes monachus) and one White-backed Vulture (Gyps africanus) at different ambient temperatures (-7 to +34 °C). In (so far) three Griffon Vultures the heart rate (HR) and body temperature (Tb) were measured by telemetry, simultaneously with MR. The three vulture species show very similar physiological mechanisms. In all cases measured MR is significantly below allometrically expected values (G. fulvus -46%, N. monachus -24%, G. africanus -6%). Fasting for 4 days results in an additional MR reduction of up to 27-35%. There is a very small change of MR with ambient temperature (Ta). Therefore no obvious thermoneutral zone was observed in the broad Ta-range tested (see above). Ta-independent MR is the largest yet measured in birds. Thermal conductance (TC-wet) lies dramatically below expected values (-21.5 to -53.7%), and is extensively used to control heat loss. All these special MR-strategies save energy expenditure. Tb of resting griffons shows a clear sinusoidal diurnal rhythm. The average Tb during the night has a mean value of 37.7 ± 0.49 °C; the mean daytime value is 38.9 ±0.25 °C; the total average is 1.3/1.1 °C below expected values for Falconiformes, an effect significantly reducing energy expenditure. At Ta higher than about 25-30°C, Tb increases significantly with increasing Ta, whereas MR does not vary significantly. Thus, the MR-independent variation of Tb may function as an additional and very effective mechanism for saving energy.
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