Movement ecology of migration in turkey vultures

Abstract

We develop individual-based movement ecology models (MEM) to explore turkey vulture (Cathartes aura) migration decisions at both hourly and daily scales. Vulture movements in 10 migration events were recorded with satellite-reporting GPS sensors, and flight behavior was observed visually, aided by on-the-ground VHF radio-tracking. We used the North American Regional Reanalysis dataset to obtain values for wind speed, turbulent kinetic energy (TKE), and cloud height and used a digital elevation model for a measure of terrain ruggedness. A turkey vulture fitted with a heart-rate logger during 124 h of flight during 38 contiguous days showed only a small increase in mean heart rate as distance traveled per day increased, which suggests that, unlike flapping, soaring flight does not lead to greatly increased metabolic costs. Data from 10 migrations for 724 hourly segments and 152 daily segments showed that vultures depended heavily upon high levels of TKE in the atmospheric boundary layer to increase flight distances and maintain preferred bearings at both hourly and daily scales. We suggest how the MEM can be extended to other spatial and temporal scales of avian migration. Our success in relating model-derived atmospheric variables to migration indicates the potential of using regional reanalysis data, as here, and potentially other regional, higher-resolution, atmospheric models in predicting changing movement patterns of soaring birds under various scenarios of climate and land use change.energetics ͉ flight ͉ meteorology T raditionally, bird migration has been treated separately relative to other movements within an individual's life history (1-2). Although long-distance migration operates on different scales and produces different patterns than those of other movement types in a bird's life cycle, there are also many similarities (cf. ref.3). As in other biotic movements, migration involves the assessment of internal state of the organism, external factors, and past behavior to make decisions about motion and navigation (4).One significant challenge of migration research is measuring the extent to which migratory routes and schedules of individual migrants are influenced by external factors, including wind direction and speed (5-6), food availability and habitat (2), and the behavior of other migrants (1, 7). One important axis of variation among migratory birds is the extent to which environmental factors act as facilitators of, as opposed to barriers to, movement. Determining the effects of environmental factors is particularly important for soaring birds, whose movements rely upon environmental factors such as deflection updrafts and thermal convection as their principle means of propulsion, whereas those using primarily flapping flight are, in principal, not directly dependent on environmental forces for propulsion and lift. Although we recognize that this categorization can be overly simplistic (see, for example, ref. 8) and that other categorizations based on ecological function exist (9-10), the dichoto...

Influence of weather conditions on the flight of migrating black storks

“…The utilization of the MEM in a migration study on turkey vultures (Cathartes aura) supports the hypothesis that proximate route choices are influenced by external meteorological and topographic factors (rugged terrain) (Mandel et al 2008). Thermal convection (upward movement of a parcel of air to a higher altitude) can be a second possible factor influencing flight speed (per hour) and direction, altitude and daily distance, especially in the larger soaring migrants (some Accipitriformes and the Ciconiiformes).…”

“…A recent movement ecology model (MEM) now gives us the possibility to evaluate the roles played by different factors, both external (turbulence, horizontal winds and topography), and internal ones (heart rate), as well as the influence of present state (altitude, speed) and past behaviour in determining the navigation and movement of soaring migrants (Mandel et al 2008;Nathan et al 2008). The mechanisms of soaring flight (including phases of glide and flapping) influence the energy budget of birds (Welham & Ydenberg 1993;Hedenström & Alerstam 1995).…”

Environmental drivers of variability in the movement ecology of turkey vultures (Cathartes aura) in North and South America

“…As a result, the sample sizes of most existing studies have restricted the use of robust statistics and hypothesis testing [11,12]. Additionally, the limited spatial extents involved in most of these studies may not be fully representative of a species' broader migratory syndrome [4,[13][14][15] (but see [3,16]). To date, moreover, research has mainly focused on 'complete migrants' (sensu [17]; i.e.…”

“…However, until the emergence of porro-prism binoculars in the late 1800s [1] and modern bird banding in the early 1900s [2], the study of this phenomenon was anecdotal at best. More recently, satellite tracking has allowed researchers to follow the movements of individual birds at frequent and systematic intervals, enabling analyses of dynamic environmental conditions along movement tracks [3]. Satellite tracking coupled with the emerging discipline of movement ecology offers a new working paradigm for understanding the internal and external factors that affect the movements of birds and, in turn, their behavioural ecology and conservation biology [4].…”

Where eagles soar: Fine‐resolution tracking reveals the spatiotemporal use of differential soaring modes in a large raptor

“…Migration of golden eagles is faster and more energetically efficient when thermal soaring combined with gliding is used compared to orographic soaring (Duerr et al., 2012), and migratory flight has been positively correlated with weather conditions promoting thermal uplift, suggesting that eagles preferentially travel when conditions favor thermal soaring over orographic soaring (Duerr et al., 2015). Terrain ruggedness has been identified as an important determinant of increased heart rate in turkey vultures Cathartes aura due to its effect on decreasing the spatiotemporal predictability of uplift (Mandel, Bildstein, Bohrer, & Winkler, 2008), again potentially representing the cost associated with soaring in highly variable mountainous conditions. However, whether these advantages would apply equally to resident eagles ranging within their own territories is debatable.…”