Flight altitudes and flight activities of adult Red Kites (Milvus milvus) in the breeding area as determined by GPS telemetry

Abstract

The Red Kite has come to the forefront of general consciousness in recent decades. A major contributing factor has been repeated collisions of these raptors with wind turbines and the important role they play in the approval process for new turbines. Efforts to improve their protection sometime encounter challenges due to limited knowledge about some life history aspects, e.g., their flight altitude and flight activity. We investigated these parameters from 2012 to 2018 in an approximately 1000-km2 study area in the vicinity of Weimar (Federal State of Thuringia, Federal Republic of Germany) in 29 breeding birds (19 males and 10 females) equipped with GPS loggers. In addition to more than 11 million GPS data records, accelerometer data from the loggers were evaluated. The start of morning activities correlated with sunrise. Most frequently, Red Kites initiated their first hunting flights immediately at sunrise; males started hunting at 9 min and females started hunting at 12 min after sunrise (medians). The Red Kites mostly foraged and hunted their prey during flight. The proportion of time spent flying during their activity phase was highest during midday hours, reaching 30–80% in males depending on the phase of the breeding season. For males, the time spent flying was approximately two and a half times that for females. The birds sporadically reached flight altitudes of up to 1600 m above ground in the breeding area, while they maintained lower altitudes between 5 and 60 m more frequently and predominantly while foraging (56% of location fixes). Higher altitudes were occupied much less frequently than lower altitudes and were often used to travel relatively long distances in an energy-saving manner. The end of activity was well before sunset, at 87 min prior to sunset for males and 154 min prior to sunset (medians) for females.

Nesting flight statistics for wind turbine planning: a MoveApps workflow

“…Further improvement could be gained by even higher data resolution (Schaub et al 2020). Our average range of 50% flight altitude of red kites (50-75 m) is almost the same as previously estimated (50-60 m) for a data set in central Germany (Pfeiffer and Meyburg 2022). Furthermore, the issue of ellipsoid vs. mean sea level height at estimating height above ground has to be considered.…”

“…Fourth, to evaluate how far from a nest wind turbines can be erected, proportional use of the area around the nest site must be evaluated. This parameter has been provided as evaluation area radii in the German Federal Nature Conservation Act (Federal Law Gazette 2009) and estimated for the red kite by different studies (Mammen et al 2013; Pfeiffer and Meyburg 2022), so we can compare them with our outcomes. Our workflow calculates the proportion of area used in different distances around the nest cumulatively for a set of circular distances.…”

“…Many GPS tracks have been collected by a large number of scientists, wildlife managers and conservation groups worldwide and uploaded and archived in online databases like Movebank (Kays et al 2022). For some species, the data have been analysed in relation to collision risk (Schaub et al 2020; Pfeiffer and Meyburg 2022), wind turbine avoidance behaviour (Chamberlain et al 2006; Watson et al 2018; Santos et al 2022) and habitat loss (Marques et al 2020). However, much available tracking data has not been analysed for wind turbine collision risk applications.…”

Habitat geometry rather than visual acuity limits the visibility of a ground‐nesting bird's clutch to terrestrial predators

“…The horizontal distance required to achieve the viewing angles was calculated from different fixed observer heights: that of the average European red fox (0.4 m) and a matrix of increasing corvid flight heights (1.6, 3.2, 6.4, 12.8, 25.6 m). Flight heights were chosen as octaves relative to fox and human height (1.6 m) and based on the flower flight altitudes of foraging birds, observed even in higher flying raptors (Pfeiffer & Meyburg, 2022 ).…”

“…horizontal distance required to achieve the viewing angles was calculated from different fixed observer heights: that of the average European red fox (0.4 m) and a matrix of increasing corvid flight heights(1.6, 3.2, 6.4, 12.8, 25.6 m). Flight heights were chosen as octaves relative to fox and human height (1.6 m) and based on the flower flight altitudes of foraging birds, observed even in higher flying raptors(Pfeiffer & Meyburg, 2022).F I G U R E 2 3D scan energy at different spatial scales relative to clutch size: x1/8, x1/4, x1/2, x1, x2, x4. The left-hand side shows the original height map and associated regions of interest (ROIs): clutch, nest, and background.…”