Dodelijke verstrikking van een jonge Boerenzwaluw Hirundo rustica in niet-stekelige vegetatie

On 24 August 2012, a fresh dead Barn Swallow Hirundo rustica was found entangled in non-thorny, perennial vegetation in a grassland bordering a brook in western Drenthe. In the preceding days, this particular patch of vegetation had been the foraging site of a small flock of Barn Swallows, which were attracted by the abundance of flies and hoverflies (including Eristalis tenax, E. arbustorum or E. abusivius and Helophilus trivittatus) attending the flowering Aegopodium podagraria. Apparently, this juvenile bird had become entangled when making a turn in flight whilst the tip of the right wing had been positioned in between several woody stems of vegetation. Primaries 7-9 (counted descendantly) had been turned around the stems several times. It was difficult to extract the bird from its trap, and the primaries were so heavily deformed that it was impossible to realign them with the undamaged primaries. The bird weighed only 13.4 g (maximum wing chord 120.5 mm), its stomach was empty and the surrounding vegetation showed abundant traces of uric acid; these data suggest that the bird starved to death. Surprisingly, the bird had not been spotted by a member of the local predator guild, which was particularly well represented at this time of the year as nearby grasslands had just been mowed. The area was frequented by at least 9 Buzzards, 4 Kestrels, 2 Sparrowhawks, 2 Marsh Harriers, a juvenile male Goshawk, an adult Red Kite and 5 Ravens (and at night by Red Foxes and Badgers), but none of these specialists had taken advantage of (or seen) the dangling swallow. This observation shows that entanglement in vegetation (or barbed-wire) is not always associated with thorny or sticky plants (unlike the cases recorded in the literature).