Sparrow Hawk hunting technique.
This spring at Amble Marshes the bulk passage of hirundines arrived a little later than usual; in most springs it’s the norm to find at least one Merlin hanging around to take full advantage of this annual seasonal influx. This spring was no different, but I was surprised to see on several occasions a tiny adult male Sparrow Hawk (photo with prey) sitting unusually close to a Merlin, then appearing to fly around chasing the Merlin, again unusually close. Later the same tiny male Sparrow Hawk soon perfected the technique of ‘fly-catching Hirundines’ from a convenient perch, its tiny proportions (hardly larger than a Sharp-shinned Hawk) plus it’s amazing agility enabled it to very quickly become extremely successful, so successful that on two occasions I observed the Hawk pluck a Sand Martin from the air and fail to hold on to the injured Martin letting it fall into water, making no attempt to retrieve the struggling bird from the water surface, this just a few yards away from the hunting position, on both occasions preferring to wait for another dry victim to come within range. This feeding bonanza appeared to continued for at least three weeks, with at least two more male Sparrow Hawks (one more adult and a 1st winter (photo) later adopting the Hirundine fly-catching technique, the second adult not quite as successful as the first and the 1st winter only managed one Sand Martin, at least on my limited watch. While it lasted I believe this behaviour accounted for a significant number of migrating Hirundine casualties mostly Sand Martin but also some Barn Swallow, we will never know the true figure though I would estimate the number to be no less than 100 individual casualties, not all of these were consumed, as with Sparrow Hawk attacks in the vicinity of buildings and bird tables a significant number of bird prey are panicked and killed by hitting windows and are not necessarily consumed. Given the apparent association between male Sparrow Hawk and Merlin at the onset of Hirundine migration it’s tempting to make some sort of connection; did the original male observe the Merlin hunting technique and copy it? Did successive male Sparrow Hawks then follow suit? If nothing else this helps to explain the large amount of sexual size dimorphism found in Sparrow Hawk, I’m confident that no normal sized female would be agile enough to be successful at the ‘fly-catching Hirundine technique ‘and perhaps a tiny male would struggle to overcome a Wood Pigeon, just one example of extreme sexual size dimorphism expanding the range of available prey items. A photo of a Sparrow Hawk with more usual prey (young House Sparrow) at Pentire Glaze this Saturday.