Grey Herons Ardea cinerea hunting and eating Little Swifts Apus affinis

This note reports on Grey Herons' (Ardea cinerea) predation on Little Swifts (Apus affinis) at Bloemhof Dam Nature Reserve, North-West Province. 


Observation
Before entering Bloemhof Dam Nature Reserve, North-West Province, we stopped on the bridge of the Bloemhof Dam to observe the birds in the area. There were large numbers of swifts and swallows in flight. From one end of the bridge, we could see Grey Herons Ardea cinerea sitting on pylons. Some of them were pecking at something indeterminate which we assumed were fish.
We soon realized that the herons were atempting to catch Little Swifts Apus affinis. For a few minutes, we watched them stabbing into the air when the swifts passed nearby. Several herons were observed taking flight and making a lunge to capture a bird in the air, taking advantage of the commotion which had formed around the colony of swifts. After several minutes one of the herons managed to catch a Little Swift with a quick movement of its neck. For about four minutes, the heron hit the swift against a pylon until the swift stopped moving and then started swallowing it, using the procedure they usually use with large prey (Cook 1978). One of the herons located nearby showed, at the corners of its bill, traces of black feathers compatible with having eaten a small bird. Minutes later another heron flew under the bridge and managed to hit another swift which fell into the water. One of the herons that had been resting nearby dropped into the water, picked up the swift, still alive, and flew off to go eat it on one of the other bridge pylons.
This surprising behaviour has been mentioned for the first time a few years ago (Power 2013); amazingly, this previous record was from exactly the same place, but nine years earlier. The author mentioned not having observed the capture method but mentions that the park manager had also observed herons catching swifts in flight.

Power (2013) compiled a series of references on predation on birds by both Grey Heron and its terrestrial congener, the Black-headed
Heron Ardea melanocephala (Power 2013). In many of these observations, predation was on offspring of waterbirds. In both species, records of predation on birds occurred on land or in shallow water, capturing individuals that are not flying (Murphy 1976, Marquiss & Leitch 1990. Even so, there are rare observations of herons of several species capturing birds such as swallows (Carrasco 2018).
The size of the prey does not seem to be a limiting factor as Grey Herons often catch fish weighing up to 0.5 kg and waterfowl offspring of up to 0.3 kg (Marquiss & Leitch 1990); in terms of length, they catch fish of up to 40 cm (Del Hoyo et al. 1992) and Eels Anguilla anguilla up to 60 cm are taken (Owen 1955, pers. obs). There is limited data (Voisin 1991, pers. obs.) of adult Little Grebe Tachybaptus ruficollis (25-29 cm, 120-240 g) (Cramp & Simmons 1977) being caught. However, the speed of movement of the birds in flight, and especially that of swifts, does seem an important inconvenience. Although in fact they usually maintain a consistent moderate speed of only 36-43 km/h (Henningsson et al., 2010). In the static capture method it would resemble the standby an fish harpooning (Meyerriecks, 1960). On the other hand, the capture of birds in flight or even knocking them so that they fall to the substrate, seem an even more exceptional behaviour (Keighley & Hall 1995), which may have been facilitated by the density of swifts flying in this