The 'raptor-flight' of the Cuckoo. By J. S. Ash

Transcription

1 British Birds Vol. 58 No. 1 JANUARY 1965 The 'raptor-flight' of the Cuckoo By J. S. Ash ON FOUR OCCASIONS in the past eleven years I have noticed Cuckoos Cuculus canorus flying in a rather unusual manner, and I have incomplete notes on what was probably an earlier case of similar behaviour. This method of flight is presumably the same as that briefly mentioned by Chance (1922,1940), but I have been unable to trace any other reference to it in an admittedly far from exhaustive search through such books as Armstrong (1947), Baker (1942), Bannerman (1955), Kirkman (1911), Rothschild and Clay (1952) and Witherby et al. (1938). This is all the more remarkable because the flight concerned is utterly unlike any normally associated with this species. In fact, the bird so closely resembles a Sparrowhawk Accipiter nisus or even a Montagu's Harrier Circus pygargus at these times that the term 'raptor-flight' is used here to describe it. The fact that this flight has been noticed on at least four occasions by an observer who was paying no particular attention to Cuckoos suggests that it is, although perhaps infrequent, at least a regular feature of this bird's behaviour. It seems strange, therefore, that the habit has not been commented on more often by those engaged upon a study of Cuckoos, for, if seen, such unusual behaviour is not likely to be overlooked unless of course its close resemblance to a raptor's has indeed led the observer into believing that that is what he is seeing. Probably the best way to describe the raptor-flight is to quote in some detail from the notes made at the time of each observation. In these excerpts from my journals it will be seen that in each case the bird involved was first thought to be either a harrier or a Sparrowhawk. Indeed, the bird seen in 1961 so closely resembled a Sparrowhawk in both outline and behaviour that even after watching it for quite a long time, during which the characteristic shape of the Cuckoo's head and the pale streak on the underwing could clearly be seen, I found it most difficult to convince myself that it was not in fact a hawk. In such 1

2 BRITISH BIRDS circumstances, even an experienced observer, if he were unaware of this aspect of Cuckoo behaviour, could be excused for passing the bird over as a Sparrowhawk, (i) 'Portland Bill, Dorset, 27th April With N. P. Ashmole. At about GMT a Cuckoo was seen perched on a bramble; at it was again seen flying round the same spot in a very odd manner. In fact at first sight it was thought to be a harrier(!), having a rather slow flapping flight and alternately gliding as it quartered over the same bit of ground. It settled several times and was constantly mobbed by a pair of Meadow Pipits Anthm praknsis. At one stage it flew up and circled round at about 100 feet, alternately flapping and gliding (or soaring) for long distances the striking feature being the extended and separated (fingered) primaries, the first looking as if it were considerably extended forward. It finally settled and was flushed on our approach from the vicinity of a Meadow Pipit's nest containing three eggs. It then flew right away. At about it returned, and alighted on the bramble near the nest for about one minute; it then settled in the grass at an<^ spent about eight minutes hopping about apparently looking for the nest. At about lt flapped and apparently pounced on the nest; at the same time the Meadow Pipit appeared from above and mobbed it for a few seconds before alighting in the grass about six feet away. At about the Cuckoo reappeared with an egg between its mandibles and flew to a bramble about 100 yards away. There it almost immediately swallowed the egg, but with some difficulty, and it probably spent about 1 \ minutes over the operation whilst on the bush. It then flew away and settled on a bramble bush about a quarter of a mile away. An immediate examination of the Pipit's nest showed there were only two of its eggs and one Cuckoo's.' (2) 'Near Stoney Cross, New Forest, Hampshire, 5th June With* my wife. Cuckoo seen flying in an odd manner, looking very much like a soaring Sparrowhawk, and not at all like a Cuckoo. A very few wing beats then long periods of glides; shape of head was the only characteristic Cuckoo thing about it. Very like the bird at Portland a few years ago.' (3) 'Millersford Bottom, New Forest, Hampshire, 14th June, i960. At GMT in bright sunshine, light SW wind, what at first was taken to be a female Sparrowhawk was seen quartering low over the heath, about 100 yards away slightly uphill, and mostly over a slight hollow in dead ground. This bird was so extraordinarily like a Sparrowhawk, that if it had not been for the pale underwing streak, and the fact that I had seen Cuckoos doing this before, I should not have given it a second thought. Not only the shape of the bird (rounded wings, spread primaries, and long tail), but also the flight 2

3 'RAPTOR-FLIGHT' OF THE CUCKOO action (gliding, slower powerful wing beats and, particularly when disturbed from a resting position, the series of four or five rapid full strokes characteristic of Sparrowhawk) was so unlike a Cuckoo; one point I have noticed previously in this type of flight was the extended bastard wing. Both at rest and on the ground, and when presumably nest searching, it was constantly attacked and followed by a Meadow Pipit and at times by a cock Whinchat Saxkola rubetra. When at rest it spent much time with its wings half raised above its body, like a pigeon in defensive posture. No sound was heard at any time. Unfortunately the proceedings were disturbed by the approach of a gamekeeper on a motor-bicycle.' (4) 'On road to Applecross, Wester Ross, 20th May A "harrier" gliding over a hillside was judged to be about 200 yards away when first seen from the car. On stopping to examine it through binoculars it turned out to be a Cuckoo which continued to beat leisurely in wide circles in typical harrier fashion for about one minute. It then alighted on a telephone wire (with its wings folded above its body), after which I was unfortunately unable to watch it any longer.' (5) The following incident is not so well documented, but in retrospect I recall that it was, in fact, probably another example of raptor-flight. 'Fusilier Wood, Blagdon, Northumberland, 5 th June With Hon. M. W. Ridley. On seeing what we took to be a soaring Sparrowhawk fly down to the ground in a young plantation, we approached the area carefully. Two Tree Pipits Anthus trivialis and several Whinchats were mobbing it. Loud bubbling calls from a female Cuckoo were then heard, and at the exact spot where the "hawk" had landed we saw the bird. At first it remained on the same spot, bobbing its head up and down, but soon began to walk about calling repeatedly, and continually opening and closing its mouth. After about twenty minutes a calling male Cuckoo arrived on a Scots pine near-by, and the hen flew up to join him calling loudly too. On going to the place from which she flew we found a Tree Pipit's nest with five eggs near to hatching.' DISCUSSION Chance referred to a type of gliding flight adopted by Cuckoos just before egg-laying and he used such phrases as: 'her flight to the nest' was in the nature of an aeroplane glide to earth. Such occasional flaps of the wing as she might require to reach the nest were slow and laboured, somewhat resembling the lazy flight of Buzzard or Owl' (1922: 102); 'the Cuckoo suddenly glided from her look-out tree with a most unusual and fascinating flight' (1922: 65); 'gliding down in aeroplane fashion to settle beside the nest' (1922: 71); and 'circling and floating 200 feet up' (1922: 91). He referred to other Cuckoos 3

4 BRITISH BIRDS simply as floating or gliding down to nests. Such brief descriptions hardly give adequate credit to this unusual method of flight. There does not seem to be any doubt that the 'raptor-flight' is the method of flight used by Cuckoos before egg-laying. However, among the five incidents described above, the nests of only two of the prospective foster-parents were found. One was a Meadow Pipit's, in which the Cuckoo subsequently laid and the other was a Tree Pipit's which contained five eggs near to hatching; the latter brood of five nestlings was later ringed and there was thus no disturbance by the Cuckoo in that case. In all the cases mentioned the behaviour was restricted to a very limited area of ground, probably not much more than fifty yards in diameter, which certainly suggests that the bird is in the final stages of finding the nest. What is the purpose of this method of flight? Superficially Cuckoos resemble Sparrowhawks in having the greyish-blue upper-parts and the barred under-parts of the adults, yellow legs and eyes, and even in the case of young birds the white nape-patch of some males. But the Cuckoo's usual rather weak-looking flight, with most of the wingbeat characteristically below the horizontal mid-line of the flying bird, is very unlike a Sparrowhawk's. The most likely explanation for the raptor-flight is that it is merely an adaptation for soaring flight, although it is not clear why the Cuckoo needs to soar at certain times. Possibly it is able to slow itself down in this way, thus facilitating nestsearching from the air. Perhaps, also, it is indulged in more by Cuckoos in open country where there are few elevated perches from which to watch for nesting birds. The close resemblance to the flight of a raptor is presumably quite fortuitous, for it is difficult to see what advantages this could have unless it serves to keep mobbing small birds sufficiently far away to prevent undue distraction from its primary aim. SUMMARY A method of flight adopted by Cuckoos Cmulus canortts apparently an adaptation to soaring flight used as an aid to the final pin-pointing of the nest of a potential fosterer is remarkably like that of certain birds of prey, particularly Sparrowhawks Accipiter nisus. The term 'raptor-flight' is coined to describe it. Several incidents are detailed. REFERENCES ARMSTRONG, E. A. (1947): Bird Display and Behaviour. London. BANNERMAN, D. A. (1955): The Birds of the British Isles. Edinburgh and London. vol. 4, pp BAKER, E. C. S. (1942): Cuckoo Problems. London. CHANCE, E. (1922): The Cuckoo's Secret. London. (1940): The Truth about the Cuckoo. London. 4

5 'RAPTOR-FLIGHT' OF THE CUCKOO KIRKMAN, F. B. (1911): The British Bird Book. London and Edinburgh, vol. z, pp ROTHSCHILD, M., and CLAY, T. (1952): Fleas, Flukes and Cuckoos. London, pp WITHERBY, H. F., JOURDAIN, F. C. R., TICEHURST, N. F., and TUCKER, B. W. (1938): The Handbook of British Birds. London, vol. 2, pp