OBSERVATIONS ON A PAIR OF NIGHTJARS AT THE NEST

Transcription

1 OBSERVATIONS ON A PAIR OF NIGHTJARS AT THE NEST By H. R. TUTT INTRODUCTION IN 1952 observations were made at the nest-site of a pair of Nightjars (Caprimulgus europceus) in Essex from the time the young were hatched till the birds migrated. The habitat was so different from the Brecks where E, Selous {Zoologist, 1899, pp and ) studied the birds, and from Salthouse on the Norfolk coast where D. L. Lack (Ibis, 1932, pp ) did, that the behaviour of both adults and young was observed till fledging occurred and for some time afterwards. There was only one pair of Nightjars in the woodland. The nestarea was sited' beneath a stool of hornbeam on which the underwood was about 15 feet high, this having been left when the rest of the underwood in the area was felled. Opposite to the hornbeam was a stool of sweet chestnut with shoots 5 feet high in their second year of growth. The space between these was roughly circular, 6 feet in diameter, and surrounded by a dense growth of tall grass, bracken and other herbage. The young Nightjars occupied this site till they were 28/29 days old, when they were fully fledged; day roosting continued in the nest-site by one or both birds, and the place was last used by both juveniles together on 2nd August. The nest with 2 eggs was located on 12th June and no other visit was made to it till 18th June at hours.* The eggs were hatched, probably that day, as three half-shells lay just outside the nest-area and the fourth against a chick. The down was dry. The chicks made a low cheeping noise, and by the time we left had shuffled a foot away from the nest depression, so that already they could move about. FEMALE LURE-FLIGHT 21st June: chicks 3/4 days old. Keeper Steffan came with me to the hide, which we approached in full view of the female bird. She flew in slow, rolling flight, her wings hitting the tops of the herbage, tail partly fanned: she seemed to be pulling herself along by the wing-action on the grass and bracken. She settled in the dense growth about 30 yards away. Ten minutes after the keeper left the female passed behind and over the hide with a low, staccato "chuk-chuk-chuk". She flew to my right, behind the nest, over the hide to my right "again, rose higher repeating "chuk-chuk-uk" and dived into the nest area landing on my side of the chicks, where she lay like a log on her * All times are British Summer Time 261

2 262 BRITISH BIRDS [VOL. XLVIII side as if supported by the shoulder of the opposite wing resting on the ground, her head turned to the hide, the left flank and breast exposed to my view. She lay frozen in that position for five minutes before righting herself, waddling to the chicks and shuffling down upon them. On another occasion she rose, circled behind the hornbeam, then over the nest-site, rising and falling over the herbage as if semidisabled ; she glided to a bare branch of a young oak tree, sat along it, dropped the right wing, which hung as if broken. Then she dived in twisting flight to the herbage, flapped along the surface and disappeared. MALE LURE-FLIGHT At hours on 2nd July I made towards the nest area through tall underwood. The male was churring and when I emerged into the nest-area about 60 yards from the nest-site, he flew round me in wide circles in dancing (i.e. rising and falling) flight uttering an excited "twick-twick" at intervals of about two seconds; the flight changed to circling at great speed. Nearer the nest-site he came just ahead of me and hovered about 12 feet high like a Kestrel (Falco tinnuncidus), the white spots in the plumage shining distinctly; he went ahead of me in dancing, butterfly flight; the wings beat quickly, carrying the bird higher with very little forward motion, and were then stretched high over the back to their extreme length, when the bird parachuted lower, till the quick beats were resumed. Close to the nest it made with rapidly beating wings to the branch of a birch as if attempting to reach it and alight upon it; but it fell several feet when its head almost touched the branch; it tried again, and then again, giving a most realistic idea of failure through inability to fly normally; then the butterfly flight continued as he went round the hornbeam. I was in the hide on several occasions in the evening before activity commenced till after it ended; on two occasions before activity commenced in the early morning till after it ended; and' one whole night beginning before feeding started and finishing after the female was settled brooding for the day a period of about seven hours. Activity started from to an^ ended at about hours as a general rule; it began again about and ended just after hours. The maximum number of times the adults came into the nest-site to feed the chicks during any one period of activity was eight, and whilst the chicks remained in the nest-site they never made less than five visits for feeding: normally it was seven or eight. At the longest, feeding activity took place for no more than 2 J hours out of the 24, yet the chicks throve well, so that the food must have been of high nutritional value. A SAMPLE MORNING ACTIVITY 26th June: chicks 8/9 days old. I reached the hide at (see "Female lure-flight" above).

3 VOL, XLVHI] NIGHTJARS AT THE NEST 263 The female flew off about five minutes after she returned following her lure-flight. A few minutes later the male flew in (white spots flashed as he alighted). There was a rhythmic sound: to me it resembled a very low, breathy "chur, chur, chur," or it might be rendered by a breathy "yah, yah, yah" this is no doubt the "croodling" noise mentioned by Selous. After some time the male flew and churred near for about 15 seconds. The female arrived next and flew off after very few seconds. There is no "croodling" when the visit is a quick one. The female*made five more visits, but the male did not come to feed again. Though I saw the female alight three times it was too dark for me to see exactly how the feeding was done. The last time the female fed the chicks the male flew into the nest-site, with wings stretched to their full extent vertically over his back: his toes seemed to touch the ground, but he arose and flew without folding the wings. The female flew off just afterwards but was back in about seconds. She shuffled over the young and sat like a statue. Time I left the hide at without disturbing the female or seeing any sign of the male. ALL NIGHT IN THE HIDE ist-and July: chicks 13/14 days old. A lad had flushed the female from the chicks just before I arrived at Churring occurred for a few seconds as I was approaching the hide. The young had begun to stretch their wings to the fullest extent on 24th June when 6/7 days old. I heard something leave the ground and alight again with a flutter only just audible, and saw first one and then the other chick fly up 3 to 4 feet like butterflies, and descend again sometimes to the spot from which they rose, at other times 2 to 4 feet away from it. Neither went outside the nestarea. The wing-beats were quick and the flight very rapid'. The male churred at f r ten minutes; soon afterwards he arrived and fed the chicks, who greeted him with loud churring cheeps as soon as they saw him; he left immediately but returned in a few minutes to feed again. The feeding was quick: the food seemed to be given from the mouth, the chick putting its beak to the male's gape. He flew and churred again for many minutes. He fed again just after the churring ceased, and returned very quickly to feed yet again. He then churred for a considerable period. A bird showing no white spots arrived, fed and flew; the same bird came back quickly and as the male was churring in the distance this was confirmed' as the female. The chicks cheeped loudly every time they saw an adult and if the visit was delayed but the adult was still in sight, the cheeping grew in intensity, the sound carrying to a considerable distance. The male fed next; he left and churred for 2 or 3 minutes. Deep silence fell, except for very, very faint cheeps every 2 or 3 minutes

4 264 BRITISH BIRDS [VOL. XLVIII from the chicks. Time I looked at the watch again at and about 2 or 3 minutes afterwards a bird arrived showing no white spots the female. There was the cheeping greeting; then the rhythmic sound (the "croodling") for what seemed 3 or 4 minutes. This sound seems to occur whilst food is given, but the darkness blacked out everything. Complete silence followed and continued till hours when the male began churring and continued with one or two short intervals of about 3 minutes till 04.00, The female left without my hearing or seeing her go (the normal flight is almost silent), but I knew she was gone by the vertical flights of the chicks as seen last evening. The female flew in with "quirk, quirk, quirk" very low notes at 03.00, fed one chick and left. After a time the male flew in and fed in one of his brief pauses in churring. The female fed every other time seven in all. The chicks were active in vertical flights during all the intervals. The female was away a long time before her final return and then fed first one and then the other chick, the rhythmical "yah, yah, yah" breathy sound all the time. Feeding ended at and the female settled to brood. The male churred for a few seconds at 04.12, then silence. I crept out without disturbing the female at and stayed in the vicinity till The behaviour this night suggested the possibility of a second nest: the absence of the female from near to midnight (unknown earlier), the long outbreak of churring after only brief outbursts for some days, seemed factors pointing to further breeding, but as events proved there was no second nest. Under the hornbeam the light was never good enough for me to see exactly how the feeding was carried out. On two occasions I saw the chick put its beak into the gape of the adult. The rhythmical sound never occurs unless the adult has been away for some time, seeming to imply that a considerable amount of food has been collected: it is then that the feeding seems to last for a long time, and only then that the "croodling" occurs. When the return of the adult is very quick the stay for feeding is a matter of seconds: as early as 5/6 days the chick runs with waving wings to the adult, which takes off again immediately, suggesting the food is given straight from the gape. Can it be that the Nightjar feeds direct from the bill on quick visits, and by regurgitation after longer absence? Or is the great gape, frequently shown when adults and young yawn during the day, capable of holding a large amount of food, the croodling note being uttered by the adult as the young take this food from the gape. Selous stated that when the chicks begged by putting their bills to the female's gape, she sometimes fed one. I saw begging, but no food was ever given till the female returned from flight. The first time a chick flew out of the nest-area was on 2nd July

5 VOL. XLVIII] NIGHTJARS AT THE NEST 265 at G. J. Lawrence was arranging his camera for a photograph of the chicks squatting, when a sudden incautious movement made one chick take wing, fly about ten yards and alight in the herbage. This was the first time a chick had left the nest site 14/15 days. I entered the hide at There was a high, cool north wind and a clear sky. Five minutes later, the chick that had flown out earlier, flew across the nest site, landing beyond it; this chick gave a high pitched squeaky "churr". The chick on the site began vertical flights up to 6 feet; the other chick flew in and both joined in the exercise, rising and descending, like huge butterflies, without pause, for several minutes, and then squatted together awaiting the adults. During the intervals between feeding, the flying exercise continued, the up-and-down flights being varied by swift circling of the nest site. 5th July: 17/18 days. For the first time the chicks were alone in the nest-site. From 6th to 12th July one, or both chicks were present each day, both being there on the 12th at age 24/25 days. 13th July: 25/26 days. In hide at One juvenile cheeped faintly from the site. At about a bird flew into the site; no excited cries greeted it this was the other juvenile. Flight activity followed; I think both birds took part but could not certainly determine this. The bird(s) went over and behind the hide, back into the nest-area and out again, one eventually settling just behind the hide where the herbage was trodden flat. Just before I heard the low, sharp "quick, quick" note of the male: he was greeted by loud churring cheeps; a juvenile flew to him as he alighted: he was gone in 2-3 seconds. He came again in about 4 minutes and churred after leaving for a few seconds. Next time he arrived the juvenile behind the hide greeted him and was fed the first time one had been fed outside the nest-site during observation time. Activity ceased at 04.15; one juvenile was on the site: it cheeped faintly for a time, then waddled to the place it occupied the previous day, rolled (see later) and preened, before becoming still. I left at th, 15th and 16th July. Both juveniles were in the nest site all day. On the 16th (28/29 days) I entered the hide at 21.05, both then squatting close together. One made the "rolling" movement and was then still again. At heads were raised and lowered, wings stretched to the full extent. One flew up and alighted again ; both made short flights and at they sat a little apart in the middle of the site; at ^ey uttered low cheeps ; at both flew out of the nest area but were in the near vicinity as both were cheeping for the next 5 minutes. At the male churred and from that time till I left at no bird came, nor did I hear any sound to indicate one was in the vicinity both had evidently gone with the adults to feed. 2nd August: 45/46 days. The keeper saw both juveniles on the

6 266 BRITISH BIRDS [VOL. XLVIII nest-site ; the female was 5 feet above them perched along a branch of the hornbeam and the male was flushed from a spot 50 to 60 yards away. 3rd September. The keeper saw one Nightjar on the branch of a tree near the nest site and another on the ground not far away at This was the last time Nightjars were seen. ROLLING Both the female and the young indulged in a rhythmic movement, which I have termed "rolling". The body "rolls" from side to side, first one way and then the other. On occasions I could see the feet move beneath the bird, showing that it was due to alternate pressure on each foot. The opinion I formed was that this was purely a relief-activity after long sitting; it did not introduce preening or other movements; often it was performed for a few seconds and then the bird was quite still again. PREDATORS One afternoon two Jays (Garrulus glandarius) flew into the hornbeam arriving with a harsh cry. The young had been moving about prior to their arrival, but instantly all froze into perfect immobility, the female closing her eyes, and remained like that till after the Jays departed, ten minutes later. FEEDING One could not see that food was actually given at each visit, but when the chicks were old enough their excited greeting showed clearly they expected to be fed. Some visits were so brief that the adult was gone again in a very few seconds, and others much more protracted, when the rhythmic note already mentioned occurred. This was not an interval note it proceeded steadily without break, to what I considered was the end of feeding. Could the bird "croodle" (Selous) whilst regurgitating, or was there one big regurgitation to the gape and then "croodling" as the young received the food in what manner I cannot say? Certainly the very quick visits seemed to deny regurgitation on those occasions. On 2nd July Keeper Steffan took up a position where he could look into the nest about 11.00; he could see the female and the two juveniles. At he saw the male fly into the nest-area carrying what he thought was either a butterfly or a moth in the beak, and alight. The chicks ran to him; the female flew up round the hide and settled in the other side of the nest area. She sat dust-bathing and preening. He could not see how the young obtained the food from the male. They were still in that position when he left an hour later.