Phil Palmer
The January speaker was Phil Palmer, who has a lifetime of ornithological experience, which includes being a leader of birdwatching tours, and writing the acclaimed First for Britain and Ireland. He has been watching Nightjars in Nottinghamshire since childhood, and in the 1990's was involved with a radio-tracking project in the Sherwood Forest area and on the Thorne and Hatfield moors. Hatfield is easier than Thorne for nocturnal bird-watching as there is less water and bog to fall into in the dark, and the limited vegetation makes the birds easier to see.
The Nightjar we see in Britain is actually the "European Nightjar" and is one of about 80 species of Nightjar and Nighthawk that are distributed worldwide. All species are of a similar size. They are well camouflaged, but males often have white spots which are visible when they display - and are necessary for species that live their lives in darkness. Although very similar in appearance, the species are differentiated from each other by particular features such as elongated feathers, variation in calls, etc. Nighthawks differ from Nightjars in that they are not quite so strictly nocturnal.
Most bird species have two requirements for breeding: a safe nesting site and a supply of food. For Nightjars, the nest is a scrape on the ground, and the ideal is a slightly raised area on sandy soil; they do not like cold damp boggy ground. In Sherwood Forest, the preferred nest site is in bracken, with heather second choice. For food, they need access to deciduous trees such as oak, willow or lime where they can find ample supplies of nocturnal flying insects, particularly moths, in and around the upper canopy on still nights; conifers do not support the same level of insect life.
Budby Common formerly supported up to eight pairs of Nightjar, but the introduction of sheep caused loss of eggs and chicks through trampling. The birds have now moved into the surrounding conifer forest (clear fell in conifers plantations offer good nesting habitat) and fly back to Budby Common for food. There now seems to be a move to introduce some cattle, and these should pose less of a threat to ground nesting birds than sheep do.
At Hatfield there are vast open areas where peat has been extracted, but this has now mercifully stopped. In the midst of the devastation is a small area of the original moorland, where the (heroic) owner refused to sell to the peat companies. This area was doubtless appreciated by many bird species, but was not used for nesting by many Nightjars until clearings were created artificially. Also, for reasons that are not understood, they will not cross extensive open spaces to get to food. However, there is a band of birch trees surrounding the peat extraction area, and the Nightjars fly along these corridors and nest close to these. Thanks to the peat companies, Hatfield moor offers far from ideal nesting sites for Nightjars, but unfortunately they always return to the same area to breed, and will endure a second-rate location rather than move six or seven miles to a better one.
At Thorne and Hatfield, efforts are being made to introduce sphagnum moss in order to regenerate the peat, and other vegetation is gradually recovering. This has encouraged other bird species such as Black-headed Gull to move into areas which were previously the preserve of Nightjars, so the Nightjars are breeding in amongst the newcomers.
Fortunately, both Thorne and Hatfield moors have an abundance of insect life, so there is no shortage of food. Nightjars feed from just after sunset until about midnight, but this is ample time for them to get all the food they need. The preferred method of hunting is to operate like a flycatcher from a perch, but they will also fly around with their mouths wide open, trawling for insects. Bristles around the mouth help prevent the catch from escaping.
It has been estimated that on Hatfield moor, up to 80% of first nesting attempts are predated. Fortunately, Nightjars generally lay two clutches and, because the vegetation is now higher, the second is more successful with up to 80% surviving. The main predator is the fox, but there are also a lot of adders on these moors, and they will predate young Nightjars. In Sherwood, crows pose a considerable threat and dog walkers have caused losses too.
The normal plumage of a male Nightjar is to have three white spots on each wing, and white tips to the outer tail feathers. However, some birds have only two wing-spots, and one individual had four (he also had more than average amount of white on his tail, plus white under-tail coverts, and appeared to attract a lot of females). Even amongst the two-spotters, there is much variation in the shape and size of the spots, and in fact no two birds are the same. Females are split about 50/50 into those with no white at all on them, and those which have creamy coffee-coloured wing spots that can appear whitish. It is virtually impossible to tell the age of a Nightjar, even when held in the hand for ringing, despite what the ringing books say. Some first-year birds do retain some juvenile markings after their first moult, but many do not.
Another feature of the Nightjar anatomy is the smallness of the feet and legs, doubtless linked to the fact that they do not walk about much, nor do they use their feet for catching insects. Photographs of roosting Nightjars often show them with half-closed eyes. Although they normally have their eyes wide open, they will half-close their eyes to a slit if danger approaches as a wide-open beady eye can attract the notice of a predator.
In some areas of Hatfield moor, the birch trees are too dense for Nightjars to breed, but clearings have been created, the clearings have been colonised by heather, and these are much used by the Nightjars. It was in one clearing at Sherwood that Phil erected his hide for the radio-tracking project, so he could watch the nightly activities of his pair of Nightjars. During the course of the project he also saw, and in some cases ringed, Long-eared Owls (yet another predator of Nightjar chicks), Nightingales and Woodcocks.
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The key to the Life of a Nightjar is the male's roosting place which in the south of England is reportedly in a tree, but in the study area was normally on the ground (although a bird may sometimes turn up in unlikely places such as garden sheds, washing lines, fence posts, etc.). When the male returns from Africa in spring, he returns to the roosting place he used at the end of the previous season, and awaits the return of the female. Provided this site is not disturbed (i.e. not a washing line ...) it will be used as the first nest site. Whilst the female is incubating the first clutch of eggs, the male will roost in the vicinity, and again, provided there is no disturbance, this will be used as the second nest site. As before, the male will roost in the vicinity, and it is this site that he will return to the following spring. The crucial feature of a roost site is that there must be no disturbance: he will stay put throughout torrential rain, thunderstorms, etc., but as soon as danger threatens, he will abandon that site and find a new one. The roost site thus acts as a test bed for the nest site.
Normally Nightjars lay two eggs on consecutive days, and start incubating after the first, so one chick is a day older than the other. The eggs are white, as is typical of nocturnal species, but with brown markings to give a little camouflage. There is considerable variation of patterning of eggs. But each female retains the same patterning throughout her life.
Once the eggs are laid, Nightjars do not do much during the daytime; they may shuffle around a bit, or sunbathe, but the female does not leave the nest scrape. If an intruder approaches an incubating female, she will fake a broken wing, in order to draw the predator away from the nest. If grabbed, she will open her massive gape and hiss like a snake.
Throughout the nesting period, the male leaves his roosting place at dusk, flies to the nest site, and calls to the female. She then flies up to meet him briefly before going off for about 50 minutes to feed, before returning to continue incubation. The eggs are usually left alone whilst she is away, although the male may occasionally incubate them. The first egg hatches after 18 days, and the incubating female sits with slightly raised tail so that the chicks get a little air. This behaviour is very useful to the observer, who wishes to know hatching dates, but does not wish to flush the sitting bird. As soon as the first egg hatches, the chick will tug feverishly at the female's beak, to prompt her to regurgitate an insect mush. She will ram as much of this as she can down the throat of the chick and, when the chick is full and can take no more, she will re-swallow the rest, and try again after about 40 minutes. Initially the female will brood the chicks, and the male brings in the food, but when they are about 7-8 days old, both adults will hunt for food. There is keen competition between the chicks when an adult arrives with food, but in fact there is always enough to go round, and it is extremely rare for one chick to survive, and one to die through lack of food. Food is mostly moths, but remains of ants and beetles have been found in dissected corpses of adults. Surprisingly, Phil has witnessed a beetle making its way across a nest scrape, over the body of the sitting bird, and out of sight, all without interference; this suggests the bird did not recognise it as food, and they feed only on flying insects.
When the chicks are left unattended, they will keep absolutely still (except when the food arrives). If a predator threatens, they will not move until the last possible minute, when they will suddenly stretch up as tall as they can, with mouth agape, and will finally jump up at the intruder, hissing like a snake. Although this behaviour would probably not deter a fox or stoat, it might serve to ward off a less dangerous foe, or prevent accidental trampling.
Weather is of crucial importance before the chicks get their adult plumage at about 14 days, and a heavy rainstorm at the wrong time will wipe out the entire chick population in that area. It is imperative that the chicks are not disturbed when they are at the vulnerable stage, so ringing must be done when they are 9 days old.
The radio transmitters were fitted to adults only, and were attached to the central tail feather using superglue. Extreme care was taken with this operation, as a spot of glue in the wrong place could be fatal. The transmitters are very light in weight, the battery (a watch battery) being the heaviest part of it. The whole thing weighs about one gram, which as a percentage of a 70 gm bird is not likely to affect it. When the bird has its first moult, the transmitter is lost with the feather, so the whereabouts of the bird is no longer traceable.
The chicks fledge at about 18-19 days, by which time they are roughly the same size and shape as the adults, and initially stay within a few hundred yards of the nest site, and are still fed by the adults. Phil found one fledged chick that had fallen into a ditch and worn away part of all its primary feathers in an effort to scramble out. He returned it to the nest scrape where it was fed by the adults, and new feathers had grown after about 10 days. A moth diet is a very nutritious one.
No one yet knows exactly when the young are left to fend for themselves - and of course, they will have to undertake their migration to Africa. Adults whose nest has failed too late in the season for them to re-lay, may leave at the end of July, but normal departure times for adults and young is mid to late August with late breeders staying to early September. There have been birds recorded on the coast as late as October, but these are likely to be from the continent.
Phil was thanked for his most stimulating and entertaining talk. We always enjoy talks by people who have been actively involved with research, and Phil's breadth of knowledge, passion for his subject matter, wonderful photographs, and humour had given us a very memorable evening.
Wendy Thomson |
