BRITISH BIRDS NUMBER 2, VOL. XLVI, FEBRUARY, 1953.
THE BEHAVIOUR AND BREEDING BIOLOGY OF THE HEBRIDEAN WREN. BY EDWARD A. ARMSTRONG. THE Hebridean Wren (Troglodytes t. hebridensis) was described by Meinertzhagen (1924) and details of the plumage were published by Witherby (1928). As Meinertzhagen acknowledged, some of its distinctive characters had long been known. Peel in 1901 and Harvie-Brown in 1902 had remarked that Outer Hebridean wrens were darker than mainland birds. Harvie-Brown regarded them as intermediate in this respect between the wrens of St. Kilda and those of the mainland. He commented : " Here is an opportunity for some investigator who likes to make out ' new species ' to minutely describe and claim it ! " During a short visit to Lewis and Harris in June, 1951, I was able to make some observations on the behaviour of this bird. APPEARANCE AND GENERAL BEHAVIOUR. T. t. hebridensis I found to be less readily distinguishable from the European Wren (T. t. troglodytes) than the other races which I have had the opportunity to observe carefully in the field—islandi- cus, zetlandicus and hirtensis. The upper-parts appear darker than in T. t. troglodytes (Meinertzhagen, 1934), the breast rather more buff and the barring on the flanks somewhat more conspicuous. The tails of two or three seemed long relative to the size of the bird, but presumably this impression was due to some peculiarity in their attitudes as it is not borne out by skin measurements. The Hebridean Wren has not the robust, stocky appearance of the Shetland Wren. It is no less spry and lively than the European Wren and is constantly on the move here and there, poking into crannies in turf banks, piled boulders, heather tufts and so forth. Males (in June) fly up to rocks, walls, fence posts or twigs to sing a few phrases now and then, but females are much less conspicuous. Although Hebridean Wrens can scarcely be called shy they are wary and less tolerant than Shetland Wrens of the presence of human beings whether at the nest or away from it. None the less they will usually approach the nest when an unconcealed observer is only ten or fifteen feet away and grow bolder as they become accustomed to the intruder. Best, Turner and Haviland (1914) exaggerate their timidity, remarking that they found them " much shyer than the mainland wren." Beveridge (1918) is even more emphatic, calling it " the shyest of creatures." At the nest females are apt to be bolder than males, due probably to the greater strength of the parental drive. However, I tried to photograph a female at 38 BRITISH BIRDS. [VOL. XLVI. the nest without a hide as I had succeeded in doing with a Shetland Wren, but failed. When alarmed away from the nest the birds squat and hide in low undergrowth and along the courses of streams, as described later.
DISTRIBUTION AND HABITAT. The Hebridean Wren is commoner than a casual observer might suppose and is widely distributed, being found on suitable islets, such as some of those in the Sound of Harris, as well as on the principal islands. In 1884 MacRuray described it as an abundant and permanent resident. It is not known whether the population shows considerable fluctuations like the Shetland, St. Kilda and Fair Isle Wren populations (Armstrong, 1953 ; Williamson, 1951b) but probably the Hebridean Wren is no less vulnerable than other races to severe winter conditions. We noticed it on the coast below low cliffs, on rough heather-clad hills and boulder-strewn screes, among peat hags, along burns, by roadside cottages and in woods. There were wrens at regular intervals along the bare hill-side in Rodel Glen but not on the other side of the glen across the road in the stretch of sparse, weather-beaten trees. However, Dr. Campbell tells me that he saw a family there in July, 1938, and several wrens among the trees in May, 1939. We found two nests on the out skirts of woods, one in Harris at Horgabost and another in Lewis in the Castle grounds at Stornoway. Both were built under turf banks although there were other eligible sites available among neighbouring trees and bushes. The Stornoway nest was in an area where the bird had a choice of sites in dilapidated stone build ings as well as in trees only a few yards away. In such a habitat a European Wren would hardly have built in the cavity of the bank chosen by this bird. Mr. James Matheson tells me that on July 5th he found another nest in the Castle grounds situated in the river bank. Apparently T. t. hebridensis has adapted itself to an open environment to such an extent that its normal choice of nesting- place differs from that of T. t. troglodytes. Dr. Campbell, who considers it typically a bird of the heather, recalls that he has never found a nest in ruins or dilapidated buildings. Such sites are chosen by the Iceland, Shetland, St. Kilda and European races (Armstrong, 1950a, 1952, 1953, in.press). Hebridean Wrens feed along stone dykes in areas in S. Uist and elsewhere and favour scrub-covered islets in lochs, though they are by no means confined to these (G. K. Yeates, in litt: J. W. Campbell, in litt.). They show a preference for the neighbourhood of water, such as streams, however small, and marshy ground where food is more plentiful than in dryer areas. Many territories are situated along the coast. The Hebridean Song Thrush (Turdus ericetorum hebridensis) and the Wren are often found together. In the "forest" of North Harris a Wren was noted singing at a height of approxi mately 500 feet on a steep scree and a Thrush at about 600 feet. VOL. XLVI] BEHAVIOUR OF THE HEBRIDEAN WREN. 39
The Hebridean Wren has accommodated itself to open environments better than the European Wren and approximately as well as the Shetland Wren, but does not breed in areas of sparse vegetation such as the traigh nor in areas of low homogeneous vegetation, such as SaV^MS-covered " flow" country (Campbell, 1938). It is at home on cliffs, like the Fsroe Wren T. t. borealis and the sub species of St. Kilda and Shetland. On Mingulay, for example, " any deep indentation in the line of the cliffs holds a singing Wren " (Sergeant and Whidborne, 1951). The European Wren is plentiful in Sutherlandshire on some precipitous parts of the coast (Pennie, 1951) and is found " in the very wildest places on the hill... all along the burn-sides up to their sources, even in winter " (Buckley ; 1881). Thus local populations of this race may achieve some adaptations approximating to those of the North Atlantic insular races. TERRITORY. Hebridean Wrens' territories are relatively large and comparable in size with those of the Iceland and Shetland Wrens (Armstrong, 1950a, 1952). Two males divided a wood of 32 acres between them —though it is not certain that they patrolled the whole of it. Elsewhere, on a heather-clad hill a bird sang from a number of places suggesting a territory of about 12 acres. In Rodel Glen the males along the hill-side were at distances of about 250 yards— approximating to the distance commonly separating Shetland and St. Kilda Wrens on cliffs (Harrisson and Buchan, 1934). As the birds were restricted by each others' territories only along the glen it was impossible to estimate how far they ranged in the undefended areas at right-angles. Probably, as with other races, the area patrolled may vary within wide limits. SONG AND CALLS. The Hebridean Wren's most distinctive characteristic is its song, To my ear the phrase differs more from that of the European Wren than that of other British races, T. t. islandicus, T. t. koenigi of Corsica or, possibly, T. t. kabylorum. Its most remarkable feature is a high-pitched, sibilant and slightly metallic trill. Occasionally there are two prominent trills and when a second trill occurs towards the end of the phrase it seems about an octave higher than the final notes. The preliminary notes of the song reminded me of the beginning of the song of the Willow Warbler (Phylloscopus trochilus) and the trill was reminiscent of the utterance of the Grasshopper Warbler (Locustella ncevia). The preliminary notes leap up and down in an animated way and the song impressed Dr. Westall and myself as being more interesting musically than that of the European Wren. Duncan (1929) speaks of the Hebridean Wren's song as " more of a ripple and less disjointed than that of the main land Wren." This appears to be a reference to the fluent, rather twittering, warble which constitutes much of the phrase. We 40 BRITISH BIRDS. [VOL. XLVI.
heard T. t. hirtensis, hebridensis and troglodytes (in Scotland and England) on successive days and were impressed by the musical dullness of the songs of hirtensis and troglodytes compared with hebridensis. The latter's phrase seems higher pitched than that of troglodytes and heard in woodland it has a reedy timbre. The song of the European Wren sounds more repetitive and shrill than that of either of the other races. The duration of the phrase is commonly about four seconds but phrases with the double trill may last 5-6 seconds. As with the songs of other Wrens there is variability in duration, especially when a bird is not singing a constant series of territorial songs. If he is interested in a female very short subdued phrases of hardly more than a note or two may be heard or, on the other hand, exceptionally long phrases. The volume also varies greatly but the normal utterance seems softer than that of T. t. troglodytes. The description by Best, Turner and Haviland (1914) of the song as " particularly loud and sustained" does not accord with our observations. As Stornoway woods provide a setting similar to that in which the European Wren is commonly heard we were able to form opinions uninfluenced by the effect of rocks and open spaces in amplifying sound. In regular territorial song there are 4-5 songs per minute, but once I heard double that number during half a minute. None of the birds kept up the sustained reiteration of phrases characteristic of European Wrens in good song, especially in the early morning, which they were still uttering in England in late June. In the Hebrides the spring had been exceptionally late, as in England, but, in contrast, had been very dry. Probably more regular song was uttered shortly after dawn by the Hebridean birds but we were unable to make notes before 08.30 G.M.T. The follow ing series of pauses between songs is typical:
TABLE I. HEBRIDEAN WREN. PAUSES (IN SECONDS) BETWEEN SONGS. 8/6/51. 11.53 G.M.T. 6, 13, 14, 3, 12, 12, 5, 42, 32, 11, 14, 6, 9, 6, 7, 9, 8, 7, 13, 8, 7. This Wren had young in the nest which he fed occasionally but he was stimulated to sing every now and then by the songs of two neighbouring birds. Undoubtedly reduction in song output tends to occur when the male is feeding nestlings. Another male, more active at the nest, was never heard to sing during \\ hours watching, apart from occasional subdued warbling when the female was near. The rather greater prominence of song in the life of the European Wren is correlated with its polygamous tendencies. The songs of a Wren tend to arouse his neighbours and counter- singing occurs similar to that of T. t. troglodytes (Armstrong, 1944). Hebridean and St. Kilda Wrens apparently sing in flight more frequently than European Wrens. Song in flight is particularly characteristic of unmated birds and is rare among Wrens feeding VOL. XLVI] BEHAVIOUR OF THE HEBRIDEAN WREN. 41 young in the nest. I would suggest that the term " flight-song " be used of song uttered on the wing expressive of unusual stimulation or excitement, but not associated with specific display movements, as when a Song Thrush (Turdus ericetorum) sings in flight, but "song- flight " should be confined to a form of territorial or epigamic display and utterance. Song-flight is most typical of birds of open habitats. The first state towards acquiring this form of display would be an accentuation of flight-song. Perhaps the flight-song of the Hebridean Wren is tending to become song-flight. Courtship song uttered when the male is close to the female is delightfully soft and sweet but, as already mentioned, may vary greatly in duration and volume. According to Campbell (1938) winter song is frequent, suggesting that territory may be retained in winter. The Hebridean Wren is less prone to utter call-notes than T. t. troglodytes and in this resembles T. t. zetlandicus. Kearton (1897) commented on the few calls heard from St. Kilda Wrens and although other observers mention calling similar to that of the European Wren it seems that, on the whole, the St. Kilda Wren is less vocal. The silence of Hebridean Wrens interrupted while feeding nestlings was remarkable. In general the notes we heard were not markedly distinct from those of the European Wren. Double or multiple ticking notes resembling the noise made when two small stones are rapidly knocked together are uttered by the male, especially when accompanying fledged young. If, as is possible, the female utters such notes it is only rarely. The female with fledged young utters a "chitter " alarm and the young also give a slightly higher-pitched version when uneasy. This call is first heard from young European Wrens when they leave the nest. Indeed they utter it as they fly out if disturbed prematurely. It is also uttered by young Shetland Wrens and I have heard what seemed to be an incipient version of it while they were in the nest. I never heard it uttered by four young European Wrens reared from the nestling stage and kept for two months at the Cambridge Ornithological Field Station, even when being caught for experiments or presented with a stuffed Tawny Owl (Strix aluco) or a fur " model" to represent a cat. Both in the nest and out of it young Hebridean Wrens, like the young of other races, utter high-pitched squeaks which serve to attract the food-bearing parent to the chicks and also enable the members of the party to keep together. The ground-predator alarm call of Hebridean Wrens is mentioned later.
DISPLAY. Nest-invitation. About 14.30 G.M.T. a male was heard singing in Stornoway woods. From time to time he perched with tail cocked, singing and looking intently downwards, alert for the appearance of the female who was in the dense undergrowth. Sometimes he 42 BRITISH BIRDS. [VOL. XLVI. sang a short, excited snatch and once he sang in flight. He worked down the hill from perch to perch in the trees during the next quarter of an hour and then, after a loud, complete phrase followed by a brief snatch, flew about fifteen yards to the nest, which was under an overhanging turf bank by an old mill. He stayed ij minutes inside and sang shortly after flying out. This was obviously a rather perfunctory and abbreviated version of the nest-invitation display as the female did not put in an appearance near the nest. The performance suggested that the full procedure may be more similar to the nest-invitation display of the Shetland Wren than that of the European Wren (Armstrong, 1944, 1952). In view of the frequency of the flight-song by the male Hebridean Wren it would seem that in this context it is stimulated by the female's presence and has the function of attracting attention to the location of the nest. The distinction between such behaviour and true song-flight is slight. The direct flight with song to the nest, rather than the approach from twig to twig with quivering wings characteristic of T. t. troglodytes, is an adaptation to the usual open habitat of the Hebridean Wren as distinct from wooded surroundings. Thus it seems that the nest-invitation display characteristic of the European Wren may have become modified and adapted to open habitats. Epigamic display. Pre-nuptial display, apart from the procedure just described, was not observed, but near one of the nests at which the nestlings were fed by the male he displayed occasionally in a manner which suggested that the pre-nuptial display is, in the main, similar to that of T. t. troglodytes and the other races whose display has been described (Armstrong, 1950a, in press). The most complete display occurred while I was photographing the nest. One of the birds had been uttering alarm notes, then the male perched on a post, singing a subdued, brief strophe, quivering his half-opened wings above the female who was perched lower on the fence about eighteen inches away. In acknowledgment she drooped her wings slightly. Possibly this display and related displays by birds of other races elicited by the presence of an observer at the nest should be regarded as displacement-display (Armstrong, 1950b). This bird on two previous visits, when the female was absent, raised and gently waved his half-open wings a few times. His display was apparently a displacement-activity due to seeing me, but on a subsequent visit he perched with half-open, quivering wings, uttering three or four low, sweet notes just after the female had flown from the nest. On the next occasion his mate appeared as he left and he emitted a few twittery, subdued notes in flight. Thus it seemed that the excitement caused by an intruder near the nest accentuated the tendency to epigamic display, the threshold of which was already low. In comparable situations involving alarm or excitement birds of many species will sing (Armstrong 1947). Display in general, whether vocal utterance or visual posturing, appears to be, to a great extent, the outcome of conflicting VOL. XLVI] BEHAVIOUR OF THE HEBRIDEAN WREN. 43
drives and such incidents illustrate its probable origin as a by product of the clash of incompatible impulses, which, in the course of evolution, has attained adaptive value by acquiring ritualized signal functions. Aposematic display. When I placed a mounted Wren in a posture somewhat resembling that of a female soliciting coition eighteen inches from the nest the male hopped around it at a distance of a few inches with partly spread wings and fanned tail—an attitude which probably expressed suspicion and threat. The female's reaction was a milder form of the same posturing. She hopped about for a minute, crouching while eyeing the mount closely. On her second visit she nipped her wings rapidly out and in. This reaction seems to be a generalized excitement reaction.
NEST-SITE AND NEST. The three nests which we found were under turf banks. Two of them were so situated that the entrance faced outwards, but the third, in Stornoway woods, was in precisely the type of situation typical of many Shetland Wren nests, apart from being among trees. The nest was built in a cavity of the overhanging turf facing the bank so that it was extremely well hidden. All three nests were within a few yards of streams. According to Campbell nests are often found in crevices among rocks as well as in long heather, gorse and ferns. A newly-fledged family frequented a dilapidated thatched building and stone walls near a croft, but the nest was not discovered. Although Hebridean Wrens breed near crofts they apparently find such places congenial on account of the insect food available in the long herbage rather than because of finding suitable nesting-sites in buildings. The three nests examined were in recesses so that the bird did not have to shape a complete dome but had packed material into the cavity. Nests in heather may be fully fashioned. The entrance to one nest was large—two inches across. This nest was constructed mainly of withered grass ; brown pine needles were used as rein forcement for the threshold. The other two were almost entirely of withered grass and the Stornoway nest had a small, neat aperture which was, like the entrance to the nest just mentioned, oval rather than circular. The nests were neater than the St. Kilda Wren's nests I have seen. Their appearance suggested that they had been built with damp material. To what extent multiple nest-building occurs is not known, but the absence of records of " cock's nests " and the tendency for the male to feed the young, which would reduce the time and energy available for nest-building, suggest that the male builds fewer nests than the male T.t. troglodytes (Kluijver el al., 1940), hiemalis (Bent, 1948) or pacificus (Bowles, 1899) and approximates in this respect to the behaviour of zetlandicus and hirtensis. The only observation 44 BRITISH BIRDS. [VOL. XLVI. consistent with the building of more than one nest by the Hebridean Wren concerns the nest in Stornoway woods. Although, as already described, the male was seen enticing a female to it in mid-June it was never occupied. The male may have had another nest available. LINING. The lining, which is placed in the nest by the female, is mainly of feathers, mostly white and grey, these being most readily avail able. A feather about z\ inches long, probably from a Heron {Ardea cinerea), protruded partly across a nest entrance while a female brooded the chicks. As she departed she seized it and carried it away. Female European and Shetland Wrens will bring lining material to the nest when the eggs are well incubated and European Wrens may even bring material when the young are nearly fledged, but this bird's behaviour shows that at this stage a feather may have merely nuisance value. A female Southern House-Wren (Troglodytes musculus) in Surinam has been seen removing feathers from an old nest in order to lay in it (Haver- schmidt, 1952). Males of various races remove feathers from near the nest (Armstrong, 1952).
EGGS. The eggs are dull white, lightly spotted with brownish red, mainly at the large end. In the two nests containing young there were respectively five and six. Mr. James Matheson, head keeper of the Stornoway Castle grounds, tells me of clutches of ten and seven eggs respectively which he found on June 25th and July 5th, 1951. Such clutches are probably exceptionally large. It is some times difficult to ascertain the number of eggs in a nest exactly. I regret that I was unable to check these counts personally.
INCUBATION AND BEEEDING SEASON. The female incubates, but the period has not been determined. Incomplete data for one nest indicate not less than fourteen days. On June 6th we found a brood which had probably left the nest a day or two earlier ; on June 7th a nest (at Horgabost) with young about five days old and on June 9th another with nestlings which seemed a day younger. On June 14th the male mentioned above was seen inviting a female to an unlined nest. Another nest in Stornoway woods contained a full clutch on July 5th. It was deserted later. In yet another nest there hatching took place on or about July 9th. These observations suggest that, as is apparently true of Shetland and St. Kilda Wrens, the Hebridean Wren may " spread " its nesting. Mr. Seton Gordon tells me that his observa tions are consistent with this. Unfortunately to what extent this holds cannot be known until it is ascertained how frequently second broods occur. It is doubtful whether they are as regular as among European Wrens. VOL. XLVI.] BEHAVIOUR OF THE HEBRIDEAN WREN. 45
NESTLING PERIOD. The newly-hatched nestlings found by Mr. Matheson in the nest on July 9th were still there, but on the point of leaving on July 29th. There is some evidence that the nestling periods of some of the northern insular races may be rather longer than the nestling period of the European Wren (Heath, 1920; Armstrong, 1952) but data on which to base a definite opinion are lacking. If such be found to be the case it might be correlated with less predation pressure and greater difficulty in obtaining sufficient food for the young. The male helped his mate to feed the chicks at both nests at which observations were made but was less bold and assiduous. The tempo of feeding during observation periods at the two nests is shown in Table II.
TABLE II. TEMPO OF VISITS TO HEBRIDEAN WREN NESTLINGS WITH FOOD AND FREQUENCY OF REMOVAL OF FAECES. Time of Number of Number of Site Date count Number of visits with times fwces [G.M.T.) nestlings food removed HORGABOST . • 7/6/51 12.47-13.47 5 12 (
The Scarista Wrens never went upstream where rough ground soon merged into moorland. They searched for food mainly in a weedy garden enclosure 20 yards away and downstream in a pasture some 60 yards off across the road. Once I saw the female foraging under the wall by the roadside. I noticed the female at the other nest securing prey some 60-70 yards from the nest on a marshy patch but she sometimes went in the opposite direction. These distances should not be assumed to indicate the maximum foraging range. On two occasions a bird, after leaving the nest, noticed an insect a few feet away and took it to the nestlings. The female which I watched hunting for prey in marshy ground 60 yards distant from the nest poked here and there under tussocks and in crannies, securing two insects in two minutes. At the Horgabost nest I noted the Wrens bringing the following items of prey—a damsel fly, daddy-long-legs, various unidentified insects, apparently Diptera or Hymenoptera, three brown cater pillars and three or four brown, buff, or brown and buff moths. During two hours and eighteen minutes the Scarista wrens brought altogether four moths, twelve daddy-long-legs (Tipulids), twenty-six winged insects about half-an-inch in length and one spider. There may be a slight margin of error so far as the winged insects are con cerned. I have never known so much large prey brought to a European Wren's nest but the diet of Shetland Wren nestlings is rather similar (Armstrong and Thorpe, 1952). All the moths were cryptically coloured. Carrick (1936), however, showed that Euro pean Wrens capture non-cryptic animals more readily than cryptic. Different types of organism may be brought in one beak-load, e.g., a caterpillar and a winged insect. Once a male came with two daddy-long-legs. After delivering them he noticed a large brownish moth about 20 feet from the nest. He pecked at it several times, mauled it on the ground, pecked it again repeatedly and then took it to the young. At the other nest the female brought a large moth of varied shades of brown. She tried five or six times to induce the chicks to take it and then flew to the ground and savaged it, appar ently breaking off the wings or the greater part of them. The chick to which it was then offered accepted and swallowed it. Another similar incident was noted. I have never observed such treatment of prey by European Wrens, though when the young are out of the nest large caterpillars are sometimes macerated by being flogged against a branch. There was no attempt to trim the legs or wings off daddy-long-legs. Once a Wren brought a load consisting of some flies held in its bill and a daddy-long-legs dangling, held only by the ends of a couple of legs. While the female was brooding the young the male brought food twice in ten minutes. On another occasion he would have done so had he not caught sight of me near the nest. Such behaviour would be exceptional at the nest of a European Wren. VOL. XLVI] BEHAVIOUR OF THE HEBRIDEAN WREN. 47
The young Wrens in one of the nests could be heard calling at a distance of 40 yards—about the distance at which European Wren chicks can be heard in favourable conditions. They begged and cheeped as I was extracting them from the nest. Pin feathers were sprouting on the wings and there was a tuft of down on their heads, but otherwise they were almost naked. At the other nest at Scarista one bird uttered a tiny squeak and a kind of chirrup as I was lifting out the fifth nestling. These youngsters were clothed a little on the crown and along the back and had sprouting wing feathers. When at the nest holding food a Wren sometimes uttered a very quiet but rather harsh, high-pitched note, usually quickly repeated twice or several times. This was evidently a signal for the young to receive food but occasionally it was uttered after feeding as if to stimulate defecation. Attentive observation was necessary to make sure that these squeaky calls were uttered by the parent and not by the chicks. Somewhat similar notes, as well as a sibilant whisper-song, are uttered by female European Wrens at the nest, and occasionally by males during territorial altercations. Males may utter such notes at the nest, but I have no definite record of one doing so. A female removing faeces occasionally wiped off the sac on a twig. THE FLEDGED YOUNG. The newly fledged young are adept at creeping about among crevices and through interstices in old walls. From the way in which a family keeps in touch towards evening it seems likely that the young roost together.
PREDATOR REACTIONS. The Hebridean Wren, when frightened, commonly seeks refuge in a small gully among the peat hags, tiny runnels, streamlets overhung with heather and other such places, squats there and ultimately hops and creeps through whatever cover there is and appears some yards away. Probably it was due to having noticed this that Beveridge (1918) referred to " this bird's retiring nature and its habit of taking cover at a moment's notice." A Wren chased from its squatting place will flit low over the ground, drop down a few yards off and squat again. It will repeat the ruse several times if the terrain is suitable, as, for example, where a trickle of water flows down rough pasture. This procedure is characteristic of males and females alike and, so far as I am aware, has not been noted in any other race of T. troglodytes, although, of course, indi viduals of all subspecies are apt to retire to any available cover when alarmed. It is an ecological adaptation appropriate to a particular kind-of habitat and would seem to be correlated with alarm caused by a large potential ground predator or intruder 48 BRITISH BIRDS. [VOL. XLVI. rather than a small mammal or bird of prey, though there is no evidence that the Hebridean Wren was ever persecuted by man or any other large mammal. Experiments with a dark brown fur tippet to represent a ground predator were somewhat inconclusive, as such experiments are apt to be. At one nest the female hopped around for a few minutes in an excited and suspicious way. At the other the female reacted by uttering regular kreeee calls—very like those uttered by both sexes of the European Wren when a furred predator is near. She continued to call in this way for a short time after I removed the mount and while I was photographing the nest. In similar experiments Shetland Wrens did not utter the kreeee note (L. S. V. Venables, in litt.).
PAIR BOND. The information available suggests that Hebridean Wrens, unlike European Wrens, are usually monogamous. Both parents com monly feed the nestlings. There is a correlation between polygamy in Wrens and habitats in which food is readily available. The races inhabiting relatively bleak areas tend to be monogamous but where T. t. troglodytes is resident in garden-woodland areas it tends to be polygamous. The observations of the tempo of feeding young and the types of food brought to the nests of Hebridean Wrens support this view. Elsewhere I hope to discuss the evidence that availability of food has an important bearing on the share taken by male birds in incubating and tending the young.
DISPERSAL. Probably there is a post-breeding spread-out similar to that noted in other races of the Wren. In autumn and winter Hebridean Wrens may be found frequenting boulder-strewn parts of the shore, culverts and other sheltered spots (Clyne, 1915). A considerable number of reports, mainly in the Scottish Naturalist from the Flannans, Monach and Barra Head show that Wrens are reported in autumn, winter and early spring in isolated places where they do not breed. No critical examination of such birds has been conducted to determine to which race they belong. Thus it is not known to what extent Hebridean Wrens ever make long journeys but the evidence for other races suggests that on islands Wren populations tend to be sedentary. The distinctiveness of the Hebridean Wren's song is alone sufficient to prove that the race cannot be much diluted by immigrants from the mainland. Williamson (1951a) has shown that the Wrens of Fair Isle have distinctive morphological features although separated by only 25 miles from the Shetland stock. He cites as evidence of the import ance of water as a barrier between insular wrens the alleged inability of T. t. alascensis of the Pribilof Islands to cross the 27 miles between St. George Island, where it is known to breed annually, and St. Paul Island (Bent, 1948). This example lacks cogency, as Dr. Karl VOL. XLVI.] BEHAVIOUR OF THE HEBRIDEAN WREN. 49
Kenyon (in litt.) informs me that he often finds a few Wrens on St. Paul—sometimes about a dozen—and it may well be that the more severe climate of St. Paul is less favourable to breeding ; yet there is, in general, good evidence that insular races of the Wren are mainly sedentary.
SUMMARY. I. The behaviour and breeding biology of the Hebridean Wren are described from observations made in the field during June, 1951. 2. The song of this race is distinctive and some of its intruder- reactions apparently differ from those recorded of other subspecies. 3. In the nature of the pair-bond, nest-site selection and, possibly, the nest-invitation display, behaviour resembles the be haviour of the Shetland Wren rather than that of the European Wren. 4. The Hebridean Wren tends to approximate ethologically to an insular northern type rather than the "continental " type of the European Wren and Winter Wren (T. t. hiemalis and pacificus).
ACKNOWLEDGMENTS. The writer is indebted to the Committee of the Leverhulme Research Fellowships for the Research Grant which enabled him to meet part of the expense of the journey to the Outer Hebrides and is very grateful to Dr. Peter Westall for his valuable assistance in the field. We are both much indebted to Mr. and Mrs. L. Lomas for their kind hospitality in Harris and to Mr. J. Cullen and Mr. J. M. Cook for facilitating our travels. Mr. James Matheson sent useful information and Dr. James Campbell kindly criticised this paper and supplied several references.
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