NOTES ON THE WREN IN THE ARAN ISLANDS, IRELAND

NOTES ON THE WREN IN THE ARAN ISLANDS, IRELAND By EDWARD A. ARMSTRONG WHAT MAY be described as the integrative pattern of the breedingbehaviour of the Wren (Troglodytes troglodytes) varies in different types of environment (Armstrong, 1950-57). Differences in behaviour patterns are so integrated in this species, and no doubt continued... 29

30 BRITISH BIRDS [VOL. LI in others, that variation in one tends to be associated with correlated variations in others. In theory, if a given population of an organism evolved a sufficiently distinctive group of behavioural adaptations, related to the environment and all correlated with one another in a biologically advantageous way, a barrier would be established to the inter-breeding of this population with other related populations, and divergence towards the formation of a separate species would occur. The Wren is an outstanding example of a species able to vary a group of such adaptations according to the environment. Its adaptability lies, not merely in the extent to which a number of behaviour-patterns may be modified to suit circumstances, but in the nicety with which these adaptations are related to, and integrated with, each other. Wren adaptations vary according to the degree to which the habitat may be classified, for our purpose, as "bleak" or "fertile". The distinction is essentially ecological rather than geographical, but in geographical terms the extreme types may be roughly divided into "northern insular" and "mainland" or "continental". The St. Kilda Wren (T. t. hirtensis) represents one extreme, the Wren in average garden-woodland areas in England and on the Continent the other. The adaptations of the latter include a strong tendency to be polygamous, the building of a considerable number of auxiliary nests, a prolonged period of song reaching two maxima of output in April and June, and second broods as a normal procedure. This type is characteristic of habitats containing a readily available food-supply. The tendencies of the Wrens of bleak habitats are towards monogamy, less nest-building, a shorter period of vigorous song, fewer second broods and greater activity by the male in tending the brood in and out of the nest. The fundamental environmental factor determining the type of behaviour is, in my view, the availability of food. Where food for the young is relatively scarce and brood-size remains the same as where it is abundant, the male's aid in feeding the young is indispensable. In bleak habitats the broods of polygamous males would be in jeopardy from malnutrition, as, even if the male were to devote himself to helping his females, he would have to distribute his efforts over two or more broods. Selection has operated in such areas in favour of monogamy. Thus a species may adapt itself to different habitats by modifying behaviour rather than altering brood-size. Comparison of the behaviour of bleak area * and fertile area Wrens shows that in bleak areas the male is more attentive to the young than in fertile areas, but observation indicates that in fertile areas, where the female relaxes her efforts, the male may act to supplement them. If the female disappears when the chicks are a few days old, he may devote his energies almost wholly to tending them and behave to all intents and purposes like a female. The stimulus which triggers such behaviour is evidently the

VOL. LI] ARAN ISLAND WRENS 31 begging- behaviour of the young. This behaviour-mechanism, operating in bleak areas, wouid tend to attach the male more definitely to domestic duties and thereby reduce polygamous tendencies, but as it would not have any effect until the eggs had hatched it would not be sufficient to account for the difference between bleak area and fertile area behaviour. We may assume that latent in both types of Wren is the capacity to behave in some measure according to the pattern of the other extreme. But, theoretically, adaptation to one or the other type might advance beyond the possibility of reverting to the other behaviour-type even on return to an environment which strongly favoured it. The elucidation of the genetic bases of such a group of correlated adaptations would be of great interest. The Aran Islands, Inishmore, Inishmaan and Inisheer, at the entrance to Galway Bay in Ireland, provide Wren habitats which are intermediate between the two extremes, though of "fertile" rather than "bleak" type, and therefore an enquiry into the behaviour of the birds there was made to try to discover to which pattern their activities most closely conformed. My stay on Inishmore was from 18th to 22nd May 1957. In spite of its brevity and the inadequacy of the investigation, some clues useful for the solution of the problem were obtained. Only six miles separates the smallest of the three islands, Inisheer, from the Clare coast. In default of meteorological records, accurate comparison between the climates of the Aran Islands, St. Kilda and Shetland is impossible and the difficulties of comparison are further accentuated owing to the differences in geological formation and vegetation. Aran is of carboniferous limestone clothed with calcicole plants whereas the Shetland Isles are mainly composed of schist. The general impression is of a milder climate and richer flora and fauna than is found on St. Kilda or islands of comparable size in Shetland. Arum lilies grow out of doors in Aran and dracaenas (Cordyline ausiralis) reach a height of twenty feet. Frost is rare. There is little cultivated land, but on Inishmore a good deal of pasture land intersected by innumerable dry stone walls as along the Connemara coast. The "undeveloped" areas are mainly limestone pavement with a rich and interesting flora growing in the interstices sheltered from the wind. HABITAT Although Inishmore is bare and windswept there are a few small groves of trees and, near the houses, much scrubby vegetation. There are, of course, no woods or heather moors such as shelter some Wrens in the Hebrides and Shetland. Brambles, ivy and thick herbage grow along the walls and on rocky declivities. High winds are mainly responsible for preventing the growth of more luxurious vegetation. The Wrens are found mainly near the

32 BRITISH BIRDS [VOL. LI cottages, where rocky banks occur and in the bramble tangles bordering the walls. Territories sometimes extend some way into the stony areas, but not to any extent into the limestone pavement nor at all on the short flower-spangled turf sloping up to the cliffs. It is not surprising that there are no Wrens on the cliffs themselves for they are without vegetation and exposed to the impact of waves which are sometimes strong enough to destroy the stonework of ancient dwellings on the tops of cliffs 100 feet high. In contrast, Wrens on St. Kilda and the Shetland Isles establish territories on the vegetated cliffs. Thus, on Aran, as contrasted with St. Kilda and Shetland, wren habitats are mainly due to the influence of man, for human labour has created not only the dwellings and walls but also the pasture land, built up from the sand and seaweed carried up from the shore by generations of islanders. Robin (Erithacus rubecula) habitats always hold W'rens, but Wren territories extend into rougher, more open ground. This is in keeping with the greater adaptability of the Wren. The greater the distance of islands from the British mainland the poorer the avifauna (Lack, 1942 ; Darling, 1947) and the Robin drops out of island bird lists much sooner than the Wren, Judging by the appearance of the vegetation and the greater concentration of insectivorous Passerines as compared with St. Kilda or Shetland, food suitable for Wrens would be more readily available than in these island groups. Wrens are more abundant than on the Burren, the corresponding limestone formation on the mainland, and this seems to be related to the meagreness of human population and activity there. TERRITORY A road runs longitudinally across Inishmore. The main human and Wren population is concentrated along it. Wren territories were located at distances apart of 200-300 yards somewhat closer, it seemed, than Wren territories on low cliffs in Shetland. Territorial aggressiveness was apparent. Song by a male elicited song from neighbours, and in at least two instances the menace of encroachment by a singing rival caused the territory owner to advance and sing against him with great vehemence. Such behaviour at the stage of the breeding cycle which these birds had reached is more typical of fertile, mainland regions than of bleak, insular areas. This is because polygamous males, neglectful of nestlings and ardent to secure mates, have a greater song output than males preoccupied with feeding young. I was unable to estimate the area of territories, but I formed the impression that they were comparable with those in southern England. SONG Now that objective methods of analysing bird song are available, subjective estimates have limited value, but it seemed to me that the song differed in some respects from that of the Wrens I had

VOL. LI] ARAN ISLAND WRENS 33 been hearing near Cambridge. (I also thought that Wrens at Clew Bay and Galway sang differently from Cambridge birds.) Aran songs were remarkably variable. I listened to one bird at 05.00 G.M.T. for 15 minutes before I could be certain it was a Wren. Its song had no trace of a trill. Another bird repeated a long, elaborate song in which the first of three trills seemed to alter its pitch half-way. One bird sang five songs to the minute, another ten. Making allowance for the extent to which any Wren can alter its song according to circumstances, and also for variability being accentuated towards the end of a breeding cycle, there appeared to be more variability between individuals than I had noted elsewhere. There was a considerable amount of song, not only early in the morning but at all hours of the day. A male, assiduously feeding nestlings, and no doubt stimulated by the presence of his mate, also feeding the chicks, sang very brief, soft songs consisting of a trill on a single note, with a slurred end note. Sometimes he made slight fluttering movements with his wings reminiscent of the more active courtship wing-quivering of Wrens earlier in the season. Such behaviour is most typical of northern insular W r rens, for the males are more frequently close to their mates at the nest. NESTING Finding nests on Aran was more difficult than in the Hebrides, Shetland or St. Kilda. On these northern islands a bird feeding young can be readily followed up and the nest discovered, usually without much trouble. On Inishmore the birds disappeared into the dense briar thickets bordering the dry-stone walls and I was unable, in the time at my disposal, to locate the nests. I was near enough to one nest to hear the chicks calling. Some nests are probably situated quite out of sight in crevices of the overgrown stonework. No doubt other nests are placed in more conspicuous and vulnerable niches, for the Wrens of all habitats do not keep to any sterotyped type of site. Irish boys have never indulged in birdnesting to the extent that boys in England have, and the only time the Wren is persecuted is in the midwinter ritual of the Wren Hunt (Armstrong, 1957b, and in press). Such effective concealment of the nest appears to be due to the ample number of wellhidden cavities rather than the selective pressure of local predators. NESTING-SEASON A group of newly-fledged young was noted on "19th May, a female carrying prey the next day, and a pair feeding nestlings on 22nd May. As the period of the nesting cycle of Wrens from the end of egg-laying to fledging takes approximately just over a month, egg-laying on Aran evidently occurs about mid-april or a little later. Allowing for seasonal variations, breeding seems to begin no later than in southern England and Holland. In contrast the nestlings of Wrens in the Hebrides, Shetland and St. Kilda are commonly still unfledged during the first week or two of

34 BRITISH BIRDS [VOL. LI June and the chances of the parents raising second broods are correspondingly reduced. This is a crucial consideration, so far as the relationship of the Aran birds' behaviour to one or other of the types is concerned, for the inference is that in the matter of second broods the Aran Wrens approximate to the breeding pattern of fertile area birds. DISPLAY AND PAIR-BOND During periods of observation on two days a male was constantly "ticking" and replying vigorously with song to a neighbouring male who was trying to encroach. Sometimes he sang on the wing an indication of an excitable sexual condition. He flew towards his rival and compelled him to retreat. This bird was preoccupied with a female who behaved as if she had no family responsibilities. From time to time he pursued her in sexual chase and once or twice performed the fluttery courtship flight with rapidly beating wings and comparatively slow progress. These activities suggest that in mid-season a male is ready to start a second brood and pair-up with a roving female. Such behaviour would be consistent with polygamy. A female was seen carrying food for young which, judging by her behaviour, were in a nest close by. About 150 yards along the road I noted a female feeding a fledged brood with the male singing near at hand. No other male was noted in this area. This suggests, though it does not prove, bigamy. DISCUSSION Meagre as these data are, and much in need of supplementation by observers able to spend long periods observing the Wrens of other islands, they indicate, in my opinion, that the breeding behaviour of Aran Wrens is more like that of the mainland, fertile area type than that of the bleak, northern island type. This confirms that the distinction is ecological rather than geographical. The relatively early inception of breeding, the vigorous defence of territory and sexual ardour at mid-season, the indications that second broods occur and the suggestions of polygamy are all consistent with the fertile area pattern of behaviour. On the other hand, the behaviour of the male ardently feeding chicks and performing wing-flutters near the nest is rare among fertile area Wrens, but, so far as my observations and those of others go, is frequent among northern insular Wrens. I conclude that while the behaviour of Aran Wrens conforms mainly to the fertile area type there are indications that, in response to the more rigorous conditions, there is a tendency towards the bleak area type. A study of Wrens in mountainous marginal habitats would be of interest. One would expect them to conform to the latter type. SUMMARY The breeding behaviour of Wrens on the Aran Islands, Ireland, conforms more to the fertile area type than the bleak insular area

VOL. LI] ARAN ISLAND WRENS 35 type. Bleakness, with relative inavailability of food, is the factor governing the modification of the integrated behaviour patterns. ACKNOWLEDGEMENTS I am grateful to Mr. Sean Sweeney, Mr. Ciaran Barrett, and to Professor Sedn Delargy and other members of the Irish Folklore Commission, for making arrangements for my visit to the Aran Islands and coastal areas of the west of Ireland. REFERENCES ARMSTRONG, E. A. (1950): "The behaviour and breeding biology of the Iceland Wren". Ibis, 92: 384-401. (1952): "The behaviour and breeding biology of the Shetland Wren". Ibis, 94: 220-242. ; (1953a): "The behaviour and breeding biology of the Hebridean Wren". Brit. Birds, xlvi: 37-50. (1953b): "The history, behavior and breeding biology of the St. Kilda Wren". Auk, 70: 127-150. (1953c): "Island Wrens". Brit. Birds, xlvi: 418-420. (1955): The Wren. London. (1956): "Territory in the Wren". Ibis, 98: 430-437. (1957a): Birds of the Aran Islands". Irish Nat. Journ., xii, 207-208. (1957b): "The wren-boys' ritual". Country Life, 122: 1417-1418. (in press): The Folklore of Birds. London. DARLING, F. F. (1947): Natural History of the Highlands and Islands. London. LACK, D. (1942): "Ecological features of the bird faunas of British small islands". /. Anim. Ecol., 10: 9-36.