Bird Study

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Snow Bunting Moult in Northeast Greenland G. H. Green & R. W. Summers To cite this article: G. H. Green & R. W. Summers (1975) Snow Bunting Moult in Northeast Greenland, Bird Study, 22:1, 9-17, DOI: 10.1080/00063657509476435 To link to this article: http://dx.doi.org/10.1080/00063657509476435

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Date: 28 January 2017, At: 05:30

Snow Bunting Moult in Northeast Greenland

W. Summers by G. H. Green and R.W In Scoresbyland, northeast Greenland, the duration of Snow Bunting moult was estimated to be about 28 days, and the whole population may complete moult over a period of 48 days. Farther north the change may be even more rapid, birds being rendered flightless for a time.

SNOW BUNTINGS Plectrophenax nivalis moult at their Arctic breeding places before autumn migration. The moult is rapid and at times the birds may be unable to fly because many wing feathers are either missing or partly grown (Manniche 1910, Salomonsen 1950, NethersoleThompson 1966, Parmelee 1968). Stresemann and Stresemann (1970) gave a more detailed description of the moult than earlier authors, based on 28 museum skins collected in Greenland and Labrador between 1906 and 1948, but no quantitative study of the moult has been reported. The present paper describes its progress at one place in northeast Greenland in 1972 where 23 adult Snow Buntings (18 males and five females) were collected between 24 July and 30 August in the neighbourhood of Mestersvig in Scoresbyland, 72°14'N. 23°55'W. The moult was recorded and analysed in the usual way (Evans 1966, Newton 1966, Snow 1967). Gut contents were collected and the food was identified. THE MOULT

Wing moult The order of moult of the flight feathers was typical of small passerines. Moult started at the junction of the primaries and secondaries and proceeded outwards through the primaries from 1 to 10 and inwards through the secondaries from 1 to 6. The tertials were replaced during the moult of the primaries. Figure 1 shows primary moult scores plotted against dates. The best estimate of moult duration derived from regression analysis is 28 days. This figure must be regarded with caution as there is considerable scatter of the points, and therefore a regression line has not been drawn on Figure 1. The first birds probably started to moult about 14 July and finished about 13 August, and the last started about 1 August and finished about 30 August. The whole population probably completed moult within a period of about 48 days. Figure 2 (a) shows the relationship between primary and secondary moult scores for each bird. Moult of the secondaries started after the inner five primaries were well grown, and when primaries 6 and 7 had dropped. It continued rapidly and was complete by the time primary 9 .

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SNOW BUNTING MOULT

had grown. The outer two secondaries were well grown before the inner four were dropped. The duration of moult of the secondaries was about 15 days (estimated by eye from secondary scores plotted against dates). Figure 2 (b) shows the relationship between primary and tertial scores for each bird. The centre tertial was usually dropped first. The duration of moult of the tertials was about 17 days (estimated by eye from scores plotted against dates). The primary coverts moulted with their associated primaries. The greater coverts were dropped simultaneously when the inner primaries were about two-thirds grown, and growth was complete by the time the inner five primaries were full grown. The alula moulted rapidly after the inner five primaries had grown, and during the moult period of primaries 6 and 7. The tiny outermost primary 10 was moulted during the moult of primaries 8 and 9. It had completed growth before these feathers. It has been omitted from the primary moult scores. PRIMARY SCORE 45

8

8

40 35

••

30 25 20 15 10

• 20

25

aal

5

10

JULY

15

20 AUGUST

25

301

3 SEPTEMBER

Figure 1. Primary moult scores plotted against date : o = male and • = female.

Tail moult Figure 2 (c) shows the relationship between primary and half-tail moult scores for each bird. The tail feathers were dropped almost simultaneously, although the outer pair sometimes remained a little longer than the rest. Several of the inner primaries were well grown before tail moult started. Tail moult was completed shortly before primary 9 reached full length; its duration was about 23 days (estimated by eye from half-tail moult scores plotted against dates). Body moult There was simultaneous moult of many of the contour tracts during the moult period of the primaries. Contour feather growth was almost complete when primary 9 reached full length, but many feathers showed sheath remnants at the base. 11

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MOULT IN RELATION TO BREEDING SEASON Observations at nine nests gave a mean date for completion of clutch of 23 June (range 19 to 26 June), mean hatching date 5 July (range 1 to 8 July, 13 days incubation period) and a mean fledging date of 16 July (range 12 to 19 July, 11 days fledging period). Salomonsen (1950) stated that fledged birds are fed by the adults for about ten days, and Parmelee (1968) suggested a period of dependence ranging from ten to seventeen days. Our own observation of dye-marked juveniles showed that they were fed by the adults for at least 13 days after fledging. Salomonsen (1950) stated that males moult in mid-July while they are still feeding nestlings, but Parmelee (1968) said that males start to moult about fledging time. Nethersole-Thompson (1966), summarising the results of various authors, wrote that cocks moult in mid-July while feeding young, the hens a little later. Figure 1 suggests that most birds started to moult about 20 July, four days after the estimated mean fledging date (16 July). On 26 July a male, which had been observed feeding a juvenile, was collected and was found to have shed five inner primaries. Its moult score of five suggests (from Figure 1) that the moult started about 23 July, a few days after the likely fledging date of its brood. Asbirk and Franzmann (1975), working in the Mestersvig area in 1974, found that some males started to moult their inner primaries while they were feeding nestlings. At one nest the male was caught five days before the brood fledged and was found to be growing primaries 1 and 2. The female was not moulting. At a second nest the male dropped primary 1 one day before the brood fledged, and again the female was not moulting. Observations at two other nests of birds which were not caught showed the males to be moulting inner primaries while the females showed no sign of moult. It is noteworthy that the two males caught were moulting the inner two primaries only. In 1972 we often found that the five inner primaries were dropped almost simultaneously (see Figure 4). WEIGHT The weights and wing lengths of Snow Buntings collected in northeast Greenland or caught during the winter in Aberdeenshire, Scotland, are given in Table I. Birds from both areas have similar wing lengths but the Scottish birds are 5 to 6 gm. lighter. Dissection of the Greenland TABLE I. SNOW BUNTING WING LENGTH (MAXIMUM CHORD) AND WEIGHT

Origin

Age/Sex

Greenland (July to September)

Adult male Juv. male Adult female Juv. female Male Female

Aberdeenshire, Scotland (Winter)

Mean

112.3 110.3 104.8 104.0 111.7 104.2

Wing (mm.) SD n.

12

3.7 3.9 5.3 2.7 2.6 2.2

12 16 4 7 10 13

Weight (gm.) Mean SD n.

40.8 40.3 36.2 36.7 35.0 30.6

2.4 2.0 2.8 1.0 1.6 2.6

18 18 6 7 10 13



SNOW BUNTING MOULT

birds showed little fat deposition but visual examination may have been misleading. Newton (1966) suggests that fat may be deposited during moult to provide insulation during feather loss and this may occur in Snow Buntings, but we have no comparative data from nesting birds. There was no sign of weight increase during August or early September in either adult or juvenile birds. If there is a pre-migratory weight gain it must occur rapidly shortly before the birds leave in September. DISCUSSION The duration of Snow Bunting moult at 72°14'N. in Greenland in 1972 was about 28 days. Figure 3 shows Stresemann and Stresemann's (1970) moult descriptions converted to scores and plotted against dates. Examination by eye gives an estimate of 40 days for the period. Stresemann and Stresemann suggested 36 days. We think their carefully selected series of museum skins gives an accurate description of the sequence of moult, but an inaccurate estimate of its duration. A further explanation of the discrepancy between their results and our own is offered below. PRIMARY SCORE

45 40 35 30 25

•

15 10



• 20

•

0

25

301

10

15

20 AUGUST

JULY

25

301

3 SEPTEMBER

Figure 3. Primary moult scores derived from the descriptions given by Stresemann and Stresemann (1970) plotted against dates. o = male, • = female.

Evans (1966) and Evans, Elton and Sinclair (1967) showed (calculating the moult on a different basis from that used here) that male Redpolls Acanthis flammea completed their moult in 48 days in northern Norway and in 56 days at Durham, England. Females moulted in 54 days in Norway and 56 days at Durham. Hence males took eight days and females two days less to moult 15° farther north. Pitelka (1958) reported that Steller Jays Cyanocitta stelleri moulted more rapidly in the north than the south. Newton (1973) pointed out that the moult of song birds is more rapid and synchronous at higher latitudes. Pitelka (1955) reported that Snow Bunting and Lapland Bunting Calcarius lapponicus populations showed a high degree of synchrony in the moult, which occurred after breeding in early to mid-July at Barrow, Alaska. Freuchen 13

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and Salomonsen (1958) wrote of the Snow Bunting in the high Arctic: "The moult proceeds so quickly that the birds are unable to fly for some time." Salomonsen (1950), writing of Greenland, suggested that "farther south the moult may proceed more slowly; the resident birds of Iceland may not have finished the moult by the beginning of October." Stresemann and Stresemann (1970) did not agree with him and mentioned that skins from 15 Icelandic birds showed moult similar to birds from Greenland and Labrador. However, Greenland and Labrador span 32° of latitude from 53 to 84°N. and it seems unlikely that Snow Buntings moult at the same rate throughout this wide range. A possible interpreta0

Figure 4. Snow Bunting wing showing (above) the first 'ragged' stage of moult (five inner primaries in an early stage of moult) and (below) the second 'ragged' stage of moult (four outer primaries and two outer secondaries in moult). 14

SNOW BUNTING MOULT

tion of Stresemann and Stresemann's findings, in keeping with our own from Scoresbyland, is that Snow Buntings breeding in Labrador (52° to 60°N.) moult more slowly than in northern Greenland (70 to 84°N.). Icelandic birds (65°N.) may show a moult rate similar to the average for the whole Labrador-Greenland zone and therefore appear similar to Stresemann and Stresemann's findings for that zone. In Scoresbyland in 1972 we did not observe flightlessness due to moult, as reported in Manniche (1910) and Salomonsen (1950). Manniche worked in Germania Land at 76° 46'N. and, if moult is more rapid at higher latitudes, flightlessness would be more frequent there than in Scoresbyland. Furthermore, many observers were in northern Scoresbyland in 1974 and only one observation suggested flightlessness. P. N. Ferns and G. P. Mudge (pers. comm.) saw two males in moult at Orsted Dal (71°47'N. 23°15'W.) on 7 August. One "could just fly" and the other "when chased went to ground amongst a mass of loose rock." Haukioja (1971) suggested that flightlessness during moult in north European passerines occurs principally at the two most 'ragged' stages of moult, firstly when several inner primaries are dropped simultaneously, and secondly when the outer primaries and the outer secondaries moult together. The wings of Scoresbyland Snow Buntings appeared very 'ragged' at these stages as shown in Figure 4. Furthermore, some birds were growing many feathers simultaneously. For example, primaries 6 and 7 were dropped before the growth of the inner five was complete. One bird dropped primaries 8 and 9 at the same time as the two outer secondaries, and another showed growth of all nine primaries, the inner five being three-quarters grown (each with moult score 4). All these birds could fly. Further acceleration of the moult by increasing the number of feathers replaced simultaneously would increase the likelihood of flightlessness,.so this may occur farther north. The moult would then take less than 28 days. A description of the flightless wing has not been given. Newton (1973), in a summary of finch moult, mentioned that a steady and plentiful supply of food is necessary during the moult. Feather growth must continue smoothly to avoid zones of weakness (fault bars) forming. Pitelka (1958) noted that Steller Jays moult at a time of peak food abundance. During the short Arctic summer Snow Buntings take advantage of two abundant food supplies. When the chicks are in the nest, and while the fledglings are dependent on the adults, there is a plentiful supply of insects. In Scoresbyland in 1972 the chicks were fed mainly on lepidopterous larvae and tipulid imagines. During the moult the birds feed from an abundant supply of fruits and seeds. Gut analyses showed that bulbils of Polygonum viviparum, seeds of various sedges and grasses, and berries of Vaccinium uliginosum were important food items during the moult. These could all be collected early from low growing plants by birds whose flight was impaired. Flightless Snow Buntings, and also those with impaired flight, feeding 0

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far from cover, may be more easily preyed on by Snowy Owl Nyctea scandiaca, Gyr Falcon Falco rusticolus and Arctic fox Alopex lagopus. Most authors who mention flightlessness state that moulting birds are secretive, seeking hollows and broken ground where they can hide. The body feathers of the new plumage have large buff tips and the birds are less conspicuous than in the breeding plumage. The moulting birds gather into flocks and this habit, which Lack (1954) suggested might give a greater awareness of the approach of predators, coupled with their cryptically coloured plumage, may give some protection against predators. In finches, the adults usually start to moult after the young of the last brood are independent (Newton 1973). Reed Buntings Emberiza schoeniclus start to moult after breeding has finished and males may start before females (Bell 1970), but no precise data are available for other buntings. Snow Buntings start to moult before or shortly after the young leave the nest, and before they become independent. The male of a pair may start moult before the female. The whole Snow Bunting breeding and moulting cycle is adapted to the short Arctic summer The nestlings are fed from an abundant, although short-lived, insect food supply. The breeding and moulting seasons overlap and the extremely rapid moult takes place when seeds and other insects are abundant. There remains enough time and an adequate food supply for the birds to prepare for migration to the wintering grounds. If the moult rate increases with latitude, this shows a further adaptation to the shorter season at higher latitudes. SUMMARY

Study of 23 adult Snow Buntings collected in Scoresbyland, northeast Greenland, at 72°14'N. 23°55'W., showed that moult started when the brood fledged and while the young were dependent on the adults for food. The male of a pair may start to moult before the female. The entire moult was completed in about 28 days. It is suggested that the speed of moult may increase with latitude, the change taking longer in the south than in the north. If this is so, flightlessness due to moult, which has been reported from the high Arctic but which was not recorded in Scoresbyland, may occur farther north. While the young were in the nest, and while the fledglings were dependent on the adults for food, there was an abundant supply of insects. During the rapid moult there was a plentiful food supply of fruit and seeds for the adults. ACKNOWLEDGEMENTS

We wish to thank R. O'Brien, leader of the Dundee University Expedition which we accompanied to Greenland, Drs J. J. D. Greenwood and A. E. Williams who helped with field-work, H. B. Ginn who commented on a draft of this paper, Dr P. N. Ferns and Clare Lloyd who gave help with statistics, Dr F. Kurrein who translated the Stresemanns' paper, S. Asbirk and N. E. Franzmann who accompanied our 1974 expedition to northeast Greenland and kindly allowed us to use some of their observations. We are particularly indebted to R. M. Bishop who made the wing drawings (Figure 4). Kenneth Williamson made helpful comments.

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SNOW BUNTING MOULT REFERENCES

and N. E. FRANZMANN 1975. Studies On the biology of the Snow Bunting. In a report from a Joint Biological Expedition to Northeast Greenland 1974. In press. BHA., B. D. 1970. Moult of the Reed Bunting—a preliminary analysis. Bird Study, 17:269-281. VANS, P. a. 1966. Autumn movements, moult and measurements of the Lesser Redpoll Carduelis flammea cabaret. Ibis, 108: 183-216. EVANS, P. R. R. A. ELTON and G. R. SINCLAIR 1967. Moult and weight changes of Redpolls Carduelis flamtnea in north Norway. Ornis Fenn.„ 44:33-41. FREUCHEN, P. and F. SALOMONSEN 1958. The Arctic Year. London. HAUKIOJA, E. 1971. Flightlessness in some moulting passerines in northern Europe. Ornis Fenn., 48:101-116. LACK, D. 1954. The Natural Regulation of Animal Numbers, p. 255. Oxford. NIANNICHE, A. L. V. 1910. Terrestrial birds and rtiammals of northeast Greenland. Meddel. on? Gronland, 91:1-128. NETHERSOLE-THOMPSON, D. 1966. The Snow Bunting. Edinburgh and London. NEWTON, I. 1966. The moult of the Bullfinch Pyrrhula pyrrhula. Ibis, 108:41-67. NEWTON, I. 1973. Finches. London. PARMELEE, D. F. 1968, in Bent's Life Histories of North American Cardinals, Buntings, Sparrows and Allies, part 3, pp. 1652-1674. New York. FITELKA, F. A. 1955. Synchrony and control of moult in arctic passerine birds, in Science in Alaska, Proc. 6th Sci. Con f., pp. 68-69. PITELKA, F. A. 1958. Timing of moult in Steller Jays of the Queen Charlotte Islands, British Columbia. Condor, 60 : 38-49. SALOMONSEN, F. 1950. The Birds of Greenland. Kobenhavn. SNOW, D. W. 1967. A Guide to Moult in British Birds. British Trust for Ornithology Field Guide No. 11. STRESEMANN, E. and V. STRESEMANN 1970. Die vollmauser der Scheeammer Plectrophenax niyalis. Beitrage zur Yogelkunde, 16: 386-392.

ASBIRK, S.

G. H. Green, Windy Ridge, Little Comberton, Pershore, Worcestershire, W RIO 3EW. R. W. Summers, Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Rondebosch,C.P., South Africa.

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