41 the Moult of the Bullfinch Pyrrhula Pyrrhula I

1966 I. NEWTON : THE MOULT OF THE BULLFINCH PYRRHULA PYRRBULA 41 THE MOULT OF THE BULLFINCH PYRRHULA PYRRHULA I. NEWTON Received on 13 October 1964 INTRODUCTION Few detailed field studies have yet been carried out on the moult in any bird species. This paper describes some observations on the moult of the Bullfinch Pyrrhula pyrrhula nesa (Carduelinae), and its timing in relation to the breeding season and food-supply in the woodland of Wytham Estate, near Oxford (58" 80'N.). The Bullfinch is a common resident in the area, mainly in the woodland, but also in gardens, orchards, and hedge- rows. It nests in dense shrubs and hedges, and feeds for most of the year mainly on various seeds, and in spring on buds, including those of various fruit trees (Newton 1964, 1964 a). Details of moult and weight were obtained from 133 individuals in 1962, from 283 in 1963, and from 247 in 1964; many of these were handled more than once during a single moult.* They were caught in mist nets placed more or less at random in the woodland or at feeding places such as patches of Meadowsweet Filipendula ulmaria and various docks Rumex spp. Netting was restricted to two areas, the Great Wood and Marley, which have been described by Southern (1954) and Gibb (1954) respectively. The Great Wood comprises some 400 acres of deciduous trees, dominated by Oak Quercus robur, Ash Fraxinus excelsior and Sycamore Acer pseudo-platanus, and about 150 acres of conifers. Marley is an open scrubby area of 66 acres, which is dominated by Oak and Hazel Corylus avellana, with large patches of hawthorns Crataegus spp. and Elder Sambucus niger. Wytham Bullfinches started laying each year in early May, soon after fresh seeds first became available. The laying season lasted until mid-July in 1963 and 1964, but was prolonged to early September in 1962 when food was especially plentiful in late summer. After breeding the adults underwent a complete moult, and at the same time the juveniles underwent a partial moult. The term " moult )' is here taken to cover both the shedding and the renewal of feathers. Plumages and moults The number and distribution of the feather tracts in the Bullfinch, and the sequence of moults, is similar to those of some other passerines (see Dwight 1900). For the first few days after hatching the nestling Bullfinch is sparsely clothed with natal down. At the post-natal moult into juvenile plumage, each down feather is pushed out by growth of a juvenile feather and clings to the tip of the juvenile feather sometimes until it is fully formed 1-2 weeks after the bird has left the nest. Juvenile body feathers differ from those of the adult in being weaker, looser in texture and of different colour. The post-juvenile moult takes place in late summer or autumn, and is restricted to the body feathers and the small feathers of the wings and tail; the primaries, secondaries, rectrices, the two outer tertials, and primary-coverts, and a variable number of greater-coverts * Full details of moult were not obtained from every bird, and if time was short details only of wing-moult (or sometimes of wing- and tail-moult) were taken from the adults. This accounts for the different totals in some of the tables. 42 I. NEWTON : THE MOULT OF THE BULLFINCH PYRRHULA PYRRHULA IBIS108 are retained until the next moult about a year later. Birds in first-year plumage can be distinguished by some of the retained juvenile feathers, until at 11-15 months old, the next moult is so advanced that their plumage is indistinguishable from that of older birds. All subsequent moults are complete post-nuptial moults and occur at approxi- mately annual intervals. There are no pre-nuptial moults in the Bullfinch. In an adult Bullfinch, just prior to moult, the feathers are usually worn, faded and soiled, and there are often gaps in the plumage where lost feathers have not been replaced. The fading of the black flight and tail feathers to various shades of brown is presumably caused by the disintegration of some of the cornified cell-layers of the feather (Miller 1928). Fading was marked in birds moulting late, and was most pronounced in birds in first-year plumage in which the flight and tail feathers, acquired as nestlings, could have been up to 15 months old before they were replaced. The adult moult in the Bullfinch lasts 10-12 weeks and the post-juvenile moult 7-9 weeks. In adults replacement of the body plumage rarely spans the entire moult period, but averages about as long as the post-juvenile moult. The moult begins in the adults with the primaries and in the juveniles with the lesser-coverts. The latter are often the first body feathers to be moulted in adult Bullfinches. In this respect the Bullfinch differs from most other passerines in which body moult begins first on the breast, back, scapulars, and head, and only then in the lesser-coverts (Dwight 1900). THE FEATHER TRACTS AND THEIR PATTERN OF MOULT The distribution of the feather tracts (pterylae) is best seen in a nestling while the feathers are still small. In all there are eight tracts, three of which are paired, arranged as in most other passerines (see Dwight 1900). The moult begins at a number of points (loci) from which it spreads in characteristic manner. There are two loci in the dorsal and ventral tracts, four in the caudal tract, at least five in the alar tracts, and one in the head tract and in each half of the remaining tracts. Normally moult begins at different loci in turn and from each progresses along the length of the tract more rapidly than it spreads laterally. 1. The alar tract The alar tract comprises the flight feathers, their various coverts, and the alula quills. (In addition, the wing bears the scapulars on the upper surface and the axillaries below, both of whch form part of the shoulder tract.) In the Bullfinch, there are nine large primaries, six secondaries, and three tertials. The tenth primary is vestigial as in other carduelines. Moult of the primary feathers begins at the carpal joint and spreads outwards ; the primaries are here numbered 1 to 9, proximal to distal. The secondaries are replaced from the carpal joint inwards, and are here numbered 1 to 6, distal to proximal. Moult of the tertials does not follow the sequence of the secondaries: the central one is shed first, then the innermost, followed by the largest outer tertial. The length of the various flight feathers was measured by pressing the detached quill flat on a rule. The following figures are the means of measurements on 12 birds, and the standard deviation in every case is about & 1 mm. Primaries ' Secondaries Tertials 123456789 123456 123 Length (mm.): 62 63 64 66 71 74 72 69 65 61 61 60 58 56 54 50 40 28 Each primary-covert is shed with its corresponding primary, and has usually reached full length by the time the primary is half grown. The greater-coverts are shed more or less simul- taneously with each other, or in quick succession from the innermost outwards; sometimes however, the inner ones are half grown before the outer four or five are dropped. Replacement of the lesser-coverts begins near the body and spreads first towards the carpal joint and then to the median-coverts, which are moulted all more or less together; at the same time the carpal-covert and the feathers of the alula are replaced. On the underside of the wing the coverts are softer and appear more sparsely distributed; the lesser- and median-coverts are moulted more or less simul- taneously, and the under greater- and under primary-coverts are moulted in rapid succession from the carpal joint outwards. 2. The caudal tract The caudal tract is here considered to include the 12 rectrices, their upper and under coverts and the feathers circling the anus. In the Bullfinch, both upper and under tail-coverts are unusually long, the middle pair of each extending to more than half the length of the rectrices. The rectrices are all about the same length (about 71 mm.)-though in some birds the inner ones are s!ightly 1966 I. NEWTON : THE MOULT OF THE BULLFINCH PYRRHULA PYRRIIULA 43 shorter-and are replaced from the central pair outwards. The ten upper coverts were often shed from the outermost inwards, but this pattern was sometimes modified by the temporary retention of any of them, and in some individuals no orderly sequence of replacement was discerned. The under tail-coverts also tend to be replaced centripetally, though variation was even more frequent than in the upper coverts. The feathers circling the anus are all moulted together. 3. The dorsal tract The dorsal tract includes the feathers of the nape, back, and rump. It is continuous with the head tract, but posteriorly, stops in front of the preen gland. Feather replacement begins at two loci, one between the scapulars and the other just above the rump and spreads both ways along the length of the tract, the nape being the last part to acquire new feathers. 4. The ventral tract The ventral tract starts under the bill and about half way down the neck forks into two broad symmetrical bands; each in turn divides to give a short outer branch in front of the leg, and a main branch extending down the belly to end in front of the anus. Feather replacement begins at two loci, one in each of the main branches, and spreads lengthwise along the tract.

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