Postnuptial Molt Research Articles

Photoperiodic Control of the Molt Cycle in the Chaffinch (Fringilla coelebs)

Abstract The molt cycle in Chaffinches (Fringilla coelebs) has a circannual periodicity under constant photoperiodic conditions (12:12LD, 20:4LD). The molt cycle and/or rate, however, can be modified by artificial alteration of daylength. The time of onset and completion of the post-nuptial molt in Chaffinches under natural conditions is a remote expression of vernal photostimulation. The timing of the molt is initiated at the end of the unifactorial phase of photoperiodic control. The onset of molt is induced after a latent period and its termination after another period, i.e. the molt begins and ends spontaneously. Under natural conditions, daylength immediately before and during the molt does not control either the time of onset or of termination of molt. The additional control system increases the rate of the molt in its early phase under short days, whereas under long days it decreases the rate of molt in its late phase. This system may play an adaptive role in synchronizing the end of the molt among birds that begin molt at different times. The postjuvenal molt begins and finishes spontaneously under control of a program of the individual development of juveniles. Short days increase the rate of molt and initiate earlier onset and completion, whereas long days decrease the rate of the molt and delay the times of onset and completion. Juvenile birds from late broods molt more rapidly than those from early broods. A combination of different programs and photoperiodic control of the molt synchronizes the termination of the molt in juveniles from early and late broods under natural conditions in summer and autumn.

Summer food of the golden plover Pluvialis apricaria at Hardangervidda, southern Norway

Golden plover stomachs were examined through the breeding season al Hardangervidda, southern Norway. The main foods were Diptera larvae (in particular Tipula excisa), adult Coleoptera (notably Otiorrhynchus dubius and Carabidae), and in May and August berries of Empetrum hermaphroditum. Also some larvae of Coleoptera and Lepidoptera were taken. Adult Coleoptera were considerably more common in the diet than expected from abundance data, while Araneae were unimportant as food in spite of a high abundance. The males take the major parental duties after hatching, allowing the females a more undisturbed feeding, supposed to be strongly advantageous for them due to close proximity of egg‐laying and the start of the postnuptial moult. This is reflected in the diet: in July males showed a larger tropic diversity, and ate more adult insects and less insect larvae than the females.

Some endocrine correlates of renesting after loss of clutch or brood in the white-crowned sparrow, Zonotrichia leucophrys gambelii

Through the course of incubation of eggs and feeding of young there is a decline in the plasma levels of luteinizing hormone (LH), testosterone, and estrogens to almost basal values by the time of fledging the young. If eggs or young are lost before the pair has become photorefractory, there is a resurgence in the plasma levels of these hormones that culminates in the laying of the replacement clutch. The plasma levels of corticosterone remains elevated in renesting birds of both sexes until just prior to the onset of the postnuptial molt when it declines precipitously. The rapid postbreeding regression of the gonads and the onset of the postnuptial molt are delayed in renesting birds, but the duration of the molt is decreased so that it is completed at the same time as that of non-renesting birds. It appears that the loss of clutch or nestlings somehow suppresses or removes an inhibitory function that normally decreases secretion of LH and sex hormones at this time. Since day length is still sufficiently long, the levels of these hormones are presumably increased through photoperiodically induced secretion and renesting ensues. The mechanisms that delay the onset of molt and decrease its duration are not known.

SEASONAL VARIATIONS IN THE WEIGHTS OF RED BISHOPS, REDCOLLARED WIDOWS AND REDSHOULDERED WIDOWS

Summary Craig, A. J. F. K. 1978. Seasonal variations in the weights of Red Bishops, Redcollared Widows and Redshouldered Widows. Ostrich: 45:153-157. Mean monthly weights of the Red Bishop Euplectes orix, the Redcollared Widow E. ardens and the Redshouldered Widow E. axillaris were recorded over 21 months in Natal. Males of all three species were heaviest at the start of the breeding season. They then lost weight until the post-nuptial moult started, when there was a new increase. Winter weights were again lower. The maximum weights of females appeared to occur immediately prior to egg-laying. There might be a slight increase in weight during the post-nuptial moult, but only in the case of female Red Bishops were there any distinct seasonal trends in weight change.

SEASONALITY, DENSITY AND DIVERSITY OF BIRDS OF A PAPYRUS SWAMP IN WESTERN KENYA

SUMMARYThe commoner birds of a western Kenya papyrus swamp are listed. This avifauna is probably as rich as in any papyrus habitat, dominated by warblers (Sylviinae) in which interspecific competition between species of similar size is reduced by preference for swamp‐edge rather than interior habitats, preference for papyrus over standing water, or vertical habitat partitioning. Comparisons with other west Kenyan habitats show that it is a specialized avifauna with low species diversity indices and few species. Density figures for common species are higher than in forest undergrowth or thicket. There is little ecological diversity of habitat in uniform stands of papyrus which form ecological islands, and this high density may be interpreted as a density compensation on a speciespoor ‘island’ compared to a species‐rich ‘mainland’.Rainfall is the most seasonally variable climatic factor in west Kenyan papyrus habitats. In this climatic area of Uganda and western Kenya there is a modal egg‐laying period from March to June coinciding with the long rains, and a postnuptial primary moult period from June to November, which extends into the short rains of October and November. On average, a complete moult of the remiges takes six or seven months. In general the moult of immatures begins and ends about two months later than adult moult, but birds reared during the short rains had primary moult only half complete at the beginning of the following long rains. There is very little evidence of interrupted moult. The 1969 rainfall pattern was exceptional, with the heaviest rainfall in February, and there is evidence of a correspondingly early onset of postnuptial moult in that year. Females moulted significantly earlier than males in 1969 whereas males moulted marginally earlier in other years, suggesting that female moult schedules are more flexible.

The Endocrinology of a Natural Breeding Population of the White-Crowned Sparrow (Zonotrichia leucophrys pugetensis)

The levels of immunoreactive luteinizing hormone (irLH), testosterone, dihydrotestosterone (DHT), estradiol, estrone, and corticosterone have been measured through the course of the breeding season in the plasma of both sexes from a breeding population of white-crowned sparrows, Zonotrichia leucophrys pugetensis, on Camano Island, Washington. Birds were captured in nets or traps. After removal of the blood sample and performance of laparotomy to ascertain the developmental stage of the reproductive system, the birds were marked with unique combinations of colored leg bands for identification in field observations and on recapture for procurement of blood samples and for laparotomy. Males arrive on the breeding ground in late April with levels of irLH and testosterone significantly higher than in winter and with partially developed testes. During the ensuing period of establishment of territory, arrival of females, mating, and courtship, the testes attain full development, and irLH and testosterone reach maximum levels in the plasma. Females arrive after territories have been established by the males. Ovaries have begun development at that time; estrone and estradiol are detectable in the plasma; irLH and testosterone are at winter levels. During pairing, courtship, and mating, the ovary develops rapidly, and the plasma levels of irLH, estrone, and testosterone become conspicuously higher. The period of elevated testosterone is brief and coincides with the time during which the females participate in territorial defense. It returns to the winter level before the onset of oviposition at which time estrone has reached maximum level. Regression of the ovary during incubation is coincident with decreases in the levels of irLH and estrone. At this time in the males there is a decrease in irLH and a precipitous decrease in testosterone, which remains low, but above winter level, for the remainder of the year. There is a slight regression in testicular weight. Prior to the laying of the second clutch, the plasma level of irLH increases again but less conspicuously than in females. During the time of the second clutch, there is an increase in plasma androgens in females but not in males. Testes and ovaries return to the level of development attained prior to the first clutch. At the time of oviposition, plasma estrone in females is again maximal. By the time of fledging of the second brood, the levels of irLH and estrone are declining precipitously and gonads are regressing. During the postnuptial molt, testosterone, estrone, and irLH reach winter levels. In females maxima in plasma levels of corticosterone coincide with the two periods of oviposition. The single maximum in males occurs during the time of the second brood. During feeding of the young of the second brood, the corticosterone levels decline in both sexes and reach minimum levels during the postnuptial molt.

On the Significance of Spring Migratory Restlessness in Caged Birds

Caged migratory birds, normally migrating at night, develop nocturnal activity during the migratory seasons. In autumn, this migratory restlessness or often reflects the normal temporal course of actual migration in freeliving conspecifics. In spring, in contrast, persists throughout the normal breeding season and ends only with the beginning of postnuptial moult in practically all species studied. In the present paper, the interpretation of this so called summer Zugunruhe is discussed and three hypotheses are presented which might explain this phenomenon. These propose that nocturnal activity during the breeding season either (1) is not related to migration at all, but reflects a general tendency of the birds to perform various kinds of activities at night; or (2) is related to migration and results from the inability of caged birds to respond to stimuli which characterize their home area onto which they are normally imprinted in early youth; or (3) is related to migration and results from the inability of caged birds to perform reproductive activities. Although none of these three models can be excluded at present time, the available evidence favours hypothesis (3) as the most likely explanation of this phenomenon. Possible experiments for testing it are suggested.

Latitudinal Variation of Postnuptial Molt in Pacific Coast White-Crowned Sparrows

The duration of postnuptial molt in the White-crowned Sparrows of the Pacific Seaboard (Zonotrichia leucophrys nuttalli and Z. l. pugetensis) decreases northward by an average of 2.6 days per degree of latitude between the southernmost (35.2°N, molt duration 83 days) and northernmost (48.9°N, 47 days) limits of the breeding range. Males begin molting earlier than females by as much as 2 weeks. For both sexes, the date on which molt begins is independent of latitude and is correlated with the end of nesting season.

Body Composition of Captive White-Crowned Sparrows during Postnuptial Molt

-A five-compartment analysis of body composition was performed on indoor and outdoor captive White-crowned Sparrows before, during, and after their postnuptial molt. Body weight was monitored simultaneously in four experimental groups. The duration of postnuptial molt in indoor and outdoor birds averaged 60 days. The body weight of outdoor captives in Pullman changed similarly to that seen during the early stages of molt in Fairbanks captives, although late molt autumnal fattening is less intense and more irregular in Pullman captives. Birds on a constant photoperiod at 50 and 15?C exhibited early weight gains, but these gains were either unsustained or converted to weight losses as molt progressed. Total body water in lean birds averaged 70% during molt and 68% after molt. The absolute weight of body water as well as body weight increased during molt. Thus the fractional TBW was essentially unchanged. The stability of the plumage-free lean body mass during molt reflected the negligible extent to which body protein is catabolized, although nocturnal protein degradation was not examined. The lean body weight during molt averaged 23.8% of the lean wet weight, plumage free, or about 5.6 g, but both these figures were only slightly higher after the molt. Plumage weight during the molt increased about 30%. Body feathers constituted the largest fraction (ca. 75%) of the plumage mass, even during molt. Plumage weight after molt was about 24% of the lean dry weight. Body lipid reached its nadir at the onset of molt in Fairbanks captives (LI = 3.5), but increased 6to 7-fold at the end of molt (LI = 20). In Pullman outdoor captives, the increment was about 5-fold. Indoor captives vary in postmolt fattening, depending perhaps upon prior photoperiodic history before transfer to a constant photoperiodic environment. Thus some individual birds transferred later in the spring showed some degree of postmolt fattening, whereas those transferred earlier showed none. This is but a tentative conclusion. Although lipid reserves in the White-crowned Sparrow are small at the onset and perhaps most critical period of molt, the long feeding period and the mutual exclusion of the breeding and molting schedules preclude any apparent calorific drain on the avian body. It is suggested that the rapid molt period may be a selective force operating to separate temporally two events of the annual cycle that are potentially costly energetically.-Department of Zoology, Washington State University, Pullman, Washington 99164. Present address: Department of Zoology, Oregon State University, Corvallis, Oregon 97331. Accepted 26 January 1976. THE YEARLY cycle of all passerines includes an annual molt, which usually begins after breeding or during its later stages. The Gambel Sparrow, Zonotrichia leucophrys gambelii, a member of the west coast complex of North American Whitecrowned Sparrows, molts after the cessation of all breeding activities while on its Alaskan and Canadian breeding grounds (see Cortopassi and Mewaldt 1965, for the distribution of this species), and has been reported to complete its postnuptial molt in 7 weeks (Morton et al. 1969), although this may be subject to some year-to-year variation (Chilgren 1975). In several passerines studied, the molt is usually characterized at some point early in the sequence by an increase in body weight (King et al. 1965, Newton 1968, Myrcha and Pinowski 1970, Morton and Welton 1973), suggesting that the molt does not exact a physiological hardship upon the animal, as might be expected in these birds that molt within 2 months. But body weight is not an appropriate index of the physiological impact of molt, and may mask the potential nutritional stress of a molt. Thus increases in body water, for example, may appear concurrently with decreases in body lipid or protein with little or no change in the bird's live weight or energy reserves. Only a few studies of molt have examined the 677 The Auk 94: 677-688. October 1977 This content downloaded from 157.55.39.136 on Thu, 01 Dec 2016 05:45:11 UTC All use subject to http://about.jstor.org/terms 678 JOHN D. CHILGREN [Auk, Vol. 94

The Early Stages of the Postnuptial Moult in the White Wagtail Motacilla alba

The Early Stages of the Postnuptial Moult in the White Wagtail Motacilla alba

Post-breeding Moult of the Lapwing

Wing and tail feathers dropped by individuals of a roosting Lapwing flock, and collected at regular intervals by the authors, have extended our knowledge of the timing and duration of the post-nuptial moult.

Latitudinal and population specific differences in timing of daily and seasonal functions in redpolls (Acanthis flammea).

1. The daily (circadian) rhythm of activity and rest of common redpolls (Acanthis f. flammea L.) from 65°N lat. was measured for about one year in individuals outdoors at two latitudes (48° and 65°N). During winter at both latitudes, activity-time (α) of common redpolls approximated the duration of daylight (including civil twilights); onset of activity, however, occurred at lower light intensities than end of activity. During mid-summer, a rest-time (p) of ca. 5 h was maintained at both latitudes. During the times of spring and fall migration (extending into summer or winter, respectively), common redpolls showed nightly unrest or shifted their onset of daily activity into the pre-dawn hours. 2. Redpolls of two subspecies (A. f. flammea and A. f. cabaret Müller) resident at different latitudes (ca. 65° and 49°N) were maintained and measured under the same light conditions at 48°N lat. The two populations showed significant differences in their responses to the same annual changes in day length which included: (i) differences in the timing of the circadian activity rhythm with respect to the daily solar cycle; (ii) differences in the amount and range of seasonal changes in nightly unrest; (iii) differences in the mean level and range of seasonal changes of body weight; and (iv) differences in the timing of postnuptial molt. 3. In all experimental groups of redpolls, the highest "precision" (i.e. lowest mean day-to-day variation) in onset and end of activity was observed when both phases occurred during the twilights. The different effects of annually changing light conditions on onset and end of activity with respect to solar time indicated that timing of these two phases of the activity rhythm is independently controlled. It is further indicated that an annually changing sensitivity to light controls the termination of activity in common redpolls, although ambient temperature can modify this response. 4. Besides the direct influence of latitude on timing and the amount of changes of various circadian and annual functions throughout the year, the important role of long-term (genetic?) adaptation to the light and temperature conditions prevailing in the respective habitats of redpoll populations is emphasized by the results of this study.

Pterylosis and Molt in Cassin's Finch

Migratory birds which breed in the strongly seasonal high montane environment of middle and high latitudes must carefully integrate their limited time and energy to successfully reproduce, molt, and prepare for fall migration while environmental conditions are favorable. Generally these events are temporally segregated on the breeding area although some populations, including Carpodacus e. erythrinus, delay the postnuptial molt until arrival on the winter area (Stresemann and Stresemann 1966), thereby separating these energy-demanding processes. The nomadism of Cassin's Finch (Carpodacus cassinii) and inaccessibility of montane breeding populations to investigators presumably have precluded intensive field studies of this species. The few details known are from observations by resident naturalists or by those engaged in faunistic surveys (Ridgway 1877, Henshaw 1879, Grinnell 1908, Taylor 1912, Bailey 1928 and others). From the summer of 1971 through early summer 1974, I studied Cassin's Finches in an environment

Changes in the daily rhythm of plasma corticosterone concentration related to seasonal conditions in the white-throated sparrow, Zonotrichia albicollis.

Circadian variations in concentrations of plasma corticosterone were investigated in the white-throated sparrow maintained on short (10-hr) or long (16-hr) daily photoperiods. In addition, the plasma concentrations of corticosterone were determined throughout a day in birds that were in the reproductively photosensitive spring migratory condition, the reproductively photorefractory post nuptial molt condition, and the fall migratory condition. Distinct unimodal rhythms were found in photosensitive birds. The daily rise occurred 12 hr after the offset of light in birds kept on both the short and the long photoperiodic regimens. There was no discernible daily variation in photorefractory birds kept on a 16 hr daily photoperiod and there was a bimodal rhythm in the birds that were in the fall migratory condition. The results are consistent with an hypothesis that assigns an important role to the circadian rhythm of corticosteroid concentration in the photoperiodic mechanism controlling seasonal reproductive and migratory conditions in the white-throated sparrow.

Die circannuale Periodik der Fortpflanzungsaktivität beim Star (Sturnus vulgaris) unter dem Einfluß gleich‐ und andersgeschlechtiger Artgenossen

1. 30 European starlings, kept for 20 months under a constant 12-hour photoperiod and at constant temperature, were investigated at regular monthly intervals with regard to the state of gonadal development, bill coloration and moult. 8 male male lived in individual cages (group 1), 10 male male were housed together in a group cage (group 2), and 6 male male lived together with 6 female female in another group cage (group 3). All birds had acoustical contact with each other. In addition, the birds of groups 2 and 3 could see one another. 2. In all male male the testes regressed following the beginning of the experiment in April. Subsequently they carried out a complete postnuptial moult. In the following spring, all male male went through a full cycle of testicular size which was followed by a second postnuptial moult. The bills of all birds turned yellow as the testes grew and blackened as the testes regressed (fig. 1).--Most of the female female showed similar circannual rhythms of gonadal growth and regression, bill coloration and moult (fig. 2). 3. In 6 male male of groups 1 and 2, a small increase of testicular size was observed subsequent to the termination of the first postnuptial moult. This transient testicular activity most probably corresponds to the autumnal sexual activity known from freeliving starlings. Hence, these results suggest that both spring and autumnal sexual activity of the starling are endogenously preprogrammed. 4. The testes of most male male of group 3 developed to full size immediately after the termination of the first postnuptial moult; subsequently they remained active for at least 7 months. This observation suggests that stimuli emitted by the female female augment the endogenously preprogrammed readiness for autumnal sexual activity and prevent the subsequent testicular regression. It is concluded that exogenous factors from the social environment are capable of modifying the endogenous annual pattern of testicular function in the starling.

Moult Seasons of the British Corvidae

This description of the annual post-nuptial moult among British crows shows that one-year-old Magpies and Carrion Crows begin ahead of the adults, and that the timetable is different in these two species.

NOTES ON GEOGRAPHICAL VARIATION AND THE ANNUAL CYCLE IN PATAGONIAN POPULATIONS OF THE RUFOUS‐COLLARED SPARROW ZONOTRICHIA CAPENSIS

Summary Zonotrichia capensis australis inhabits Argentina from the northernmost limits of the Patagonian steppe south through Tierra del Fuego, and extends westward to the Pacific slope in southern Chile. At least part of the population has a north‐south migration along the Andean foothills of Argentina as far north as southwestern Bolivia. The breeding range of australis is bounded on the north and northwest by subspecies of Z. capensis (chilensis, choraules, and possibly hypoleuca) having conspicuous black lateral crown‐stripes. Topotypical australis (Tierra del Fuego) have plain grey crowns, but the frequency of black nuchal markings and faint lateral crown‐lines increases northward in the coastal populations. In inland populations (Andean piedmont) the frequency of black crown markings is apparently reversed, increasing southward. The size (wing‐length, tarsus, bill, and probably body‐weight) of australis decreases northward in both coastal and inland samples.The nesting season of australis begins in late November and early December and extends to mid January and early February. Postnuptial moult begins from mid December to early January. Moult proceeds while the testes are apparently still functional. Postnuptial moult terminates from late January through mid March. There is no evidence in the current data of geographical trends in the chronology of nesting and postnuptial moult. The calendars appear to be about the same throughout the range of australis.Postjuvenal moult begins about 4–5 weeks later than the onset of postnuptial moult and terminates in the latest birds in about mid March. Northward migration begins at about this time.

Thyroid gonadal interactions in the male domestic duck in relationship with the sexual cycle

The annual variations of the plasma testosterone concentrations (PT), and the metabolic clearance rate (MCR) of 3H-testosterone, that permits evaluation of the secretion rate (SR = PT × MCR) of the hormone, have been measured in Pekin ducks reared outdoors. Three salient features were observed: (1) during the progressive phase of the reproductive cycle, there is no close parallelism between the testis weight (spermatogenetic activity) and the SR of testosterone; in 1971–1972 both rhythms followed a particularly asynchronous course; (2) in late May the PT falls down to almost autumnal values when the testis weight is still high; (3) this breakdown of the PT is concomitant with a 80% rise in the MCR of testosterone, which contributes, together with a depressed SR to lower the PT. The two latter events (lowered PT in association with an enhanced MCR) can be reproduced by thyroxine administration (0.1 mg or 1 mg/day over 9 days) either during the vernal progressive phase, or during autumn in ducks photo-stimulated by “long days.” The recently evidenced increase in thyroid function in May–June in ducks reared under similar conditions led to the assumption that a seasonal hyperthyroidism may, at least partially, account for the characteristic pattern of testosterone secretion and metabolism at the onset of the regressive phase of the sexual cycle. The postnuptial molt occurs once this peculiar endocrine balance (hyperthyroidism associated to hypoandrogenism) is fulfilled.

Behavioural and morphological changes in the mallard and their relationship to plasma oestrogen concentrations.

The seasonal behavioural and morphological changes of the male bird are well documented (Carpenter, 1932; Domm, 1939). In the mallard the post-nuptial moult into the 'eclipse' or cryptic, female-type plumage coincides with alteration in behaviour from active aggressive territoriality into a quiescent non-territorial phase, which lasts until the bird reassumes the characteristic male nuptial plumage in the autumn. Castration prevents the assumption of the eclipse plumage (Walton, 1937), but the effect is delayed for a year if castration is carried out before or during the breeding season. It would appear that a testicular product is involved. Höhn & Cheng (1967), using paper chromatography and spectrophotometry, found that the oestrogen content of mallard testes in the breeding season exceeded that of testes removed after the breeding season. In order to correlate plasma oestrogen concentrations of mallard with seasonal changes in plumage and behaviour, the following methods were used; the results are

Annual Testicular Cycle and Bill Color Change in the Eastern American Goldfinch

THE avian testicular cycle of seasonally-breeding birds consists of three phases: a regeneration phase when the tissues of the regressed gonad are reorganized, an acceleration phase characterized by development and growth of the testis, and a culmination phase in which the birds are responsive to certain environmental end stimuli that result in their nest building and gamete deposition (Marshall, 1961). Among wild populations of north-temperate passerines such a cycle has been demonstrated by histological examination of the testis in only a few early nesting species (e.g. Blanchard, 1941; Bullough, 1942; Blanchard and Erickson, 1949; Threadgold, 1956a, 1956b; Marshall and Coombs, 1957). Comparative study of the cycles of more species, particularly late nesters, is desirable. An analysis of seasonal changes in external characters that reflect seasonal changes in the gonad may provide an indirect method of determining the testis cycle in other species quickly. Bill color and postnuptial molt are well-suited for such an analysis as, in certain species, they are readily measurable from museum skins. Both characters have been correlated with changes in the titer of one or more of the gonadal hormones (Witschi and Fugo, 1940; Kobayashi, 1954a, 1954b, 1954c, 1958; Witschi, 1961; Engels, 1962), and Marshall (1961) associates the onset of the postnuptial molt with early regeneration phase and the termination of postnuptial molt with the onset of acceleration phase. The Eastern American Goldfinch, Spinus t. tristis, exhibits both a seasonal change in bill color and a late breeding season, and is principally single-brooded. Throughout the northern part of its range this goldfinch generally does not nest until July and later (Walkinshaw, 1938; Stokes, 1950; Nickell, 1951; Berger, 1968), and breeding behavior occurs seasonally later in this species than in other passerines nesting in northeastern North America. Field experiments conducted in Ithaca, New York revealed that not until late June or early July do female goldfinches begin gathering cotton artificially supplied them in their nesting habitat since early June, and they do not begin collecting thistle papus, a major natural nesting material, until July or, more rarely, in the last week of June (Mundinger, 1968). This correlates temporally with the onset of nest construction. In a study field in Ithaca only about 6 percent (2 of 35 nests) of all nests were initiated as early as the period mid-June to 1 July in 1963-65. Likewise the males do not engage in the defense of a geographically fixed area with flight song display and other territorial behaviors until nest construction begins or, in some cases, only a few days