Winter survival and breeding success of dominant and subordinate Willow Tits Parus montanus

We studied the effect of winter rank on survival rate and reproductive success in Willow Tits Parus montanus, a resident passerine living in dominance-structured flocks during the nonbreeding season, in 6 years. Winter survival was dependent on both the birds' age and rank. Adults survived better than first-year birds, and within first-year males, dominants survived better than subordinates. In other sex and age classes, rank did not contribute to survival. Although first-year males were in excess among nonbreeders, no connection existed between breeding status and rank. Female rank did not explain the variation in the start of laying, clutch size, number of fledglings or recruit production. We conclude that social status in Willow Tits affects individual fitness mainly through rank-dependent survival. Acquiring a high rank position seems to be most important for first-year birds, especially first-year males.     

THE WINTERING AND MOULT OF RUFFS PHILOMACHUS PUGNAX IN THE KENYAN RIFT VALLEY

Some 5700 Ruffs were ringed in the southern Kenyan rift valley during 1967–79, mainly at Lakes Nakuru and Magadi. These have produced 15 recoveries outside East Africa, 14 in Siberia between 73° and 154°E and one in India. Adult males returned to Kenya mainly during August, and females during late August and early September. Females greatly outnumbered males at all times. Most wintering males departed late in March and early in April, but females not until about a month later. First-year birds appeared from the end of August, but remained in low numbers until late October or November. Most departed during April and May, but a few females oversummered. First-year birds typically accounted for about 25% of the wintering Nakuru females, but about 50% of those at Magadi. At both sites they accounted for a higher proportion of male birds than females. Most of the birds at Nakuru throughout late August to May appeared to be local winterers, and many individuals remained in the area for many months each year. Retrapping indicated that approximately 60% of each season's birds returned the following season. Adult males and most adult females commenced pre-winter wing moult before arrival, but completed most of it in Kenya. Males moulted 3–4 weeks ahead of females, and most had finished before December. Females typically finished during December and early January. Most second year birds timed their pre-winter moult similarly to older adults. Suspension was recorded in over 15% of all moulting birds examined. Adult pre-summer moult involved most or all of the tertials, some or all of the tail feathers, most of the inner wing coverts and the body and head plumage. It occurred mainly during January to March (males) or February to April (females), although tertial renewal commonly began a month earlier. Males showed no sign in Kenya of the supplementary prenuptial moult. First-year birds moulted from juvenile into first winter body plumage during late September to November. They underwent a pre-summer moult similar in extent and timing to that of adults, and again about a month earlier in males than females. Spring feathers acquired were often as brightly coloured as those of adults. About 15% of first-year birds renewed their outer 2–4 pairs of large primaries during January to April. Adult and first-year birds fattened before spring departure, commonly reaching weights 30–60% above winter mean. Weights of adult males peaked early in April, those of adult females early in May, and those of first-winter females later in May. Weights were relatively high also during August and September. This was due to the arrival of wintering birds carrying ‘spare’ reserves, and also apparently to the presence of a late moulting fattening passage contingent. The wing length of newly moulted adults was about 3 mm longer than that of newly arrived first-year birds, but there was no evidence of an increase in the wing kngth of adults with successive moults. Adult wing length decreased by 4–5 mm between the completion of one moult and the middle stages of the next. The migrations and annual timetable of Kenyan wintering Ruffs are discussed, and their moult strategy is compared with that of other Holarctic waders.     

Social rank and habitat use in willow tit groups

One view depiets dominance and subordination as roles with equal fitness played as parts of a mixed behavioural strategy, but subordination can also be maintained as a transient strategy of ‘hopeful dominants’. Resource access in groups of non-kin willow tits, Parus montanus, was related to social rank. Dominants excluded subordinates from the preferred microhabitat. Fitness in terms of survival was correlated with access to the preferred foraging sites, indicating that a mixed-strategy explanation is inadequate. Social rank was linked to age, and first-year subordinates behaved as predicted for hopeful dominants. They were not ‘herded’ by dominant group mates because subordinates actively maintained contact with dominants. One possible reason for subordinates joining winter groups might be the opportunity to reduce dominants' pay-off from aggression.     

WEIGHTS OF SOME PALAEARCTIC WADERS WINTERING IN KENYA

Palaearctic waders were caught and weighed at Lake Nakuru in the Kenyan rift valley on 22 occasions in the non-breeding season between March 1967 and May 1969. The weights of four species are presented:Curlew Sandpiper, Little Stint, Ruff and Marsh Sandpiper.
Winter weights were relatively low and varied little. It is thought that waders had very little fat reserve at this time.
The mean weights of early autumn samples tended to be higher than corresponding mean winter weights, and autumn populations included some markedly heavy birds.
An increase in the mean weight, and a dramatic rise in the maximum weights of each species occurred shortly before its main spring departure time. The great majority of waders apparently gained considerable weight before migration from the area in April and May.
The spring migration of waders from Kenya is briefly discussed.     

MIGRATION OF THE NORTHWESTERN EUROPEAN POPULATION OF THE CUCKOO CUCULUS CANORUS, AS SHOWN BY RINGING

The migration of the Cuckoo Cuculus canorus is described from recoveries of ringed birds. Young birds begin to migrate in August and most go southwards by September—those in continental Europe move southeast, south or southwest, while those from the British Isles move southeast. In spring, migrants arrive in Europe in April/May, second-(calendar) year birds doing so later than post-second-year birds. In autumn old birds depart in advance of first-year birds; and the individual bird may move stepwise through Europe. Old birds showed a marked tendency to return to the same places inhabited in previous breeding seasons, and birds ringed as nestlings subsequently tended to return to the general vicinity of the natal site.     

Social dominance in free-living Willow Tits Parus montanus: determinants and some implications of hierarchy

Several features of social dominance among Willow Tit Parus montanus winter flocks were examined during a four-winter study. Birds of both sexes were evenly distributed over the 33 flocks studied. In nearly half of the flocks there was an adult pair accompanied by yearlings, but one-third of the flocks consisted of more than two adults with yearlings. Males were found to be dominant over and larger than females. Within a sex, yearlings were usually subordinate to adults. The effect of size on dominance, after controlled for sex and age, remained obscure in our field data. The hierarchical status of an individual was found to rise or at least stay the same in different years, which supports the "hopeful dominants" hypothesis, i.e. birds stay in flocks hoping to achieve a higher status in the future. The ranks of mates correlated highly significantly, implying that high-ranking birds were paired with other high-ranking birds and low-ranking birds with other low-ranking birds. Birds of different age and sex did not show any differences in the proportion of initiated aggressive encounters directed at other individuals. However, males were more aggressive to other males than to females and also tended to behave less aggressively towards their own mates than towards other individuals in the flock. This could be a male strategy to strengthen the pair-bond and to enhance mate protection described earlier in     

A RINGING STUDY OF MIGRATORY BARN SWALLOWS IN WEST MALAYSIA

The Barn Swallow is a non-breeding winter visitor to West Malaysia (Malaya), abundant in season, by day feeding aerially over a wide range of habitats and by night normally roosting gregariously in trees, reed-beds or on service wires in towns. Records of ringed birds have demonstrated that those reaching Malaya breed in the Palaearctic region from 108°E eastwards between 37° and 51°N. Recoveries south of the breeding range suggested that migrating birds may follow either a continental route or a more easterly track through the Philippines and Borneo. Counts at roost sites in a reed-bed and in towns demonstrated a seasonal increase in numbers from late July to a peak in November, followed by a decline of about 20% to a level maintained until mid-February when departure commenced. Most birds had left by early May, but a few lingered and possibly overlapped with the first returning migrants in June. There was no evidence that any individuals remained in Malaya through the nuptial period. Repeats during winter at three regularly sampled urban roosts indicated that many birds on passage were present until November and again in late March–early April; from December to February the winter population was relatively stable and comparatively sedentary. Although the distances between towns were small in relation to the demonstrated foraging range of Barn Swallows, only 17% of 1,955 repeats of ringed birds represented a shift in roost site. Most shifts were towards the centrally situated and most populous roost of the three; interchanges between the outer pair of towns were few. A complete moult occurred on the wintering grounds, during which young of the year acquired adult plumage. Replacement of the primaries extended virtually throughout the moulting period, at an average rate of 2.4 feathers per month in the proximal part of the tract and 1.3 feathers per month in the distal part. Adults on average moulted slightly earlier than juveniles, but there was a wide scatter in timing between individuals of both age groups. There was no evidence that the initiation of moult was related to the dates of post-nuptial migration. The date of departure on prenuptial migration, however, was normally delayed until primary moult was complete. Large weight gains in March and April occurred only in swallows which had completed the moult. At this period the mean weight of birds in fresh plumage was about 30% above the lowest winter mean, and was significantly higher than that of contemporary samples of birds in which moult was continuing. In final samples in late April and early May mean weights showed a decline, indicating that late birds departed with reduced deposits of metabolic reserves. The gonads of adults of both sexes among passage and arriving birds in July and August had largely completed post-nuptial regeneration, and subsequently remained quiescent. Preliminary stages of recrudescence were observed in females from February onwards, and in males from March. Recrudescence was most advance in specimens which had completed the moult, but did not approach breeding condition in any bird before departure. Returning birds tended to be conservative in their choice of winter roost. Among 1,276 records, 82% were recaptured in the town of original ringing. Again shifts towards the centrally situated roost were more numerous than between the peripheral pair. The frequency of returns varied significantly with the month of ringing, being higher for December-March, lower for July-November and April-May. Survival rates, calculated from returns after one and two breeding seasons, indicated an annual mortality of 60–72%, higher among juveniles than adults. Comparison of results of successive years suggested that unfavourable conditions in 1967 resulted in lower survival of juveniles in particular than in 1966. There was no evidence of mortality at the roost sites, and it is argued that heavy losses probably occur during the migratory journeys.     

Carotenoid-based ornamentation and status signaling in the house finch

The status signaling hypothesis (SSH) was devised primarilyto explain the adaptive significance of avian ornamental colorationduring the nonbreeding season. It proposes that conspicuousmale plumage serves as an honest signal of social status withina population of birds. However, to date this hypothesis hasbeen well tested and supported for only one type of plumage coloration, melanin-based coloration. Carotenoid-based pigmentationis known to positively reveal male health and condition duringmolt in a variety of species, but it is poorly understood whetherthis ornament type can also function as a status signal duringthe winter. We tested the SSH in male house finches (Carpodacusmexicanus) by manipulating the carotenoid-based plumage brightnessof first-year males and then pairing unfamiliar birds of differingcoloration in a series of dominance trials in captivity. Manipulated plumage color was unrelated to win/loss outcome in these trials.Similarly, the natural pigmentation of males was a poor predictorof winter dominance; as in other studies with this species,we found only a weak tendency for naturally drab males to dominatenaturally bright males. These results suggest that carotenoid-basedcoloration is not a reliable indicator of social status inmale house finches during the nonbreeding season. In fact, carotenoid-based coloration may function only in mate choice in this species,and it may be retained throughout the year either because timeconstraints preclude a second plumage molt or because it aidsin pair formation that begins in late winter.     

Effects of population growth on Crested Tit Parus cristatus post-fledging settlement

From 1987 to 1993, the winter density of Crested Tits Parus cristatus in north Belgium increased 2.76 times. The increase was the result of high annual survival rates of both adult and first-year birds despite a low reproductive success (number of fledglings per female) due to high predation of nestlings. A fc-factor analysis assuming intermediate costs of post-fledging dispersal and settlement gave the best fit. First-year birds had two options when trying to settle in a prospective breeding territory: (1) establish a new territory during August or early September and defend it against neighbouring flocks during winter or immigrants in early spring or both, or (2) overwinter as a subordinate in a mixed-age flock and pair with a widowed adult or replace a territory owner in early spring ("hopeful dominant stategy"). Settlement strategies varied with density; at low density, only the hopeful dominant strategy was observed, whereas at higher density, both strategies occurred.     

Seasonal, size- and age-related patterns in body-mass and composition of Purple Sandpipers Calidris maritima in Britain

The masses of 3229 Purple Sandpipers Calidris maritima from Britain were analysed for differences related to age, season and size. First-year birds were lighter by 2 g. There was only a slight increase in mass in mid-winter, in contrast to other waders wintering in Britain, suggesting that Purple Sandpipers are less at risk to cold weather and food shortages. Their winter fat reserves were low but their breast muscles were relatively larger than other small waders wintering in Britain. Their plumage was slightly heavier and their breast and belly feathers were longer. There was a large increase in mass in May by first-year and adult birds prior to migration. The 'long-billed' population showed a greater relative increase in May, compared with the 'short-billed' population, perhaps reflecting different migration distances.     

Demography of Bristle-thighed Curlews Numenius tahitiensis wintering on Laysan Island

We studied the nonbreeding ecology of Bristle-thighed Curlews Numenius tahitiensis from 1988 to 1991 on Laysan Island in the Northwestern Hawaiian Islands. Using capture-recapture analysis, we estimated that 300–350 curlews wintered on the island. Annual survival was >85% for adults and 92% for first-year birds. Young birds remained on the island until at least their third calendar year, when some individuals made "exploratory" visits to other islands in the Northwestern chain. Most of the birds marked in their first year migrated north to the breeding grounds when they were 3 years old; several birds remained on the island until they were at least 4 years old. Adults returned to the same discrete home ranges year after year, whereas subadults (which do not migrate) tended to use a greater portion of the island. At least 60% of the subadults marked from 1988 to 1990 returned to the island to winter as adults. Because young curlews arrived after adults and experienced high survivorship while on the island, there did not appear to be intense competition for space at Laysan even though the island is at the northern end of the species' winter range.     

Population ecology of the Rice rat (Oryzomys palustris) in a coastal marsh

Rice rats were studied for four years by grid trapping in a tidal marsh on the northern Gulf of Mexico. Preliminary trapping indicated that marshes are preferred over other coastal habitats. Population densities fluctuated from spring lows of about 2/ha to highs of about 25/ha in the autumn and early winter. Reproduction occurred throughout the year, the major season being late spring to late autumn. Recruitment of juveniles was at a maximum from May to September. Males were more abundant than females in population samples, and had a higher mean body weight. This was because weight classes of 40 g and below were slightly skewed in favour of females and weight classes above 40 g heavily favoured males. The survival rate was low, with less than 20% of animals marked remaining on the grids for more than three months. Maximum longevity was 24 months. Results are compared to those of previous studies done on an offshore island and in the Florida everglades.     

The relationship between dominance behaviour, bill size and age group in Greater Sheathbills Chionis alba

A dominance hierarchy developed within a wintering flock of Greater Sheathbills which fed regularly at a concentrated artificial food source. Each bir's dominance position was determined from the proportion of interactions in which it was displaced, and from the number of other birds which it was seen to displace.
Most dominant birds were known to be over 6 or 7 years of age. They had larger bills than their subordinates had and initiated displacement interactions more often. After each interaction the displacer resumed feeding more quickly than the bird it displaced. Although dominant birds had a higher average peck rate, they did not maintain a higher body mass throughout the winter, nor did they show a higher survival rate than their subordinates.     

Nocturnal loss of body reserves reveals high survival risk for subordinate great tits wintering at extremely low ambient temperatures

Winter acclimatization in birds is a complex of several strategies based on metabolic adjustment accompanied by long-term management of resources such as fattening. However, wintering birds often maintain fat reserves below their physiological capacity, suggesting a cost involved with excessive levels of reserves. We studied body reserves of roosting great tits in relation to their dominance status under two contrasting temperature regimes to see whether individuals are capable of optimizing their survival strategies under extreme environmental conditions. We predicted less pronounced loss of body mass and body condition and lower rates of overnight mortality in dominant great tits at both mild and extremely low ambient temperatures, when ambient temperature dropped down to ?43 °C. The results showed that dominant great tits consistently maintained lower reserve levels than subordinates regardless of ambient temperature. However, dominants responded to the rising risk of starvation under low temperatures by increasing their body reserves, whereas subdominant birds decreased reserve levels in harsh conditions. Yet, their losses of body mass and body reserves were always lower than in subordinate birds. None of the dominant great tits were found dead, while five young females and one adult female were found dead in nest boxes during cold spells when ambient temperatures dropped down to ?43 °C. The dead great tits lost up to 23.83 % of their evening body mass during cold nights while surviving individuals lost on average 12.78 % of their evening body mass. Our results show that fattening strategies of great tits reflect an adaptive role of winter fattening which is sensitive to changes in ambient temperatures and differs among individuals of different social ranks.     

Weights and growth rates in the Mountain hare Lepus timidus scoticus

Mountain hares were weighed during live trapping on a study area near Dufftown, Banffshire, from June 1958 to August 1966. Hares shot or killed by other means on the study area and elsewhere were also weighed. Females were heavier than males throughout the year and this difference became apparent in juveniles by August of their year of birth. Male hares lost weight during the breeding season (January to June) but regained it in late summer. Young hares gained weight initially at about 14 g per day, then at about 6 g per day to adult weight. Small juveniles, or those born late in the season, tended to become small adults, large or early juveniles to become large adults. Small hares moulted less completely andjbegan to breed later in the season than large hares. The effects of disease, starvation, severe weather and injury on hare weights were considered. Female weights were greater when the population was small, due to more late pregnancies or more embryos per female. Weight could not be used to distinguish between adult and juvenile hares above 2.1 kg, nor between young and older adults.     

Vererbung einer populationsspezifischen Mauser bei Kreuzung von M?nchsgrasmücken (Sylvia atricapilla) verschiedener Populationen

A comparative study of migratory blackcaps from Central Europe (S. Germany) and resident conspecifics from the Cape Verde Islands revealed marked differences in annual periodicity. European blackcaps, with one breeding season per year, have a single-peaked annual gonadal cycle whereas the African birds with two breeding seasons per annum have a two-peaked gonadal cycle. The European birds go through a post-juvenile moult (partial moult in first-year birds) or postnuptial moult (complete moult in adults) and, in addition, through a partial winter moult (all age classes) before the next gonadal cycle and breeding season. Their African conspecifics, on the other hand, have only one moult between two gonadal cycles, the summer moult also being the complete one. Here, we demonstrate that the additional winter moult of European blackcaps is heritable and can be transmitted into interpopulational hybrids. When blackcaps from S. Germany and the Cape Verdes were cross-bred, 16 out of 21 hybrids displayed the partial winter moult of their German parents. The fact that not all but only 76% of the F1 hybrids passed through this moult favours the idea that its incidence is controlled by a polygenic rather than a single locus system. Most likely winter moult in European blackcaps represents a threshold character as several migratory features do.     

Differential response to the odor of familiar intruder mice in male mice (Mus musculus)

Responses to the odor of familiar intruder male mice according to their dominance were investigated. Responses were classified into 2 aspects: the investigation of the odor and the decision-making regarding avoiding it or not. The results varied according to the dominance of the respondents and the odor donor, and also according to the context of previous encounter situations. The dominants that had attacked an intruder dominant mouse responded randomly to its odor, whereas the dominants that had fought with it tended to avoid the odor. The subordinates that had observed an intruder dominant mouse being attacked by its dominant cagemate preferred the passage with the intruder's odor. The odor of a subordinate mouse was neither avoided nor preferred by either the dominants or subordinates. It was suggested that mice distinguished the dominance of the odor donor regardless of the context of the previous encounter situation, but they responded differently according to it and also according to their own dominance status.     

Piping as a display of dominance by wintering Oystercatchers Haematopus ostralegus

Although Oystercatchers Haematopus ostralegus wintering in the Exe Estuary performed the piping display in any type of aggressive encounter, it was predominantly observed in two contexts. ‘Solitary piping’ occurred when one individual piped without an obvious opponent being in the immediate vicinity. In ‘piping ceremonies’, two or more individuals piped at each other for prolonged periods at close distance. Prolonged contests over mussels were usually won by the individual that had initially started piping. The most aggressive and successful birds (the dominants), engaged most often in solitary piping and piping ceremonies, using up to 10% of their time this way. This suggests that the behaviour was associated with dominance rank. The hypothesis is that the two birds are likely to start piping if their relative status has not already been established, so that a quick end to a dispute over a mussel or feeding site is not achieved. A dominant individual performs solitary piping from a distance to suppress the aggressive activities of other birds within its feeding range. If this signal fails, the dominant may join the ceremony, explaining why three was the most frequent number of birds involved in piping ceremonies. The ‘butterfly’ flight, used mainly by apparently dominant birds as they arrived on the feeding grounds, may signal their high status to birds already there. The outcome of several piping ceremonies involving birds of known dominance was consistent with this explanation. The location of piping ceremonies involving only two birds (interpreted as piping ceremonies not joined by dominants) at the extremities of the feeding ranges of the most dominant individuals is also consistent with this hypothesis, because this is where their dominance would be expected to decline and would therefore be more likely to be contested. This explanation of piping and butterfly displays assumes that individuals can recognize other individuals or quickly assess their dominance. Since dominant individuals were attacked less often than subdominants and attacking birds were rebuffed less than would be expected if recognition did not occur, we suggest that some form of dominance or individual recognition did exist. The width of the white collar did not correlate with dominance, but the individual variations in this feature may enable birds to distinguish each other and thus learn their relative status. It is intriguing that the diplomatist posture, which is typically used to rebuff misguided attackers, seems almost designed to give the opponent a particularly clear view of the white collar.     

A population study of the japanese wood mouse,Apodemus speciosus (Mammalia: Muridae), with reference to its social behavior

The role of social behavior on the population regulation of the Japanese wood mouse, Apodemus speciosus, was studied in the Ashu Experimental Forest of Kyoto University by monthly trapping and direct observation on the social behavior at the artificial feeding site. The census was carried out from May to October in 1974 and 1975, and the direct observation in June, August and October, 1975. In the study area, the Japanese wood mouse has two breeding seasons in a year: in spring and in autumn. Minimum survival rate was high in the non-breeding season and low in the breeding season. It was negatively correlated to the number of sexually active adults in both sexes. Home ranges of females tended to be mutually exclusive, and female residents prevented the settlement of female immigrants. On the other hand, home ranges of males overlapped largely and males had a straight social hierarchy. Subordinate males tended to disappear more often than dominant males did, but male residents did not hinder the settlement of male immigrants. Males may regulate their number by driving out the subordinate males, while females by spacing behavior.     

Survival rates of Redshank Tringa totanus wintering on the Moray Firth

Long-term mark–recapture data were used to estimate the annual survival rates of Redshank wintering on the Moray Firth in Scotland. Survival modelling required the exclusion of all birds caught during the main passage months (August, March and April), and a highly variable annual catching effort limited the precision of annual survival estimates. Survival rates of juvenile Redshank (between the first and second winters of life) varied markedly from year to year and averaged 43% (se 3.6%). Adult survival rates were less variable between years and were age-dependent, with 67% (se 5.0%) surviving and returning between the second and third winters of life, compared to 74% (se 1.4%) for older birds. Year-to-year variation in adult survival was weakly (and negatively) related to the number of snow days in winter. Year-to-year variation in first-year survival was non-linearly related to winter rainfall, with low survival during dry (and cold) winters, higher survival during winters with average rainfall and lower survival during wet winters. Having accounted for these weather relationships there was no evidence that survival was related to the size of the local wintering Redshank population. Organized annual ringing programmes of wintering waders on British estuaries have the potential to monitor long-term changes in survival rates and productivity. Although constant effort sampling may be difficult to achieve for wintering waders, the utility of mark–recapture data collected on estuaries is likely to depend heavily on careful study design.