First-year Males Research Articles

Can 16-18-year-old elite ballet dancers improve their hip and ankle range of motion over a 12-month period?

To determine the effect of a 12-month intensive ballet training regimen on hip and ankle range of motion in male and female, first- and second-year professional dancers. 12-month longitudinal follow-up. National classical ballet school in Australia. 28 female and 20 male full-time ballet students with a mean +/- 1 SD, ages 16.8 +/- 0.8 and 17.7 +/- 1.2 years, respectively. Degrees of range of motion of left and right sides for the following movements: standing plié in parallel-passive ankle dorsiflexion (DF); standing turnout in the balletic first position--lower leg external rotation (LLER); supine hip external rotation (ER); supine hip internal rotation (IR). An additional range of motion was calculated: external rotation below the hip joint (BHER) derived by subtracting hip ER from LLER. In all subjects combined, hip and ankle ranges increased statistically on the right. However, the amount was generally minimal and most at the borderline of the amount of error associated with the measurement tool. While there was no change in LLER, there was a decrease in BHER. There were no overall gender differences, and year differences existed only for left hip ER and total hip ER with first-year dancers showing significant improvements in these ranges. For DF and sum of hip IR, first-year males and second-year females had increases in range. There was a negative relationship between baseline range and the amount of change over the 12 months. Dancers ages 16-18 years who enter full-time ballet training did not augment their ankle dorsiflexion to any appreciable degree. Some, but certainly not all, increased their hip active external rotation over 12 months without increasing their total lower limb turnout. Hip ER was more likely to improve in the first-year rather than second-year student in this elite full-time training school.

Social inhibition of territorial behaviour in yearling male collared lizards,Crotaphytus collaris

In central Oklahoma, collared lizard males display age-dependent differences in social behaviour, whereby sexually mature first-year (yearling) males adopt subordinate tactics, and males 2 years and older establish and defend all-purpose territories. We tested the hypothesis that the social activities of adult males inhibit the expression of territorial tactics in yearling males by recording the behaviour of yearlings in the presence of adult males, when all adult males were removed from study plots for 4 days, and then again when adult males were returned to their territories. The rates of yearling male patrol, display and intrasexual encounters increased during removals, especially during the last 2 days, following which the rates of these behaviour patterns declined when adult males were replaced. Yearling males also increased the frequency with which they interacted with females when adult males were removed. Moreover, the duration of intersexual encounters during the last 2 days of removal was over twice that during the first 2 days of removal, suggesting that females became more receptive to yearling males the longer adult males were absent. Our results suggest that the stable age-related behavioural differences in male collared lizards is governed by social feedback, where sexually mature yearling males are capable of displaying territorial behaviour patterns but are inhibited from doing so by the activities of adult males.

Callers and satellites: chorus behaviour in anurans as a stochastic dynamic game

Males often compete for mates using alternative tactics whose relative success could be simultaneously influenced by four factors: subsequent behaviour, physiological state, the frequency of expression of alternative tactics and the density of competing males. Here the payoffs to two alternative male mating tactics (call and satellite) were examined in anurans using a stochastic dynamic game. The basic model considers an iteroparous species with a prolonged breeding season and fairly low energetic costs and predation risks. The model assumes that female chorus attendance is affected by weather, time of year and male chorusing intensity. Results show that interactions between energetic costs of calling, density-dependent predation risk and female arrival rates, and frequency-dependent mating success produce distinct temporal waves of male chorusing despite continuously favourable environmental conditions. Relative to second-year males, first-year males attended choruses less often and were more likely to become satellites. When the energetic costs of calling were increased, waves became shorter and less frequent, and some older calling males switched to satellite behaviour. Satellites were less common when breeding season length was constrained by extrinsic factors such as seasonal weather patterns. Extrinsic constraints may also affect system stability: if female arrival rates are independent of male chorusing intensity, an evolutionarily stable strategy occurs only if the breeding season is short. Even without extrinsic constraints, the breeding season may be short if predation rates on adults are sufficiently high, or if satellites intercept a large fraction of incoming females. Thus, the ‘explosive’ breeding systems observed in many anuran species could result from either biotic or abiotic causes.

On Alternative Reproductive Tactics in Anurans: Dynamic Games with Density and Frequency Dependence

Intense mating competition and mate choice has favored the evolution of alternative mating tactics in many species. We developed a stochastic dynamic game to evaluate the choice among three alternative mating tactics by male anurans: call, satellite, or leave the chorus to forage or hide. The strategies were assumed to differ in mating success (call > satellite forage = hide), predation risk (call > satellite > forage > hide), and energetic expense (call > satellite = hide > forage). Six major predictions were derived. First, in relatively stable environments, males should enter a chorus in a synchronous pulsed pattern, with first-year males primarily choosing to be satellites on older calling males. The pulsed pattern is caused by the relatively high energetic cost of calling and the dependence of female arrival rates on chorus size (which promotes synchronization). In unstable environments, energetic constraints are reduced because favorable conditions are rare, so most males should call on favorable ni...

Trade-offs between life-history traits and a secondary sexual character in male collared flycatchers

IT has often been suggested that sexual selection may have important consequences for life-history evolution and vice versa1-5. We manipulated the parental effort of male collared flycatchers (Ficedula albicollis) by changing the number of offspring in their nests and found a trade-off between parental effort and the size of the male's forehead patch (a secondary sexual character) in the following year. We report here that, in addition to this intra-generational trade-off, we found an inter-generational trade-off: the size of the forehead patch in first-year males was negatively related to the change in brood size of the nest in which they were raised. This has consequences for reproductive success because males with large patches mate with more females and have higher lifetime reproductive success. To our knowledge, this is the first experimental demonstration that life-history traits and secondary sexual characters trade off against each other. Our results support the suggestion that the life-history consequences of sexual ornaments are important in their evolution2-4.

Alarm calling by willow tits, Parus montanus, as mate investment

The response of captive willow tits to a life-like, stuffed sparrowhawk, Accipiter nisus, was studied during four consecutive winters in Central Norway. Birds from 31 flocks, usually consisting of one adult mated pair, with two first-year males and two first-year females (non-kin), were studied in an outdoor aviary. When the sparrowhawk, kept 4 m away out of sight of the tits, was suddenly presented to individual birds, all the tits froze and some gave alarm calls. Adult birds gave alarm calls more frequently than juveniles, adult males more than juvenile males, and adult females more than juvenile females. Adult males gave an alarm call more frequently when they could see their mates than when they could not and alarm calling may therefore be a form of investment in the mate.

Song copying and cultural transmission in indigo buntings

Abstract. First-year male indigo buntings, Passerina cyanea, copy the song of a neighbouring male during their first breeding season. To determine whether they assess their neighbours and copy selectively the songs of certain males, the following predictions were made from hypotheses of assessment and socially biased learning: (1) first-year males assess a neighbour and copy his song if he meets a minimum standard; (2) first-year males prospectively assess the breeding success and survival of several neighbours, then copy the song of one that has a high breeding success, and (3) first-year males sample their neighbourhood for a common song and conform to it. The 'song model' was identified and the male's breeding success determined in 580 cases of cultural transmission. More males than expected at random had either zero or more than two other males copy their song. One predictor of song transmission by potential 'models' was age (first-year or adult), a trait assessable by plumage colour. Adult males were more likely to transmit their song than were first-year males. In one population the bluer first-year males were more likely to be copied than were the browner first-year males. Also, a male that arrived early in the breeding season was more likely than a later arrival to be copied. The first-year males in a dense neighbourhood were more likely to copy a neighbour's song, but they did not generally conform to the most common song in their area. Although time of arrival and a minimal standard of plumage and behaviour may explain some variation between males in cultural success, much of the variation was unexplained. Many adults were not copied, because of the age structure of the population with more adults than first-year males. Also, many males that had a successful breeding season were not copied, perhaps because their success was unpredictable early in the season when most first-year males acquire a local song.

Differences in Timing and Number of Molts for Baltimore and Bullock's Orioles: Implications to Hybrid Fitness and Theories of Delayed Plumage Maturation

We compare the molt and migration schedules of Baltimore (Icterus g. galbula) and Bullock's (I. g. bullockii) orioles, describe how bullockii and Black-backed Orioles (I. g. abeillei) in juvenile plumage can be distinguished, and present a simple quantitative character that serves to distinguish the juvenile and basic plumages of bullockii. Galbula undergoes the first and later prebasic molts on the breeding grounds, while bullockii in both juvenile and worn breeding plumage almost certainly migrate to the American southwest prior to undertaking the fall molts. This early migration by bullockii has probably been favored as a mechanism for them to escape the dry late summer conditions that prevail in most of their breeding range and to exploit for molting the food flush caused by the late summer monsoon rains in the southwest. With but one exception, every bullockii specimen taken in late summer or fall south of the breeding range in Mexico was in fresh basic plumage. Thus, the fall migration of bullockii may be interrupted for the prebasic molts. Bullockii almost entirely lacks a prealternate molt in all sex and age classes. The prealternate molt in galbula is fairly extensive in first-year males but limited in females and in older males. First year galbula males initiate this molt in their throat in early winter, perhaps to acquire a badge that helps distinguish them from first-year females, which have light throats, and from those older females that have light throats. Some galbula males that are almost a year old also undergo part of the prealternate molt after their arrival on the breeding grounds. Implications of these observations for theories of subadult plumages are discussed. These differences between galbula and bullockii in the timing of the fall molts relative to the fall migration and in having or not having a prealternate molt may provide strong sources of selection against hybrids. One specimen illustrating some of the potentially deleterious recombinations of molt and migration schedules among hybrids is described in detail.

Is the absence of first-year males on breeding grounds in the scarlet rosefinch related to a male-biased sex ratio?

Etude, chez Carpodacus erythrinus, de l'absence de mâle de un an dans les populations. Cette etude examine l'influence jouee par la predation sur les femelles dans ce sex ratio biaise

Status signalling in dark-eyed juncos, Junco hyemails: plumage manipulations and hormonal correlates of dominance

Status signalling in dark-eyed juncos was investigated by using plumage manipulations and observing interactions within pairs of birds. Plumage manipulations included darkening of the hood and mantle and the addition of white tail feathers to mimic the appearance of adult males. Plumage characteristics predicted dominance relationships within pairs of first-year males when body size and prior residence in cages was controlled. These characteristics were also strong enough to reverse previously established intra-class relationships within pairs of first-year males and first-year and adult females. The results fail to support the incongruence hypothesis ( Rohwer: Behaviour, 1977, 61, 107–129; Rohwer & Rohwer: Anim. Behav., 1978, 26, 1012–1022). In contrast to recent studies using exogenous testosterone to investigate dominance behaviour, circulating plasma levels of testosterone were measured and a comparison made between those of dominants and those of subordinates. Plasma levels of corticosterone were also analysed as a measure of stress. No correlation between either hormone and dominance status was found. Hypotheses are proposed to explain the absence of a relationship between circulating levels of testosterone and winter aggression in flocking birds.

Distribution and Dispersal in the Piping Plover

Abstract Individually marked Piping Plovers (Charadrius melodus) were studied from 1981-1987 in Manitoba and Minnesota relative to dispersal patterns of age and sex classes. Unlike monogamous passerines, males returned to former breeding sites only slightly more often than females. Dispersal distances did not differ between the sexes. Across North America, 24-69% of adults exhibited breeding-site fidelity, a variability equivalent to that among species of migratory shorebirds. Distribution of Piping Plover habitat across the species range accounts for some of this variability: birds used local sites if they were available, rather than disperse long distances. Similar to most migratory shorebirds, few (1.6-23%) Piping Plover chicks returned to natal sites to breed. No difference was found in return patterns between first-year males and females, nor in distances either sex dispersed from natal sites. First-year birds were found in the vicinity of their natal sites when habitat was available. During winter, birds from the Northern Great Plains and Great Lakes were seen primarily in mixed population flocks on the Gulf of Mexico. Piping Plovers from Atlantic coast breeding areas wintered further south on the Atlantic.

Social Status, Circulating Levels of Hormones, and Competition for Food in Winter Flocks of the White-Throated Sparrow

We measured plasma levels of luteinizing hormone (LH), testosterone (T), 5α-dihydrotestosterone (DHT) and corticosterone (B) in flocks of wintering white-throated sparrows. This species occurs in two colour morphs that are distinguishable by white or tan colour of the median crown stripe and differ in frequency of agonistic behaviour during the reproductive season. During winter, white-throated sparrows form flocks that are characterized by dominance hierarchies, in which social rank was correlated with sex and age, but not with crown colour. Plasma levels of LH and androgens (T and DHT) were basal in most free-living and captive birds and not correlated with sex, age, morph or social rank. Plasma levels of testosterone did not increase in captive groups, when aggressive interactions increased due to experimental manipulation of distribution and amount of food. These results suggest (1) that dominant-subordinate relationships during the wintering phase are not based on differential aggression of plumage types and (2) that they are not maintained by elevated plasma levels of androgens in high-ranking birds. Plasma concentrations of B increased rapidly with duration of capture stress in females and first-year males, but not in adult males. Since adult males were of highest rank it appears that high social status may restrain acute adrenal response to stress. Further, baseline levels of B were highest in low-ranking first-year females and lowest in high-ranking adult males. In captive groups, amount and distribution of food resources altered levels of B. Levels appeared to be most variable and very high in some birds of intermediate rank, when agonistic interactions in competition for food were most frequent. This suggests greater impact of change in food distribution on those birds, whose social status is less clear than that of high or low ranking birds.

Territory takeover and sexually selected infanticide in tropical house wrens

Tropical house wrens in lowland central Panama are, with rare exception, permanently monogamous. During a 3-year demographic study of 54–56 pairs of these brids, both males and females committed infanticide in association with takeover of breeding territories. New males and new females replaced previously identified (color-banded) parents before the termination of parental care in 13% of 328 breeding attempts. Replacement was accomplished by physical takeover in at least some if not all cases. Total nest failure at the egg, nestling, or fledgling stage occurred in 73% of the male replacements and 70% of the female replacements. Nest predation was excluded as a possible cause of nest failure. 76% of male replacements and 50% of female replacements bred in the same season. Infanticidal replacement males bred sooner than did non-infanticidal males arriving at similar stages of the nesting cycle. Contexts in which infanticide occurred included takeovers by first-year males and females of territories and mates, re-entry into the breeding population by males that had recently lost their mates, acquisition of neighboring females by bigamous males, and the elimination of one female of a bigamous male by the other. Sexually selected infanticide in these birds is promoted by a lengthy breeding season and extremely limited breeding opportunities for individuals not already part of the breeding population. Mate limitation appears to be more important than habitat or nestsite limitation in restricting new breeding opportunities once the breeding season has begun.

Effects of Muscle Biopsy on Survival and Breeding Success in Indigo Buntings

Breeding Indigo Buntings (Passerina cyanea) were sampled by pectoral muscle biopsy for electrophoretic analysis, and their breeding success and survival were compared with buntings that were only handled and color-banded and with buntings banded in an earlier year. Behavioral and reproductive comparisons showed little difference in males or in females among the three groups. First-year males were more likely to disappear (and presumably to disperse to a new breeding site) after being caught and biopsied before breeding than after being caught and only marked. Mating and fledging success of breeding buntings was not affected by biopsy or by capture and marking. Annual survival of adults was independent of biopsy. Nestling buntings survived to fledging equally well in biopsied and in banded broods, but were less likely to survive when their mother was netted near the nest than when she was not, due to predation. Buntings biopsied as nestlings returned and bred in the study area but at a lower incidence than control buntings banded as nestlings. Muscle biopsy appears to be a nondestructive technique that is compatible with most aspects of long-term population studies of small songbirds.

Endocrine Correlates of Autumnal Behavior in Sedentary and Migratory Individuals of a Partially Migratory Population of the European Blackbird (Turdus merula)

Abstract Plasma levels of luteinizing hormone (LH), testosterone, 5α-dihydrotestosterone (5α-DHT), estradiol-17β, and corticosterone were measured in free-living and captive European Blackbirds (Turdus merula) during autumn. Free-living birds were designated as sedentary or migratory according to whether they remained in or disappeared from the study area during the winter season. Captive birds that increased body weight, deposited fat, and developed Zugunruhe in autumn were designated as migratory, whereas those that failed to do so were regarded as sedentary. The results do not support the hypothesis that plasma levels of gonadal hormones are elevated in sedentary birds, thus inhibiting autumnal migration. Plasma levels of LH and of testosterone were low in both adult and first-year free-living males, although testosterone levels were higher in migratory than in sedentary free-living first-year males. In captivity, however, testosterone levels were not different between first-year sedentary and migratory males. In both free-living and captive first-year females levels of 5α-DHT were higher in migratory than in sedentary individuals. Our analyses suggest that the sedentary and migratory habit may be a consequence of different reactions of genetically different individuals to a slightly increased secretion of gonadal hormones in autumn. The variable plasma levels of corticosterone suggest that this hormone is not directly involved in the initiation of migratory behavior, although circulating levels of corticosterone may be influenced by energetic demands during migration.

ADAPTIVE SIGNIFICANCE OF DELAYED PLUMAGE MATURATION IN MALE NORTHERN ORIOLES.

The Northern Oriole (Icterus galbula) is one of 105 sexually dichromatic species of passerine bird in North America. Like 29 other species in this group, it exhibits delayed male plumage maturation: although reproductively mature during their first potential breeding season (Flood, 1980; Sealy, 1980), male Northern Orioles do not acquire fully adult breeding plumage until the following year. Females, which do attain adult appearance when less than a year old, are variable in coloration. Individual females may be bright, although most are much duller than the brilliantly-colored black and orange adult males. During their first potential breeding season males possess a variable plumage that is, on average, intermediate between that of females and older males. The appearance of females and first-year males overlaps considerably, however, and it is impossible to determine with certainty the sex of a dullcolored bird on the basis of plumage alone. Delayed plumage maturation poses an interesting evolutionary problem. If, as is thought, the bright coloration of males in some way facilitates their ability to breed, what is the advantage to first-year birds of looking like females? Two hypotheses have been proposed to explain the adaptive significance of delayed male plumage maturation in passerines. The first, suggested by Lack (1954) and developed in more detail by Selander (1965, 1972) has been termed the Sexual Selection Hypothesis (SSH) (Wittenberger, 1978; Rohwer et al., 1980). The basic premise of the SSH is that in certain situations, the life-time fitness of males is increased if reproduction is deferred until after the first potential breeding season. In some taxa, the intensity of male aggression may exclude young, inexperienced males from breeding. Also, colorful males-especially while displaying-must be exposed to greater risk of predation than ones that are cryptic in plumage and action. According to Selander (1965, 1972), first-year males should be selected to minimize their conspicuousness if there is little chance for them to breed. This could be achieved by the adoption of a cryptic plumage and the avoidance of competition and courtship during the first year. More recently, Rohwer and others have advanced an alternative explanation for delayed maturation which they term the Female Mimicry Hypothesis (FMH) (Rohwer, 1978; Rohwer and Niles, 1979; Rohwer et al., 1980). In contrast to the SSH, the FMH suggests that delayed maturation is not a handicap to, but actually facilitates, breeding by first-year males. The dull coloration of yearling males allows them to mimic females and thereby deceive adult males; it allows them to exploit the tendency of such males to defer to females. By this deceit young males may establish residency within or near the high quality territories of adult males, and acquire sufficient site dominance (Maynard Smith, 1974; Parker 1974) to be able to retain a space for breeding, and attract a female. Although the FMH and the SSH are not mutually exclusive, they do give rise to a number of differing predictions. In this study I investigate the adaptive significance of the delay in acquisition of bright plumage by male Northern Orioles, and test various predictions arising

Arrival and pre-nesting period of the snow bunting Plectrophenax nivalis in East Greenland

The first snow bunting males arrive in Northeast Greenland in early April, 6-8 weeks before nesting and 2 4 weeks ahead of the females. At this time temperatures regularly reach -25 to -30°C and snow storms may rage for days. The living conditions during this long-lasting pre-nesting period and its possible function are described and discussed. Based on 781 birds caught. .ringed, and measured, and on observations on phenology, diurnal rhythm, night roosts, etc., it is shown that the age ratio in males is close to 50/50 first living year/adults, that adult males arrive and occupy territories earlier than first year males, that first-year males have shorter wings and are leaner than adult males, that the birds lose weight during spells of inclement weather early in the season, that diurnal rhythm is apparently governed by direct insolation, that males apparently greatly outnumber females in the populations, and that competition for the optimal territories is probably the selective force behind the prolonged pre-nesting period in males.

The social context of song mimicry: Song-matching dialects in indigo buntings ( Passerina cyanea)

First-year male indigo buntings ( Passerina cyanea) that match the song of an adult neighbour gain an advantage in acquiring a female, in nesting and in fledging young, when compared with first-year males that do not match a neighbour's song (Payne 1982). Four hypotheses of the mechanisms responsible for the mimics' success were tested in the field. Song matching among neighbours was not involved with recognition of local demes or with assortative mating; the population structure of song neighbourhoods is open and songs are not signals of kinship or community. Song matching was not directed towards females in sexual mimicry, and females rarely switched from an old mate to a younger one with the same song. Song mimicry was not directed towards the neighbouring male whose song was copied, as he was no less aggressive towards a song mimic than towards non-mimics. Song mimicry was associated with the timing of territorial establishment and of associated dispersal and residence in the first-year males. Four out of six predictions of a hypothesis of intraspecific competitive mimicry among male buntings were realized. The results best fit the hypothesis that a male that mimics the song of an older neighbour may deceive his territorial competitors, the other first-year males, in mistaken individual recognition.

Arrival and pre-nesting period of the snow bunting Plectrophenax nivalis in East Greenland

The first snow bunting males arrive in Northeast Greenland in early April, 6-8 weeks before nesting and 2 4 weeks ahead of the females. At this time temperatures regularly reach -25 to -30°C and snow storms may rage for days. The living conditions during this long-lasting pre-nesting period and its possible function are described and discussed. Based on 781 birds caught. .ringed, and measured, and on observations on phenology, diurnal rhythm, night roosts, etc., it is shown that the age ratio in males is close to 50/50 first living year/adults, that adult males arrive and occupy territories earlier than first year males, that first-year males have shorter wings and are leaner than adult males, that the birds lose weight during spells of inclement weather early in the season, that diurnal rhythm is apparently governed by direct insolation, that males apparently greatly outnumber females in the populations, and that competition for the optimal territories is probably the selective force behind the prolonged pre-nesting period in males.

The biology of the stoat (Mustela erminea) in the National Parks of New Zealand IV. Reproduction

Abstract The gonads of 528 female and 821 male stoats were examined. The weights of ovaries and testes in adults peaked simultaneously in October, the season of births and of post-partum oestrus. Of 73 females, 78% had even numbers of nipples, mostly 8 or 10. The mean number of embryos in 13 pregnancies was 8.8 (6–13), and embryo weights ranged from 0.005 g to 2.9 g. Of 11 pregnant females, 8 contained fewer embryos than corpora lutea, and there was evidence of transuterine migration of blastocysts in 6. All but 2 of 451 females caught in December–July inclusive carried corpora lutea of delay. Few adult and no young females were found in oestrus in September–October, though adult males were fertile from August to February (no first-year males were fertile). There was some evidence that the breeding season started later at more southerly latitudes in both males and females. The mean number of corpora lutea per female was 9.7 (n = 439), and there was a significant inverse correlation between counts for the 2 ovaries of one individual. There was generally no significant variation in fecundity of females with age, body weight, or year. Of 11 females which were considered to have lost their litters, 10 were collected in beech (Nothofagus) forests. Four females and 9 males had abnormal gonads; the most severe abnormality was an ovarian teratoma of unknown pathology.