Identification of different song types in the European Nightjar Caprimulgus europaeus

ABSTRACT

Capsule: Two distinct song types were identified for male European Nightjars Caprimulgus europaeus with their relative frequency of use changing through the breeding season, indicating a possible link to paired status.

Aims: To test whether two song types could be defined in audio recordings and whether use differed in relation to the paired status of males.

Methods: Unattended acoustic recording devices were placed at a Nightjar study site in Nottinghamshire, United Kingdom, and recordings of churring vocalizations were made during two periods of the breeding season. These recordings were then analyzed to identify the presence/absence of the song terminal phrase and associated audible features.

Results: Two distinct song types were identified in the recorded audio data that differed in their terminal phrasing and overall song duration. The number of Nightjar songs with a terminal phrase increased significantly between the two sampling periods, from lower levels during the site arrival period, to higher levels during the first clutch initiation period.

Conclusion: This study showed that the use of Nightjar song types appears to vary through the breeding season, with males being more likely to produce song with a terminal phrase during the first clutch initiation period, when they are more likely to be paired or in the presence of a female. The unattended acoustic recording method may provide a minimally intrusive means of assessing the number of Nightjar breeding pairs and not just singing males.     

Effects of reproductive state on vocalizations in squirrel monkeys (Saimiri sciureus)

Vocalizations and behavior of a group of 6 squirrel monkeys, 2 males and 4 females, were recorded during the nonbreeding and breeding seasons. Behavioral and physical criteria were used to determine the presence of estrus. During the breeding season the types of vocalizations uttered by estrous females changed, and the adult male increased his rate of vocalizing. Err vocalizations by estrous females were associated with increased following and initiation of affiliative behavior with the adult male, and may have functioned to facilitate these interactions. Errs appeared to be related to changes in female reproductive state rather than to the behavior of others. The adult male increased vocalizations associated with sexual and aggressive behavior (squeals and cackles), primarily in response to the estrous females' persistent initiation of interactions with him. We concluded that certain vocalizations in Saimiri reflected changes in the reproductive state of males and females, and functioned to mediate changes in social bonding during the breeding season.     

THE BIRDS OF BLYTHSWOOD AND SOME NOTES ON BIRDS OF THE DISTRICT

Wintle, C. C. &; Taylor, P. B. 1993. Sequential polyandry, behaviour and moult in captive Striped Crakes Aenigmatolimnas marginalis. Ostrich 64:115-122.

Captive Striped Crakes showed sequential polyandry, the female laying for a second male when the clutch of her first mate was about to hatch. Where aviary space permitted each male set up a breeding territory and each female defended a larger area encompassing the territories of one or two males. Non-territorial subordinate males and females did not breed. The female initiated breeding by attracting the male and soliciting copulation, and the male incubated the eggs and cared for the young. Incubation took 17–18 days, the chicks left the nest at 4–5 days of age and were fully grown and capable of flight at 46–53 days. Breeding occurred from September to March and males normally reared two broods per season. Territoriality was evident only during the breeding season. Juvenile plumage was a duller version of the sexually dimorphic adult plumage; post-juvenile moult bean at 13–15 weeks and was complete at 21 weeks. Remex moult was simultaneous and a complete moult regular1 occurred twice a year in adults, in December and April (males) and September and March/April (females).     

‘Good-genes’ and ‘compatible-genes’ effects in an Alpine whitefish and the information content of breeding tubercles over the course of the spawning season

Some models of sexual selection predict that individuals vary in their genetic quality and reveal some of this variation in their secondary sexual characteristics. Alpine whitefish (Coregonus sp.) develop breeding tubercles shortly before their spawning season. These tubercles are epidermal structures that are distributed regularly along the body sides of both males and females. There is still much unexplained variation in the size of breeding tubercles within both sexes and with much overlap between the sexes. It has been suggested that breeding tubercles function to maintain body contact between the mating partners during spawning, act as weapons for defence of spawning territories, or are sexual signals that reveal aspects of genetic quality. We took two samples of whitefish from their spawning place, one at the beginning and one around the peak of spawning season. We found that females have on average smaller breeding tubercles than males, and that tubercle size partly reveals the stage of gonad maturation. Two independent full-factorial breeding experiments revealed that embryo mortality was significantly influenced by male and female effects. This finding demonstrates that the males differed in their genetic quality (because offspring get nothing but genes from their fathers). Tubercle size was negatively linked to some aspects of embryo mortality in the first breeding experiment but not significantly so in the second. This lack of consistency adds to inconsistent results that were reported before and suggests that (i) some aspects of genetic quality are not revealed in breeding tubercles while others are, or (ii) individuals vary in their signaling strategies and the information content of breeding tubercles is not always reliable. Moreover, the fact that female whitefish have breeding tubercles of significant size while males seem to have few reasons to be choosy suggests that the tubercles might also serve some functions that are not linked to sexual signaling.     

Age at sexual maturity of males and timing of the mating season of polar bears (Ursus maritimus) in Greenland

Age at sexual maturity among male polar bears (Ursus maritimus) and timing of the mating season were studied by microscopic and macroscopic analysis of the reproductive organs from 165 male and 92 female Greenland polar bears. Males became sexually mature in the spring following their fifth birthday. Testes sampled during the spring reached 95% of their asymptotic length at 5.8 years. Some spermatozoa were found in 2- to 4-year-old bears during the spring, but only in low concentrations in a mixture of other cell types. The first corpus luteum was found on 1 April and most ovulations were estimated to occur before mid-May which indicate that the peak of the mating season begins in late March and ends in May. These findings are somewhat different from a similar study from Svalbard, where the mating season is estimated to peak later and male polar bears are found to become mature earlier. We hypothesize that these differences occur because adolescent males have their peak testicular activity after the main breeding period and therefore appear to be fully sexually mature during summer and not during spring.     

Double brooding and offspring desertion in the barn owl Tyto alba

Many bird species produce two annual broods during a single breeding season. However, not all individuals reproduce twice in the same year suggesting that double brooding is condition‐dependent. In contrast to most raptors and owls, the barn owl Tyto alba produces two annual clutches in most worldwide distributed populations. Nevertheless, the determinants of double brooding are still poorly studied. We performed such a study in a Swiss barn owl population monitored between 1990 and 2014. The annual frequency of double brooding varied from 0 to 14% for males and 0 to 59% for females. The likelihood of double brooding was higher when individuals initiated their first clutch early rather than late in the season and when males had few rather than many offspring at the first nest. Despite the reproductive benefits of double brooding (single‐ and double‐brooded individuals produced 3.97 ± 0.11 and 7.07 ± 0.24 fledglings, respectively), double brooding appears to be traded off against offspring quality because at the first nest double‐brooded males produced poorer quality offspring than single‐brooded males. This might explain why females desert their first mate to produce a second brood with another male without jeopardizing reproductive success at the first nest. Furthermore, the reproductive cycle being very long in the barn owl (120 d from start of laying to offspring independence), selection may have favoured behaviours that accelerate the initiation of a second annual brood. Accordingly, half of the double‐brooded females abandoned their young offspring to look for a new partner in order to initiate the second breeding attempt, 9.48 d earlier than when producing the second brood with the same partner. We conclude that male and female barn owls adopt different reproductive strategies. Females have more opportunities to reproduce twice in a single season than males because mothers are not strictly required during the entire rearing period in contrast to fathers. A high proportion of male floaters may also encourage females to desert their first brood to re‐nest with a new male who is free of parental care duties.     

Effects of blood parasites on sexual and natural selection in the pied flycather

The occurrence of the blood parasites Haemoproteus and Trypanosoma in the pied flycatcher, Ficedula hypoleuca , was examined to test current hypotheses that parasites reduce the expression of secondary sexual traits, mating success, breeding success, and survival of infected individuals. The results showed that there was no significant relationship between male plumage brightness and Trypanosoma infection, but males infected with Haemoproteus tended to be brighter than uninfected males, partly because first-year males were less often infected than older males. Polygynous males did not have fewer parasites than monogamous males. Females did not choose uninfected males among those they had sampled. Clutch size and laying date were not related to female infection status, and the number and quality of nestlings was not related to parasite infections of either male or female parent. The ability of males to provide parental care was not related to their infection status. The return rate from one breeding season to the next of infected males was not lower than that of uninfected males. The lack of correlations between parasites and male plumage colour and female mate choice apparently do not support the Hamilton-Zuk hypothesis of sexual selection. However, the absence of demonstration of any negative effects of parasites suggests that infection status may not be a direct measure of parasite resistance, or the degree to which the host suffers. Instead, the results support the alternative view that infected individuals have demonstrated their ability to survive and to cope with the parasites, while uninfected individuals are probably not yet tested for their resistance. This points to problems in using parasite prevalences and distributions, at least of some protozoan blood parasites, for tests of Hamilton-Zuk hypothesis, even though this was done in the first test by Hamilton and Zuk and by many later researchers     

Within‐season variation in sexual selection in a fish with dynamic sex roles

The strength of sexual selection may vary between species, among populations and within populations over time. While there is growing evidence that sexual selection may vary between years, less is known about variation in sexual selection within a season. Here, we investigate within‐season variation in sexual selection in male two‐spotted gobies (Gobiusculus flavescens). This marine fish experiences a seasonal change in the operational sex ratio from male‐ to female‐biased, resulting in a dramatic decrease in male mating competition over the breeding season. We therefore expected stronger sexual selection on males early in the season. We sampled nests and nest‐holding males early and late in the breeding season and used microsatellite markers to determine male mating and reproductive success. We first analysed sexual selection associated with the acquisition of nests by comparing nest‐holding males to population samples. Among nest‐holders, we calculated the potential strength of sexual selection and selection on phenotypic traits. We found remarkable within‐season variation in sexual selection. Selection on male body size related to nest acquisition changed from positive to negative over the season. The opportunity for sexual selection among nest‐holders was significantly greater early in the season rather than late in the season, partly due to more unmated males. Overall, our study documents a within‐season change in sexual selection that corresponds with a predictable change in the operational sex ratio. We suggest that many species may experience within‐season changes in sexual selection and that such dynamics are important for understanding how sexual selection operates in the wild.     

Factors influencing the onset and duration of receptivity of female purple rock crabs, Hemigrapsus sexdentatus (H. Milne Edwards, 1837) (Brachyura: Grapsidae)

The effects of males, field, and laboratory conditions on the receptivity of females were tested in the New Zealand purple rock crab Hemigrapsus sexdentatus. Onset and duration of female receptivity is of interest because it influences the time available for mating and therefore the operational sex ratio (OSR), male-male competition, and the extent of sperm competition. Females were receptive once a year for a short time prior to oviposition. The breeding season was highly synchronised and lasted for about 3 weeks (from the end of March to mid-April; southern autumn), after which, almost all females carried eggs. We found few receptive females in the field (0% to 4.9%) during the breeding season despite a large number of crabs examined (935 in 1999 and 555 in 2000), suggesting that females are receptive for less than a day. The onset of the breeding season was the same for the wild crabs and those held in field cages, but the duration of receptivity increased to several days for caged females. The onset of the breeding season of females in the laboratory was earlier compared to females in the field and had, overall, a longer breeding season. Females isolated from males stayed receptive significantly longer (5.5 days) than females caged with males (3.3 days), suggesting that the duration of female receptivity is adjusted according to the presence or absence of males. Our results suggest that females have some control over their receptivity in relation to male presence, and this could influence the outcome of sexual selection.     

Behavioural and hormonal responses of male rhesus monkeys introduced to females in the breeding and non-breeding seasons.

Six adult male rhesus monkeys were introduced individually to an all-female group for 10 days during the mating season. The initial aggressive responses of the females were rapidly replaced by positive social behaviour, and each male achieved alpha status and had access to social and sexual partners. A repetition of this paradigm in the non-breeding season produced significantly more female aggression, and no male attained high rank or engaged in sexual or other social behaviour. Male testosterone levels rose following introduction to the females in both seasons, but were significantly higher during the breeding season. Hormonal levels following removal from the females suggest a complex interplay between social, sexual and seasonal variables and recent social experiences. The differences in female social behaviour with newly introduced males, as a function of season, suggest an explanation for the seasonal limitation of male troop transfers.     

BEHAVIORAL SIGNIFICANCE OF UNDERWATER VOCALIZATIONS OF CAPTIVE LEOPARD SEALS, HYDURGA LEPTONYX

Two groups of underwater vocalizations were identified in a three-year study of two captive leopard seals, Hydurga leptonyx (one female and one male at Taronga Zoo, Sydney). This was supplemented by recordings over three months from a male at Marineland, New Zealand. The sexual state of the seals at Taronga was deduced from serum hormonal concentrations: the female was considered to be in estrus at specific times during the breeding season. The seal at Marineland, New Zealand was assumed to be sexually mature on the basis of size and age. Of 12 different underwater sound types recorded, six were produced by the seals at Taronga Zoo during agonistic interactions (local calls) and were heard through most of the year. The other six sound types were produced by lone seals. These broadcast calls were produced by the female only when sexually receptive, and by the mature male during December and January, months believed to be the breeding season of wild leopard seals. We propose that underwater acoustic behavior is important in the mating system of this species, and that broadcast calls are used by mature females to advertise their sexual receptivity, and possibly by mature males in search of mates.     

Initiation of the breeding season in ewe lambs and goat kids with melatonin implants

Sixty-eight female and 4 male lambs of the Chios breed born in autumn (September–October) and 48 female and 4 male kids of the Damascus breed also born in autumn (November), were used to evaluate the effect of melatonin implants (Regulin^®) on the initiation of the breeding season. For each species and sex, half of the animals were either left untreated to serve as controls (C) or received ear implants (females one and males two implants) of melatonin (MEL) in May (spring). Each C and MEL group of females was kept separately and away from males for 5 weeks after implantation and then, C and MEL males were joined with the respective groups for 45 (sheep) and 35 days (goats). Animals not conceiving during the early June–July breeding season, were mated again in September (natural breeding season). The reproductive performance and the 60-day milk yield of animals giving birth during the two seasons were compared. Early in the season (mid November–December), significantly more MEL than C ewes and goats gave birth (75.5% versus 23.5%, p < 0.01; 70.8% versus 37.5%, p < 0.05, respectively). For both species, most of the other characteristics examined were significantly affected by season, but not by treatment. Females giving birth early in the season were approximately 80 days younger at parturition and recorded a lower body weight at mating than those giving birth in the natural February–March season. In the first mating period, the animals mated and conceived had similar body weights to those not mated. The natural, compared with the early June–July mating season, was associated in sheep with higher litter weight at birth (7.0 kg versus 5.8 kg, p < 0.05) and in sheep and goats with a higher number (p < 0.05) of offspring born live (1.78 versus 1.38; 2.0 versus 1.61, respectively) and weaned (1.74 versus 1.36; 1.82 versus 1.35, respectively). Total litter size at birth and 60-day milk yield after weaning, were not significantly different between the two seasons. It could be concluded that melatonin implants administered during the last month of spring in autumn-born female Chios sheep and Damascus goats, advanced the initiation of their breeding season by about 80 days when joined with young males also treated with melatonin implants. The overall reproductive performance and milk yield of animals breeding early, was satisfactory and comparable to that of animals breeding in the natural breeding season.     

A preliminary study of olfactory behavior of captiveLemur coronatus during the breeding season

The olfactory behavior of a captive population of crowned lemurs (Lemur coronatus)was studied during their annual breeding season in order to investigate its possible role in the fine-tuning of mating synchrony after photoperiodic initiation of reproductive activity. The frequencies of five stereotyped olfactory behavior patterns were recorded in four male-female groups during 315 1-hr observation sessions between October and March. The mean total scent-marking frequency of all males was positively correlated with their mean testicular size. Male anogenital-, head-, and allomarking frequencies decreased during the breeding season, whereas hand-marking frequencies remained constant. Male head-marking increased significantly in the 5 days preceding female vaginal estrus. Furthermore, males responded to many female scents by olfactory investigation and/or overmarking, whereas females never showed an observable behavioral response to male scent marks. The marking frequencies of two females did not change significantly during the breeding season, while those of two others decreased significantly. These results suggest qualitative changes of female scents during estrus and a less important role of male scents in intersexual communication in the context of reproduction than previously thought.     

The sexual strategy of the central long-toed salamander, Ambystoma macrodactylum columbianum, in south-eastern Washington

The sexual strategies of salamanders are largely'unobservable'owing to the low visibility typical of their preferred breeding habitats. We conducted both field and laboratory studies to investigate the sexual strategy of the North American central long-toed salamander, Ambystoma macrodactylum columbianum. Capture-recapture and cohort-marking of salamanders at an aquatic breeding site indicated that males arrive before females and remain in the water for longer periods of time (measured in weeks, rather than days as for females). We estimate that the overall duration of the breeding season is short, three weeks or less. Courtship between single males and females is characterized by repeated bouts of axillary amplexus, separated by multiple episodes of spermatophore deposition. Amplectant males provide females with considerable tactile stimulation in the form of head-rubbing. Unpaired males attempt to displace amplectant males from their partners by wrestling with them. In addition, unpaired males appear to interfere in ongoing courtship encounters during the spermatophore deposition stage, perhaps attempting to 'steal'inseminations. We suggest that explosive scramble-competition polygyny best describes the mating system of A. m. columbianum. Operational sex ratios are probably male-biased throughout the short breeding season, leading to intense competition among males for mates. Mate choice (by either sex) probably is of little importance as a determinant of mating success.     

Effect of adults on juvenile reproduction of Calomys venustus (Muridae: Sigmodontinae)

Abstract We tested the hypothesis that adult overwintering Calomys venustus inhibit maturation and reproduction in young‐of‐the‐year from the first cohort. The study was carried out in four 0.25‐ha enclosures (two control and two experimental), each situated on natural pasture. This study was conducted between August 1997 and March 1999 and had two parts: removal of overwintering male (ROM) and removal of overwintering female (ROF). For the ROM treatment overwintering males were removed immediately after the first cohort of juveniles were born, in the ROF treatment overwintering females were removed after the first cohort were weaned. Weekly censuses were taken for three successive days over 6 weeks. The sexual maturation and reproductive condition of juveniles were compared between treatments (overwintering male or female removal) using repeated‐measures anova . The repeated measures factor was the age of juveniles. Removal of overwintering males and females did not affect sexual maturation of juveniles, however, overwintering males influenced the onset of reproductive activity of juvenile females at the beginning of the breeding period.     

Seasonal changes in courtship song and the medial preoptic area in male European starlings (Sturnus vulgaris)

In male starlings (Sturnus vulgaris) courtship song plays a critical role in mate attraction. During the breeding season courtship song occurs prior to copulation and appears to reflect male sexual arousal. Outside the breeding season starlings sing, but song appears unrelated to reproduction. The aromatization of testosterone (T), likely within the medial preoptic nucleus (POM), is critical for the expression of male sexual arousal. The present study was performed to determine whether seasonal changes in the POM might relate to seasonal changes in courtship singing behavior in male starlings. T concentrations, the volume of the POM, and aromatase within the POM were examined both during and outside of the breeding season in male starlings. Song was also recorded at these times both with and without a female present. The POM was largest and contained dense aromatase immunostaining only during the spring breeding season, when T concentrations were highest and males responded to a female with an increase in courtship song. Outside the breeding season the volume of the POM was small, T concentrations were low, and males displayed no changes in song expression in response to female conspecifics. Song bout length was positively related to POM volume, and males sang longer songs in spring. Only males with nestboxes in spring responded to a female, and the POM tended to be larger in these males, suggesting that nestbox possession might influence neuroplasticity within the POM. Overall, the findings suggest that T-dependent plasticity and aromatase activity within the POM might regulate courtship singing in a wild songbird.     

NATURAL SELECTION AND SEXUAL SIZE DIMORPHISM IN RED-WINGED BLACKBIRDS

Patterns of overwinter mortality in the sexually dimorphic red-winged blackbird (Agelaius phoeniceus) were examined to test the predictions of the sexual-selection hypothesis that male size is limited by directional selection favoring small males and that female size is maintained by stabilizing selection wherein extreme phenotypes experience higher mortality. Museum specimens collected from Ontario over a 95-yr period were used to compare the sizes of males and females collected in fall and spring. In a separate field study, body sizes of returning and nonreturning male and female red-winged blackbirds were compared over a 6-yr period. Overall, there was no evidence of higher overwinter mortality among larger males. Among adult (ASY) males, large individuals appeared to have higher survival than small individuals, although among subadult (SY) males, large size may have been disadvantageous. Weak evidence of stabilizing selection on female body size was found. Among adults, sexual size dimorphism seemed more pronounced after winter than before winter. Our results do not support the hypothesis that body size in male red-winged blackbirds is limited by selective mortality outside the breeding season. It is possible that size selection occurs earlier in life, when males are still in the nest. Our results suggest that caution should be exercised when interpreting interspecific evidence showing higher adult male than female mortality in sexually dimorphic species. Such patterns could arise as a cost to males of sexual selection and yet provide no insight into how natural selection opposes sexual selection for increased male size.     

Inbreeding avoidance in rhesus macaques: Whose choice?

Whether nonhuman primates avoid copulating with close kin living in their social group is controversial. If sexual aversion to relatives occurs, it should be stronger in females than in males because of females' greater investment in each offspring and hence greater costs resulting from less viable offspring. Data presented here show that adult male rhesus macaques breeding in their natal groups at Cayo Santiago experienced high copulatory success, but copulated less with females of their own matrilineages than with females of other matrilineages. Adult females were never observed to copulate with males of their own matrilineage during their fertile periods. Although natal males sometimes courted their relatives, examination of two measures of female mate choice showed that females chose unrelated natal males over male kin. Female aversion to male kin was specific to the sexual context; during the birth season, females did not discriminate against their male relatives in distributing grooming. Evolved inbreeding avoidance mechanisms probably produce different outcomes at Cayo Santiago than in wild rhesus macaque populations. Gender differences in sexual aversion to relatives may be partly responsible for differences between studies in reported frequency of copulations by related pairs. © 1993 Wiley-Liss, Inc.     

Spatial and Temporal Distribution of Song in the Yellowhammer Emberiza citrinella

The temporal and spatial distribution of song was studied in a population of yellowhammers Emberiza citrinella. Song was most frequent during the breeding season, and within the breeding season during the fertile period of both first, second, and replacement clutches. Song activity peaked at sunrise and sunset. During the fertile period most singing took place in the central parts of the territory. Song post heights peaked during the fertile period, and more song posts lacked foliage at that time. Intrusions by male conspecifics peaked in the fertile period and in territories where males sang relatively little. Song activity and mate guarding were strongly positively correlated. Song volume was loud and song was thus apparently used in long-distance communication. These observations are in accordance with a male deterrence hypothesis, suggesting that males sing to deter neighbouring males from trespassing during the fertile period of their mate. A female attraction hypothesis, suggesting that males sing to attract neighbouring females and thereby obtain extra-pair copulations, and a female reproduction hypothesis, suggesting that males sing to start the female reproductive cycle, were partly supported by observations.     

The mating system and male mating success of the Virginia opossum (Didelphis virginiana) in Florida

The mating system of the Virginia opossum, a solitary, nocturnal marsupial, was studied over a period of two years in north–central Florida. There were two mating seasons each year, both lasting about four weeks and starting in mid-January and late April, respectively. Radio-tracking males and females revealed that, independent of body size, males doubled their home ranges during these periods to include an average of 5.9 females within their new ranges. Females were visited regularly and, on the night of oestrus, males directly competed for access to the female. Dominance and hence mating success was strongly related to body mass but not age. Dominant males weighed on average 3.18 kg (N = 20) compared to 2.65 kg of unsuccessful males. The largest of the competing males was successful in 20 of 23 cases involving at least two competitors. Individual male mating success varied from zero to three matings during a breeding season, but the range was probably underestimated. Mate searching activities were costly, as most males lost weight during both mating seasons. Weight changes were a function of body mass, with males over 2.2 kg losing up to 23% in weight and smaller males gaining weight. There was also evidence that male breeding activities entailed a survival cost.