Consequences of a female-biased sex-ratio in a socially monogamous bird: female-female pairs in the Roseate Tern Sterna dougallii

In the socially monogamous gulls and terns, female-biased sex ratios are sometimes revealed by the occurrence of ‘supernormal clutches’, which are usually attended by female-female pairs or other multi-female associations. We studied these phenomena in the endangered Roseate Tern Sterna dougallii at Bird Island, USA, from 1970 to 1995. DNA-techniques were used to sex breeding adults in 1992–94. Supernormal clutches (with three or four eggs) have comprised 1–7% of all Roseate Tern clutches at Bird Island since at least 1970, probably increasing in frequency since 1980. Supernormal clutches were spatially clustered; most were laid late in the peak period of nesting during each season. More than 80% of supernormal clutches and at least 7% of normal clutches were attended by multi-female associations; most of these were female-female pairs, with a few trios (male + two females, or three females) and one quartet (four females). More than half of the multi-female associations attended normal clutches. Some female-female pairs were maintained for up to five years. The age-distribution of females mated to females did not differ significantly from that of females mated to males. Females mated together usually laid eggs synchronously (±2 days). Such females laid fewer eggs than females mated to males (means 1.20 versus 1.73), and had lower fertility and hatching success (about 46% versus 98%); they were less successful in raising young from eggs that did hatch (means 58% versus 73%), but this difference was not significant. Their overall breeding success was much lower (about 0.34 fledglings per female versus 1.35). The sex-ratio of breeders was about 127 females to 100 males; about 20% of breeding females did not have male mates. Female Roseate Terns that do not obtain male mates appear to be of low phenotypic ‘quality’ - based on late laying, small clutches and small eggs. Our data support the hypothesis that such females have a higher fitness if they mate with each other and raise a few young than if they do not breed at all.     

Inter-island movements and population differentiation in a pelagic seabird

We used mark-resight data and amplified fragment length polymorphism (AFLP) markers to assess movements and gene flow between Central Pacific breeding colonies of the great frigatebird, Fregata minor. Of 715 adult frigatebirds marked on Tern Island and Johnston Atoll, 21.3% were resighted at other frigatebird colonies at least 582 km away. Mark-resight data indicated regular movement of males and females between Tern Island and Johnston Atoll (873 km apart), and less frequent movements to other islands; no birds marked on Tern or Johnston were seen on Christmas Island, but one was seen in the Philippines, 7627 km from where it was marked. Despite the regular occurrence of interisland movements, Bayesian analyses of AFLP data showed significant genetic differentiation between Tern Island and Johnston Atoll, and more pronounced differentiation between these two islands and the more distant Christmas Island. The AFLP profiles of three birds breeding on Tern Island fell within the profile-cluster typical for Christmas Island birds, both in a nonmetric multidimensional scaling analysis and in a population assignment test, suggesting dispersal events from Christmas Island to Tern Island. Several factors could explain the persistence of genetic structure despite frequent movements between colonies: many movements occurred during the nonbreeding season, many breeding-season movements did not involve mate-acquisition behaviours and individuals that do disperse may be selected against, as suggested by morphometric differences between colonies. The persistence of genetic structure among breeding colonies despite significant interisland movements suggests limits to the effectiveness of migration as a homogenizing force in this broadly distributed, extremely mobile species.     

The breeding season duration hypothesis: acute handling stress and total plasma concentrations of corticosterone and androgens in male and female striped plateau lizards (Sceloporus virgatus)

Acute glucocorticoid elevations can be adaptations to short-term stressors. The breeding season hypothesis predicts reduced glucocorticoid responsiveness to acute stressors in populations or species with short breeding seasons. The striped plateau lizard (Sceloporus virgatus) has a short breeding season in Arizona. We measured plasma corticosterone and total androgen levels (dihydrotestosterone and testosterone) following one of the four stress-handling treatments (0, 10, 60, or 180 min). In both sexes, longer handling stress yielded higher corticosterone; females had higher corticosterone than males at all time points. Androgens did not vary with handling duration, in either sex. Combining treatments, plasma androgens correlated positively with corticosterone (CORT) in females but not in males; plasma CORT and body mass residuals were negatively correlated in both sexes, suggesting lizards in poor body condition and/or not investing heavily in reproduction (follicle mass) have higher acute corticosterone. Total plasma androgens and body mass residuals were positively associated in males, but showed no association in females. The maximal CORT elevation after handling stress in this single-clutching species was of comparable magnitude to responses in related multi-clutching lizard species with longer breeding seasons. Using data from studies of multiple populations of three Sceloporus species, we found no relationship between the relative magnitude of the CORT increase and either latitude or elevation, two variables in the literature correlated with duration of the breeding season, and only weak relationships with geographic elevation and actual (not relative) stress-elevated CORT values in this multi-population comparison.     

Androgen correlates of socially induced changes in the electric organ discharge waveform of a mormyrid fish

Weakly electric fish from the family Mormyridae produce pulsatile electric organ discharges (EODs) for use in communication. For many species, male EODs are seasonally longer in duration than those of females, and among males, there are also individual differences in EOD duration. While EOD elongation can be induced by the administration of exogenous androgens, androgen levels have never before been assessed under natural or seminatural conditions. By simulating the conditions occurring during the breeding season in the laboratory, we provide evidence of a sex difference in EOD duration as well as document levels of circulating androgens in males. In this study, we analyzed the nature of social influences on male EOD duration and plasma androgen levels in Brienomyrus brachyistius. Individual males, first housed with a single female and then placed into social groups consisting of three males and three females, showed status-dependent changes in EOD duration. Top-ranking males experienced a relatively large increase in EOD duration. Second-ranking males experienced a more modest increase, and low-ranking males experienced a decrease in EOD duration. These changes were paralleled by differences in circulating levels of plasma 11-ketotestosterone (11-KT), but not testosterone, suggesting that the changes in EOD duration may have been mediated by changes in plasma 11-KT levels. Thus, it appears that EOD duration is an accurate indicator of male status, which is under social and hormonal control.     

Social monogamy in a territorial salamander

Social monogamy, which does not necessarily imply mating or genetic monogamy, is important in the formation of male-female pair associations. We operationally define social monogamy as occurring when two heterosexual adults, exclusive of kin-directed behaviour, direct significantly less aggression and significantly more submission towards each other, and/or spend significantly more time associating with each other relative to other adult heterosexual conspecifics. Long-term pair associations (i.e. those lasting through a lengthy breeding season) that are characteristic of social monogamy are common in some taxa but are virtually unknown in amphibians. Recent studies, however, have suggested that red-backed salamanders, Plethodon cinereus, have complex (for amphibians) social systems. Our laboratory experiments tested the hypothesis that red-backed salamanders found in pairs in the forest display behaviours consistent with social monogamy. During the summer noncourtship season, newly collected male-females pairs showed no preference to associate with their partners more than with a novel conspecific of the opposite sex. However, during the autumn courtship season, paired males and females significantly directed preferential behaviours towards their partners rather than towards a surrogate or a novel paired salamander. Focal animals showed no significant preferences when presented with their partner and a novel single salamander, but they never directed preferential behaviours towards a novel salamander (whether paired or single) or a surrogate. These results are the first to suggest that a salamander species engages in social monogamy. Furthermore, our results suggest that social monogamy may not inhibit paired males and females from displaying alternative strategies: preferring partners when extrapair associations may be disadvantageous (i.e. the extrapair animal is already paired) but not preferring partners when extrapair associations may be advantageous (i.e. the extrapair animal is single). Copyright 2000 The Association for the Study of Animal Behaviour.     

Parental care and testosterone in males of the bank vole (Myodes glareolus): Sensitization and androgenic stimulation of paternal behavior

The relationship between parental responsiveness of bank vole males and their body weight, testes mass, and plasma and gonadal testosterone levels were examined. Two groups of voles were studied: Group I consisted of 14 breeding pairs where females gave birth to young within a month after formation of pairs, and Group II represented 13 pairs without offspring and signs of pregnancy in females. Males in Group I, unlike those in Group II, had contact with pups before the tests on parental responsiveness. In Group I, males were found to have larger testes and to exhibit a higher level of care-giving activity (pup retrieval) as compared to males in Group II. Both the plasma and gonadal testosterone levels in males exhibiting pup retrieval were revealed to be significantly higher than those for males exhibiting infanticide. Thus, promiscuity, competition for receptive females, and a higher level of testosterone secretion, which are characteristic of bank vole males during the breeding season, are not out of the realm of possibility of the males to care of young. Our findings suggest that factors promoting parental responsiveness in bank vole males are sensitization due to contact with pups and an increase in testosterone secretion. Obviously, there is a need to reexamine the role that testoster-one plays in regulating rodent paternal behavior.     

Competing females and caring males. Sex steroids in African black coucals, Centropus grillii

The black coucal is the only known altricial bird species in which females mate with and lay eggs for more than one male and males are responsible for all parental care (classical polyandry). In this species, the left testis is atrophied and it has been speculated that this may result in a reduction of circulating androgens, providing a unique mechanism for reversals in sex roles. We therefore investigated whether there is a reversal in circulating androgens and oestrogens in black coucals. Despite the reversals in sex roles, males had significantly higher levels of plasma testosterone than females, in a pattern typical of that of monogamous male passerines. Testosterone levels of both sexes were higher during the mating than during the premating stage and were low in males during the nestling stage. The concentrations of androstenedione, dehydroepiandrosterone and oestradiol did not differ between the sexes and were generally low. A physiological challenge with gonadotropin-releasing hormone (GnRH) resulted in a significant increase in testosterone in males but not in females, suggesting either that females are not responsive to GnRH or that they express patterns of testosterone that are similar to those of males of species with a polygynous mating system without paternal care, in which testosterone is expressed at maximum levels throughout the breeding season. We conclude that the absence of one testis does not provide a mechanism for sex role reversal in black coucals. Either androgens are not involved in the regulation of male-like traits in females or females are sensitive to relatively low levels of these steroids.     

Nestmate recognition in burying beetles: the "breeder's badge" as a cue used by females to distinguish their mates from male intruders

Burying beetles use small vertebrate carcasses as food for theirlarvae and defend these carcasses against intra- and interspecificcompetitors. Breeding associations on carcasses can consistof single females, heterosexual pairs, or various combinationsof males and females. When a heterosexual pair collaborate ina breeding attempt, they do not typically exhibit aggressivebehavior toward each other, but do attack newly arrived conspecificsthat attempt to usurp the carcass. We investigated the cuesinvolved in discrimination between breeding partners and intrudersby female burying beetles. We found that resident females toleratemales that have cared for a brood, as well as males that havenot cared for a brood but have been on a carcass for a day ortwo. Males that have had no prior contact with a carcass areattacked. Females appear to use a chemical cue, the "breeder'sbadge," an apolar substance on the male's cuticle that can beremoved by washing with pentane. This cue is reliably correlatedwith recent male experience with a carcass that is suitablefor reproduction. The breeder's badge develops as a result ofprolonged contact with such a carcass, and disappears on removalfrom the carcass; its presence does not require contact witha female or with larvae. Female recognition of their male partnersin burying beetles thus does not involve individual recognition,but rather recognition of reproductive condition.     

Contrasting effects of opposite- versus same-sex housing on hormones,behavior and neurogenesis in a eusocial mammal

Competitive interactions can have striking and enduring effects on behavior, but the mechanisms underlying this experience-induced plasticity are unclear, particularly in females. Naked mole-rat (NMR) colonies are characterized by the strictest social and reproductive hierarchy among mammals, and represent an ideal system for studies of social competition. In large matriarchal colonies, breeding is monopolized by one female and 1–3 males, with other colony members being socially subordinate and reproductively suppressed. To date, competition for breeding status has been examined in-colony, with female, but not male, aggression observed following the death/removal of established queens. To determine whether this sex difference extends to colony-founding contexts, and clarify neural and endocrine mechanisms underlying behavioral change in females competing for status, we examined neurogenesis and steroid hormone concentrations in colony-housed subordinates, and NMRs given the opportunity to transition status via pair-housing. To this end, Ki-67 and doublecortin immunoreactivity were compared in the hippocampal dentate gyrus (DG) and basolateral amygdala (BLA) of colony-housed subordinates, and subordinates housed with a same-sex (SS) or opposite-sex (OS) conspecific. Results suggest that OS pairing in eusocial mammals promotes cooperation and enhances hippocampal plasticity, while SS pairing is stressful, resulting in enhanced HPA activation and muted hippocampal neurogenesis relative to OS pairs. Data further indicate that competition for status is confined to females, with female-female housing exerting contrasting effects on hippocampal and amygdalar neurogenesis. These findings advance understanding of social stress effects on neuroplasticity and behavior, and highlight the importance of including female-dominated species in research on aggression and intrasexual competition.     

Behaviour of cyclic bank voles under risk of mustelid predation: do females avoid copulations?

Mustelid odours have been shown to suppress breeding in captive bank voles (Clethrionomys glareolus) from cyclic populations (Ylönen 1989; Ylönen and Ronkainen 1994). The mechanism behind the suppression is unknown. Based on a series of behavioural trials and breeding experiments with pairs of bank voles in breeding condition, we suggest that the primary cause for breeding suppression is a change in female mating behaviour. Experimental female-male pairs (n=34) exposed to mustelid odour decreased their general activity compared to control pairs (n=34). When encountering males in behavioural trials, females exposed to stoat odour were more aggressive and actively avoided precopulatory behaviours of males. No copulations were observed in experimental pairs compared to five in control pairs during the behavioural trials. Males actively approached females in general but male behaviour did not change under exposure to mustelid odours. We suggest that females are more vulnerable to mustelid predators than males and therefore actively avoid copulations in the (indirect) presence of mustelids. As well as this behavioural response, internal abortive mechanisms (cf. Bruce 1959) could play a role in the observed breeding suppression.     

Successful same-sex pairing in Laysan albatross

Unrelated same-sex individuals pairing together and cooperating to raise offspring over many years is a rare occurrence in the animal kingdom. Cooperative breeding, in which animals help raise offspring that are not their own, is often attributed to kin selection when individuals are related, or altruism when individuals are unrelated. Here we document long-term pairing of unrelated female Laysan albatross (Phoebastria immutabilis) and show how cooperation may have arisen as a result of a skewed sex ratio in this species. Thirty-one per cent of Laysan albatross pairs on Oahu were female-female, and the overall sex ratio was 59% females as a result of female-biased immigration. Female-female pairs fledged fewer offspring than male-female pairs, but this was a better alternative than not breeding. In most female-female pairs that raised a chick in more than 1 year, at least one offspring was genetically related to each female, indicating that both females had opportunities to reproduce. These results demonstrate how changes in the sex ratio of a population can shift the social structure and cause cooperative behaviour to arise in a monogamous species, and they also underscore the importance of genetically sexing monomorphic species.     

Pair territoriality in the longnose filefish,oxymonacanthus longirostris

The longnose filefish,Oxymonacanthus longirostris, usually lives in heterosexual pairs, the male and female swimming together and sharing the same territory. Pair territoriality in the species was examined in detail in relation to sexual differences in territorial defense activities. Rigorous pair territoriality was maintained only during the breeding season, although pairs used their home ranges exclusively to a certain extent, during the non-breeding season. The frequency of aggression against other conspecific pairs in the breeding season was higher than in the non-breeding season. Agonistic interactions appear to be over both mates and food resources, the strict pair territoriality in the breeding season possibly being due to mutual mate guarding. In intraspecific aggressive interactions, males usually led their partner females when attacking intruders. The feeding frequency of males was much lower than that of females in the breeding season. Mate removal experiments indicated that females could not defend their original territories solitarily and their feeding frequency decreased. Conversely, males could defend territories solitarily without a decrease in feeding frequency. These results suggest that males contribute most to the defense of the pair territory, with females benefiting from territorial pair-swimming with their partner males.     

Impacts of human visitors on breeding success and long-term population trends in Adélie Penguins at Casey,Antarctica

Breeding populations of Aélie Penguins Pygoscelis adeliae have been counted at two localities near Casey Station in Wilkes Land, East Antarctica since 1959/60 and 1968/69. At Whitney Point, the breeding population increased from 1122 pairs in 14 colonies in 1959/60 to 4714 pairs in 36 colonies in 1992/93. All new colonies at Whitney Point established on relict colony sites identified in 1959/60. On Shirley Island, the total breeding population has remained at 7770 pairs ±10% between 1968/69 and 1992/93, except in 1990/91 when the population peaked at 8719 pairs. An association between the age of a colony and its rate of increase was observed at Whitney Point, with new colonies (those established since 1971/72) increasing more rapidly than colonies extant in 1959/60. At Shirley Island, where most of the colonies extant in 1968/69 have decreased in population, the establishment and growth of 13 colonies has offset this decrease; these new colonies also exhibited the association between age and rate of increase. Breeding success (chicks fledged per nest) was significantly lower for Shirley Island colonies than for those at Whitney Point. Human visitors to Shirley Island from Casey station are believed to be responsible for the observed changes in the distribution and abundance of breeding pairs and for maintaining the stable population by reducing overall breeding success through the disturbance associated with visits.     

Testing multiple hypotheses for the maintenance of male homosexual copulatory behaviour in flour beetles

Diverse animal groups exhibit homosexual interactions, yet the evolutionary maintenance of such behaviours remains enigmatic as they do not directly increase reproductive success by generating progeny. Here, we use Tribolium castaneum flour beetles, which exhibit frequent male homosexual copulations, to empirically test several hypotheses for the maintenance of such behaviours: (1) establishing social dominance; (2) practice for future heterosexual encounters; and (3) indirect sperm translocation. We found no evidence that Tribolium males use homosexual copulations either to establish dominance or to practice behaviours that increase their subsequent heterosexual reproductive performance. Our results provide limited support for the hypothesis of indirect sperm translocation: when males from two genetic strains mated with females immediately following a homosexual copulation, females produced progeny sired not only by the directly mating male, but also by that male’s homosexual partner. However, this phenomenon was detected in only 7% of homosexual pairs, and in each case such indirectly sired progeny accounted for < 0.5% of females’ total progeny. Direct observations indicated that mounting males often released spermatophores during homosexual copulations. These observations suggest that homosexual copulations may be a behavioural mechanism that allows males to expel older, potentially low‐quality sperm. Additional work is needed to test this new hypothesis, and to determine whether sperm release during homosexual copulations occurs in other groups.     

Sexual and asexual colony foundation and the mechanism of facultative parthenogenesis in the termite <Emphasis Type="Italic">Reticulitermes speratus</Emphasis> (Isoptera,Rhinotermitidae)

Summary. Facultative parthenogenesis has great adaptive significance, especially with regard to low pairing efficiency. In the termite Reticulitermes speratus, females that fail to mate with males reproduce parthenogenetically and found colonies cooperatively with partner females or even alone. Comparison of colony foundation success at 400 days between colonies founded by single females (F), female-female pairs (FF), and male-female pairs (FM) showed that female-female cooperation promoted colony survivorship over monogamous foundation. We report here for the first time the mode of parthenogenesis in Isoptera. Combining chromosome observations and genetic analysis using microsatellites, we show that the mode of parthenogenesis is diploid thelytoky and that the restoration of ploidy is most likely accomplished by terminal fusion. Parthenogens show a higher mortality and a longer egg-development time than sexually produced offspring, probably due to reduced heterozygosity. In addition Wolbachia bacteria were detected in R. speratus. However, since Wolbachia was also detected in non-parthenogenetic R. flavipes, it is unlikely that Wolbachia is the cause of parthenogenesis in R. speratus.Received 30 October 2003; revised 4 March 2004; accepted 17 March 2004.     

Seasonality and Hormonal Control of Territorial Aggression in Female Song Sparrows (Passeriformes: Emberizidae: Melospiza melodia)

Male and female song sparrows perform similar aggressive behaviors including flights, wing-wave threat displays, and growls. Females very rarely sing, however. To investigate the seasonal variation and hormonal control of territorial aggression in females, we simulated female intrusions during the pre-breeding, breeding and post-molt seasons in the field. Circulating levels of testosterone, dihydrotestosterone, estradiol, progesterone and corticosterone in females experiencing simulated intrusion were compared to those of passively netted females matched for breeding stage. Female aggressive responses to female intrusion dropped from the pre-breeding to the post-molt seasons. Levels of circulating androgens were significantly higher in control females than in females experiencing a simulated intrusion. There were no significant differences in any of the other hormones measured. Although song sparrow female-female aggression appears to be behaviorally similar to male-male aggression, the seasonal variation and hormonal support of aggression differ between the sexes.     

Season and testosterone affect contractile properties of fast calling muscles in the gray tree frog Hyla chrysoscelis

In anurans, circulating levels of androgens influence certain secondary sexual characteristics that are expressed only during the breeding season. We studied the contractile properties of external oblique muscles (used to power sound production) in a species of North American gray tree frog, Hyla chrysoscelis, during the breeding season and also in testosterone-treated captive males and females after the breeding season. Compared with the muscles of breeding-season males, the trunk muscles of postbreeding-season males have 50% less mass, 60% longer twitches, and 40% slower shortening velocities. Testosterone levels similar to those found in breeding-season male hylid frogs restore the contractile speed and mass of male trunk muscles and also convert the small slow trunk muscles of females into larger fast-contracting muscles. We conclude that androgens likely play a key role in altering the contractile properties of these muscles in males during the annual cycle, allowing them to operate in the breeding season at the frequencies required to produce the characteristic rapidly pulsed calls of this species. Females as well as nonbreeding-season males do not produce advertising calls, and therefore the slower muscles found in these animals may allow more economic operation of these muscles. The effects of testosterone on female trunk muscles indicate the potential of this hormone in contributing to the sexual dimorphism in size and contractile properties of these muscles, but this dimorphism is likely due to the interaction of more than one hormone.     

Homosexual Mating Displays in Penguins

More than 50 yr ago, field studies recorded the same‐sex pairs (and trios) of penguins displaying to each other during the mating season, using behavior patterns typical of heterosexual mating displays. Such observations led to a hypothesis that due to a lack of sex recognition pairing occurs at random with respect to sex, an idea countered by the argument that sex recognition is highly accurate. No quantification of same‐sex mating displays has tested the frequency of such displays in penguins or tested the hypothesis of random display partners with respect to sex. During their mating season, we studied displaying and paired king penguins, Apenodytes patagonicus, at Kerguelen Island and sexed them using a DNA marker, to quantify any occurrence of this behavior. Indeed, same‐sex courtship displays were common (28.3% of 53 displaying pairs), the great majority of which were between males. Some homosexually displaying males eventually paired with females, but such males were significantly slower in heterosexual pairing than males that did not display homosexually. In two extraordinary cases, same‐sex pairs learned each other’s calls, an essential step in the pairing process. The frequency of such pairs was much lower than among displaying couples, significantly so for males. Finally, the frequency of homosexually displaying pairs was significantly lower than expected from random assortment of displaying birds, for both males and females. We examined possible explanations for same‐sex display and its biological significance. A population sex‐ratio bias in favor of males and high concentration of male sex hormones may help to explain non‐reproductive homosexually displaying pairs.     

The reproductive status of nonbreeding group members in captive golden lion tamarin social groups

Reproductive activity is limited to only one female in many species of callitrichid primates (marmosets and tamarins): daughters and subordinate females do not produce offspring. A suppression of ovulatory cyclicity is responsible for the lack of reproductive activity in three species of callitrichids studied to date. This study evaluated the endocrine status of golden lion tamarins (Leontopithecus rosalia) housed as daughters or sons in family groups and of individuals housed in isosexual peer groups. Daughters 17 months of age and older and a subordinate female had high levels of estrogen excretion. Mean levels of estrogen excretion in these females were similar to those of nonpregnant, breeding adult females (17.14 ± 6.82 versus 11.93 ± 6.33 μg/mg creatinine, respectively). Estrogen profiles were similar to those of breeding adult females, with sinusoidal cycles in estrogen excretion. Younger daughters in family groups (10 and 12 months old) showed markedly lower levels of estrogen excretion (0.84 ± 0.58 μg/mg creatinine). Estrogen profiles lacked the sinusoidal nature of cycles in older daughters and breeding females, and elevations in estrogen excretion occurred frequently and remained elevated for 1 or 2 days. Plasma testosterone levels in males varied widely, but mean concentrations did not differ among males housed in different social conditions. These results suggest that older daughters and subordinate females may be capable of expressing normal ovarian function in the presence of a breeding adult female. This finding may account for two unusual observations in the lion tamarin: the high level of female-female aggression and the presence of groups in the wild with more than one actively breeding female.     

Gonadal and hormonal characteristics of captive adult mourning doves during the nesting cycle

Paired mourning doves ($\text{Zenaida}$$\text{macroura}$) of a captive breeding colony were selected and sacrificed on specific day intervals postlaying and posthatching during 1976–1977. Blood plasma samples were analyzed for androgens, estradiol, and progestins using radioimmunoassays. Testes, ovary and oviduct weights, spermatozoan numbers, diameter of the three largest follicles in the ovary, the presence or absence of eggs in the reproductive tract, and crop gland characteristics also were recorded. Differences (P<0.05) existed between nonbreeding and breeding pairs in testes weights, spermatozoan numbers, and ovary and oviduct weights. No distinct cyclic pattern was observed in gonadal variables among breeding males and females during the nesting cycle, although trends were observed. No differences (P > 0.05) in androgen and progestin concentrations in males, or estradiol and progestin concentrations in females, between nonbreeding and breeding pairs, or among breeding pairs during different stages of the nesting cycle, were observed. Analysis of reproductive variables by stage of crop gland activity tended to indicate an inverse relationship between gonadal and crop gland activity in both male and female doves during the nesting cycle.