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1.
William A. Mackin 《Behavioral ecology and sociobiology》2005,59(2):326-332
Neighbor–stranger discrimination (NSD) occurs when animals respond with more aggression to strangers than to territorial neighbors. NSD has been reported in many species that defend multi-purpose territories for breeding and foraging, but it is rare among species that defend other types of territories. For birds that defend only their nest sites, there is no experimental evidence for NSD, and observational studies have provided mixed results. In a colony of Audubon's shearwaters (Puffinus l. lherminieri), I played back the calls of a neighbor and a stranger to males defending nest sites. Subjects responded with longer calls to playbacks of strangers than to those of neighbors. In shearwater colonies, strangers are often birds looking for future breeding sites. In contrast, there is no evidence that established breeders compete with their neighbors for any resources. Shearwaters should benefit from NSD because strangers represent a “real enemy” and established neighbors do not. 相似文献
2.
Joan Navarro Maite Louzao José Manuel Igual Daniel Oro Antonio Delgado José Manuel Arcos Meritxell Genovart Keith A. Hobson Manuela G. Forero 《Marine Biology》2009,156(12):2571-2578
Pelagic seabirds obtain food from oceans where the availability of their prey changes rapidly both seasonally and spatially.
Here, we investigated changes in the trophic habits of the critically endangered Balearic shearwater (Puffinus mauretanicus) through the breeding season and tested for dietary differences between sexes and age classes. We analysed δ15N and δ13C values in blood of adults during the pre-incubation, incubation and chick-rearing periods and of their chicks. Using a two-isotope
mixing model, we estimated dietary contributions based on isotope values from potential prey species which included small
pelagic species available naturally and demersal fish species available only from trawling discards. Balearic shearwaters
showed clear isotopic and dietary variation through the breeding season. During pre-incubation, breeding adults appeared to
exploit demersal fish, whereas during the incubation and chick-rearing period, they fed mainly on pelagic anchovies (Engraulis encrasicolus) and pilchards (Sardina pilchardus). Similarly, chicks were fed mainly with anchovies, a resource with a high energetic value. This variation in the dietary
habits of adult shearwaters during the breeding season was probably related to both natural and fishery-induced seasonal changes
in the availability of potential prey species within their main feeding grounds. However, changes in the nutritional requirements
of the shearwaters could also play an important role. Indeed, diet differed between sexes during pre-incubation: females fed
less on trawling discards and more on small pelagic fish than males. This sexual segregation in diet could be the consequence
of higher nutritional requirements of females during this period. Our study reveals the differential importance of both trawling
discards and small pelagic fish species for a pelagic seabird depending on the breeding period and illustrates the importance
of considering the entire breeding season when making inferences about the importance of specific prey in seabird dietary
studies. 相似文献
3.
An organism’s pattern of development can have important long-term fitness effects. In species where the sexes differ in size
or other phenotypic traits, they may also have different optimal developmental rates. This influences both parental sex allocation
strategies and susceptibility of the sexes to early developmental conditions. However, sex differences in developmental rate
and vulnerability to environment during the embryonic period are not well understood. In birds, sibling competition and hatching
asynchrony may select for accelerated embryonic development of the last offspring in order to reduce their competitive disadvantage
after hatching. They may advance their hatching in response to vocal stimuli by the older siblings. It is, however, unclear
whether this flexibility in developmental rates is sex specific. In this study, we experimentally manipulated between-embryo
contact and tested whether this affected the pre-natal developmental rate and post-hatching performance of male and female
offspring from last-laid eggs in the herring gull. Post-hatching performance was measured both in competitive and non-competitive
situations. Among young incubated in isolation, males hatched faster than females, but both sexes fledged in similar, relatively
good condition. Among young incubated with normal between-embryo contact, hatching time did not differ between sexes, but
males fledged in poorer condition than females, regardless of whether they were reared singly or in a brood. These results
suggest that male and female offspring differ in their ability to mitigate the costs of hatching asynchrony. 相似文献
4.
Summary
Hyla ebraccata, H. microcephala and H. phlebodes commonly occur together in Panama. The three species have calls exhibiting broad frequency overlap and call during the same season and time of day from similar microhabitats, frequently in close proximity. The vocal repertoires of the three species are structurally and functionally similar. All employ multi-part advertisement and aggressive calls which consist of a primary note followed by a variable number of clicks. H. ebraccata males often responded to heterospecific calls with multi-note synchronized responses, and calls with primary notes greater than 150–200 ms were most effective in eliciting synchrony. Playback experiments with synthetic 1-note advertisement calls of different durations and both synthetic 1-note advertisement calls and 200 ms tones of different frequencies demonstrated that H. ebraccata males will synchronize with stimuli which are similar in frequency and duration to conspecific calls. Data from a two-choice experiment with female H. ebraccata demonstrate that calls of individual H. microcephala can reduce the attractiveness of a H. ebraccata male's calls if primary notes overlap. By synchronizing response calls to those of H. microcephala, a H. ebraccata may reduce the chances that his calls are rendered less attractive to potential mates.Aggressive calls of these species are graded and are characterized by higher pulse repetition rates and often longer durations than advertisement calls. H. ebraccata males respond to aggressive calls of H. microcephala and H. phlebodes as they do to their own calls. Heterospecific aggressive interactions probably occur because the species interfere acoustically. Our results demonstrate that H. ebraccata males behave in ways which enhance their ability to communicate in a noisy assemblage of conspecific and heterospecific males. 相似文献
5.
Studies on spatiotemporal pattern of population abundance predict that close populations should exhibit a high level of synchrony, reflected in a parallel time variation of at least one demographic parameter. We tested this prediction for two threatened species of Procellariiformes sharing similar life history traits: the European Storm Petrel (Hydrobates pelagicus) and the Balearic Shearwater (Puffinus mauretanicus). Within each species, we compared adult survival, proportion of transients (breeders that do not settle), and average productivity at two neighboring colonies. Physical and environmental features (e.g., food availability) of the breeding sites were similar. However, while Balearic Shearwater colonies were free of predators, aerial predators occurred especially in one colony of the European Storm Petrel. Despite this difference, we found similar results for the two species. A high proportion of transient birds was detected in only one colony of each species, ranging between 0.00-0.38 and 0.10-0.63 for the petrels and shearwaters, respectively. This seems to be an emergent feature of spatially structured populations of seabirds, unrelated to colony size or predator pressure, that can have important demographic consequences for local population dynamics and their synchrony. Local survival of resident birds was different at each colony, an unexpected result, especially for predator-free colonies of Balearic Shearwater. Productivity varied between the two colonies of European Storm Petrels, but not between the two colonies of Balearic Shearwaters. We demonstrated that within each species, several demographic parameters were colony specific and sufficiently different to generate short-term asynchronous dynamics. Our findings suggest that, in spatially structured populations, local factors, such as predation or small-scale habitat features, or population factors, such as individual quality or age structure, can generate unexpected asynchrony between neighboring populations. 相似文献
6.
Males of the parapatically distributed myobatrachid frogs Geocrinia laevis and G. victoriana have highly divergent advertisement calls. Furthermore, the two species differ strongly in the complexity of their vocal repertoires, with males of G. victoriana possessing, and those of G. laevis lacking, a distinct territorial vocalization (encounter call). We investigated the territorial vocal behavior of males in a persistent natural hybrid population. Most hybrid males possessed encounter calls functionally equivalent to those of G. victoriana, that were produced following exposure to playback of recorded advertisement calls presented at >110 dB peak sound pressure level. The territorial acoustic responses were not associated with an index of hybridity derived from the structure of the advertisement call, suggesting genetic and functional decoupling of the two components of the vocal repertoire; i.e., advertisement calls and encounter calls. This decoupling may be the result of sexual selection favouring those hybrids with pronounced territorial behavior and the associated vocalization, regardless of the structure of their advertisement calls.Communicated by A. Mathis 相似文献
7.
Michael S. Reichert 《Behavioral ecology and sociobiology》2011,65(9):1739-1751
In addition to producing signals, males of chorusing species also act as receivers by adjusting properties of their vocalizations
in response to those of other nearby individuals. Although it is likely that males are responsive to more than one other individual,
most playback studies investigating male response have involved dyads in which vocal responses are measured to stimuli presented
from a single speaker. In this study, I explored changes in both the propensity to give aggressive calls and the temporal
properties of those calls in response to the playback of multiple aggressive call stimuli in the treefrog Dendropsophus ebraccatus. I found that males were sensitive to both the number of simulated aggressive callers and their specific call characteristics.
Males generally gave a highly aggressive response to the first stimulus presented, but their response to the modification
of this stimulus by the addition or subtraction of a simulated competitor depended on the degree of aggressiveness of the
stimuli. Males tended to decrease their aggressive responses when either a more aggressive call was silenced or a less aggressive
call was added and to increase their aggressive responses in the opposite situation. Aggressive calling in this species is
clearly affected by complex changes in the social environment and I suggest that future studies explore these issues in other
species to improve the understanding of communication interactions. 相似文献
8.
The identification of appropriate companions and mates is essential to both speciation and the maintenance of species through
prezygotic isolation. In many birds, social assortment is mediated by vocalizations learned through imitation. When imitative
vocal learning occurs throughout life, emergent shared signals reflect current social associations. However, when vocal and
genetic variation arises among populations, shared learned signal variants have a potential to reflect cultural or genetic
origin and to limit social and reproductive intermixing, provided that signal learning occurs prior to dispersal. The red
crossbill (Loxia curvirostra) is a bird species in which discrete contact call variants are associated with morphological variation, raising the possibility
that learned calls play a role in limiting intermixing. I examined the process of early call learning to determine if contact
call variants have a potential to limit intermixing in crossbills. I conducted a captive playback study to nestlings to evaluate
potential learning predispositions. I also cross-fostered nestlings to adoptive adult pairs of either their own or a different
call variant than their biological parents to assess the degree of vocal learning plasticity. Results show that young crossbills
imitate the call structures of adoptive parents, generating shared family-specific calls, which could facilitate family cohesion.
Learning processes that generate family-specific calls could also ensure that discrete call variants are transmitted across
generations, making call variants reliable signals of crossbills’ morphological and genetic backgrounds. 相似文献
9.
Tobias ML Corke A Korsh J Yin D Kelley DB 《Behavioral ecology and sociobiology》2010,64(11):1791-1803
Male Xenopus laevis frogs produce underwater advertisement calls that attract gravid females and suppress calling by male competitors. Here we
explore whether groups of males establish vocal ranks and whether auditory cues alone suffice for vocal suppression. Tests
of male–male pairs within assigned groups reveal linear vocal dominance relations, in which each male has a defined rank.
Both the duration over which males interact, as well as the number of competitive opportunities, affect linearity. Linear
dominance across the group is stable for about 2 weeks; rank is dynamic. Males engage in physical interactions (clasping)
while paired but clasping and vocal rank are not correlated. Playbacks of advertisement calls suppress calling and calls from
high- and low-ranking males are equally effective. Thus, auditory cues alone suffice to suppress vocal behavior. Playback
intensities equivalent to a nearby male advertising effectively suppress calling while low-intensity playbacks are either
ineffective or stimulate vocal behavior. X. laevis advertisement calls are biphasic, composed of alternating fast and slow click trills. Approximately half the males tested
are more vocally suppressed by all slow than by all fast trills; thus, these males can distinguish between the two phases.
The fully aquatic family Pipidae diverged from terrestrial ancestors approximately 170 mya. Vocal suppression in the X. laevis mating system may represent the translation of an ancient anuran social strategy to underwater life. 相似文献
10.
Discrimination of different social companions in spectacled parrotlets (Forpus conspicillatus): evidence for individual vocal recognition 总被引:1,自引:0,他引:1
Ralf Wanker Jasmin Apcin Bert Jennerjahn Birte Waibel 《Behavioral ecology and sociobiology》1998,43(3):197-202
Individual recognition is generally assumed to be a prerequisite for establishing and maintaining a complex social system.
Indeed, there is good evidence that highly social species have complex systems of vocal communication with individual recognition
by acoustic cues. In this study, we provide experimental evidence that vocal class and individual recognition is present in
a non-passerine bird, the spectacled parrotlet (Forpus conspicillatus). Spectacled parrotlets live in a complex system of social relationships. Soon after fledging, the young establish close
sibling relationships which are important for successful socialization, pairing and reproduction. In a series of playback
experiments we tested if spectacled parrotlets use contact calls for vocal recognition. The results showed that spectacled
parrotlets discriminate between the contact calls of different social categories. Adult birds preferred to respond to the
contact calls of their mates. Subadult individuals recognized the contact calls of their siblings. During the period of pair
bond formation, the affiliative contacts to the siblings decrease, but the parrotlets continue to respond to the calls of
their siblings. This is the first evidence that vocal sibling recognition might outlast the period of strong sibling interaction
and extends into the period of pair bond formation. In cases of mate loss or divorce, the acoustic contact to their siblings
might facilitate the re-establishment of close sibling relationships.
Received: 29 October 1997 / Accepted after revision: 5 April 1998 相似文献
11.
Eugene S. Morton Bridget J. M. Stutchbury Ioana Chiver 《Behavioral ecology and sociobiology》2010,64(6):947-954
We investigated sexual conflict over parental care in blue-headed vireos (Vireo solitarius) and documented the first example of unvarying unisexual brood desertion in passerines. Females at all nests (N = 24) that were monitored closely near fledgling, deserted their broods on or near the day of fledging leaving males alone
to complete parental care of young. No males deserted. This observational evidence was confirmed with radiotracking of females
(2004, 2007) and both pair members (2008). Radiotracked females began visiting distant males 1–4 days before young left the
nest, subsequently paired with males 355–802 m away, and laid first eggs in new nests less than 5 days after deserting. In
contrast, females suffering nest predation did not desert and renested with the same male. We suggest equal parental care
(nest building, incubation, feeding) in the sexes, genetic monogamy, and an adult sex ratio biased towards males has led to
female control of brood desertion in this species. Unisexual desertion may be more important in altricial birds than generally
realized and we discuss prerequisites to predict its occurrence. One is genetic monogamy, which may be a female tactic that
reduces the likelihood of males evolving counter-adaptations to female desertion. 相似文献
12.
Irene M. van den Heuvel Michael I. Cherry Georg M. Klump 《Behavioral ecology and sociobiology》2014,68(8):1245-1252
Many socially monogamous bird species follow a genetically promiscuous reproductive strategy. Duetting birds may be an exception, as they appear to exhibit very low levels of extra pair paternity—which is thought to be connected to duetting. Duets are predicted to function either in paternity guarding or as signals of commitment to the pair bond, reciprocally reducing extra pair mating in both sexes. In this study, we used four microsatellites to document paternity loss in the Crimson-breasted Shrike (Laniarius atrococcineus), a socially monogamous subtropical duetting species. Extra pair paternity was surprisingly high, with extra pair males siring 20 % of young in 30 % of broods. Furthermore, we compared the levels of extra pair paternity of each pair to certain characteristics of their duets to test the paternity guard and the commitment hypotheses. Our results offered no support that duets function in paternity guarding, although the fact that males which had been cuckolded answered more of their female’s calls could represent an adaptation to avoid future cuckoldry. We also found no evidence for duets functioning as signal of commitment. Female vocal behaviour was in fact the reverse of that predicted: Levels of infidelity amongst social females were positively related to female answer rate of their mates’ songs. These results indicate that females may use increased answer rates as a form of manipulation, in an attempt to avoid potential costs associated with their extra pair matings. 相似文献
13.
Hansjoerg P. Kunc Valentin Amrhein Marc Naguib 《Behavioral ecology and sociobiology》2007,61(4):557-563
Seasonal patterns of bird song have been studied intensively with a focus on individual males. However, little is known about
seasonal patterns of singing during vocal interactions between males. Vocal interactions have been shown to be important in
sexual selection as males may signal aspects of motivation or quality. Here, we investigated in nightingales (Luscinia megarhynchos) whether a male’s behaviour in vocal interactions at different stages of the breeding season is influenced by its mating
status. We examined how males that differ in their subsequent mating success respond to a non-interactive, nocturnal playback
presented during the period of mate attraction and subsequently during the egg-laying period. We found that mated males overlapped
fewer songs and had a lower song rate during the egg-laying period compared to their responses during the mate-attraction
period, whereas unpaired males did not vary in their responses between the two periods. Our results suggest that mating status
is a key factor affecting singing behaviour in vocal interactions and that a time-specific singing pattern like song overlapping
is used flexibly during vocal interactions. Because song overlapping is thought to be a signal of aggression in male–male
vocal interactions, it seems that males vary the level of aggression in vocal interactions according to their mating status
and to the stage in the breeding season. 相似文献
14.
Carlos César Martínez-Rivera H. Carl Gerhardt 《Behavioral ecology and sociobiology》2008,63(2):195-208
Senders and receivers influence dynamic characteristics of the signals used for mate attraction over different time scales.
On a moment-to-moment basis, interactions among senders competing for a mate influence dynamic characteristics, whereas the
preferences of receivers of the opposite gender exert an influence over evolutionary time. We observed and recorded the calling
patterns of the bird-voiced treefrog Hyla avivoca to assess how the dynamic characters of calls vary during interactions among groups of males in a chorus. This question was
also addressed using playback experiments with males. Playback experiments with females showed how changes in dynamic call
properties are likely to affect male mating success. Frogs calling in pairs, groups, or in response to playbacks produced
longer calls than did isolated males. During call overlap, males often increased the duration of the silent interval (gaps)
between the pulses of their calls so that the pulses of the calls of two neighbors interdigitated. This change resulted in
increased variability of pulse rate, a traditionally static acoustic property; however, males also produced high proportions
of non-overlapped calls in which variability in pulse rate was low and had species-typical values. Females preferred long
calls to short- and average-duration calls, and non-overlapped calls to overlapped calls. Given a choice between pairs of
overlapped calls, females preferred pairs in which the proportion of overlap was low and pairs in which the pulses of such
calls interdigitated completely. The observed patterns of vocal competition thus reflect the preferences of conspecific females,
which have influenced the evolution of the calling behavior of H. avivoca.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
15.
Julia Bartmess-LeVasseur Carrie L. Branch Sheri A. Browning Jessica L. Owens Todd M. Freeberg 《Behavioral ecology and sociobiology》2010,64(7):1187-1198
Evidence from different chickadee species (Poecile genus) indicates that birds can modify the note composition of their “chick-a-dee” calls in the presence of predator stimuli.
Here, we tested the effects of predator models and the distance of those models on calls of three species foraging together
at feeding stations: Carolina chickadees (Poecile carolinensis) and tufted titmice (Baeolophus bicolor), both members of the Paridae family, and white-breasted nuthatches (Sitta carolinensis), a member of the Sittidae family. Model and distance affected seed-taking rates in all three species. “Chick-a-dee” calling
rates were higher in the predator context for both chickadees and titmice, but we detected no predator context effects on
“quank” call rates for nuthatches. Predator and distance contexts affected acoustic parameters of notes of the “chick-a-dee”
calls of chickadees and titmice; no such effects were detected for nuthatch “quank” calls. These results suggest species differences
in encoding of information in the primary social calls of these three species that commonly occur in multi-species flocks.
Chickadees and titmice are “nuclear” species and nuthatches are “satellite” species, and these different roles might be related
to the differences in vocal signaling that we detected. 相似文献
16.
Behavioral Ecology and Sociobiology - In many tropical birds, both sexes use conspicuous vocal signals during territorial interactions. Although a growing number of studies examine male and female... 相似文献
17.
Randy Thornhill 《Behavioral ecology and sociobiology》1992,30(5):357-363
Summary Fluctuating asymmetry (FA) is defined as small, random deviations from bilateral symmetry in a generally perfect bilaterally symmetrical morphological trait. FA in forewing length affects the outcomes of interspecific contests for food items (dead arthropods) between two species of Japanese scorpionflies, Panorpa nipponensis and P. ochraceopennis, in nature. FA differences between same-sex contestants are more important than either body size or ownership of food in determining the outcomes of interspecific contests; for both sexes, winners statistically significantly more often have relatively low FA. Two condition-dependent mating tactics are used by the males of each species: (a) a male may defend a dead-arthropod nuptial gift, or (b) a male without such an arthropod may wait near a male with one. In both tactics, males release long-distance sex pheromones. Groups of pheromone-releasing males are made up of one male with a nuptial gift and his satellites; the males in a group may be conspecifics or heterospecifics. Males that lose contests for nuptial gifts often become satellites of the contest winners whether or not winners are conspecific. Satellite males have statistically significantly greater FA than males with nuptial gifts in heterospecific male display groups. Satellite males mate infrequently and briefly compared to resource-holding males. Satellites of heterospecific males copulate with conspecific females displaced from nuptial gifts by the resource-holding males of the other species. In both species, the largest and smallest individuals have the greatest FA, and intermediate-sized individuals have the least; this same pattern often occurs in other animals. 相似文献
18.
The pay-off of deserting and leaving a mate to care for the offspring alone is generally assumed to depend mainly on the availability of alternative mating partners and on the potential spawning rate of males and females. Eretmodus cyanostictus is a monogamous mouthbrooding cichlid in which the clutch is successively incubated first by the female and then by the male. It has been suggested that parents are constrained to monogamy due to low remating probabilities for both sexes. We tested this hypothesis by varying the sex ratio experimentally. Mate desertion by either sex was not significantly higher when additional potential mates were present (males: 8.3%, females: 0%) than when there were no other same-sex conspecifics present (males: 0%, females: 0%). Males lost their mate to a male intruder during their incubation in 26.7% of cases. Pair members were more active and showed more aggression when same-sex conspecifics were present. Behavioural differences between treatments were strongest during the incubation period of a given sex. If no desertion takes place, sexual conflict may be expressed also on a second level, the amount of parental care each parent provides. Indeed, males took the offspring later when additional females were present, although male incubation time did not differ between treatments. A hitherto undescribed display behaviour of females was clear evidence of a conflict about the timing of shift of young. In conclusion, offering alternative mating opportunities did not strongly favour mate desertion in E. cyanostictus. It rather revealed a conflict between mates about when to shift the young.Communicated by M. Abrahams 相似文献
19.
Edward M. Sykes Tabitha M. Innocent Ido Pen David M. Shuker Stuart A. West 《Behavioral ecology and sociobiology》2007,61(11):1751-1758
Sex allocation theory offers excellent opportunities for testing how animals adjust their behaviour in response to environmental
conditions. A major focus has been on instances of local mate competition (LMC), where female-biased broods are produced to
maximise mating opportunities for sons. However, the predictions of LMC theory can be altered if there is both local competition
for resources during development and an asymmetry between the competitive abilities of the sexes, as has been seen in animals
ranging from wasps to birds. In this paper, we test the extent to which asymmetric larval competition alters the predictions
of LMC theory in the parasitoid wasp Nasonia vitripennis. We found that the body size of both sexes was negatively correlated with the number of offspring developing within the host.
Further, we found that when faced with high levels of competition, the body size of females, but not males, was influenced
by the sex ratio of the competing offspring; females were smaller when a higher proportion of the brood was female. This asymmetric
competition should favour less biased sex ratios than are predicted by standard LMC theory. We then develop a theoretical
model that can be parameterised with our data, allowing us to determine the quantitative consequences of the observed level
of asymmetric larval competition for sex allocation. We found that although asymmetric competition selects for less biased
sex ratios, this effect is negligible compared to LMC. Furthermore, a similar conclusion is reached when we re-analyse existing
data from another parasitoid species where asymmetric larval competition has been observed; Bracon hebetor. Consequently, we suspect that asymmetric larval competition will have its greatest influence on sex ratio evolution in species
that have smaller clutches and where local mate competition is not an issue, such as birds and mammals. 相似文献
20.
Robert L. Thomson Veli-Matti Pakanen Diane M. Tracy Laura Kvist David B. Lank Antti Rönkä Kari Koivula 《Behavioral ecology and sociobiology》2014,68(8):1261-1272
Males of many species theoretically face a fitness tradeoff between mating and parental effort, but quantification of this is rare. We estimated the magnitude of the mating opportunity cost paid by incubating male Temminck’s stints (Calidris temminckii), taking advantage of uniparental care provided by both sexes in this species. “Incubating males” provide all care for an early clutch, limiting subsequent mating possibilities. “Non-incubating” males include males that failed to obtain, lost to predation, or actively avoided incubating clutches. These males were free to pursue extrapair copulations and to mate with females laying later clutches, which females usually incubate themselves. Male incubation classes did not differ in measures of quality, and many individuals changed classes between years, suggesting the use of conditional reproductive tactics. However, specialist non-incubators may also exist. Using microsatellites to assign parentage, we compare males’ total fertilizations and the subset “free of care” fertilizations between incubation classes. Incubators were more likely to gain at least one fertilization per season and averaged one more per season than non-incubators. However, successful non-incubators were more likely to gain “free of care” fertilizations, averaging two more than successful incubators. The relative success of male incubation classes also changed with local sex ratios. With higher female proportions, non-incubators gained disproportionately more offspring, suggesting that the use of tactics should be partly determined by the availability of potentially incubating females. Overall, we estimate the opportunity cost of incubating to be 13–25 % of the potential annual reproductive output. 相似文献