Male Yellow Warblers Research Articles

Pairing status moderates both the production of and responses to anti‐parasitic referential alarm calls in male yellow warblers

AbstractDefending offspring incurs temporal and energetic costs and can be dangerous for the parents. Accordingly, the intensity of this costly behavior should reflect the perceived risk to the reproductive output. When facing costly brood parasitism by brown‐headed cowbirds (Molothrus ater), where cowbirds lay eggs in heterospecific nests and cause the hosts to care for their young, yellow warblers (Setophaga petechia) use referential “seet” calls to warn their mates of the parasitic danger. Yellow warblers of both sexes produce this call only in response to cowbirds or seet‐calling conspecifics. Seet calls are mainly produced during the laying and incubation stages of breeding, when risk of brood parasitism is highest, rather than during the nestling stage. On the other hand, general alarm calls (chips) are produced throughout the nesting cycle and are also used in conspecific interactions unrelated to nesting. We hypothesized that context shapes responses prior to breeding as well, such that yellow warblers without a mate and active nest would be less likely to respond to playbacks that simulate brood parasitism risk. To test this hypothesis, we presented playbacks of two nest threats, cowbirds (brood parasite) and blue jays (Cyanocitta cristata; nest predator), on territories of unmated male warblers (unpaired) and male warblers with a known mate (paired). We found that unpaired males were unresponsive toward playbacks indicating nest threats, whereas paired males were significantly more aggressive and vocal toward these playbacks compared to control playbacks. However, both paired and unpaired males were vocally responsive toward chip calls, which are informative for males regardless of pairing status. Male yellow warblers appear to adjust their responses during the earliest stages of breeding depending on the contextual relevance of specific threat stimuli, and together with prior studies, our work further supports that referential seet calls are associated with stage‐specific risk of brood parasitism.

Context-dependent relationships between multiple sexual pigments and paternal effort

Elaborately ornamented males may provide more paternal services than less ornamented males in some contexts but may alternatively invest in territoriality or mating over paternal effort. Two outstanding questions involve whether different types of sexual pigmentation communicate distinct information about paternal strategy and whether highly ornamented males adjust paternal effort to context-dependent benefits. In yellow warblers (Setophaga petechia), we explored whether carotenoid- and phaeomelanin-based pigmentation show distinct or complementary relationships to paternal effort and song rate and how males differing in pigmentation adjust behavior to nesting stage, brood size, and territorial challenge. Past studies have suggested that highly melanic male yellow warblers invest in territoriality or mating over paternal effort. However, genetic paternity data from our population indicate that males with high levels of both pigment types retain within-pair paternity but gain little extrapair paternity. Therefore, we predicted that these males should also exhibit higher paternal effort. Highly melanic males sang at high rates during incubation and provisioned incubating females at relatively low rates late in the incubation stage, but showed high late-stage nestling provisioning effort, and did not greatly reduce nestling provisioning rate under territorial challenge. Moreover, as predicted based on genetic paternity data, the relationship between melanin pigmentation and paternal effort varied with the level of carotenoid pigmentation expressed by males, with males expressing high levels of both pigment types provisioning late-stage nestlings at enhanced rates. Thus, the pigment types in combination may signal paternal benefits, and results suggest flexible investment in paternal effort by highly pigmented males.

Plumage coloration and ornamentation as predictors of nest survival and number of young fledged in Yellow Warblers

ABSTRACT Previous studies of Yellow Warblers (Setophaga petechia) indicate that males with heavy melanin-based brown breast streaking are more territorial and obtain more extra-pair copulations than lightly streaked males that provide more parental care and are cuckolded more often. Because carotenoid-based plumage characters can also signal quality in male songbirds, we examined relationships between yellow carotenoid-based breast coloration and brown breast streaking and measures of the reproductive performance of male and female Yellow Warblers in northwestern Ohio from April to June 2007–2008. We used an information theoretic approach to examine relationships between reproductive measures (daily nest survival rate and number of young fledged) and brown breast streaking, yellow breast coloration, extent of prealternate wing molt, age, year, and first-egg date. Males with paler yellow breast plumage (Beta hat =–0.213) and those with more brown breast streaking (Beta hat =–0.000036) fledged fewer young, but we found no associations between number of young fledged per male and age, year, or extent of prealternate wing molt. In addition, none of the measured variables was associated with the number of young fledged per female. Age was positively associated with daily nest survival rates for male Yellow Warblers (Beta hat = 1.127), but we found no association between daily nest survival rate and brown breast streaking, yellow breast coloration, extent of prealternate wing molt, age, year, and first-egg date. None of the measured variables was associated with daily nest survival for females (null model was top-ranked). Because brown breast streaking and the intensity of yellow breast coloration of male Yellow Warblers were negatively related to number of young fledged, we suggest that these plumage characteristics function differently in male–female and male–male interactions; yellow breast coloration signals age and reproductive experience, whereas brown breast streaking signals degree of territoriality or parental care. Estudios previos en Setophaga petechia indican que los machos, que tienen rayas pardas oscuras en el pecho, producto de altas concentraciones de melanina, son más territoriales y obtienen mayor número de copulaciones, con hembras que no son su pareja, que machos que tienen rayas claras y que a su vez proveen mayor cuidado parental y son engañados más a menudo. Debido a que características del plumaje asociados a carotenoides, pueden también señalar la calidad de los machos en aves canoras, se llevó a cabo un estudio, en el noroeste de Ohio de abril a junio de 2007–2008, para examinar la relación entre la coloración del pecho basado en carotenoides-amarillo y rayas pardas en este, y medidas de ejecución reproductiva en hembras y machos de S. petechia. Utilizamos un marco de vista teórico para examinar la relación entre medidas reproductivas (sobrevivencia diaria del nido y número de volantones) y rayas pardas en el pecho, coloración amarilla en el pecho, extensión de la muda prealternada en el ala, edad, año, y la puesta del primer huevo. Machos con pecho amarillo pálido (Beta hat = 0.213), y aquellos con mayor colorido pardo en las rayas del pecho (Beta hat = 0.000036), produjeron menos volantones, aunque no encontramos asociación entre el número de volantones por macho, su edad, año y extensión de la muda prealternada del ala. Ninguna de las variables estudiadas pudo ser asociada al número de volantones producidos por las hembras. La edad fue positivamente asociada con la tasa de sobrevivencia diaria de los nidos, en los machos (Beta hat = 1.127), pero no encontramos asociación entre la tasa de sobrevivencia diaria, las rayas pardas en el pecho, la coloración amarilla en el pecho, la extensión de la muda prealternada del ala, edad, año y la fecha de puesta del primer huevo. Ninguna de las variables medidas, para las hembras, estuvo asociada con la sobrevivencia diaria de los nidos (hipótesis nula fue la de mayor jerarquía). Debido a que las rayas pardas y la intensidad de la coloración amarilla en el pecho de los machos estuvo negativamente relacionada al número de volantones producidos, sugerimos que estas características del plumaje funcionan diferente en las interacciones macho-hembra, y macho-macho; la coloración amarilla del pecho, señala edad y experiencia reproductiva, mientras que las rayas pardas señala el grado de territorialismo o cuidado parental.

Are Nestlings the Cue for Reduction of the Adrenocortical Response to Stress in Male Yellow Warblers Breeding at High Latitude?

AbstractAbstract. Acute corticosterone secretion helps individuals survive perturbation, particularly when faced with unpredictable conditions. However, elevated corticosterone is often incompatible with reproduction. Male Yellow Warblers (Dendroica petechia) breeding at high latitude avoid this conflict by exhibiting a reduced adrenocortical response while provisioning nestlings. To determine if this reduction is cued by nestlings, in June 2000 we switched clutches between nest pairs to manipulate hatching date. We sampled males with early-hatching clutches for the adrenocortical response 24 hr after nestlings hatched, but 24 hr prior to the premanipulated (original) hatching date. Similarly, we sampled males with late-hatching clutches 24 hr after the original hatching date, but prior to nestlings hatching. Males with early-hatching clutches (n = 6) showed no reduced adrenocortical response, while males with late-hatching clutches (n = 6) appeared to show a reduced response even without nestlings, suggesting that nestlings do not cue the reduction. An endogenous clock, day-counting mechanism, or hormonal changes may be associated with the reduced adrenocortical response.

ARE NESTLINGS THE CUE FOR REDUCTION OF THE ADRENOCORTICAL RESPONSE TO STRESS IN MALE YELLOW WARBLERS BREEDING AT HIGH LATITUDE?

Abstract Abstract. Acute corticosterone secretion helps individuals survive perturbation, particularly when faced with unpredictable conditions. However, elevated corticosterone is often incompatible with reproduction. Male Yellow Warblers (Dendroica petechia) breeding at high latitude avoid this conflict by exhibiting a reduced adrenocortical response while provisioning nestlings. To determine if this reduction is cued by nestlings, in June 2000 we switched clutches between nest pairs to manipulate hatching date. We sampled males with early-hatching clutches for the adrenocortical response 24 hr after nestlings hatched, but 24 hr prior to the premanipulated (original) hatching date. Similarly, we sampled males with late-hatching clutches 24 hr after the original hatching date, but prior to nestlings hatching. Males with early-hatching clutches (n = 6) showed no reduced adrenocortical response, while males with late-hatching clutches (n = 6) appeared to show a reduced response even without nestlings, ...

The functions of multiple singing modes: experimental tests in yellow warblers, Dendroica petechia

In several groups of songbirds, including the North American wood warblers (Parulidae), males subdivide their song repertoires into two different categories, or ‘modes’, of singing. Previous studies of wood warblers suggest that the two singing modes in this group are each specialized for interacting with one of the two sexes: Type 1 singing for interacting with females and Type 2 for interacting with other males. Here I examine the responses of male and female yellow warblers to the two singing modes produced by males. Using song playback experiments, I found that male yellow warblers responded to potential intruders with Type 1 singing, rather than Type 2 singing, as predicted. In tests using the copulation solicitation assay, females implanted with oestradiol responded equally strongly to both Type 1 and Type 2 singing. These results suggest that male wood warblers use both singing modes to interact with males and females, and that the singing modes do not have distinct, sex-specific functions as previously thought. Factors other than intra- and intersexual selection are therefore likely to have helped shape the evolution of distinct singing modes.

Rapid decline of host defences in response to reduced cuckoo parasitism: behavioural flexibility of reed warblers in a changing world

On Wicken Fen and nearby watercourses eastern England, parasitism by cuckoos, Cuculus canorus, declined from 26 and 16 of reed warbler (Acrocephalus scirpaceus) nests in 1985 and 1986, respectively...

Reproductive synchrony and extra-pair mating strategy in a socially monogamous bird,Dendroica petechia

Depending on the circumstances under which extra-pair mating occurs, theory makes opposing predictions about how reproductive synchrony should influence extra-pair paternity. This study investigated which sex initiated extra-pair mating in the yellow warbler, whether extra-pair behaviour and extra-pair paternity were related to reproductive synchrony, and whether synchrony affected the mating success of all males equally. Observations and captures of individuals making territorial intrusions indicated that males initiated extra-pair mating. Spatial patterns of male territorial intrusions and of extra-pair paternity were similar. Males’ extra-pair activity was reduced when their social partner was fertile. More offspring were sired by the extra-pair male when the female nested asynchronously with that sire's social mate. Neither population-wide synchrony, nor synchrony with neighbours, however, seemed to predict the incidence of extra-pair parentage or the identity of the sire, indicating factors other than synchrony were also important. Males with more breast streaking (a plumage ornament) were more successful as extra-pair sires, and were least affected by the constraint of synchrony. Larger males were less often cuckolded, and achieved extra-pair success mainly when their partner was not fertile. Thus, male yellow warblers apparently use different mating tactics depending on their plumage and size. More generally, the results suggest how mating strategies are affected by which sex initiates extra-pair mating and by the relative contributions of within-pair and extra-pair paternity to total reproductive success.

Extra–pair mating, male plumage coloration and sexual selection in yellow warblers (Dendroica petechia)

Extra-pair mating has been proposed as a source of sexual selection responsible for secondary sexual traits that are common among socially monogamous birds, although supporting evidence is scant. In the socially monogamous yellow warbler, males are larger than females, and unlike females, have extensive reddish streaking on their breasts. Using DNA fingerprinting we show that within-pair parentage was positively related to male size, and that extra-pair mating success was positively related to the amount of streaking on the breast. To our knowledge, this is the first intraspecific evidence of an association between a male plumage ornament and gains of extra-pair paternity that is apparently independent of age. This study confirms that extra-pair mating can be an important mechanism of sexual selection even when the most successful sires are commonly cuckolded, and refutes a previous hypothesis that the variation in plumage and behaviour among male yellow warblers is an example of alternative, equally successful, evolutionarily stable strategies (ESS). More generally, the demonstrated independence of within-pair and extra-pair success and their associated traits indicates that where animals have multiple secondary sexual traits, different traits may be selected by different mechanisms that contribute to total reproductive success.

Cuckoldry and lack of parentage-dependent paternal care in yellow warblers: a cost–benefit approach

Theory suggests that a male strategy of reducing parental care in response to reduced parentage should evolve only under certain conditions. Expected paternity in subsequent matings is predicted to be primary in effect, because it determines whether there is a future benefit to compensate males for the cost of reduced care. This study, tested whether provisioning of nestlings by socially monogamous male yellow warblers, Dendroica petechia, varied with the males' parentage in the brood and how males' paternity varied in subsequent matings. Analysis included observations of parental care from 40 nests (31 of which had paternity determined by multi-locus DNA fingerprinting) and paternity results from 130 families over 3 years. Male care was variable but unrelated to parentage, and males were observed to provide typical amounts of parental care to broods in which they had no parentage. Individual males' within-pair parentage generally declined within a season (with re-nesting), varied inconsistently between years and was unrelated to age or breeding experience. Survival between breeding seasons was low (30%) and independent of within-pair parentage. These patterns collectively suggest that the benefit of facultatively reducing parental care when parentage is reduced rarely exceeds the costs. Thus, selection for parentage-dependent care is apparently absent or weak, which could explain the absence of parentage-dependent care in this population of yellow warblers.

Extra-pair paternity and the opportunity for sexual selection in a socially monogamous bird (Dendroica petechia)

We used multi-locus DNA fingerprinting to characterise the genetic mating system of the socially monogamous yellow warbler (Dendroica petechia). Over 2 years there were no instances of brood parasitism, but 59% of families (n = 90) contained extrapair sired young and 37% of offspring (n = 355) were of extra-pair paternity. Most hypotheses for extra-pair mating in monogamous species assume a paternity benefit to extra-pair sires, and focus on the benefit(s) to females. However, the assumption of male benefit has been little tested. Among yellow warblers, known extra-pair sires were just as likely to be cuckolded as any male in the population, and there was at least one reciprocal exchange of extra-pair paternity. Nevertheless, among known extra-pair sires, the paternity gains from extra-pair paternity were, on average, greater than the losses in their own families. These results show there is a paternity benefit to certain males. However, the benefit is not absolute but relative and therefore more difficult to measure. The results also suggest that patterns of extra-pair fertilisation are not determined by female choice alone. Most confirmed extra-pair mates were territorial neighbours, but some resided as far as three territories apart, and greater spatial separation was implied in other cases. Thus, the opportunity for extra-pair mating is great. We estimate that as a result of extra-pair fertilisations, variance in male mating success is increased somewhere between 3-fold and 15-fold over that which would result from within-pair reproduction alone. These findings affirm the potential importance of extra-pair reproduction for sexual selection in monogamous species and they support earlier suggestions that extra-territorial forays by male yellow warblers are for the purpose of extra-pair mating.

Hatching Asynchrony and Feeding Rates in Yellow Warblers: A Test of the Sexual Conflict Hypothesis

T. Slagsvold and J. T. Lifjeld have proposed that hatching asynchrony in bird species in which only the female incubates is a strategy used by females to extract more parental investment from their mates. We examined this hypothesis by comparing feeding rates of female and male yellow warblers (Dendroica petechia) tending asynchronously and synchronously hatched broods. Regardless of brood size, feeding rates during the early, middle, and late nestling periods were similar for females tending asynchronously and synchronously hatched broods. Nevertheless, there was a general trend for females tending asynchronous broods to have lower feeding rates, which suggests that females may prefer hatching asynchrony. This is consistent with the sexual conflict hypothesis. Male feeding rates exhibited trends similar to those of females. That is, although the result is not statistically significant, males tending asynchronous broods, regardless of brood size, generally made fewer feeds than males tending synchronously hatched broods. However, males tending asynchronous broods of five did make significantly fewer feeds during the early nestling period than males tending similar-sized synchronous broods. This was also true when the data were combined across brood sizes. This suggests, contrary to the sexual conflict hypothesis, that males, especially those tending larger broods, should favor hatching asynchrony. Consequently, the sexes do not appear to be in conflict as to when incubation should begin, but rather females and males prefer, or at the very least are neutral with respect to, the initiation of incubation prior to clutch completion.

Geographical Morphology of Male Yellow Warblers

Morphological measurements were taken on study skins of breeding Yellow Warbler (Dendroica petechia) males collected from near the Arctic Circle to the Equator. The data were smoothed using LOESS (a non-linear, non-parametric scatterplot smoother), to elucidate patterns of geographic variation. Individuals are generally larger in the south than in the north, although birds from the Caribbean region show the reverse trend. Wing length follows the overall size trend poorly. Proportionate wing length is much shorter and more rounded in the non-migratory tropical populations, than in the far north. This finding supports the hypothesis that variation in wing length is related to migratory distance. Therefore, wing length is a poor choice for an overall size measure in this species. Comparison of morphological variation with climatic variation in this species provides counter-evidence to James's (1970) modification of Bergmann's Rule, that larger birds should occur in colder, drier climates; the largest Yellow Warblers are in warm, humid climates. In addition, no support for Bergmann's Rule can be detected analyzing the North American or tropical populations separately. Likewise, Allen's Rule (that appendages should be smaller or shorter in cold climates) also is unsupported by the Yellow Warbler.

The Singing Behaviour of Yellow Warblers

Yellow warblers (Dendroica petechia aestiva), like other wood-warblers (Parulinae), use different songs in different circumstances. Analysis of recordings of 28,697 songs from 17 wild male yellow warblers from 1983 to 1988 at Amherst, Massachusetts, U.S.A., showed a consistent pattern of singing behaviour. I found that each male yellow warbler has a repertoire of songs divided into a single Type I song and a group of Type II songs. The patterns of song use are standardized, but the song types used as Type I and Type II songs are not; some males' Type I songs were similar to others males' Type II songs. Type I songs are sung relatively slowly in long runs of the song during daylight, are used near females, and, as demonstrated by mate removal experiments, are used more by unmated than by mated males. Type II songs are used in a dawn song bout, are sung relatively rapidly with much switching among song types, and are used in interactions with other males. Type I songs seem to have higher frequencies of modal intensity, especially in the initial phrase, and to have a greater increase in amplitude at the start of the song than do Type II songs. There may be some minor variation in the ways individual males use Type I and Type II songs, but the overall pattern of use is similar among males. Types I and II songs seem to be male-female and male-male signals, respectively. Thus, female response to song may have selected for a relatively simple signal with a high frequency of modal intensity, while male response to song may have selected for a relatively complex, low frequency signal.

Influence of age and territory quality on the reproductive behaviour of male Yellow Warblers

Individual male Yellow Warblers (Dendroica petechia) exhibit differences in their level of parental investment, which correlate with the amount of brown streaking on the breast. We tested two alternative hypotheses to explain these patterns. The age effect hypothesis proposes that the variation in plumage and parental behaviour is an effect of differences in male age. This was tested by analyzing the nest visit rates and plumage scores of banded males present in the study in more than 1 year. The age effect hypothesis is rejected because there was no evidence of significant within-male variation due to increasing age, nor of any consistent directional change in either parental effort or plumage pattern between years. The territory quality hypothesis proposes that the quality of territory occupied has an important proximate influence on male parental effort. By observing the same territories over different years we were able to compare nest visit rates of different males with different plumage scores while holding the effect of territory quality constant. Analysis of variance revealed that male plumage rank had a highly significant effect on nest visit rate, while the effect of territory occupied was not significant. Rejection of these two alternative hypotheses provides further support for the hypothesis that phenotypically different males are using alternative and irreversible lifetime reproductive strategies.

Differential allocation of reproductive effort to territorial establishment and maintenance by male yellow warblers (Dendroica petechia)

We tested the hypothesis that the basis of the variation in reproductive strategy among male yellow warblers (Dendroica petechia) is a tradeoff in the allocation of reproductive effort to intrasexual competition (territorial effort) and to parental care (parental effort). Since a negative correlation between level of parental effort and amount of brown streaking on the breast (plumage score) has already been demonstrated in this species, this study looked for evidence of a positive correlation of territorial effort with plumage score and a negative correlation with parental effort. Analysis of the spatial and temporal use of territories, prior to egg-laying, by males with different plumage scores supported the prediction that brighter (higher plumage score) males allocate more effort to territorial establishment and maintenance (Fig. 1). Male plumage score was positively and highly significantly correlated with six different measures of the relative amount of time spent, rate of energy expended, and risk of injury assumed by each male during territorial activities. The level of territorial effort was also found to be negatively correlated with the level of parental effort expended by the same males later in the season, confirming that there is a tradeoff in allocation of reproductive effort to these two major components. Further analysis revealed that territory quality was positively correlated with male plumage score (Figs. 3 and 4), while average nestling growth rate and other indices of reproductive success were not (Fig. 6). These results suggest that increased territorial effort by brighter males enables them to occupy higher quality territories where high levels of parental effort are not necessary to maintain high levels of reproductive success. Since reproductive success was not correlated with plumage score, this study further supports the differential allocation hypothesis that different males are using alternative strategies for the allocation of reproductive effort.

Age-related variation in song repertoire size and repertoire sharing of yellow warblers (Dendroica petechia)

Songs of male yellow warblers (Dendroica petechia), ranging from 1 to 6 years of age, were recorded in the spring and summer of 1984. Recorded repertoire size and number of songs shared with neighbours varied positively with age in the spring but not in summer. Neither clutch initiation date nor fledging success varied with age or number of songs shared but both measures of reproductive success varied with size of recorded song repertoire.

Evidence for reliable badges of status in territorial yellow warblers ( Dendroica petechia)

We examined the continuous variation in the breeding plumage of male yellow warblers ( Dendroica petechia) to determine if the amount of brown streaking on the breast functions as a badge of relative status in territorial males. Conspecific mounts differing in the amount of breast streaking were presented as simulated intruders to a sample of territorial males. Individual males exhibited higher levels of total aggressive response toward brighter models, i.e. those with more brown streaking. This indicates that the streaking is used to assess prospective opponents prior to a response, and that bright intruding males are regarded as more of a threat to the resident than are duller males. The level of response was also correlated with the brightness of the resident males. Bright males responded more aggressively than duller residents to model presentations, and also allocated more time and effort to territory maintenance. We conclude from this that bright males are signalling social dominance, but suggest that the proximate source of high status is a costly increase in the level of aggressive motivation, and not simply an intrinsic superiority in fighting competence. Thus the amount of brown streaking would be a reliable signal of the level of aggressive effort a male is willing to expend in escalating contests and defending resources. We propose that the reliability of the signal is ultimately maintained by the use of different but, overall, equally successful reproductive strategies by males of different appearance. An important implication of this is that ‘cheating’ on signalled status may be neither possible nor necessary.

Sexual selection and variation in reproductive strategy in male yellow warblers (Dendroica petechia)

Male yellow warblers (Dendroica petechia) exhibit extensive variation in the amount and conspicuousness of the sexually distinctive brown streaking on the breast. We investigated this intraspecific variation in degree of sexual dichromatism to see if male plumage rank (essentially the amount of brown streaking) is correlated with the amount of reproductive effort allocated to parental investment, as sexual selection theory would predict. As predicted, the average rate of feeding visits to the nest by males was negatively correlated with the plumage rank of the male in 1982 (Fig. 1) and 1983 (Fig. 2), and varied little between years or among study areas. Within one study area, the higher nest visit rate of dull (low plumage rank) males was correlated with higher nestling growth rates. But in the other two study areas, where bright (high plumage rank) males predominated, nestlings of bright males tended to have the highest growth rates despite minimal nest visit rates. Thus, overall there was no correlation between male plumage rank and nestling growth rate, a potential index of relative reproductive success, in either year (Figs. 3 and 4). This overall equal nest success likely helps to maintain the behavioral and plumage polymorphism. Since we could find no evidence that the high nestling growth rates of bright males were due to an adjustment of female parental effort to compensate for low male parental effort, there must be some other benefit of being bright which contributes to nest success. To address this, we used the relationship between parental feeding rates and nestling growth rates for each nest as an index of relative territory quality. This analysis suggests that bright males generally occupy the best territories available, possibly because they are more aggressive in obtaining and defending them than dull males. Dull males appear to be relegated to poorer territories, where an increase in male parental contribution would be necessary to achieve high nestling growth rates. We propose that different males are using alternative but evolutionarily stable reproductive strategies, in a way that is consistent with the predictions of sexual selection theory. Allocation of limited reproductive effort to parental investment decreases as sexual dichromatism increases, which probably reflects an increased investment in intermale competition for the best territories.