Male Parental Effort Research Articles

Male parental effort predicts reproductive contribution in the joint-nesting, Smooth-billed Ani (Crotophaga ani)

Co-operative breeders provide parental care to non-filial offspring—a behaviour known as ‘alloparental care’. While inclusive fitness benefits are a widely accepted driver of alloparental care in kin-based social groups, such indirect benefits are lost in non-kin societies. Among such societies, theory predicts that the degree of parental and alloparental effort should therefore be proportional to an individual’s genetic contribution to mixed broods—depending upon reproductive options. Using genotyping data across five to 12 microsatellite loci for individuals from 20 social groups (67 adults and 153 nestlings), we assessed whether kinship or proportional reproductive success explained trends in parental and alloparental effort in the Smooth-billed Ani (Crotophaga ani), a joint-nesting cuckoo species. Nocturnal incubation in this species appears to be performed almost exclusively by a single male. We first report significantly higher degrees of relatedness between adults within social groups (\(\bar{r}\) = 0.208, n = 114 dyads), than between social groups (\(\bar{r}\) = 0.120, n = 893 dyads), suggesting that inclusive fitness benefits may in part explain uneven allocation of parental effort. Second, we show that nocturnal incubation status is a significant predictor of reproductive success in males, as nocturnal incubators sire a greater proportion of nestlings in mixed-parentage broods. While patterns of reproductive skew appear high at 80% paternal confidence (\(\bar{B}\) = 0.052, p = 0.061), we report no significant deviation from an egalitarian breeding framework. Our results revealed similar patterns of reproductive allocation to closely related Groove-billed Anis (Crotophaga sulcirostris); however, differences in male reproductive skew and within-group relatedness across crotophagids are highlighted and offer insight into social evolution among anis.

Females manipulate behavior of caring males via prenatal maternal effects

In species with biparental care, there is sexual conflict as each parent is under selection to minimize its personal effort by shifting as much as possible of the workload over to the other parent. Most theoretical and empirical work on the resolution of this conflict has focused on strategies used by both parents, such as negotiation. However, because females produce the eggs, this might afford females with an ability to manipulate male behavior via maternal effects that alter offspring phenotypes. To test this hypothesis, we manipulated the prenatal conditions (i.e., presence or absence of the male), performed a cross-fostering experiment, and monitored the subsequent effects of prenatal conditions on offspring and parental performance in the burying beetle Nicrophorus vespilloides We found that offspring were smaller at hatching when females laid eggs in presence of a male, suggesting that females invest less in eggs when expecting male assistance. Furthermore, broods laid in the presence of a male gained more weight during parental care, and they did so at the expense of male weight gain. Contrary to our expectations, males cared less for broods laid in the presence of a male. Our results provide experimental evidence that females can alter male behavior during breeding by adjusting maternal effects according to prenatal conditions. However, rather than increasing the male's parental effort, females appeared to suppress the male's food consumption, thereby leaving more food for their brood.

Maternal effects likely coevolve with plasticity in male care: a comment on Paquet and Smiseth

Parental care is in many ways the quintessential example of conflict between the sexes. Paquet and Smiseth (2016) suggest that maternal effects may affect this conflict by allowing females to induce males to provide more care. This represents a promising generalization of the more specific hypothesis that females adjust the androgens in their eggs to increase male care. The strength of this review is that it not only examines the empirical evidence for this specific hypothesis but it also gives concrete suggestions for future research. Here, I highlight some promising insights this research could provide, but question whether it is useful to frame these maternal effects as female manipulation of male care. One research direction I find particularly intriguing is their suggestion that conflict over parental care might shape female life histories, including the classic trade-off between offspring size and number. Is it possible that some of the variation we see both within and between species can be explained by how males adjust paternal effort in response to egg size (or number)? We already know total maternal investment in the current brood (Kempenaers and Sheldon 1997) as well as maternal allocation between egg size and number (Kindsvater et al. 2013; Kindsvater and Alonzo 2014) can be influenced by paternal effects. Studying the connection between maternal effects and male parental effort would represent a useful extension of our existing understanding of female differential allocation in response to mates. Another interesting implication—though they do not present it this way—is that a between-generation form of plasticity in females (i.e., maternal effects) evolves in response to a within-generation form of plasticity in males (e.g., male plasticity in parental care). A link between withinand between-generation phenotypic plasticity in response to predators has recently been demonstrated empirically (Walsh et al. 2015), but to date these ideas have not been applied to interactions between the sexes. It is interesting to consider when selection will favor plasticity in maternal allocation and male care and how this interaction will affect observed patterns of reproduction. It is precisely this link, however, between female and male plasticity that makes me question whether framing this interaction as female manipulation is productive. For females to manipulate males, males must first exhibit a behavioral reaction norm in parental care that responds to the maternal effect. And for the maternal effect to represent a manipulation, this adjustment must also decrease male fitness (compared with no change in male care). In essence, the females must cause the male to adjust in a way that is not in the male’s interests. Paquet and Smiseth (2016) suggest that this will be detected as the maternal effect moving the male away from his optimal level of paternal care (thus representing manipulation, sensu Dawkins 1999). Although I find the suggestion that maternal effects may evolve in response to male parental care rules exciting, I find this part of the argument flawed. The argument that females can adjust their allocation to manipulate male care only works if we focus on short-term behavioral adjustments. For example, males might have evolved to increase paternal care if females produce smaller eggs (perhaps because this is a general cue of food limitation). If females make smaller eggs (even in the absence of food limitation) then this maternal effect may cause males to provide more care to the offspring even at a net cost to male fitness in the short term. However, not only is parental care plastic but plasticity in care evolves in response to selection (Royle et al. 2014). If we take a long-term evolutionary view, we would expect the male’s parental care reaction norm to evolve in response to female manipulation. Assuming the male’s parental care reaction norm is adaptive, the male response to the female’s adjustment (i.e., the maternal effect) should increase not decrease the male’s lifetime reproductive success (otherwise no plastic adjustment in male care would be expected to evolve). Thus, one cannot detect the interesting dynamics they suggest by asking whether the male adjustment moves the male away from an abstract and unmeasurable male optimum. This not only poses a problem for our ability to demonstrate whether maternal effects allow females to manipulate males but also questions whether it is productive to frame this interaction as manipulation. I would argue that the interesting piece of this interaction and the ideas contained in this review are not whether one sex manipulates the other. Instead, the proposed general interaction between maternal effects and male care suggests an even more fascinating question for future research. First, how do plastic parental effects in one sex coevolve with plasticity in paternal care in the opposite sex? And second, can these coevolutionary dynamics help explain any of the striking but to date puzzling patterns of male and female behavior we see in nature?

Asynchronous hatching provides females with a means for increasing male care but incurs a cost by reducing offspring fitness.

In species with biparental care, sexual conflict occurs because the benefit of care depends on the total amount of care provided by the two parents while the cost of care depends on each parent's own contribution. Asynchronous hatching may play a role in mediating the resolution of this conflict over parental care. The sexual conflict hypothesis for the evolution of asynchronous hatching suggests that females adjust hatching patterns in order to increase male parental effort relative to female effort. We tested this hypothesis in the burying beetle Nicrophorus vespilloides by setting up experimental broods with three different hatching patterns: synchronous, asynchronous and highly asynchronous broods. As predicted, we found that males provided care for longer in asynchronous broods whereas the opposite was true of females. However, we did not find any benefit to females of reducing their duration of care in terms of increased lifespan or reduced mass loss during breeding. We found substantial negative effects of hatching asynchrony on offspring fitness as larval mass was lower and fewer larvae survived to dispersal in highly asynchronous broods compared to synchronous or asynchronous broods. Our results suggest that, even though females can increase male parental effort by hatching their broods more asynchronously, females pay a substantial cost from doing so in terms of reducing offspring growth and survival. Thus, females should be under selection to produce a hatching pattern that provides the best possible trade-off between the benefits of increased male parental effort and the costs due to reduced offspring fitness.

Analysis of the Optimal Duration of Behavioral Observations Based on an Automated Continuous Monitoring System in Tree Swallows (Tachycineta bicolor): Is One Hour Good Enough?

Studies of animal behavior often rely on human observation, which introduces a number of limitations on sampling. Recent developments in automated logging of behaviors make it possible to circumvent some of these problems. Once verified for efficacy and accuracy, these automated systems can be used to determine optimal sampling regimes for behavioral studies. Here, we used a radio-frequency identification (RFID) system to quantify parental effort in a bi-parental songbird species: the tree swallow (Tachycineta bicolor). We found that the accuracy of the RFID monitoring system was similar to that of video-recorded behavioral observations for quantifying parental visits. Using RFID monitoring, we also quantified the optimum duration of sampling periods for male and female parental effort by looking at the relationship between nest visit rates estimated from sampling periods with different durations and the total visit numbers for the day. The optimum sampling duration (the shortest observation time that explained the most variation in total daily visits per unit time) was 1h for both sexes. These results show that RFID and other automated technologies can be used to quantify behavior when human observation is constrained, and the information from these monitoring technologies can be useful for evaluating the efficacy of human observation methods.

The Spotted Barbtail (Premnoplex brunnescens): male and female parental effort during the nestling period

We document male and female roles in nestling care of Spotted Barbtails (Premnoplex brunnescens) including feeding rates and temporal patterns of provisioning by each sex. Using 128.5 hrs of video from color marked and molecularly sexed individuals at two nests, we confirm that both sexes of Spotted Barbtail provision nestlings. Spotted Barbtail females in our study invested more heavily in nestling care than males, making 73% of feeding visits. Females also visited the nests nearly twice as often as males, averaging 1.24 visits/nestling/hr compared to 0.69 visits/nestling/hr for males. While Spotted Barbtails exhibit many of the features assumed to favor social and genetic monogamy, intriguing aspects of nest building and incubation leave open the possibility that this species is unusual among the Furnariidae and utilizes extra-pair matings as a part of the reproductive strategy.

Attractive males are less than adequate dads in a multimodal signalling passerine

Parental attractiveness influences paternal and maternal efforts in a wide range of animals that exhibit biparental care. However, we still lack an understanding concerning the direction of the covariance between attractiveness and parental effort, perhaps because studies typically consider only one or a subset of multiple attractiveness signals. In this study we investigated predictions of four hypotheses about the relationship between attractiveness traits (plumage coloration, song and leap display traits) and parental effort (feeding rates) in a wild population of the blue-black grassquit, Volatinia jacarina , a Neotropical sexually dichromatic bird with biparental care. Paternal effort was negatively correlated with male blue-black coloration (UV chroma) and maternal effort was positively correlated with male provisioning rate. Thus, more attractive males relative to the UV chroma are worse fathers relative to less attractive males in this trait. However, female provisioning rate was positively correlated with another male attractive trait: the blue-black plumage coverage. The song, leap display and other features of male coloration were not associated with either male or female parental effort. Taken together, these results support the parental–mating trade-off hypothesis for paternal behaviour, which predicts that attractive males should invest less in current offspring in order to acquire extrapair matings. Also, our results partially support the positive differential allocation hypothesis: although females invested highly in offspring of males with more blue-black plumage coverage, they did not compensate for the low investment of males with UV-shifted blue-black plumage. We highlight the need for future studies to consider multiple sexual traits in order to investigate the relationship between attractiveness and parental investment.

Phenotypic plasticity in hormonal and behavioural responses to changes in resource conditions in a migratory songbird

An emerging question in animal behaviour is whether and how behavioural plasticity will enable organisms to adjust to human-induced, rapid environmental changes that affect breeding conditions. Adaptive behavioural plasticity in response to changing resource conditions will depend on the sensitivity of the neuroendocrine system to food stimuli and on constraints in the mechanisms mediating the expression of reproductive behaviours. We tested the hypotheses that food availability mediates plasticity in androgen and corticosterone (CORT) responses, and that circulating concentrations of these hormones in turn mediate investment into competing mating and parental behaviours in a migratory songbird. We provided supplemental food to black-throated blue warblers, Setophaga caerulescens , breeding in habitats with natural low and high food abundance. The effects of supplemental feeding were most pronounced in food-poor habitat. During their social mates' fertile stage, fed males sang less near their nest sites, had lower plasma androgen and CORT levels, and had higher residual mass than control males. Fed males benefited indirectly from their mates' access to supplemental food because fed females provided more parental effort than control females. Fed males did not increase their own parental effort. Our results suggest that fed males increased mate-guarding effort over extrapair mate attraction while their social mates were fertile and invested additional resources into territorial defence or self-maintenance during the parental stage. These findings reveal plastic patterns of covariation among endocrine parameters and mating behaviours, but not parental behaviours, in response to food supplementation. These responses enabled individuals to adjust their reproductive effort rapidly to changes in resource conditions. Our findings suggest that adaptive reproductive investment in response to environmental change is unlikely to be constrained by the hormonal mechanisms underlying the mediation of competing mating and parental behaviours. • Behavioural plasticity can buffer breeding individuals from changes in food resources. • Behavioural plasticity may be constrained by underlying neuroendocrine mechanisms. • Food supplementation increased male mating effort and female parental effort in black-throated blue warblers. • Male behavioural responses to food supplementation covaried with endocrine responses. • Hormone mediation of reproductive investment did not constrain behavioural plasticity.

Filial cannibalism in a nest-guarding fish: females prefer to spawn in nests with few eggs over many

In fish, fecundity correlates with female body size and egg-tending males often eat small broods. Therefore, small females may prefer to spawn in nests that already contain many eggs, to ensure the brood is as large as possible. In contrast, large females may prefer nests with few eggs, if high egg number or density has a negative effect on egg survival, or if there are drawbacks of spawning last in a nest. To test the hypothesis that female body size affects nest (and male mate) choice, using the sand goby (Pomatoschistus minutus), we allowed small and large females to choose between two males that were matched in size — one guarding a small clutch and the other a large clutch, respectively. We recorded where females spawned (measure of female preference), the combined brood size, male courtship, egg care and nest building. We also quantified the effect of brood size and egg density on egg survival in a separate data set. Although the combined broods did not exceed the small brood sizes that are at risk of being eaten, both small and large females preferred to spawn in nests with smaller clutch sizes. This preference could not be explained by more courtship or male parental effort, nor by reduced survival of larger or denser broods. Instead, our result might be explained by females avoiding the danger of cannibalism of young eggs by males or the risk of reduced egg health associated with being near the nest periphery.

The role of male nest building in post-mating sexual selection in the monogamous red-necked grebe

AbstractIn monogamous birds, early male parental effort, such as nest building, may serve as a post-mating sexually-selected display allowing female assessment of male quality. We examined the functional significance of male nest building and the potential role of nest size as a sexually-selected signal in the red-necked grebe (Podiceps grisegena), a species with high mate fidelity. Time-activity budgets showed that no behaviour was performed exclusively by one sex in the pre-laying period, but males spent significantly more time nest building and were more often involved in aggressive intra- and interspecific interactions. Nest building in pairs attempting a second brood was also performed predominantly by males. Greater participation in nest construction by males allowed females to allocate more time to self-maintenance activities in the period prior to egg-laying. The positive relationship found between the relative contribution of males to nest building and later to brood provisioning indicates that male nest building is an honest indicator of future paternal effort. Males obtained copulations solicited by females proportionally to the time spent on nest building, and the extent of male participation in nest construction was of importance for explaining variation in clutch size. Nest size itself is not very likely to be sexually selected in red-necked grebes, as it was found to depend on nest site conditions such as water depth and exposure to wave action. We suggest that greater investment of males in energetically demanding pre-laying activities is functionally similar to post-mating courtship feeding; it constitutes males’ indirect contribution to clutch production and may help to negotiate the relative investment each sex makes in the different stages of the breeding cycle. The results support the idea that, in monogamous birds, naturally selected male characters related to parental care may evolve into important sexual signals to females, although not into extreme displays.

An experiment on the function of the long-term pair bond period in the socially monogamous bearded reedling

Pair bond duration and age are suggested to be important determinants for reproductive success in long-term monogamous pair bonding. These two effects are generally difficult to separate, however, and experimental approaches are scarce. We experimentally examined the role of the extended pair bond period, controlling for age and experience, in the bearded reedling, Panurus biarmicus. In this species pairs form in juvenile flocks and usually remain stable for life. We experimentally manipulated the pair-formation period in aviary pairs prior to their first breeding season and observed the effect of varying pair bond duration on breeding success, male parental effort and breeding coordination. This was done for pairs with long (6.5 months), medium (4 months) and short (2 weeks) formation periods. Our results suggest that the length of the bonding period does not influence male parental effort, as males with medium and short formation periods did not reduce their parental effort in nest building, during incubation or in nestling provisioning. Nevertheless, coordination of pair partners (in terms of simultaneous start of nest building) occurred more often when the pair bond period was long, and these pairs also started breeding earlier. Pairs with long bonds succeeded more often in breeding attempts and had higher hatching and fledging success than pairs with medium and short formation periods. Thus, our results support the hypothesis that the duration of the pair bond may improve coordination within a pair before the start of breeding and thereby may result in enhanced reproductive success.

Do Male Desert Gobies Compromise Offspring Care to Attract Additional Mating Opportunities?

Males often play a critical role in offspring care but the time and energy invested in looking after young can potentially limit their ability to seek out additional mating opportunities. Recent studies, however, suggest that a conflict between male parental effort and mating effort may not always be inevitable, especially if breeding occurs near the nest, or if parental behaviours are under sexual selection. Accordingly, we set out to experimentally investigate male care and courtship in the desert goby Chlamydogobius eremius, a nest-guarding fish with exclusive paternal care. Despite courtship occurring near the nest, we found that when egg-tending males were given the opportunity to attract additional females, they fanned their eggs less often, engaged in shorter fanning bouts, and spent more of their time outside their nests courting. Our findings highlight the importance of understanding the circumstances under which reproductive tradeoffs are expected to occur and how these, in turn, operate to influence male reproductive decisions.

The effects of male mating behaviour and food provisioning on breeding success in snow buntings Plectrophenax nivalis in the high Arctic

For passerine birds breeding in the Arctic, paternal effort in parental care is necessary for successful breeding. Behavioural strategies, such as mate guarding, to ensure paternity should therefore also be common in this environment. In order to investigate the relation between such behaviour and breeding success, when controlling for the effect of environmental factors, we recorded male mate-guarding behaviour, parental effort and breeding success amongst snow buntings, Plectrophenax nivalis, in the high Arctic environment of Spitsbergen, Svalbard. Mate-guarding intensity tended to positively affect male feeding frequency per nestling in one of the study years, negatively in 1 year and without effect in the 3rd year. The negative effect in 1999 was strong, but variation in estimates of the 2 other years was high and the effect of mate guarding may be negligible in these 2 years. We assume that this pattern might be related to yearly variation in the prevalence of extra-pair young. Male food provisioning was not positively related to breeding success, but late breeders had higher breeding success than early breeders. Thus, the effect of male mate guarding is highly variable and mainly affects food provisioning rates, but the benefit for total breeding success seems to be marginal, at best.

Yolk androgens do not appear to mediate sexual conflict over parental investment in the collared flycatcher Ficedula albicollis

Males and females are in conflict over parental care, as it would be favourable for one parent to shift labour to the other. Yolk hormones may offer a mechanism through which female birds could influence offspring traits in ways that increase the relative investment by the male. We studied the role of yolk androgens in mediating sexual conflict over parental care in the collared flycatcher ( Ficedula albicollis). In a cross-fostering experiment, the male's proportion of total feeding visits increased with increasing androgen levels in the foster eggs. This could suggest that sexual conflict over parental care may be influenced by the female's differential allocation of yolk androgens or a maternal effect associated with yolk androgens. However, when we experimentally elevated yolk androgen levels, male feeding rates did not differ between control and androgen-manipulated nests. This suggests that other egg components correlated with yolk androgen levels, rather than yolk androgen levels per se, may influence male parental effort. In conclusion, yolk androgens per se do not appear to mediate sexual conflict over parental investment in the collared flycatcher.

Eggshell pigmentation pattern in relation to breeding performance of blue tits Cyanistes caeruleus

1. We test the consequences, in terms of breeding success and parental effort, of eggshell pigmentation pattern in a hole-nesting bird, the blue tit Cyanistes caeruleus that lays eggs asymmetrically speckled with reddish spots (maculated eggs). 2. We assess the effect of distribution of spots (pigment 'spread') and spot size and pigment intensity (pigment 'darkness') on eggshell physical properties and breeding parameters concerning nestling condition, investment of parents in offspring care and reproductive output in two different habitat types: a deciduous oakwoodland and an evergreen forest. 3. Blue tit clutches with more widely distributed spots showed a thicker eggshell, a shorter incubation period, a lesser amount of mass loss per day and a higher hatching probability than those with spots forming a 'corona' ring. While eggs with larger and darker (more pigment intensity) spots showed a thicker eggshell and a shorter incubation period. In the light of 'signal function hypothesis', these egg traits may reflect female health status and, consequently, this could affect male parental effort. 4. Here we show supports for some of the necessary assumptions of this hypothesis. We found a positive relationship between egg pigment 'spread' and male but not female provisioning rates per day. On the other hand, pigment 'darkness' of blue tits' clutches was positively related to female tarsus length, while pigment 'spread' was positively related to clutch size, male body mass and nestling tarsus length. Our study shows that eggshell pigment 'spread' can be used as an indicator of clutch quality. Further investigations are needed to understand the role of calcium availability as possible causal agent of deviant eggs and its relation to the maculation phenomenon.

Female alternative reproductive behaviors: The effect of female group size on mate assessment and copying

Extensive theoretical and empirical research has focused on male alternative reproductive tactics. In comparison, female alternative tactics have attracted little attention, and further theoretical and empirical research are needed. Using a game theoretical model, we examine female choice alternatives (1) by considering assessment errors in a novel and more realistic manner than done previously, and (2) for the first time, by highlighting the formation of groups of females as an important consequence of copying behavior. We consider two alternatives: direct assessment of male quality by females and female copying of the choice of other females. Assessment and copying are predicted to coexist under a wide variety of circumstances and copying is favored when females make assessment errors, when high-quality males are either common or very rare, and when female fitness declines with the number of other females choosing the same male. We also find that the frequency of copying at equilibrium is predicted to decrease when the presence of other females mating with the same male has a positive effect on female fitness (e.g. through increased male parental effort, decreased predation risk or cooperation among females). Female alternative choice tactics also influence the potential for sexual selection. In our model, when the frequency of copying females is low, the potential for sexual selection can be higher than in the absence of female copying. However, contrary to previous theory, we find that as copying females become more common than assessing females, the potential for sexual selection will be low as more females copy the mate choice of other copiers without assessment.

Female mate choice copying affects sexual selection in wild populations of the ocellated wrasse

Explaining the factors that determine the distribution of mating success among males is essential to our understanding of sexual selection. Classic theory has focused on how competition among males and female choice for traits of the male or his territory drive sexual selection. Recent theory has also shown that female mate choice copying can alter the strength and direction of selection on male traits. Yet, we know very little about the prevalence and importance of nonindependent female choice in wild populations. In a species with male territoriality and paternal care (the ocellated wrasse, Symphodus ocellatus), I first show that females express nonindependent mate choice, responding both to the recent mating success of the male and to the presence of other spawning females rather than to variation in male courtship or defence of the nest. Females were significantly more likely to spawn with the same male when another spawning female was present than when they were alone at the nest, providing some of the first direct evidence of female mate choice copying under natural conditions in the wild. I further show that a short-term experimental increase in a territorial male's mating success attracts more females in the future and increases male paternal care. These observed patterns of female choice and male care are consistent with female choice for the direct benefits of male care where the best indicator trait of male parental effort is the mating behaviour of other females rather than male courtship behaviour or physical traits.

Are blue eggs a sexually selected signal of female collared flycatchers? A cross-fostering experiment

Impressive variation in egg colouration among birds has puzzled evolutionary biologists for a long time. The most frequently studied selective forces moulding egg colouration—predation and brood parasitism—have either received little empirical support or may play a role in only a minority of species. A novel hypothesis has suggested that egg colour may be significantly influenced by sexual selection. Females may deposit a blue-green pigment biliverdin into eggshells instead of using it for themselves as a powerful antioxidant. By this handicap, females may signal their quality to males, which are then hypothesized to increase their paternal effort. We experimentally tested the hypothesis in the collared flycatcher (Ficedula albicollis), a species laying blue-green eggs. We cross-fostered clutches between nests to disentangle effects of female/territory quality and egg colour on paternal effort and nestling quality. The results supported two assumptions of sexual signalling through egg colour hypothesis: Blue pigment seems to be a limited resource for females, and female quality is positively correlated with the intensity of the blue-green colour. However, we did not find support for the main prediction of the hypothesis, as male parental effort parameters (feeding frequencies to nestlings and intensity of nest defence) were unrelated to egg colour. We discuss possible reasons for the discrepancy between our results and previous correlative analyses that supported the hypothesis that blue egg colour may be a postmating, sexually selected signal in females.

The Influence of Exogenous Testosterone on the Dynamics of Nestling Provisioning in Dark‐Eyed Juncos

AbstractIn many songbird species, application of exogenous testosterone (T) during the breeding season has the general effects of reducing male parental investment and increasing allocation of time and energy to mating. Most studies record the number of feeding trips made by males as a function of their hormone treatment, but few have investigated the ways in which testosterone affects the dynamics of male and female provisioning behavior or the quantity of food delivered by males. We attempt to fill these gaps in our understanding of testosterone and male parental effort by utilizing data from a long‐term study on the behavioral endocrinology of the dark‐eyed junco (Junco hyemalis). We found that male and female feeding rates covaried positively, although to different degrees, throughout the nestling period, but that this relationship was degraded in pairs in which males were given T implants. We also found that the coefficients of variation in the duration of intervals between successive feeding trips by males and females were highly positively related in broods of older nestlings. Male hormone treatment, however, had no effect on the coefficients of variation in either male or female feeding intervals. Finally, we examined the quantity of prey delivered by males and found no significant effect of hormone treatment.

Is Mate Provisioning Predicted by Ornamentation? A Test with Northern Cardinals (Cardinalis cardinalis)

AbstractMale birds of many species feed their mates during courtship and incubation. The amount of food provided can be substantial and even essential for successful reproduction in some species, and can influence female nest attentiveness in many others. Additionally, mate provisioning may predict later nestling feeding rates. Females may thus benefit from being able to determine male provisioning effort. We assessed the expression of several ornaments, known to indicate condition in male northern cardinals (Cardinalis cardinalis), and compared these with mate provisioning rates, nestling feeding rates, and nest attentiveness. We found that male ornamentation may not be indicative of mate provisioning rates. Mate provisioning rate did not co‐vary with reproductive success, male feedings to nestlings, or nest attentiveness of females. However, females which were fed more often during incubation tended to provision nestlings less. Reduced female parental effort following extensive incubation feeding may be indicative of females using incubation feeding to assess future male parental effort. Male hormonal condition that favors high rates of nestling provisioning may be a proximate cause of mate provisioning during incubation, even in the absence of selection, favoring high rates of mate provisioning. Both sexes may have capitalized on this unselected behavior.