Parental Alarm Calls of the White‐Crowned Sparrow Fail to Stimulate Corticosterone Production in Nest‐Bound Offspring

Alarm calling by parents is widespread among animals and has strong implications for parent and offspring fitness, yet it is virtually unknown whether parental alarm calls can initiate a corticosterone response in offspring. We investigated whether parental alarm calls of the white‐crowned sparrow, Zonotrichia leucophrys, activated the corticosterone response of their nest‐bound young, as such a response might prepare older nestlings for premature fledging and increase their survival when contacted by a predator at the nest. We conducted an experiment in which nestlings were either exposed to parent alarm calls (treatment) or experienced a period without parental alarm calls (control) immediately prior to blood sampling. We then sampled nestlings to measure corticosterone levels within 4 min of first contact (baseline corticosterone) and 60 min later (handling‐induced corticosterone). Young nestlings (i.e. 3–4 d post‐hatch) did not exhibit a corticosterone response to parental alarm calls or to handling, as mean corticosterone levels were similar in the control and treatment groups for both baseline and 60‐min post‐baseline samples. Against our predictions, there was no difference in mean levels of baseline corticosterone between control and treatment groups in older nestlings (i.e. 7?8 d post‐hatch) that were capable of surviving out of the nest. However, we did find a significant increase in mean levels of corticosterone after handling in both groups, which indicated that older nestlings were able to mount a functional corticosterone response when confronted with a potential predator. Why older nestlings did not initiate a corticosterone response after exposure to parental alarm calls is unclear but may have occurred because the costs of mounting such a response outweighed the benefits, perhaps because of growth or developmental costs.     

Effect of alarm calling by male Red‐winged Blackbirds on nestling begging and female provisioning behavior

ABSTRACT Nestling begging and parental provisioning can attract nest predators and reduce reproductive success, so parents and their offspring might be expected to respond adaptively by minimizing predator‐attracting cues when predators threaten nests. Male Red‐winged Blackbirds (Agelaius phoeniceus) are well known for their antipredator alarm calls that contain information about the approach of potential nest predators. We examined the begging behavior of nestlings and the provisioning behavior of females in response to antipredator alarm calls of males to test the adaptive response hypothesis. Playback experiments provided no evidence that alarm calls function to switch off vocal begging; nestlings were equally likely to beg vocally during playback and control periods. Video recordings showed that male alarm calling had no significant effect on inappropriate vocal begging (in the absence of an adult), but significantly reduced the incidence of spontaneous calling (in the absence of begging). Adult females responded to male antipredator alarm calls by delaying their provisioning visits. In addition, although having no significant effect on use of nest‐arriving calls by females, male alarm calling significantly reduced their use of nest‐leaving calls. We conclude that nestling and female Red‐winged Blackbirds respond to male alarm calls in ways that might reduce the risk of predation, but nestlings beg vocally when females arrive to feed them, regardless of male alarm calling, perhaps to avoid a competitive disadvantage with broodmates.     

Females compensate for moult‐associated male nest desertion in Hooded Warblers

Uniparental offspring desertion occurs in a wide variety of avian taxa and usually reflects sexual conflict over parental care. In many species, desertion yields immediate reproductive benefits for deserters if they can re‐mate and breed again during the same nesting season; in such cases desertion may be selectively advantageous even if it significantly reduces the fitness of the current brood. However, in many other species, parents desert late‐season offspring when opportunities to re‐nest are absent. In these cases, any reproductive benefits of desertion are delayed, and desertion is unlikely to be advantageous unless the deserted parent can compensate for the loss of its partner and minimize costs to the current brood. We tested this parental compensation hypothesis in Hooded Warblers Setophaga citrina, a species in which males regularly desert late‐season nestlings and fledglings during moult. Females from deserted nests effectively doubled their provisioning efforts, and nestlings from deserted nests received just as much food, gained mass at the same rate, and were no more likely to die from either complete nest predation or brood reduction as young from biparental nests. The female provisioning response, however, was significantly related to nestling age; females undercompensated for male desertion when the nestlings were young, but overcompensated as nestlings approached fledging age, probably because of time constraints that brooding imposed on females with young nestlings. Overall, our results indicate that female Hooded Warblers completely compensate for male moult‐associated nest desertion, and that deserting males pay no reproductive cost for desertion, at least up to the point of fledging. Along with other studies, our findings support the general conclusion that late‐season offspring desertion is likely to evolve only when parental compensation by the deserted partner can minimize costs to the current brood.     

Features of begging calls reveal general condition and need of food of barn swallow (Hirundo rustica) nestlings

Altricial offspring of birds solicit food provisioning by complexbegging displays, implying acoustic and visual signals. Differentcomponents of begging behavior may function as reliable signalsof offspring state and thus reproductive value, on which parentsbase optimal parental decisions about allocation of criticalresources (e.g., food). We experimentally manipulated componentsof general condition of nestling barn swallows (Hirundo rustica)by (1) altering brood size by cross-fostering an unbalanced number of nestlings between pairs of synchronous broods andthus manipulating the level of within-brood competition forfood, (2) injecting some nestlings with a harmless immunogen,simulating an infection, and (3) preventing part of the nestlingsfrom receiving food for a short period while establishing controlgroups. We recorded rate of begging response by individual nestlings as parents visited the nest and recorded begging calls usinga DAT recorder to analyze six sonagraphic features of vocalizations.Our factorial experiment revealed that nestlings deprived offood begged more frequently when parents visited the nest comparedto their non—food-deprived nest mates. Food deprivationincreased duration of syllables forming begging calls, whereas brood size enlargement resulted in increased latency of responseto parental calls. Heavy nestlings in good body condition vocalizedat a relatively low peak frequency. To our knowledge, thisis the first study in which begging rate and sonagraphic structureof begging calls are shown to reliably reveal a diverse setof components of offspring general state, on which parental decisions may be based.     

Effect of conspecific alarm calls in the parental behaviour of nesting southern house wrens

Alarm calls are usually used to signal the presence of a threat to members of the same species and have been studied broadly in social foraging species. We analysed the effects of conspecific alarm calls on the parental behaviour of a territorial species, the southern house wrens (Troglodytes aedon musculus), during nestling stage. We compared the parental response of adults feeding 9–11-day-old nestlings when faced with conspecific alarm calls and with a control non-sympatric species’ song broadcast from a neighbouring territory. We measured the time required by parents to return to the nest (latency) when exposed to the stimuli and estimated parent’s nest visitation rate and mean visit duration. Parents took longer to resume parental activities when we broadcast a conspecific alarm call, but they did not modify their nest visitation rate or the mean visit duration. Heterospecific songs did not seem to affect parental behaviour. Our results suggest that nesting southern house wrens can use alarm calls uttered from neighbouring territories to assess the presence of a threat and adjust their parental behaviour accordingly.     

Parental alarm calls suppress nestling vocalization

Evolutionary models suggest that the cost of a signal can ensure its honesty. Empirical studies of nestling begging imply that predator attraction can impose such a cost. However, parents might reduce or abolish this cost by warning young of the presence of danger. We tested, in a controlled field playback experiment, whether alarm calls cause 5-, 8- and 11-day-old nestlings of the white-browed scrubwren, Sericornis frontalis, to suppress vocalization. In this species, nestlings vocalize when parents visit the nest ('begging') and when they are absent ('non-begging'), so we measured effects on both types of vocalization. Playback of parental alarm calls suppressed non-begging vocalization almost completely but only slightly reduced begging calls during a playback of parental feeding calls that followed. The reaction of nestlings was largely independent of age. Our results suggest two reasons why experiments ignoring the role of parents probably overestimate the real cost of nestling vocalizations. Parents can warn young from a distance about the presence of danger and so suppress non-begging vocalizations that might otherwise be overheard, and a parent's presence at the nest presumably indicates when it is safe to beg.     

Sex‐Specific Parental Care in Response to Predation Risk in the European Roller,Coracias garrulus

Sublethal effects of predation constitute an important part of predation effects, which may modulate prey population and community dynamics. In birds, the risk of nest predation may cause a reduction in parental activity in the care of offspring to reduce the chance of being detected by predators. In addition, parents may modify their parental food allocation preferences within the brood in response to predation risk. Our aim in this study was to evaluate the effects of risk of nest predation on parental care and within‐nest food allocation in the European Roller (Coracias garrulus), an asynchronously hatching bird. We manipulated brood predation risk by placing a snake model near the nests that simulates the most common nest predator in the Mediterranean region. Our results show that males but not females increased their provisioning rate when they were exposed to the model and that despite this, nestlings’ body mass decreased in response to this temporary increase in predation risk. We did not find evidence that parents changed their food allocation strategy towards senior or junior nestlings in their nests in response to predation risk. These results show that the European roller modifies parental care in response to their perception of predation risk in the nest and a sex‐specific sensitivity to the threat, which suggests a different perception of offspring reproductive value by parents. Finally, our results show that changes in parental behaviour in response to nest predation risk might have consequences for nestling fitness prospects.     

Nestling colouration is adjusted to parent visual performance in altricial birds

Hitherto, most of the investigation on the perceptual efficacy of begging signals has dwelled on how patterns of nestling colouration adjust to predominant nest luminosity. However, visual sensitivity of birds varies across species, which raises the question of whether colouration of traits involved in begging displays is adjusted to parent visual capacities. Here, by comparing nestling colouration and visual sensitivity across 22 altricial bird species, we provide a first test of this hypothesis. Firstly, we assessed differences in performance of typical UV‐tuned and violet‐tuned bird eyes when looking at the nestling traits under the light regimes prevailing at their nests. Secondly, while controlling for common ancestry in a comparative approach, we explored variation in colouration of nestlings in relation to parent visual system. The colour discrimination model indicated a general higher performance of the ultraviolet over the violet eye at detecting gape and body skin traits in either open‐ or hole‐nest light conditions. Gape colouration was associated with parental visual system as the nestlings of UVS species displayed more yellow and less pure ultraviolet mouths than the nestlings of VS species. Thus, our results agree with an adaptive parent–offspring communication scenario where the nestlings’ colours tuned the perception capacities of their parents.     

Individual vocal signatures in barn owl nestlings: does individual recognition have an adaptive role in sibling vocal competition?

To compete over limited parental resources, young animals communicate with their parents and siblings by producing honest vocal signals of need. Components of begging calls that are sensitive to food deprivation may honestly signal need, whereas other components may be associated with individual‐specific attributes that do not change with time such as identity, sex, absolute age and hierarchy. In a sib–sib communication system where barn owl (Tyto alba) nestlings vocally negotiate priority access to food resources, we show that calls have individual signatures that are used by nestlings to recognize which siblings are motivated to compete, even if most vocalization features vary with hunger level. Nestlings were more identifiable when food‐deprived than food‐satiated, suggesting that vocal identity is emphasized when the benefit of winning a vocal contest is higher. In broods where siblings interact iteratively, we speculate that individual‐specific signature permits siblings to verify that the most vocal individual in the absence of parents is the one that indeed perceived the food brought by parents. Individual recognition may also allow nestlings to associate identity with individual‐specific characteristics such as position in the within‐brood dominance hierarchy. Calls indeed revealed age hierarchy and to a lower extent sex and absolute age. Using a cross‐fostering experimental design, we show that most acoustic features were related to the nest of origin (but not the nest of rearing), suggesting a genetic or an early developmental effect on the ontogeny of vocal signatures. To conclude, our study suggests that sibling competition has promoted the evolution of vocal behaviours that signal not only hunger level but also intrinsic individual characteristics such as identity, family, sex and age.     

Flexible communication within bird families—The consequences of behavioral plasticity for parent–offspring coadaptation

Offspring are selected to demand more resources than what is optimal for their parents to provide, which results in a complex and dynamic interplay during parental care. Parent–offspring communication often involves conspicuous begging by the offspring which triggers a parental response, typically the transfer of food. So begging and parental provisioning reciprocally influence each other and are therefore expected to coevolve. There is indeed empirical evidence for covariation of offspring begging and parental provisioning at the phenotypic level. However, whether this reflects genetic correlations of mean levels of behaviors or a covariation of the slopes of offspring demand and parental supply functions (= behavioral plasticity) is not known. The latter has gone rather unnoticed—despite the obvious dynamics of parent–offspring communication. In this study, we measured parental provisioning and begging behavior at two different hunger levels using canaries (Serinus canaria) as a model species. This enabled us to simultaneously study the plastic responses of the parents and the offspring to changes in offspring need. We first tested whether parent and offspring behaviors covary phenotypically. Then, using a covariance partitioning approach, we estimated whether the covariance predominantly occurred at a between‐nest level (i.e., indicating a fixed strategy) or at a within‐nest level (i.e., reflecting a flexible strategy). We found positive phenotypic covariation of offspring begging and parental provisioning, confirming previous evidence. Yet, this phenotypic covariation was mainly driven by a covariance at the within‐nest level. That is parental and offspring behaviors covary because of a plastic behavioral coadjustment, indicating that behavioral plasticity could be a main driver of parent–offspring coadaptation.     

Conspicuous calling near cryptic nests: a review of hypotheses and a field study on white‐browed scrubwrens

Predation is an important source of nest mortality in many bird species and calling near the nest can increase this risk, yet adults of many species regularly vocalize near their nests. Some of these calls serve clearly adaptive functions, such as alarm or provisioning calls. However, many species also give conspicuous ‘contact’ calls near the nest, which is puzzling because the function of these calls is unclear, and they might attract predators. Most studies of parental vocalizations near nests have focused on specific vocalizations and single hypotheses, yet there is a diversity of vocalization types and potential functions. We review the literature on the diversity and possible function of parental vocalizations near the nest, and then investigate the puzzle of conspicuous contact calling near nests by white‐browed scrubwrens Sericornis frontalis. In scrubwrens, ‘chip‐zz’ contact calls were almost always used when adults approached nests, and when they approached one another or changed location. Call composition also changed: the proportion of ‘chip’ elements increased as callers approached the nest or other adults. Neither adult sex nor nestling age affected calling. Thus, chip‐zz calls appear to be used as ongoing signals to other group members of the caller's activity and location, particularly relative to the nest. Nestlings appeared to use the calls as cues of adult arrival, and increased calling as adults approached nests. Further, adults called less after a predator was on the territory, suggesting that parents may be able to reduce the risk of chip‐zz calls betraying nest location, or possibly use the absence of calling as a signal of danger. This study thus demonstrates that calling near nests could inform both adults and nestlings about the caller's behaviour, and could serve multiple functions. Future studies will need to experimentally test these functions, as well as the other hypotheses reviewed here.     

Recognition of Young in A Colonially Nesting Bird

Parents ought to restrict costly parental care to their genetic offspring and, particularly when the risk of misdirecting care is high, parent‐offspring recognition may evolve. I tested whether adult cave swallows, which nest in dense colonies and feed fledglings in mixed‐family groups, discriminate against unrelated young, using temporary chick transfers at two nestling ages and a cross‐fostering experiment. Temporary chick transfers indicated that parents bias feedings toward their own offspring near fledging (18 d) but not at about halfway through the nesting period (10 d). I also examined how parents learn to identify their offspring by cross‐fostering young 3 d after hatching and testing parental response 2 wks later. Adults did not favor their own offspring over unrelated nestlings when both were unfamiliar to the focal parents. However, when parents encountered two of their own offspring, one of which was reared by foster parents, they preferentially fed the familiar nestling. By recognizing young, cave swallow parents reduce some risks of misdirected parental investment (mobile fledglings) but not others (extra‐pair young and intraspecific brood parasitism).     

Not for Parents Only: Begging Calls Allow Nest‐Mate Discrimination in Juvenile Zebra Finches

The benefits of recognition of family members may range from inbreeding avoidance to cooperative and coordinated behaviors within the family group. In birds, recognition of family members has almost exclusively been studied between parents and offspring or within cooperatively breeding societies. Yet, recognition of nest‐mates could be of special importance in recently fledged birds of colonial species by helping in locating the nest, maintaining family group cohesion, or allowing detection of feeding opportunities by recognizing the begging calls nest‐mates produced on the return of a parent. Here we study nest‐mate discrimination based on begging calls in fledglings of domesticated zebra finches (Taeniopygia guttata), a gregarious songbird living in loose colonies in which juveniles may gather in crèches and are fed by parents up to 20 d after fledging. Using playback tests, we show that fledglings called more and spent more time near the loudspeaker in response to the begging calls of their nest‐mates than to the calls of other familiar individuals. Because each fledgling was exposed to the repeated association of the begging calls of its nest‐mates and the subsequent feeding of its parents, this preferential response to the nest‐mates' calls could be a conditioned response to the food reward. Whereas fledglings answered more to male fledgling calls than to female fledgling calls, response to playback was influenced neither by the sex of the subject nor by its brood size. Discriminant function analysis based on acoustic parameters showed that begging calls carried an individual signature as well as a brood signature which might account for such nest‐mate discrimination. Begging signals are major study systems of the evolution of communication in the face of conflicts of interest between signalers and receivers. Our results suggest that eavesdropping and communication networks may be other informative frameworks to understand the design of offspring solicitation signals.     

Kea Nestor notabilis mothers produce nest-specific calls with low amplitude and high entropy

Vocal behaviour of nesting altricial birds is subject to selection pressure from several sources. Offspring beg to attract parents’ attention, thus increasing the chances of being fed, but also increasing the chances of being detected by predators. Research on passerines has shown that parents may reduce the risk of nest predation by alarm calling to warn nestlings to be quiet, and by producing food calls which solicit begging when parents are present to defend the nestlings. Both nestlings and parents may reduce the risk of predator detection by producing calls of low amplitude and high entropy which are acoustically difficult to locate. Although extensive research has been undertaken on nesting passerine vocalizations, little is known about parrots in this regard, and studies are needed to determine whether parrots show similar adaptations. We investigated the calling behaviour of Kea Nestor notabilis mothers during the nesting period to determine whether maternal vocalizations were adapted in a way that could increase the chance of brood success. A microphone was installed inside the nest to record calls produced both inside the nest and in the direct vicinity. Our prediction was that calls outside the nest would be easy to locate and could function as alarm calls to alert conspecifics or distract the predator, whereas calls inside the nest would be difficult to locate and could serve to communicate with nestlings without alerting predators. Our results accorded with these predictions. Calls produced outside the nest were loud and tonal, and corresponded to previously described Kea alarm calls. Calls produced inside the nest, however, were high-entropy and low-amplitude calls, and formed a distinct structural category. We thus provide the first evidence that a parrot species has a vocal category for communication inside the nest, and that calls within this category are structured in a way that could reduce the risk of nest predation.     

Innate development of acoustic signals for host parent–offspring recognition in the brood‐parasitic Screaming Cowbird Molothrus rufoaxillaris

Young birds communicate their need to parents through complex begging displays that include visual and acoustic cues. Nestlings of interspecific brood parasites must ‘tune’ into these communication channels to secure parental care from their hosts. Various studies show that parasitic nestlings can effectively manipulate host parental behaviour through their begging calls, but how these manipulative acoustic signals develop in growing parasites remains poorly understood. We investigated the influence of social experience on begging call development in a host‐specialist brood parasite, the Screaming Cowbird Molothrus rufoaxillaris. Screaming Cowbird nestlings look and sound similar to those of the primary host, the Greyish Baywing Agelaioides badius. This resemblance is likely to be adaptive because Baywings discriminate against fledglings unlike their own and provision nests at higher rates in response to Baywing‐like begging calls than to non‐mimetic begging calls. By means of cross‐fostering and playback experiments, we tested whether the acoustic cues that elicit recognition by Baywings develop innately in Screaming Cowbird nestlings or are acquired through social experience with host parents or nest mates. Our results suggest that begging call structure was partially modulated by experience because Baywing‐reared Screaming Cowbird and host nestlings were acoustically more similar as age increased, whereas acoustic similarity between cross‐fostered and Baywing‐reared Screaming Cowbird nestlings decreased from 4–5 to 8–10 days of age. Cross‐fostered Screaming Cowbirds developed begging calls of lower minimum frequency and broader bandwidth than those of Baywing‐reared Screaming Cowbirds by the age of 8–10 days. Despite the observed differences in begging call structure, however, adult Baywings responded similarly to begging calls of 8‐ to 10‐day‐old cross‐fostered and Baywing‐reared Screaming Cowbirds, suggesting that these were functionally equivalent from the host's perspective. These findings support the idea that, although rearing environment can influence certain begging call parameters, the acoustic cues that serve for offspring recognition by Baywings develop in young Screaming Cowbirds independently of social experience.     

Reliable Information Content and Ontogenetic Shift in Begging Calls of Grey Warbler Nestlings

The most critical assumption of communication models regarding parent–offspring conflict is that food solicitation displays of genetic offspring are honest signals to elicit beneficial parental care. A critical requirement of honesty is the reliable change of perceivable aspects of begging calls with physiological needs. We experimentally tested whether and how the acoustic structure and begging call rate of individual Grey Warbler Gerygone igata nestlings change with hunger level and age. We also examined a rarely documented component of chick begging calls, namely the temporal dynamics of acoustic modulation after nestlings heard parental feeding calls. Begging call structure narrowed in frequency range and, surprisingly, decreased in amplitude as chick hunger levels increased. We also found that begging calls changed with chick age, with the frequency increasing and the duration decreasing for older chicks. These results indicate that the acoustic properties of nestling Grey Warbler begging calls are complex and may be used to signal several aspects of nestling traits, including hunger level and age (or size, a correlate of age). Overall, begging calls of Grey Warbler chicks appear to be honest, implying that parents are likely to benefit from relying on the acoustic features of their progeny’s calls which predict chick need. Our results have important implications regarding the reliability and information content of nestling solicitation signals for the brood parasite shining cuckoo Chrysococcyx lucidus exploiting Grey Warbler parental care, in that these begging‐call mimetic specialist cuckoos might also need to match closely the dynamics of acoustic features of their host chicks’ calls.     

Blackcap Sylvia atricapilla nestlings do not produce begging calls until they are able to escape from predators

Nest predation is a major source of reproductive failure in birds and thus it can exert selection on both parental and offspring strategies. Begging calls are known to be a powerful component of parent–offspring communication but these calls can also increase predation risk. Here we demonstrate a sophisticated strategy for the development of begging vocalization in a species under high nest predation. Blackcap Sylvia atricapilla nestlings spend most of their nesting period silent, and develop begging calls just before they are able to fledge. The onset of begging vocalization matches the onset of endothermy, which enables Blackcap chicks to leave the nest. We demonstrate experimentally that begging calls function as a signal of the increased needs of homeothermic nestlings. Playback of begging calls conducted in nests with silent nestlings resulted in a significant increase in feeding rates and a decrease in brooding. Development of begging calls only at the age of endothermy allows species under high nest predation to keep the risky period of begging vocalizations and frequent feeding to a minimum. This strategy may constitute an evolutionary solution to high predation pressure in some open nesting passerines. This is the first study to demonstrate the existence of silent begging in a passerine.     

Alarm calls of the Southern House Wren Troglodytes musculus: variation with nesting stage and predator model

Alarm calls given by parents when risk is detected during nesting may be considered a form of parental defense. We analyzed variations in callings of breeding pairs of the Southern House Wren Troglodytes musculus during the nesting cycle and when faced with different predator models. Nesting birds were exposed to stuffed models at different nesting stages (early and late during incubation, and nests with younger and older nestlings). Nests were also exposed to different predator models where the calling response of breeding adults and acoustic structure variations of the calls were analyzed. The presence of a predator model increased the parents’ alarm calls along the nesting stage. This result supports the hypothesis that the higher the nest reproductive value, the higher the nest defense performed by the Southern House Wren. However, it also supports the notion that alarm calls could be used by parents to silence nestlings and reduce their detectability. Alarm calls also varied according to the predator model presented. We suggest that alarm calls variations of Southern House Wrens could encode information about the kind of predator and the risk envisaged through variations of call rates.     

Contrasting Parental Tasks Influence Parental Roles for Paired and Single Biparental Cichlid Fish

Biparental care of young occurs when both parents provide some sort of care for offspring and can include a wide variety of behaviors, yet often studies focus on single aspects of parental care when trying to determine how each parent contributes. Here, we presented the biparental convict cichlid fish (Amatitlania nigrofasciata) with two conflicting parental behaviors: retrieval of non‐swimming offspring that have been displaced from the nest and defense against a conspecific intruder, a potential brood predator. We examined single males, single females, and pairs of parents to determine how males and females each contributed to overall parental care. Traditionally in this species, parents exhibit a division of labor (in which each parent contributes to all parental activities), but also exhibit a division of roles (in which males tend to favor the role of defense and females tend to favor more direct care, spending more time with offspring). We hypothesized that single parents would compensate for their absent mate, but that males and females would still favor preferred roles. Additionally, we hypothesized that there would be an asymmetrical expansion of roles, with females being more flexible. Our results show that the preferred roles of both parents were evident even when parents were without their mates and that males and females differed in their compensatory levels, at least when compared to the behaviors of the intact pair. Contrary to our prediction, females seem unable to fully compensate for the defensive behaviors usually exhibited by males, while males shifted completely to retrieve displaced offspring.     

Parental Care Syndromes in House Sparrows: Positive Covariance Between Provisioning and Defense Linked to Parent Identity

Parents of many species provide multiple forms of care to their offspring. In many birds, parents often provision offspring with food and defend them from predators and/or nest‐site competitors. We tested how these two forms of parental care covary in a wild population of house sparrows (Passer domesticus). Using a behavioral reaction norm approach, we found that nestling provisioning exhibited between individual differences and positively covaried with a measure of nest defense: the propensity to attack a heterospecific nest box competitor, the European starling (Sturnis vulgaris). This result would seem to support parental investment theory and suggests that high‐provisioning parents have high‐value offspring, which they will defend more vigorously than low‐provisioning parents. In addition, we found that parents with nestlings that hatched earlier in the season and grew faster approached a model starling more frequently and tended to be more likely to strike the starling. However, we also found that although brood value explained significant variation in both nestling provisioning and nest defense, it did not eliminate the positive, between‐individual relationship between provisioning and defense. This suggests that some of the correlation between provisioning and defense is tied to individual identity and hence may be a behavioral syndrome in which differences between individuals in underlying attributes produce correlated behaviors.