Aggression of breeding eastern bluebirds (Sialia sialis) toward their mates and models of intra-and interspecific intruders

Hypotheses regarding the evolution of aggressive patterns during the breeding season in eastern bluebirds (Sialia sialis) were tested by placing models of eastern bluebirds and house sparrows (Passer domesticus) into territories of experimentally naive breeding pairs of eastern bluebirds during three stages of the nesting cycle. The responses of the resident males to models of male bluebirds decreased from the egg-laying to the nestling stage, and this response pattern can be interpreted as support for the protection-of-parentage hypothesis or the nest-site-defence hypothesis. The aggression of resident males to resident females during trials with models of male bluebirds weakly conforms to the pattern predicted by the protection-of-parentage hypothesis. The aggressive response to models of house sparrows also decreased from the egg-laying to the nestling phase in a manner consistent with the nest-site-defence explanation. No aggression toward mates by males or females was observed during trials with house sparrow models, an observation consistent with the predictions of the protection-of-parentage hypothesis.     

Parenting styles in white‐rumped swallows (Tachycineta leucorrhoa) show a trade‐off between nest defense and chick feeding

Studies about personalities in wild animals usually focus on five categories of behavioral traits that do not easily accommodate all aspects of parental care, a class of behaviors with direct consequence to reproductive success. Parental care can vary consistently between individuals and constitute parenting styles. Here we investigate the consistency of four behaviors of parental care across two breeding seasons of white‐rumped swallows Tachycineta leucorrhoa in southern Brazil. These behaviors are a prospection of potential nest‐sites, nest defense against predators or conspecifics, and chick feeding. If these first three behaviors are consistent, they can be classified according to the standard categories of personality as exploration, boldness, and aggressiveness, respectively. We find that all behaviors, except exploration, are consistent between individuals in the long term. We also show that, besides individual identity, couple identity is an important component explaining variation in behavior. This pattern can arise if behavior influences pair formation or if behavior is a consequence of a common environment affecting the couple. We show that, depending on the parental task, males or females are more consistent, suggesting that sexes are adopting different strategies of parental care allocation. We then investigate if there is a trade‐off between nest defense and chick feeding. We find that birds that defend more also feed the brood less often and suggest that testosterone might be the mechanism modulating this trade‐off. Lastly, we discuss the implications of our results to mate choice and highlight the need for studies linking parenting styles to fitness in swallow species.     

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.     

Repeatability of Host Female and Male Aggression Towards a Brood Parasite

Current research on behavioural consistency showed that various types of animal behaviour are highly repeatable in the context of mate choice, exploration and parental care, including nest protection. However, the repeatability of aggressive nest defence has not yet been studied in hosts of brood parasites, although host aggression against adult parasites represents a crucial line of antiparasitic defences. Here, we investigated the between‐season repeatability of the great reed warbler (Acrocephalus arundinaceus) aggression towards a stuffed dummy of the brood parasitic common cuckoo (Cuculus canorus). We found that under the relatively stable risk of brood parasitism across breeding seasons, female responses to the cuckoo were highly repeatable, whereas male responses were variable. We suggest that the potential explanation for the observed patterns of female and male behaviours may lie in female's prominent roles in offspring care and nest protection, and in her lower renesting potential in comparison with that of males. However, further studies on the relationship between host aggression and other types of behaviours (host personality) and their fitness consequences under the fluctuating parasitism pressures are required to clarify the adaptive significance of aggressive behaviour observed in hosts of brood parasites.     

Personality of hosts and their brood parasites

Brood parasites such as the common cuckoo Cuculus canorus exploit the parental abilities of their hosts, hosts avoid brood parasitism and predation by showing specific behavior such as loss of feathers, emission of fear screams and contact calls, displaying wriggle behavior to avoid hosts or potential prey, pecking at hosts and prey, and expressing tonic immobility (showing behavior like feigning death or rapid escape from predators and brood parasites). These aspects of escape behavior are consistent for individuals but also among sites, seasons, and years. Escape behavior expressed in response to a broad range of cuckoo hosts and prey are consistently used against capture by humans, but also hosts and brood parasites and predators and their prey. An interspecific comparative phylogenetic analysis of escape behavior by hosts and their brood parasites and prey and their predators revealed evidence of consistent behavior when encountering potential parasites or predators. We hypothesize that personality axes such as those ranging from fearfulness to being bold, and from neophobic to curiosity response in brood parasites constitute important components of defense against brood parasitism that reduces the overall risk of parasitism.     

Behavioral Plasticity in Response to Perceived Predation Risk in Breeding House Wrens

Predation is a significant cause of nest failure in passerine birds, and, thus, natural selection is expected to favor behavioral plasticity to allow birds to respond to perceived changes in predation risk. However, behavioral plasticity in response to perceived predation risk, and its potential fitness-related costs, are understudied. In a wild population of breeding house wrens (Troglodytes aedon), we tested the hypotheses that (1) birds show behavioral plasticity in response to perceived nest-predation risk to reduce self-risk or risk to offspring, but (2) this plasticity incurs fitness-related costs. We experimentally increased the perceived risk of nest predation by enlarging the diameter of the nestbox entrance from the standard 3.2 to 5.0 cm once incubation began. Unexpectedly, large-hole females spent significantly less time being vigilant than small-hole (control) females during late incubation. Both males and females also exhibited plasticity in their provisioning behavior. Large-hole males increased and large-hole females decreased provisioning visits with increasing brood size, whereas small-hole males and females behaved similarly and were unaffected by brood size. Females did not show plasticity in their incubation or brooding behavior. Notwithstanding this behavioral plasticity in response to increased perceived predation risk, treatment had no effect on hatching success or early hatchling survival, nor did it affect nestling body condition or fledging success. We conclude, therefore, that house wrens show behavioral plasticity in response to perceived nest-predation risk, but that any short-term fitness-related costs associated with this flexibility appear negligible.     

Individual Consistency in Parental Effort Across Multiple Stages of Care in the House Sparrow, Passer domesticus

In many avian species in which biparental care is provided to offspring, substantial variation exists within members of each sex in the level of effort contributed to various forms of parental care. Questions remain as to whether individuals that contribute more toward one parental activity also contribute more toward other activities in which they participate. We examined the contributions of male and female house sparrows (Passer domesticus) to three forms of parental care: incubation, nestling provisioning, and nest defense, and compared the investments made by individuals at each stage of care relative to other same‐sexed parents. In both males and females, nestling feeding rates were positively associated with time spent incubating, but no relationships were found between measures of nestling feeding and nest defense. The predictability of an individual's feeding behavior based on earlier incubation efforts may make incubation a good stage for individuals to evaluate the parental abilities of their partners.     

Hissing calls improve survival in incubating female great tits (Parus major)

Nest predation is among the most important selective pressure shaping nest-site selection and nest defense behavior in many avian species. In this study, we tested whether the production of one such nest defense behavior—hissing calls—may improve survival of incubating female great tits (Parus major). We found that 72.5 % of incubating females gave hissing calls when they were exposed to a stuffed woodpecker in their nest boxes. The repeatability of the number of hissing calls given was high, as was the latency to give the call. Additionally, natural nest predators attacked hissing and nonhissing females equally often. However, hissing females survived better than silent females. We tested responses of feral cats to playbacks of hissing call during their attacks of nest boxes and found that hissing calls prevented the predator attacks. Taken together, our findings indicate that hissing calls can deter predator attacks and potentially increase survival rates of nesting great tits or their offspring, or both. The propensity to give hissing calls may be related to personality type of incubating female great tits, which needs to be tested experimentally.     

How Consistently are Good Parents Good Parents? Repeatability of Parental Care in the House Sparrow,Passer domesticus

In many avian species, substantial individual variation occurs in parental food‐provisioning levels, which often is assumed to reflect variation in parental quality. Parental quality also has often been invoked as a key element in mate choice among biparental species, and many sexually‐selected traits have been investigated as potential predictors of parental quality. In recent studies of house sparrow (Passer domesticus) parents, we found that individuals behaved remarkably consistently across time, regardless of temporary manipulations of the nestling provisioning of their partners. This suggests that variation in parental competence may be attributable to quality differences among individuals. One prediction of the ‘parental quality differences’ hypothesis is that individuals also should show consistency in their provisioning behavior across broods. To test this, we compared the parental delivery rates of individual house sparrows across broods. Parents of both sexes reduced their per‐chick delivery rates as the season progressed; parents of both sexes were also responsive to changes in their brood sizes. Despite these sources of environmental variation in provisioning rates, the parental care of individual males was highly repeatable across broods. By contrast, female parental care showed extremely low repeatability, and standardized measures of among‐individual variation in parental behavior revealed females to be much less variable than males. These results indicate that females in this multi‐brooded species have much to gain from mate‐choice decisions predicated on male parental quality or accurate indicators of such, whereas males are less likely to profit from being highly selective about the ‘parental quality’ of their partners.     

Inbreeding is associated with shorter early-life telomere length in a wild passerine

Inbreeding can have negative effects on survival and reproduction, which may be of conservation concern in small and isolated populations. However, the physiological mechanisms underlying inbreeding depression are not well-known. The length of telomeres, the DNA sequences protecting chromosome ends, has been associated with health or fitness in several species. We investigated effects of inbreeding on early-life telomere length in two small island populations of wild house sparrows (Passer domesticus) known to be affected by inbreeding depression. Using genomic measures of inbreeding we found that inbred nestling house sparrows (n?=?371) have significantly shorter telomeres. Using pedigree-based estimates of inbreeding we found a tendency for inbred nestling house sparrows to have shorter telomeres (n?=?1195). This negative effect of inbreeding on telomere length may have been complemented by a heterosis effect resulting in longer telomeres in individuals that were less inbred than the population average. Furthermore, we found some evidence of stronger effects of inbreeding on telomere length in males than females. Thus, telomere length may reveal subtle costs of inbreeding in the wild and demonstrate a route by which inbreeding negatively impacts the physiological state of an organism already at early life-history stages.

     

Winter territory prospecting is associated with life‐history stage but not activity in a passerine

Finding a high quality territory is essential for many animals to reproduce successfully. Despite its importance for fitness, we know little about the process of territory prospecting in wild birds, and whether individual traits and behaviours, such as personality, co‐vary with territory prospecting. Here, we use long‐term data from a wild, insular house sparrow Passer domesticus population to test three hypotheses about territory fidelity and prospecting: 1) house sparrows show high territory fidelity between years and also during winter. 2) Individuals will prospect for a breeding territory during their first winter whereas older, more experienced individuals will keep a territory from previous years and will, therefore, show no or reduced winter territory prospecting. 3) More active behavioural types will prospect more than less active behavioural types. We use data from four winters from automatically, daily recorded nest‐box visits of 188 birds of known age. The number of nest‐boxes that each individual visited within each winter was used as a proxy of winter territory prospecting. We show that house sparrows visit multiple nest‐boxes during their first winter, whereas older individuals keep territories year‐round and, potentially because of this, indeed show reduced winter territory prospecting. Activity was not associated with the number of nest‐boxes visited. Further research is needed to investigate whether time of territory and mate acquisition differs among individuals and the possible effect on lifetime fitness.     

Eastern bluebirds Sialia sialis do not avoid nest boxes with chemical cues from two common nest predators

Chemodetection of common nest predators may be advantageous for nesting birds; however, few studies have examined the ability of songbirds to detect chemical odors from predators. Thus, in 2002, we presented eastern bluebirds Sialia sialis with pairs of nest boxes; one box in the pair was regularly scented with chemical cues from a common nest predator, the black rat snake Elaphe obsoleta , and the other with a neutral cue. In 2004, we again presented bluebirds with pairs of boxes, one scented with chemical cues from a different nest predator, the deer mouse Peromyscus maniculatus , and the other with a neutral scent. Although human females were able to correctly distinguish paper laced with predator cues from paper with neutral cues, bluebirds were as likely to lay eggs in boxes with predator cues as in boxes with neutral cues. While it remains possible that bluebirds may detect scent from potential nest predators, it appears that the presence of these chemical cues does not ultimately influence selection of nest sites.     

Is hissing behaviour of incubating great tits related to reproductive investment in the wild?

Anti-predator behaviour of breeding animals is a complex trait that depends on current reproductive investment as well as individual differences in risk-taking propensities. In response to nest predation, many bird species produce specific sounds, such as the hissing calls in incubating great tits (Parus major), that may provoke an acoustic startle response in the predator. However, it is still unclear whether the propensity of incubating females to produce hissing calls towards nest predators depends on the reproductive investment. With our 3-year study, we show that response type (females that do not hiss versus females giving hissing calls) to a potential nest predator, the woodpecker, is a repeatable trait. We found no differences in the studied reproductive traits between hissing and non-hissing birds. Interestingly, among hissing birds, fast-responding females started egg-laying earlier than slow-responding ones. Among non-hissing birds, heavier birds initiated clutches earlier. We also revealed that hissing birds breed in areas with decreased nest-box occupancy, suggesting either that they potentially select different areas to breed or that territory size is larger as a result of hissing birds being more aggressive. These findings demonstrate that response type is not related to the early reproductive value of the brood across distinct behavioural groups. However, our results do suggest that non-hissing and hissing females differ in terms of individual quality or dominance or personality related aspects.     

Dynamics of nest defense by male centrarchid fish

Field observations were conducted on four species of nesting male centrarchids to determine if guarding males discriminate intruders with respect to their potential threat to the brood, their size or position in the water column, or by the stage of the nest. Results demonstrated that bluegill (Lepomis macrochirus) and pumpkinseed (L. gibbosus) sunfish were the most frequent intruders and were attacked the most often. Nest guarding male largemouth bass (Micropterus salmoides) attacked intruders further from the nest and had the highest probability of attack of the four species studied. Rock bass (Ambloplites rupestris) males had the shortest distance of attack and one of the lowest probabilities of attack. Male black crappie (Pomoxis nigromaculatus) and pumpkinseed were intermediate in both responses. For all species, the size of intruder did not influence attack distance but larger males had a greater attack distance than smaller males. The distance of attack was greatest during the period immediately after hatch. These findings indicate species-specific differences in nest defense and males did discriminate intruders, possibly on their potential threat to the brood. The defense of the nest was related to nest stage, a finding which supports current theory of parental care.     

Breeding Season Aggression of Female and Male Eastern Bluebirds (Sialia sialis) to Models of Potential Conspecific and Interspecific Egg Dumpers

Naturally occurring aggression between female eastern bluebirds (Sialia sialis) is dramatic, resulting in severe injuries and even death. Furthermore, aggression among bluebirds is usually sex specific: males attack males, females attack females. We hypothesized that the primary function of female-female aggression is to guard against the threat of intraspecific egg dumping and that, in this context, same sex aggression is related to the possibility of advantages for males of parasitism (egg dumping) of their nests. Our hypotheses to explain variation in naturally occurring aggression predict temporal variation in aggressive tendency within nest cycles and between the sexes depending on asymmetries in threats to the residents. We report the results of experimental trials in the field designed to determine temporal variation in the aggressive tendencies of resident females to models of intruder females of two species, eastern bluebirds and brown-headed cowbirds (Molothrus ater). Both species dump eggs in the nests of bluebirds. Female aggression to eastern bluebird models is greatest during early stages of nest cycles; the patterns are most consistent with protection against egg dumping and protection of nest sites from usurpation. Male residents seldom attack female eastern bluebird models, but often attack models of female brown-headed cowbirds, a result inconsistent with the hypothesis that patterns of differential parental care control aggression of female and male residents.     

Maternal Care in the Burrower Bug <Emphasis Type="Italic">Adomerus triguttulus</Emphasis>: Defensive Behavior

Some burrower bugs (Heteroptera: Cydnidae) show complex patterns of maternal care, including defense against predators and the provisioning of food to nymphs. Recently, the subsocial cydnid bugs have attracted the interest of researchers as model systems to study the behavioral ecology of parental investment. However, there have been few attempts to quantify the fitness benefits of maternal behavior other than provisioning. Here, we examined the maternal behavior of Adomerus triguttulus and its adaptive significance in terms of offspring survival in the field. A. triguttulus young depend on fallen nutlets of myrmecophorous mints, Lamium spp. Under field conditions, females attend offspring, from eggs to second instar nymphs, in nests on the ground under the litter. When disturbed, the females showed aggressive responses against the source of disturbance. The females often carried spherical clutches of eggs away from the nest when heavily disturbed. Female-removal experiments in the field demonstrated a defensive function of the female behavior; predators, such as ants, attacked egg clutches without females and the clutches often disappeared during the experiment. Egg clutches without females sometimes also suffered from fungal infection. Selective factors on maternal defensive behavior in A. triguttulus are discussed in terms of habitat properties possibly emerging from insect–plant associations.     

The role of a synanthropic bird in the nest niche expansion of a secondary cavity nester to man‐made structures

Species with similar ecological characters often compete with each other; however, a species may also facilitate the survival or reproduction of another ecologically similar species, although such interaction is rarely documented in birds. Here, we reported a facilitative species interaction between Asian house martins (Delichon dasypus) and russet sparrows (Passer cinnamomeus), both passerines using closed nests, in a montane farming area of Taiwan. We found that Asian house martins constructed dome‐shaped nests in human houses that provided additional nest sites for russet sparrows, secondary cavity nesters with greatly declining populations in Taiwan. Russet sparrows that used house martin nests had reproductive success comparable to those that used artificial nest boxes. However, Asian house martins avoided reclaiming sparrow‐used nests, which reduced their available nest sites. Interestingly, our results imply that man‐made structures may be used as a conservation tool to improve the breeding of the endangered russet sparrows via this facilitative interaction.     

Food supplementation affects extrapair paternity in house sparrows (Passer domesticus)

Extrapair paternity (EPP) is common among birds, but the reasonswhy it varies within and among species are less clear. In particular,few studies have experimentally examined how food availabilityinfluences paternity and sexual behavior. We manipulated foodsupply in a nest-box population of house sparrows, Passer domesticus,a colonial passerine with extensive biparental care. Duringthree successive breeding attempts, we changed food availabilityat nest sites and examined behavior and genetic parentage. DNAfingerprinting revealed that the level of EPP within broodswas five times lower in pairs nesting at sites continuouslysupplied with extra food. With extra food, mates spent longertime together at the nest, but this was mainly due to a changein female behavior; females but not males increased total nestattendance. Moreover, we found that individual males did notchange within-pair copulation frequency across treatments, suggestingthat our experiment did not influence male control over fertilizationsthrough copulation behavior. Instead, our study shows that ecologicalfactors can have a strong influence on the time budgets of malesand females, which consequently affects the occurrence of EPP.     

A sex difference in the behavioural response of nesting mountain bluebirds (<Emphasis Type="Italic">Sialia currucoides</Emphasis>) to a mounted predator

Passerine nests can benefit parental fitness, but defense against predators may be costly. Although this paradigm is well studied, no studies have been conducted on mountain bluebirds (Sialia currucoides). We observed the response of 17 bluebird pairs with nestlings to a mounted bobcat (Lynx rufus) and two controls. Bluebird pairs clearly differentiated the mounted predator and males moved closer to the bobcat than to the controls whereas females did not. This system is ideal to further refine nest-defense hypotheses.     

Signaling or Not-Signaling: Variation in Vulnerability and Defense Tactics of Armored Ground Crickets (Acanthoplus Speiseri: Orthoptera, Tettigoniidae, Hetrodinae)

Male Orthoptera singing from exposed perches are at risk from acoustically- and visually-hunting predators. The defensive reactions of armored ground crickets (Acanthoplus speiseri) include falling silent, dropping from their perch, alarm stridulation and autohaemorrhaging. Male and female ground crickets show different reactivity (i.e. the number or intensity of defense tactics used) to predation, depending on level of exposure: calling males were more reactive when approached during daylight, compared with in the dark. During daylight, calling males were more reactive than silent, cryptic, males and females. The level of response presumably reflected the riskiness of the individual’s behavior and situation at that time. Plasticity of response to predation allows individuals to balance risky behavior (i.e. acoustic signaling from exposed perches) by being more reactive to potential threats.