Nest Defense Research Articles

Residual correlations, and not individual properties, determine a nest defense boldness syndrome

Different behavioral traits often covary, forming a behavioral syndrome. It is poorly known whether this covariance occurs on the between-individual level and what its selective consequences are. We used repeated measures (N = 562 observation events) of individual tawny owl Strix aluco females (N = 237) to study the integrated effects of seasonal timing of reproduction and clutch size on boldness displayed during defense of their clutch, in relation to plumage coloration, including local recruit production as a selective force on these traits. Using a Bayesian multivariate mixed model, we quantified the covariances between these traits on phenotypic, residual, and between-individual level and used a structural equation modeling approach to test the significance of presumed causal relationship between these traits in an a priori hypothesized path. On the phenotypic level, boldness was determined through early timing of breeding and larger clutch size, and early breeding increased recruitment probability. However, this relationship was entirely due to residual covariances and was not present on the between-individual level. The low individual-level correlations did not constrain the capacity of the population to respond to evolution as quantified by average autonomy (a metric summarizing evolutionary constraint on multiple traits). In the tawny owl, the association between early breeding and bold behavior, which is favored by selection, is solely due to extrinsic, nonheritable factors. We conclude that phenotypic evidence is insufficient to demonstrate syndrome covariance.

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

AbstractParents 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.

Nest defense of the red-backed shrike Lanius collurio against five corvid species

We compared the antipredation behavior of the red-backed shrike against five European corvids including the jay, nutcracker, rook, crow, and raven. These species differ in body size and in the proportion of eggs and nestlings in their diets. The jay and nutcracker are the smallest, the rook and crow are middle-sized, and the raven being the largest corvid of all. The jay, crow, and raven are habitual nest predators, whereas the nutcracker and rook are not. The harmless pigeon was presented as a control. We analyzed (1) the number of attacks executed by shrikes against intruder presented close to shrike nests and (2) the distance between the intruder and the shrikes during the trial. The small corvids (the jay and nutcracker) were attacked significantly more intensively than the other, larger, corvids (the rook, crow, and raven) and pigeon control. All three large corvids were attacked as exceptionally as the pigeon. Shrikes approached closer to the small corvids and the pigeon than to the large corvids. These results imply that shrike antipredation strategy is adjusted to intruder size, but not to the level of intruder nest plundering specialization. Shrikes weigh up their ability to chase a given intruder away and avoid pointless aggression against large, undefeatable, intruders. This suggests that shrikes are able to asses not only the dangerousness of the intruder but also the potential advantageousness, or otherwise, of active defense.

High Rates of Shiny Cowbird Parasitism on the Brown-and-yellow Marshbird Select for Complementary Host Defenses

Hosts of brood parasites may have not developed antiparasitic defenses either because host and parasite are recently sympatric or because costs of potential defenses outweigh their benefits. We studied antiparasitic defenses of the Brown-and-yellow Marshbird (Pseudoleistes virescens) against the Shiny Cowbird (Molothrus bonariensis), evaluating recognition and aggression toward female and male Shiny Cowbirds, estimating rates of rejection of cowbird eggs of different colors, and testing the effect of the size of parasite eggs on host rejection. We also observed and video-recorded host nests to estimate hosts' nest attentiveness, frequency of cowbird visits, and interactions between marshbirds and cowbirds. When marshbirds were faced with dummy models, they attacked first and more intensively those of cowbirds (both sexes) than those of a control species. Frequency of egg ejection increased as differences between cowbird and spotted marshbird eggs increased (immaculate > intermediate > spotted), and spotted eggs were ejected more frequently when laid before than during or after the hosts' laying. Marshbirds ejected artificially added immaculate eggs independently of their size. Cowbirds visited marshbird nests only at the egg stage. Hosts' nest attention was low during egg laying and increased during incubation and after hatching, but aggressiveness against cowbirds was always high. Nest defense was inefficient, as losses due to egg pecking by cowbirds were high. Ejection of cowbird eggs avoided the cost of lower survival of marshbird nestlings in highly parasitized nests. As this defense is cost-free, this small benefit would be sufficient to select for the evolutionary maintenance of egg ejection.

The Role of Agonistic Sounds in Male Nest Defence in the Painted Goby Pomatoschistus pictus

AbstractAnimals often vocalize during territorial challenges as acoustic signals may indicate motivation and fighting ability and contribute to reduce aggressive escalation. Here, we tested the function of agonistic sounds in territorial defence in the painted goby. Pomatoschistus pictus, a small vocal marine fish that defends nests during the breeding season. We first measured the number of times a male approached, avoided, explored, entered and exited two unattended nests associated with either conspecific agonistic sounds or a control: silence or white noise. Acoustic stimuli were played back when the male approached a nest. In a second experimental set, we added visual stimuli, consisting of a conspecific male in a small confinement aquarium near each nest. Even though we found no effect of the visual stimuli, the sound playbacks induced similar effects in both experimental conditions. In the sound vs. silence treatment, we found that when males approached a nest, the playback of conspecific sounds usually triggered avoidance. However, this behaviour did not last as in longer periods males visited nests associated with agonistic sounds more often than silent ones. When the control was white noise, we found no significant effect of the playback treatment in male behaviour. Although we cannot exclude the possibility that other sounds may dissuade nest occupation, our results suggest that agonistic sounds act as territorial intrusion deterrents but are insufficient to prevent nest intrusion on their own. Further studies are needed to test the significance of sound production rate, spectral content and temporal patterns to deter territorial intrusion in fish.

Fight or flight

Abstract. Patterns of nest defense against predators by ground-nesting bird species in the wild are poorly understood, largely because of a historical inability to directly monitor nests. Most nest-defense studies have observed responses elicited from artificial predators or human observers presented to nesting birds, and few have attempted to present these events in the context of predator—prey relationships found in the wild. We hypothesized that predator threat level (e.g., the threat posed to the clutch or to the clutch and the attending adult), parental characteristics, clutch investment, and future reproductive opportunities would influence avian nest-defense decisions. During 1999–2006, we examined predation events (n = 242) from 790 video-monitored Northern Bobwhite (Colinus virginianus) nests. We evaluated parental, predator, daily, and seasonal correlates that potentially contributed to patterns of nest defense by Northern Bobwhites using a model selection approach. The top model showed that nes...

High Laccase2 expression is likely involved in the formation of specific cuticular structures during soldier differentiation of the termite Reticulitermes speratus

Termite soldiers are morphologically specialized for colony defense. Analysis of the mechanisms of soldier differentiation is important for understanding the establishment of termite societies. Soldiers differentiate from workers through a presoldier stage and have well-sclerotized and pigmented cuticles. These characteristics are important for nest defense and are likely to be caused by soldier-specific mechanisms of cuticular tanning. The molecular mechanisms leading to cuticular tanning have not been elucidated. Laccase2 (Lac2) plays important roles in this process in insects, and we hypothesized that Lac2 expression may be involved in soldier-specific cuticular tanning. We observed inner and outer head cuticle changes and compared the Lac2 expression patterns among three molts (worker–worker, worker–presoldier and presoldier–soldier) in the termite Reticulitermes speratus. Quantitative analyses of head cuticle colors showed that the color properties changed more conspicuously in presoldier–soldier molts than in the other two molts. Histological observations showed that the exocuticles of soldier heads were substantially thicker than those of worker and presoldier heads, underwent tanning before or just after ecdysis, and were pigmented at earlier time points than other molts. Finally, markedly higher Lac2 expression levels were observed just before and after ecdysis only in the presoldier–soldier molt. These results suggest that specific cuticular formation occurs in the exocuticles during soldier differentiation, and that the high level of Lac2 expression during the presoldier–soldier molt is related to soldier-specific cuticular tanning. We speculate that evolution of the regulatory mechanisms of Lac2 expression were important for the acquisition of soldier-specific cuticles.

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.

Effect of egg predator on nest choice and nest construction in sand gobies

Nest defence is a particularly costly component of parental care. The costs of nest-related behaviours are affected by the nest's location, size and architecture; yet surprisingly little is known about how choice of a nesting site or nest characteristics are adjusted as a response to the threat of future nest predation. To address this topic, we investigated whether egg predation threat influenced nest choice and nest construction in the sand goby, Pomatoschistus minutus, a small marine fish with exclusive paternal egg care. We found that exposure to sand shrimp, Crangon crangon, a predator of sand goby eggs, did not affect male preferences for large nesting resources or the onset of nest-building activity. Small and large males did, however, respond differently to the presence of shrimp during the nest-building phase. In particular, large males used more sand to cover their nests in the shrimps' presence. By contrast, neither the presence of egg predators nor male size class affected the size of the nest entrance. Together, our results show that while the risk of future egg predation may not necessarily influence a male's decision to nest, during the nest construction phase it can nevertheless induce responses that strongly depend on builder phenotype.

Evidence of a nesting psychology during human pregnancy

In altricial mammals, “nesting” refers to a suite of primarily maternal behaviours including nest-site selection, nest building and nest defense, and the many ways that nonhuman animals prepare themselves for parturition are well studied. In contrast, little research has considered pre-parturient preparation behaviours in women from a functional perspective. Reports in the popular press assert that women experience “nesting” urges, in the form of cleaning and organizing behaviours. Anthropological data suggest that having control over the environment is a key feature of childbirth preparation in humans, including decisions about where birth will take place, and who will be welcome in the birthing environment. Here, we describe the results of two studies, a large online study comparing pregnant and non-pregnant women, and a longitudinal study tracking women throughout pregnancy and into the postpartum period and comparing non-pregnant women at similar time intervals, using a nesting questionnaire that we developed. We found that women exhibit nesting behaviours, including space preparation and social selectivity, which peak in the third trimester of pregnancy. As is the case with nonhuman mammals, nesting in women may serve a protective function.

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.

A Test of Radio-Transmitter Effects on Parental Investment and Productivity in the Northern Cardinal

Abstract. Researchers often attach radio transmitters and other devices to free-living birds without a clear understanding of the possible consequences for their study organisms or their data. Although transmitters may affect parental investment (nest defense and offspring provisioning), this possibility has received little attention. We tested this hypothesis by placing mock radio transmitters on male Northern Cardinals (Cardinalis cardinalis) and comparing their behavior to that of uncaptured birds and procedural controls. Birds with transmitters defended their nests less vigorously than did uncaptured birds but did not modify their provisioning effort. This behavioral modification appears to have ultimately influenced predation rates, as nests of birds with transmitters had lower daily survival rates and were less likely to fledge offspring. Control birds that were captured, handled, and bled had intermediate levels of nest defense and productivity that were statistically indistinguishable from those o...

Relationship between the age of Vespa velutina workers and their defensive behaviour established from colonies maintained in the laboratory

As the structural bases of insect societies are essential to colony survival, nests must be protected from predation. Nest defence behaviours are among the most important roles assigned to worker members. However, in hornet societies, temporal polyethism (age-dependent division of labour among workers) is assumed to be weak. Few studies have investigated this phenomenon, probably because hornet nests are aggressively defended and dangerous to approach. In the present study, we propose a method for rearing nests of Vespa velutina, a species newly introduced into Europe. This method enables the handling of hornets, and thus the design of experiments. By marking all newly emerged hornets, we recorded aggressiveness in workers of different ages from three captive colonies. We observed that nest defence behaviour in V. velutina depends on the age of the workers. Nest defence appears to be mediated by the queen, probably through pheromones that promote nest organization. We also identified a previously unreported but important behaviour in V. velutina that workers are aggressive towards male hornets. This behaviour might be a strategy to avoid inbreeding. Collectively, our results provide new research perspectives for the management of social hymenopteran predators.

Parental Risk-Taking Behaviour and Nest Defence During the Nestling Rearing Stage in Northern House WrensTroglodytes aedon

Abstract Risk-taking behaviour of short lived nesting birds is often explained in relation to the reproductive value of offspring (the reproductive value hypothesis) and the harm that the absence of parental care can cause to nestlings (risk of harm-to-offspring hypothesis). The reproductive value hypothesis predicts that the risk assumed by adults should increases with nestling age, whereas the risk of harm-to-offspring hypothesis predicts the opposite pattern. We assessed the risk-taking behaviour of nesting males and females Northern House Wrens, Troglodytes aedon, faced with a predation threat (plastic owl model) when rearing 3–4 and 10–12 days old nestlings. We used the time elapsed until parents first entered the nest-box as a measure of risk-taking behaviour and alarm calling rate as a proxy of nest defence. Females resumed sooner parental activities when exposed to the model when nestlings were young, supporting the risk of harm-to-offspring hypothesis. In contrast, the time lasted to resume paren...

Evidence of mutual benefits of nest association among freshwater cyprinids and implications for conservation

ABSTRACT Although nest association among Nocomis chubs and other minnows (Cyprinidae) is common throughout North America, the overall outcome of this relationship and its mechanisms of costs and benefits remain unclear. Because imperilment of stream fishes is affected by reproductive traits, the implications of this widespread interaction must be understood. Nest association mechanisms were explored using a multiple working hypotheses framework on fish assemblage data from 25 reaches in three tributaries of the New River, Virginia, USA. Multiple linear regression models predicting reproductive success (age‐0 abundance) of chubs and associates were compared based on model weights (wi) calculated from Akaike's Information Criterion, adjusted for small sample size (AICc), and relative change in AICc among models. For age‐0 chubs, models represented hypotheses emphasizing the additive effects of adult abundance, nest abundance, and egg dilution by juvenile associates (causing decreased egg predation). For age‐0 associates, models represented hypotheses emphasizing adult associate abundance, gravel substrate availability, nest abundance, parental care (as nest defence) from chubs, and egg dilution by chubs. Model evidence suggests that chubs can sustain themselves (w = 0.61), but their reproductive success is enhanced by a dilution effect from juvenile strong associates (w = 0.37). Strong associate reproductive success was best described by variables emphasizing nest association interactions (w = 0.46) and natural sources of habitat variability (w = 0.45), whereas that of weak associates was more closely related to availability of unmodified habitat (w = 0.50). Chubs and associates appear to receive a net benefit from the association, suggesting a mutualistic relationship. Community‐wide conservation strategies may be useful for protecting symbiotic spawning fishes. In addition to competition and predation, conservation practitioners should consider positive interactions in conservation plans of imperiled mutualists. Copyright © 2013 John Wiley & Sons, Ltd.

Linking sex differences in corticosterone with individual reproductive behaviour and hatch success in two species of uniparental shorebirds

In birds, corticosterone (CORT) appears to facilitate reproductive activity because baseline and stress-induced CORT levels are elevated in breeding individuals compared with other times of the year. In particular, CORT is lower in the sex providing most of the parental care (i.e., incubation), which could be an important adaptation to tolerate stressors that result in abandoning reproduction. Therefore, one explanation for sex differences in CORT is that lower levels are favoured during the incubation/parental phase of reproduction. Using two species of uniparental shorebird – polyandrous red phalaropes (Phalaropus fulicarius) and polygynous white-rumped sandpipers (Calidris fuscicollis) – we predicted that the incubating sex would have lower baseline and stress-induced CORT, and incubating individuals with lower CORT would more effectively defend nests against a simulated intrusion, would return more quickly afterwards, and would ultimately have higher hatch success. We found that phalaropes followed the predicted pattern: incubating individuals (males) had lower baseline and stress-induced CORT than females but for baseline CORT these differences existed prior to males commencing incubation. Incubating male phalaropes with lower baseline and stress-induced CORT returned to incubate more quickly after a disturbance and there was non-significant tendency for baseline CORT to be lower in successful nests. In sandpipers, we observed no sex differences and no significant relationships between individual CORT levels and nest defence behaviours or hatch success. Our results demonstrate that in phalaropes at least, selection favours lower baseline and stress-induced CORT during the nesting period. These results can explain sex differences in stress-induced levels of CORT, however sex differences in baseline CORT were present prior to incubation.

Temporal trade-offs between nestling provisioning and defence against nest predators in blue tits

Offspring provisioning and nest defence are important forms of parental care. In birds, parents that engage in nest defence behaviour have to interrupt nestling provisioning with potentially harmful consequences for offspring growth and condition. To maximize fitness, parents should trade off optimal levels of offspring provisioning versus nest defence, but relatively little is known about how parents allocate their time between these two activities and how parental decisions to postpone provisioning vary as a function of the intensity of nest predation risk. We found that pairs of blue tits, Cyanistes caeruleus, adjusted parental care behaviours according to perceived immediate risk levels by switching from offspring provisioning to nest defence. In the presence of a direct nest predation threat, parents interrupted offspring provisioning for longer than in response to a novel object close to the nest, but still gradually resumed provisioning activity, probably because of a decrease in perceived predation risk over time. By increasing their provisioning effort once the immediate threat had diminished, parents compensated at least partly for the lost provisioning opportunities during high-risk situations. Hence, by adaptively adjusting the temporal trade-off between different parental care behaviours according to the perceived risk, blue tits are presumably able to mitigate potential negative long-term consequences of interruptions in provisioning during high-risk situations for offspring growth and condition.

Dabbling Ducks Increase Nest Defense after Partial Clutch Loss

Abstract. Predation is the primary source of mortality of dabbling duck nests, so a key aspect of parental investment is defending the nest from predators. The hen's presence on the nest is widely considered to be a good measure of nest defense; an incubating female camouflages the nest and may physically deter nest predators. Parental-investment theory suggests that investment should increase with the reproductive benefits expected from the current clutch of eggs. We used nest-temperature loggers to study how the rhythms of waterfowl incubation changed after the nest was partially destroyed by a predator. Contrary to the expected-benefits hypothesis, we found that hens significantly increased their investment after partial clutch loss: they took fewer recesses from incubation per day and extended their incubation by more than 200 min after a partial depredation. We suggest that when predators pose little risk to the incubating adult, those hens unable or unwilling to abandon a nest after partial clutch l...

Chronic stress in infancy fails to affect body size and immune response of adult female blue‐footed boobies or their offspring

Experiments on birds, fish and mammals have shown that adverse conditions during infancy can produce diverse long‐term and delayed deficits during adulthood, prejudicing both the individual and its offspring. Natural selection should prepare animals to cope with adversity of the type, magnitude and timing that commonly occur in their natural habitat, but very little is known about such evolved developmental buffering against natural ‘poor starts’ in life. In two‐chick broods of the blue‐footed booby Sula nebouxii, the junior (younger) chick usually experiences aggressive subordination, reduced nutrition and growth and elevated circulating corticosterone. To test whether this poor start produces long‐term, delayed or intergenerational deficits in body size, body condition or cell‐mediated immune response, we measured 3–8 yr old female breeders banded as chicks, and their infant offspring. Results failed to support our predictions. Compared to former seniors and former singletons (solitary nestlings), former juniors showed no deficit in cell‐mediated immune response at any age. They showed an 8.04% deficit in body condition at age 4–6 yr but this deficit disappeared completely by age 7–8 yr. Furthermore, their offspring showed no deficits in body size, body condition or immune response. Junior chicks are affected by their poor start, but their developmental resilience, also confirmed by studies of post‐fledging survivorship, recruitment, natal dispersal, aggressive nest defense and reproduction, is evidence of evolved developmental buffering against predictable adversity during infancy.

Feathers, suspicions, and infidelities: an experimental study on parental care and certainty of paternity in the blue tit

Theoretical models on parental care predict that males should decrease their parental effort when paternity is in doubt. Males may use some cues to assess their certainty of paternity, and try to avoid rearing offspring sired by extra-pair males. We have previously reported in a socially monogamous passerine, the blue tit (Cyanistes caeruleus), that males decorate their nests with feathers, and that when this ornament is manipulated, males appear to have suspicions about the presence of an intruder male. Here, we decrease the male's certainty of paternity through experimental feather supplementation to analyse whether the outcome of our experiment supports the assumptions of the parental care theory. Male C. caeruleus responded to the feather supplementation experiment by reducing their parental investment (feeding frequency and nest defence) in comparison with control males. The occurrence of extra-pair offspring in experimental nests was double than that in controls. This suggests that the manipulation was successful not only in altering males' perceived paternity, but also, indirectly, the actual paternity. Furthermore, males that gained extra-pair young also had a higher than average probability to lose paternity in their nest, which may imply that male C. caeruleus faced a trade-off between obtaining extra-pair fertilizations and maintaining paternity in their own nest. Overall, this study supports the idea that males are prone to decrease their parental effort when they perceive that the risk of losing paternity is high.