Nest Defense Research Articles

Age and Task Modulate Olfactory Sensitivity in the Florida Carpenter Ant Camponotus floridanus.

Age-related changes in behavior and sensory perception have been observed in a wide variety of animal species. In ants and other eusocial insects, workers often progress through an ordered sequence of olfactory-driven behavioral tasks. Notably, these behaviors are plastic, and workers adapt and rapidly switch tasks in response to changing environmental conditions. In the Florida carpenter ant, smaller minors typically perform most of the work needed to maintain the colony, while the larger majors are specialized for nest defense and rarely engage in these routine tasks. Here, we investigate the effects of age and task group on olfactory responses to a series of odorant blends in minor and major worker castes. Consistent with their respective roles within the colony, we observed significant age-associated shifts in the olfactory responses of minors as they transitioned between behavioral states, whereas the responses of majors remained consistently low regardless of age. Furthermore, we have identified a unitary compound, 3-methylindole, which elicited significantly higher responses and behavioral aversion in minor nurses than in similarly aged foragers suggesting that this compound may play an important role in brood care. Taken together, our results suggest that age- and task-associated shifts in olfactory physiology may play a critical role in the social organization of ant colonies.

Parental care behaviour in response to perceived paternity is not mediated by 11-ketotestosterone in bluegill sunfish

Parental care is critical for the survival of many young animals, but parental care can be costly to the individual providing care. To balance this cost, parents can allocate their care to offspring based on their value, which can be dependent on the offspring’s relatedness to the parent. Bluegill (Lepomis macrochirus) is a fish characterized by uniparental male care and high levels of cuckoldry. While parental males of this species have been shown to adaptively adjust their care in response to paternity, the mechanisms for this adjustment are not well understood. Androgens are steroid hormones that are associated with parental care behaviours in many species including bluegill. Here, we test the hypothesis that circulating androgen concentrations mediate the adjustment in care provided by bluegill parental males by manipulating perceived paternity and then measuring circulating 11-ketotestosterone concentration and parental care behaviour. We show that males with higher perceived paternity provide higher levels of nurturing and nest defense behaviour, but contrary to expectations, we found that these males had lower concentrations of 11-ketotestosterone. Furthermore, we found positive correlations between individual circulating plasma 11-ketotestosterone concentrations and nurturing behaviour, but not with the aggressive behaviours that differed between paternity treatments. While bluegill make behavioural changes in response to perceived paternity, these changes do not appear to be modulated by 11-ketotestosterone.

Seasonal variation in defense behavior in European and scutellata-hybrid honey bees (Apis mellifera) in Southern California

Nest defense in the honey bee (Apis mellifera) is a complex collective behavior modulated by various interacting social, environmental, and genetic factors. Scutellata-hybrid (“Africanized”) honey bees are usually considered to be far more defensive than European honey bees which are therefore preferred for commercial and hobbyist beekeeping. In the most recent zone of scutellata hybridization, the southern USA, the degree to which this defensiveness differs among current strains, and the extent to which defensiveness varies across a season has not been measured. We quantified the levels of A. m. scutellata ancestry in colonies and conducted a seasonal assessment (May through November) of colony nest defensiveness in feral scutellata-hybrid and a popular lineage of European honey bee commonly used in managed environments (sold as A. mellifera ligustica) hives at two apiaries in Southern California. Standard measures of defensiveness were low in both scutellata-hybrid and European colonies during May. Defensiveness increased during the later months of the study in scutellata-hybrid colonies. Most measures of defensiveness did not increase in managed colonies. Defensiveness in the scutellata-hybrids appears lower than what has been previously documented in Brazil and Mexico, possibly due to their lower proportion of A. m. scutellata ancestry.

Evolution of the neuronal substrate for kin recognition in social Hymenoptera.

In evolutionary terms, life is about reproduction. Yet, in some species, individuals forgo their own reproduction to support the reproductive efforts of others. Social insect colonies for example, can contain up to a million workers that actively cooperate in tasks such as foraging, brood care and nest defence, but do not produce offspring. In such societies the division of labour is pronounced, and reproduction is restricted to just one or a few individuals, most notably the queen(s). This extreme eusocial organisation exists in only a few mammals, crustaceans and insects, but strikingly, it evolved independently up to nine times in the order Hymenoptera (including ants, bees and wasps). Transitions from a solitary lifestyle to an organised society can occur through natural selection when helpers obtain a fitness benefit from cooperating with kin, owing to the indirect transmission of genes through siblings. However, this process, called kin selection, is vulnerable to parasitism and opportunistic behaviours from unrelated individuals. An ability to distinguish kin from non-kin, and to respond accordingly, could therefore critically facilitate the evolution of eusociality and the maintenance of non-reproductive workers. The question of how the hymenopteran brain has adapted to support this function is therefore a fundamental issue in evolutionary neuroethology. Early neuroanatomical investigations proposed that social Hymenoptera have expanded integrative brain areas due to selection for increased cognitive capabilities in the context of processing social information. Later studies challenged this assumption and instead pointed to an intimate link between higher social organisation and the existence of developed sensory structures involved in recognition and communication. In particular, chemical signalling of social identity, known to be mediated through cuticular hydrocarbons (CHCs), may have evolved hand in hand with a specialised chemosensory system in Hymenoptera. Here, we compile the current knowledge on this recognition system, from emitted identity signals, to the molecular and neuronal basis of chemical detection, with particular emphasis on its evolutionary history. Finally, we ask whether the evolution of social behaviour in Hymenoptera could have driven the expansion of their complex olfactory system, or whether the early origin and conservation of an olfactory subsystem dedicated to social recognition could explain the abundance of eusocial species in this insect order. Answering this question will require further comparative studies to provide a comprehensive view on lineage-specific adaptations in the olfactory pathway of Hymenoptera.

The role of cognition in nesting.

For many animals, nests are essential for reproductive success. Nesting individuals need to carry out a range of potentially challenging tasks, from selecting an appropriate site and choosing suitable materials to constructing the nest and defending it against competitors, parasites and predators. Given the high fitness stakes involved, and the diverse impacts both the abiotic and social environment can have on nesting success, we might expect cognition to facilitate nesting efforts. This should be especially true under variable environmental conditions, including those changing due to anthropogenic impacts. Here, we review, across a wide range of taxa, evidence linking cognition to nesting behaviours, including selection of nesting sites and materials, nest construction, and nest defence. We also discuss how different cognitive abilities may increase an individual's nesting success. Finally, we highlight how combining experimental and comparative research can uncover the links between cognitive abilities, nesting behaviours and the evolutionary pathways that may have led to the associations between them. In so doing, the review highlights current knowledge gaps and provides suggestions for future research. This article is part of the theme issue 'The evolutionary ecology of nests: a cross-taxon approach'.

Successful nest defence of Eurasian reed warblers Acrocephalus scirpaceus against the little bittern Ixobrychus minutus

The cost–benefit approach to nest defence behaviour is based on an assumption that parents are able to distract potential predators away from their nest. However, this assumption has received little support from direct observations as predator-prey encounters near nests are rarely recorded, especially in small passerines. Here, we describe two observations of little bitterns appearing near nests of Eurasian reed warblers containing nestlings and eggs, respectively. In both cases parental birds showed anti-predatory behaviour, which was much more vigorous at the nestling stage than at the egg stage. During both observations, the heron finally flew away and did not attack the nest content, indicating that nest defence behaviour of small passerines may be effective.

Nest box entrance hole size can influence nest site selection and nest defence behaviour in Japanese tits.

Birds have the ability to assess the risk of predation in their environment and adjust their antipredation strategies based on this risk information. However, whether nest site selection has effect on subsequent nest defence behaviour has not been studied. In this study, we aimed to determine whether the Japanese tit (Parus minor) exhibits a nest-box hole size preference and whether the entrance hole sizes of nest boxes influence the nest defence behaviour of tits. We hung nest boxes with three different entrance hole sizes (diameters: 6.5cm, 4.5cm and 2.8cm) in our study sites and investigated which nest boxes were occupied by tits. In addition, by using dummy-presentation experiments, we observed the nest defence behaviours of tits that nested in boxes with 2.8cm and 4.5cm entrance holes towards common chipmunks (Tamias sibiricus, a small nest predator able to enter these holes) and Eurasian red squirrels (Sciurus vulgaris, a large nest predator unable to enter the 2.8cm entrance hole). The tits that bred in nest boxes with 2.8cm entrance holes exhibited more intense nest defence responses to chipmunks than to squirrels. In contrast, the tits that bred in nest boxes with 4.5cm entrance holes exhibited similar nest defence responses to chipmunks and squirrels. Additionally, Japanese tits that bred in nest boxes with 2.8cm entrance holes exhibited more intense behavioural responses to chipmunks than those that bred in nest boxes with 4.5cm entrance holes. Our results suggested that Japanese tits prefer to occupy nest boxes with small holes for breeding and that nest-box characteristics influenced their nest defence behaviour.

First description of injury feigning behavior in Godlewski's buntings.

Nest defense behavior helps ground-nesting birds improve their breeding success. Among such behaviors, injury feigning behavior (IFB) is one of the better ways to attract predators and protect birds' nests. IFB is generally associated with shorebirds in general and plovers in particular, however, through field observation, it has been found this behavior is also exhibited in bunting species when they facing the risk of predation. We attempt to explore the detailed description of this behavior in buntings and the factors that affect this behavior. Based on video-recordings of the nest defense behavior by the ground-nesting bird Godlewski's bunting (Emberiza godlewskii) against nest invaders, we explored the characteristic of IFB and differences in nest defense behavior during their brooding seasons. The results showed that female buntings had a distinct IFB: the wings of buntings incited within 60°-90° of the body, ran and called rapidly, pretending to be injured and unable to fly. The nest stage had significant and extremely significant effects on IFB and movement distance (MD), respectively. And IFB was more likely to occur in brooding (34.62%) than incubation period (16.42%). This indicates that there are significant differences in the IFB of buntings at different breeding stages.

Chemical aposematism: the potential for non‐host odours in avian defence

Many birds display plumage coloration and patterns that act as visual aposematic and mimetic signals for predators. Avian aposematism can also be communicated via chemical cues, where so‐called non‐host odours (NHO) emitted from the plumage, the uropygial (preen) gland or other chemical sources denote the status of birds as dangerous or unprofitable hosts for ectoparasitic and haematophagous arthropods. Avian NHO are aposematic signals that in natural concentrations repel nuisance arthropods or inhibit their attraction to hosts, as opposed to being generally unpalatable or toxic to predators. Birds that emit NHO preempt encounters with nuisance arthropods and the pathogens they transmit. Nuisance arthropods that respond to NHO avoid birds that exhibit disabling behavioural, anatomical, physiological and/or chemical defences. As with distinctive plumage patterns that evolved as visual warnings to predators, birds are selected to advertise their non‐host status to nuisance arthropods via distinctive semiochemicals. Short‐chain (C6–C10) aldehydes emitted from the plumage of some birds may act as NHO against a variety of nuisance arthropods. In some birds, the size of the uropygial gland (and presumably its secretory output) is negatively correlated with the degree of ectoparasite infestation or the incidence of malarial infection, thus implicating uropygial secretions in defence against dipteran vectors of haemosporidian pathogens. A field experiment demonstrates that volatiles emanating from the uropygial gland of the Eurasian Hoopoe Upupa epops deter some biting flies. Birds' risky habit of plucking hair from live mammals and incorporating the stolen hair tufts into their nests is hypothesized to serve as a mechanism of appropriating NHO from mammalian skin secretions for nest defence against arthropods. Feathers plucked from heterospecifics and shed snake skins that are incorporated into nests also may emit NHO. Behavioural assays measuring the repellence or attraction‐inhibition of arthropods are needed to elucidate avian NHO. Experimental efforts to elucidate the underlying defences that support avian NHO entail challenges that include the enactment of defences that are variously effective against different arthropods, and the emission of chemical signals that are variously ‘understood’, i.e. avoided, by different arthropods.

Geographical variation in nest defense among cinereous tit populations in China.

Behavioral divergence among populations is common across taxonomic groups, still we know very little about anti-predator behaviors. Animal exposure to predation risk is variable in different ecological contexts. In addition, reproduction value of animals in different geographical regions usually varies. In this study, we tested whether cinereous tits Parus cinereus in different populations exhibited nest defense behaviors similar to those of nest or adult predators and whether their nest defense behaviors showed geographical variation. By using field dummy experiments, we observed tits' nest defense behavior in nest predator common chipmunk Tamias sibiricus and red squirrel Sciurus vulgaris, adult predator Eurasian sparrowhawk Accipiter nisus and nonthreatening species Oriental turtle dove Streptopelia orientalis in the ZJ (44° N), DZ (31° N), and DLS (18° N) populations, respectively. The response scores varied significantly across the 4 dummies in ZJ-tits and DLS-tits but did not in DZ-tits. When facing the chipmunk, ZJ-tits showed the highest response score and DZ-tits showed the lowest response score. When facing the squirrel, ZJ-tits showed a higher response score than tits in the other 2 populations. However, tits among the 3 populations responded similarly to a sparrowhawk or dove with slight response behaviors. In addition, response scores to nest predators were positively correlated with brood size across the 3 populations, but no trend was found for sparrowhawks or doves. Our results indicated that the nest defense behaviors of cinereous tits have evolved in response to large-scale geographical variation in ecological contexts and reproduction value.

Importance of cooperation: How host nest defenses effectively prevent brood parasitism from the cuckoos

As the frontline defense against avian brood parasitism, nest defense is important in reducing nest parasitism and increasing host fitness. However, systematic studies on its effectiveness (i.e., on whether it successfully prevents cuckoo parasitism) are scarce. Based on 214 video recordings from 10 years of field observations, we evaluated the effectiveness of nest defenses of the Oriental reed warbler (Acrocephalus orientalis) in deterring common cuckoo (Cuculus canorus) parasitism. Under a breeding pair situation (≤ 2 hosts individuals), warblers were hardly effective in resisting the egg-laying of the cuckoo and many of the cuckoos under attack were able to complete the parasitic process without being harmed. However, when hosts ≥ 3 individuals, the warblers could effectively thwart the cuckoos and cause lethal damage to the cuckoo in partial cases. This indicated that the host group effectively resisted the cuckoo, demonstrating the importance of cooperation among host neighbors in resisting cuckoo parasitism.

Oxytocin antagonist does not disrupt rabbit maternal behavior despite binding to brain oxytocin receptors.

We explored a possible role of oxytocin (OXT) for the onset and maintenance of rabbit maternal behavior by: (a) confirming that a selective oxytocin receptor antagonist (OTA) widely used in rodents selectively binds to OXT receptors (OXTR) in the rabbit brain and (b) determining the effect of daily intracerebroventricular (icv) injections of OTA to primiparous and multiparous does from gestation day 29 to lactation day 3. OTA efficiently displaced the high affinity, selective oxytocin receptor (OXTR) radioligand, 125 I-labeled ornithine vasotocin analog (125 I-OVTA), but was much less effective at displacing the selective V1a vasopressin receptor radioligand, 125 I-labeled linear vasopressin, thus showing high affinity and selectivity of OTA for rabbit OXTR as in rodents. Further, ICV OTA injections did not modify nest-building, latency to enter the nest box, time spent nursing or the amount of milk produced, relative to vehicle-injected does. The percentage of mothers suckling the litter was also similar between both groups, regardless of parity. Together, our results do not support a role of OXT for the initiation or maintenance of rabbit maternal behavior. Future studies are warranted to determine if OXT participates in fine-tuning additional aspects of the maternal ethogram, for example, circadian periodicity of nursing and nest defense.

Colony‐nesting gulls restrict activity levels of a native top carnivore during the breeding season

AbstractAlthough nesting in colonies can offer substantial reproductive benefits for many seabird species, increased visibility to predators remains a significant disadvantage for most colony‐breeders. To counteract this, some seabird species have evolved aggressive nest defense strategies to protect vulnerable eggs and chicks. Here, we used an experimental approach to test whether colony inhabitance by breeding gullsLarusspp. in western Norway impacts visitation rates of a native, mammalian predator, the Eurasian otterLutra lutraduring the breeding season. Camera traps were placed inside of and on the periphery of seabird colonies prior to the breeding season and left to run for one continuous year. Sighting frequency of otters on these cameras was compared to a control region free of gull nesting. We found that otter activity was significantly reduced in the colonies when gulls were incubating and rearing chicks, compared to time periods when gulls were building nests and absent from the colonies. Rhythmic activity patterns did not seem to be significantly impacted by the presence of gulls. This study provides clear evidence that certain colony‐nesting species can have a direct, negative impact on visitation rates of a native carnivore. Seasonal carnivore activity patterns are likely to be highly dependent on differing nesting strategies and level of nest defense by seabirds.

Cooperative nest defense by European Starlings ( Sturnus vulgaris ) during a predatory threat

Cooperative nest defense by European Starlings ( Sturnus vulgaris ) during a predatory threat

Stingless bee (Apidae: Meliponini) foraging and predation at trunk resin sources: Rare observations captured with microcontroller-based camera traps in a lowland dipterocarp forest

An intriguing yet little studied aspect of social insect foraging is the use of resources other than food. We are interested in the collection of plant resins for nest construction and defense by tropical stingless bees. However, direct observations of stingless bee foraging and potential predation activities by natural enemies at resin sources are particularly rare and therefore require a trade-off between observation time and the number of sources observed. We used affordable remote microcontroller-based camera traps to enable for longer durations of continuous and simultaneous monitoring of resin foraging at multiple resin sources in an undisturbed lowland dipterocarp rainforest in Brunei Darussalam (Borneo). Analysis of photos from camera traps shows that stingless bee visitation to resin sources was uncommon at resin wounds in the forest understory (27.3%). Bees visiting wounds displayed a propensity for short and regular resin foraging bouts of up to a few days to particular resin sources. Where there were encounters between stingless bees and natural enemies, i.e., assassin bugs at resin sources, there was a 100% predation success rate (n = 4). Our study suggests that microcontroller-based camera traps complement or may even replace in-person field observations, in particular for observations of organisms or interactions occurring at low abundance. They allow for systemically collected observations which can form the basis for hypothesis-driven research as part of “next-generation natural history”.

Fatal mobbing and attack of the common cuckoo by its warbler hosts.

Nest defense is an effective strategy of hosts against parasites. Typically, hosts will aggressively attack brood parasites that approach or visit their nests, which can prevent the parasites from laying eggs or may even lead to the death of the parasites. Few previous studies have specifically reported such fatal cases involving brood parasites and have attributed the cause of death to either drowning or hypothermia after falling into the water following an attack from hosts. In this study, we recorded the process of multiple host individuals of the Oriental reed warbler (Acrocephalus orientalis) mobbing and attacking a female common cuckoo (Cuculus canorus) in the field. We discovered that the immediate cause of the cuckoo's death was the fatal physical damage resulting from the aggressive defense from the hosts, suggesting that frantic pecking and scratching by the hosts is the most proximate cause of mortality among egg-laying female cuckoos. This finding enhances our essential understanding of the effectiveness of host attacks.

Does fluctuating selection maintain variation in nest defense behavior in Arctic peregrine falcons (Falco peregrinus tundrius)?

Behavioral expression can vary both within‐ (i.e., plasticity) and among‐individuals (i.e., animal personality), and understanding the causes and consequences of variation at each of these levels is a major area of investigation in contemporary behavioral ecology. Here, we studied sources of variation in both plasticity and personality in nest defense behavior in Arctic peregrine falcons (Falco peregrinus tundrius) in two consecutive years. We found that peregrines adjusted their nest defense in response to nesting stage and year, revealing plastic, state‐dependent, adjustment of nest defense. At the same time, nest defense behavior was repeatable in peregrine falcons both within and between years. We tested if fluctuating selection on behavioral types (i.e., individuals average phenotypic expression) and/or assortative mating acted to maintain long‐term among‐individual differences in nest defense behavior. We found that selection on female nest defense differed across years; being positive in 1 year and negative in the other. We also found support for assortative mating in the first year, but disassortative mating in the second. We propose two potential explanations for the observed year‐specific patterns of nonrandom mating: (1) year‐specific plastic adjustment of nest defense and/or (2) changes in the age‐structure of the breeding population. These posthoc explanations are speculative, and require further study. Unfortunately, we could not evaluate this directly with the available data, and future studies are needed with more than 2 years of data on nest‐defense and fitness outcomes, and with a larger number of marked individuals, to properly evaluate these potential explanations.

Location matters: survival of artificial nests is higher in small grassland patches and near the patch edge

Nest survival is an important part of breeding success in grassland ecosystems, and the location of nests can determine vulnerability to different predators. We conducted an experiment with artificial nests to evaluate jointly the predation rate on nests at different spatial scales (landscape, patch and tussock) and the relative abundance of potential nest predators (small mammals and birds) in a temperate grassland area. In November 2014 and 2016, we installed 288 artificial nests in Common Pampas Grass Cortaderia selloana grasslands in the southeastern Pampas region, Argentina. The nests were placed in two 10‐ha plots in a continuous grassland patch (c. 900 ha) within a reserve and in two small grassland patches (1.5 and 1.8 ha) in an agricultural matrix (landscape‐scale), at the patch edge and inside the patches (patch‐scale), and at two heights within the tussock grass (tussock‐scale). In 2016, we also conducted live trapping of small mammals and surveyed birds along strip transects at the sampling sites. Nests located in patches within an agricultural matrix and near the edge had greater relative survival than those set in the reserve and inside the patches, respectively. This might be explained by the lower relative abundance of small mammals that we found outside the reserve. Artificial nest survival values recorded at the landscape‐scale contrasted with those previously observed for natural nests. Our results could be partly explained by differences in nest density between agro‐patches and those within the reserve. Future studies could also evaluate the role of parental nest defence on nest survival.

Nest defense by Mountain Bluebirds (Sialia currucoides) is related to their sex and brood characteristics but not morphological attributes

Within species, bird parents defend their nests with different levels of intensity. Previous studies have examined several hypotheses for this variation by looking at factors such as morphological characteristics of the parents and the characteristics of the brood, but few have controlled for multiple factors simultaneously. Here we examined a broad range of factors that may influence the nest defense behaviour of Mountain Bluebirds ( Sialia currucoides (Bechstein, 1798)), including the adult's morphology (sex, age, plumage colour, body size, and body condition) and characteristics of their brood (size, hatch date, and stage of nestling development). Parental aggression was triggered using a taxidermy mount of an American red squirrel ( Tamiasciurus hudsonicus (Erxleben, 1777)). We found no relationship between nest defense and any morphological characteristic of adults, but the intensity of nest defense was positively correlated with the stage of offspring development, clutch size, and hatch date consistent with parental investment theory. Males also defended nests more strongly than females, consistent with the premise of the renesting hypothesis that males have fewer future opportunities to breed and, therefore, are more invested in the current brood. Our results provide strong support for parental investment theory and renesting as the primary drivers of nest defense intensity in breeding birds.

Correlated expression of phenotypic and extended phenotypic traits across stingless bee species: worker eye morphology, foraging behaviour, and nest entrance architecture

Stingless bees are the most species-rich group of eusocial bees and show great diversity in behaviour, ecology, nest architecture, colony size, and worker morphology. How this variation relates to varying selection pressures and constraints is not well understood. Variation can be caused by selection acting on behavioural or morphological traits, both alone and in correlation across traits. Here we tested whether behavioural and morphological traits important for foraging and defence are linked to nest-entrance architecture, an extended phenotype relevant to both foraging and nest defence. Using 23 species we investigated whether eye size, nest entrance size, landing behaviour and foraging method show cross-species correlations. A phylogenetically-controlled comparative analysis revealed that species with relatively smaller eyes build relatively larger entrances, which in turn are associated with faster landing approaches and fewer landing errors by foragers, both of which could reduce predation risk. Concerning foraging, mass-recruiting species have c. 10-times larger entrance holes than species with a solitary foraging strategy. Larger entrances could help species with mass recruitment to rapidly increase forager traffic or mount a strong defensive response when under attack. Our results show that studying correlations among different traits helps understand phenotypic diversity in species rich groups.