Colonial breeding reduces nest predation in the common gull (Larus canus)

It is often suggested that colonial breeding reduces nest predation for birds with a high defence capacity, but experimental comparison of predation at solitary and colonial nests is seldom feasible within a single species. We here report on such a test in the common gull (Larus canus). The rate of predation on experimental eggs was significantly lower near colonies than near solitary gull nests, and the eggs survived longer at the edge of a colony than farther away. Communal mobbing of nest predators is the likely reason. In both of two years, almost all nests of solitary gulls were destroyed by predators, while most clutches survived in colonies. Nest predation hence selects strongly for colonial breeding in the present population of common gulls.     

Deceptive use of alarm calls by male swallows, Hirundo rustica: a new paternity guard

Male swallows (Hirundo rustica) frequently gave alarm callswhen their fertile mates left the nest vicinity without themale during egg laying. Females engaged in extrapair copulationsduring such absences when they were not guarded intensely bytheir mates. However, males were sometimes able to disrupt extrapaircopulation attempts toward their mates by giving alarm calls,causing all nearby swallows to take flight. I experimentallytested the idea that male swallows gave alarm calls when theircertainty of paternity was at stake. When colonially breedingfemale swallows were temporarily chased away from their nestduring the egglaying period in the absence of their mates, malesnearly always gave alarm calls when they returned to the emptynest. In contrast, colonially breeding males rarely gave alarmcalls when their mates were absent during the prelaying or theincubation periods. Solitarily breeding males rarely gave alarmcalls in the absence of their mates, irrespective of the timein their nesting cycle. However, solitarily breeding males didgive alarm calls when their mates were absent from the nestif a male mount previously had been presented near their nestduring the egg-laying and the prelaying periods, but not duringthe incubation period. Deceptive use of alarm calls (in theabsence of any predators) by male swallows apparently was aneffective paternity guard.     

Presence of Breeding Birds Improves Body Condition for a Crocodilian Nest Protector

Ecological associations where one species enhances habitat for another nearby species (facilitations) shape fundamental community dynamics and can promote niche expansion, thereby influencing how and where species persist and coexist. For the many breeding birds facing high nest-predation pressure, enemy-free space can be gained by nesting near more formidable animals for physical protection. While the benefits to protected species seem well documented, very few studies have explored whether and how protector species are affected by nest protection associations. Long-legged wading birds (Pelecaniformes and Ciconiiformes) actively choose nesting sites above resident American alligators (Alligator mississippiensis), apparently to take advantage of the protection from mammalian nest predators that alligator presence offers. Previous research has shown that wading bird nesting colonies could provide substantial food for alligators in the form of dropped chicks. We compared alligator body condition in similar habitat with and without wading bird nesting colonies present. Alligator morphometric body condition indices were significantly higher in colony than in non-colony locations, an effect that was statistically independent of a range of environmental variables. Since colonially nesting birds and crocodilians co-occur in many tropical and subtropical wetlands, our results highlight a potentially widespread keystone process between two ecologically important species-groups. These findings suggest the interaction is highly beneficial for both groups of actors, and illustrate how selective pressures may have acted to form and reinforce a strongly positive ecological interaction.     

Colony disturbance and solitary nest initiation by workers in the obligately eusocial sweat bee, Halictus ligatus

Sweat bees are one of the most socially polymorphic lineages on the planet. In obligately eusocial species, newly enclosed females may become either queens or workers, depending on the environmental and social circumstances of the nest into which they emerge. In socially polymorphic species, females also have the option of nesting solitarily, founding a nest and raising future reproductives alone, without the help of other adult females. Halictus ligatus is a widespread Nearctic, ground-nesting sweat bee. It has been particularly well studied in Ontario, where detailed studies have described it as obligately eusocial. Here we report evidence that the flexibility of female H. ligatus actually extends to expressing behaviour more typical of socially polymorphic species, those in which some individuals reproduce solitarily. In a population in southern Ontario, black wasps (Astata sp.) emerged from the soil beneath the nesting aggregation and proceeded to excavate their own nesting tunnels, dislocating many H. ligatus nest entrances. Young workers whose natal nests were destroyed by the wasp activity constructed new nests, so under very specific circumstances, it is possible for potential altruists to nest solitarily.     

PARASITE VIRULENCE AND HOST IMMUNE DEFENSE: HOST IMMUNE RESPONSE IS RELATED TO NEST REUSE IN BIRDS

The evolution of parasite virulence has been hypothesized to be related to the mode of parasite transmission; horizontally transmitted parasites can afford to damage their hosts more than vertically transmitted parasites because increased virulence does not reduce the probability of transmission to new hosts. This relationship between mode of transmission and virulence would particularly select for improved immune defense in hosts that are subject to horizontally transmitted parasites. Among avian hosts, hole nesters and colonial nesters frequently reuse nest sites because of nest-site limitation, and this results in an increased frequency of horizontal transmission. Comparison of the size of two organs involved in the immune defense between pairs of bird species being either hole or open nesters, or colonially or solitarily nesting birds, respectively, revealed that the size of the bursa of Fabricius and the spleen were consistently larger in hole nesters than in open nesters, and similarly in colonially breeding bird species than in solitarily breeding species. These results support the hypothesis that mode of parasite transmission affects the evolution of immune defence in hosts.     

Evidence of nest material kleptoparasitism in Worm‐eating Warblers (Helmitheros vermivorum) in east‐central Arkansas,USA

Nest material kleptoparasitism likely evolved in birds to reduce the cost of searching for and collecting material themselves. Although nest material kleptoparasitism has been reported commonly in colonially nesting species, reports for solitary breeding species are infrequent, especially for neotropical migratory species. Here, we report potential and actual nest material kleptoparasitism in the Worm‐eating Warbler (Helmitheros vermivorum). We deployed video camera systems at passerine nests (n = 81) in east‐central Arkansas during summers 2011–2012. In one video, we observed a Worm‐eating Warbler stealing nesting material from a Hooded Warbler (Setophaga citrina) nest. One day later, we later observed a Worm‐eating Warbler landing within 0.5 m of the same warbler nest when the female was incubating, which possibly deterred a second theft of nesting material. In a third video recording, we observed another Worm‐eating Warbler landing within 1 m of an Indigo Bunting (Passerina cyanea) nest. As far as we could determine, neither of these latter two nest visits resulted in nest material kleptoparasitism. Potential benefits of nest material kleptoparasitism include reduced competition for limited nest materials, easy access to suitable material, reduced travel distance, and reduction of nest predation risk; however, costs include risk of attack by host or introducing parasites to one''s nest. Importantly, this behavior could ultimately affect the behavioral and life history evolution of a species. We suggest further work should be conducted to determine the prevalence of nest material kleptoparasitism in Worm‐eating Warblers and other solitary breeding passerines, including efforts to quantify the benefits and costs of this behavior.     

Can redistribution of breeding colonies on a landscape mitigate changing predation danger?

The reproductive success of colonially breeding species depends in part upon a trade‐off between the benefit of a dilution effect against nestling predation within larger colonies and colony conspicuousness. However, there may be no net survivorship benefit of dilution if smaller colonies are sufficiently inconspicuous. This raises the question about how the size distribution of breeding colonies on a landscape might change as the predation danger for nestlings changes. In southwest British Columbia, Canada, bald eagle Haliaeetus leucocephalus populations have increased exponentially at ～5% per year in recent decades and prey upon nestlings of colonial breeding great blue herons Ardea herodias faninni. Motivated by field data on reproductive success in relation to colony size, modeling is used to ask under which circumstances trading off a dilution benefit against colony conspicuousness can improve population reproductive success. That is, which colonial nesting distribution, dispersed and cryptic versus clumped and conspicuous, best mitigates predation danger on nestlings? When predators are territorial, the modeling predicts a dispersed nesting strategy as attack rate increases, but not as predator numbers increase. When predators are non‐territorial, the modeling predicts a dispersed nesting strategy as predator numbers and/or attack rates increase. When predators are both territorial and non‐territorial, colonial nesting within a predator's territory improves reproductive success when attack rates are low. This suggests nesting in association with territorial predators may offer decreased levels of predation when compared with nesting amongst non‐territorial predators. Thus a change in the colony size distribution of colonially breeding species might be anticipated on a landscape experiencing a change in predation danger.     

Protective nesting association between the Barred Warbler Sylvia nisoria and the Red-backed Shrike Lanius collurio: an experiment using artificial and natural nests

The pressure of predators may significantly affects the distribution pattern of nesting birds. Some individuals may reduce the risk of predation by nesting near other species with an aggressive nest defence. In the present study I tested the predator protection hypothesis using experimental (artificial nests) and observational (real nests) approaches on two ecologically similar passerine birds–the Barred Warbler Sylvia nisoria and the Red-backed Shrike Lanius collurio. Studies have been conducted in eastern Poland in two types of habitat: river valley and farmland. The main predators of natural and artificial nests were birds, and to a lesser extent, also mammals. I found wide variation level of predation of both types of nests in different years. Nest survival rate of artificial nests was significantly lower in the farmland than in the river valley and in natural nests I observed reverse pattern. According to the predictions of the predator protection hypothesis the survival rates of the natural and artificial nests were significantly higher in territories of individuals breeding in the protective nesting association. This type of interspecific positive interaction between two associate species can be classified as facultative mutualism.     

Safety first: terrestrial predators drive selection of highly specific nesting sites in colonial‐breeding birds

Nesting is a critical yet hazardous life stage for many birds. For colonial‐breeding birds, the conspicuousness of the colony to predators suggests immense pressure to select optimal colonial nesting sites. But what drives selection of those sites? As with solitary nesting birds, reducing access by predators may be the single most important factor. If so, knowledge of the predators involved and the attributes of different potential colony sites can allow us to predict the features that make a site especially safe. We examined the attributes of trees used by breeding colonies of metallic starlings Aplonis metallica in tropical Australia, and experimentally tested if those attributes prevented nest access by predatory snakes. Our surveys confirmed that tree choice by starling nesting colonies is highly non‐random, with all colonies located in tall trees in rainforest clearings, with no low branches and smooth bark. Experimental tests demonstrated that the climbing ability of predatory snakes depends upon bark rugosity, and that colony access by snakes depends on tree attributes such as bark rugosity and canopy connectivity. Our study confirms that colonial‐nesting starlings select colony sites that provide a safe refuge from predation. Intense predation pressure may have driven the evolution of stringent breeding habitat criteria in many other species of colonial‐breeding birds.     

Are Blackcaps (Sylvia atricapilla) defending their nests also calling for help from their neighbours?

One hypothesized function of conspicuous mobbing of intruders by bird nest owners is to attract neighbouring birds (“calling for help” hypothesis) or third-party predators (“attract the mightier” hypothesis). These may help the nest owners by distracting and/or attacking the mobbed intruder. To date, these hypotheses have been studied solely during the mobbing of predators. Here, for the first time, I have studied mobbing attraction in the context of brood parasitism. I experimentally tested the Blackcap (Sylvia atricapilla), a small passerine with a highly aggressive and conspicuous nest defence behaviour. I elicited the aggressive responses of Blackcaps by presenting stuffed dummies of the brood parasitic Common Cuckoo (Cuculus canorus) and controls near their nests. At 32% of the nests (n = 75), the responses of the Blackcaps to dummies attracted up to 15 birds per trial from 21 passerine species. Most of the attracted birds were heterospecifics and rarely participated in mobbing; thus the “calling for help” hypothesis was not supported. No potential predators of the Cuckoo were attracted despite them living in the study area and despite prolonged mobbing by Blackcaps; thus rejecting the “attract the mightier” hypothesis. I argue that this hypothesis is unlikely to apply to typical avian predators during nest predation acts because these only last for several seconds. The number of attracted birds was a positive function of the owner’s intensity of nest defence as measured by the rates of alarm calling but not visual cues (rates of attacks). Suitable and unsuitable Cuckoo hosts did not differ in their behaviour in the vicinity of defended nests. The observed pattern of the positive correlation between the intensity of nest defence and the number of attracted birds is most likely a proximate by-product of the conspicuous nest defence by Blackcaps (but may well be adaptive for recruiting neighbours themselves). Thus, the mobbing behaviour of the Blackcap is directed towards the brood parasite and not towards other audience predators or potential recruits to the mob.     

Immune Responses of a Native and an Invasive Bird to Buggy Creek Virus (Togaviridae: Alphavirus) and Its Arthropod Vector,the Swallow Bug (Oeciacus vicarius)

Invasive species often display different patterns of parasite burden and virulence compared to their native counterparts. These differences may be the result of variability in host-parasite co-evolutionary relationships, the occurrence of novel host-parasite encounters, or possibly innate differences in physiological responses to infection between invasive and native hosts. Here we examine the adaptive, humoral immune responses of a resistant, native bird and a susceptible, invasive bird to an arbovirus (Buggy Creek virus; Togaviridae: Alphavirus) and its ectoparasitic arthropod vector (the swallow bug; Oeciacus vicarius). Swallow bugs parasitize the native, colonially nesting cliff swallow (Petrochelidon pyrrhonota) and the introduced house sparrow (Passer domesticus) that occupies nests in cliff swallow colonies. We measured levels of BCRV-specific and swallow bug-specific IgY levels before nesting (prior to swallow bug exposure) and after nesting (after swallow bug exposure) in house sparrows and cliff swallows in western Nebraska. Levels of BCRV-specific IgY increased significantly following nesting in the house sparrow but not in the cliff swallow. Additionally, house sparrows displayed consistently higher levels of swallow bug-specific antibodies both before and after nesting compared to cliff swallows. The higher levels of BCRV and swallow bug specific antibodies detected in house sparrows may be reflective of significant differences in both antiviral and anti-ectoparasite immune responses that exist between these two avian species. To our knowledge, this is the first study to compare the macro- and microparasite-specific immune responses of an invasive and a native avian host exposed to the same parasites.     

Diagnosing nest predators and anti-predator response of red wattled lapwing,Vanellus indicus (Boddaert, 1783)

Identification of nest predators and anti-predator behavior of Vanellus indicus (red wattled lapwings) were studied during two constitutive breeding periods (March-August) of 2018 and 2019. The study was performed along the river Ganges, Raebareli (Uttar Pradesh), India. The number of nesting pairs was counted by the line transect method and anti-predator responses were recorded by the focal sampling method. The nesting pairs varied significantly within and between study sites and years. A variety of predators (avian, mammalian and reptilian) were identified while some predators were designated in the unknown category. Sitting tight response was significantly different during the incubation period. The mobbing response, flying away and running away responses were significantly different during the post-incubation period. Circle noisily over the nests and alarm call were not significant between the two reproductive stages. We conclude that red wattled lapwings can differentiate among diverse predator species and adopt various anti-predator responses against them at different stages of their breeding cycle.     

Do avian and mammalian nest predators select for different nest dispersion patterns of Fieldfares Turdus pilaris? A 15-year study

The Fieldfare Turdus pilaris is an open-nesting passerine that breeds either solitarily or in colonies. The nest-spacing pattern of this species in a subalpine homogeneous Birch Betula pubescens forest in central Norway (c. 63°N) was studied during the period 1980–1994. Nest-spacing patterns varied annually, and the number of Fieldfare colonies present (0–6) within a 3.5-km² study area was positively correlated with the annual density of small rodents and the birds' fat index and mean clutch size. After the rodent population crashes, prey switching seems to occur among mustelids. The nest-spacing pattern of Fieldfares in the Birch forest therefore provides indirect support for the alternative prey hypothesis. Since the nest predation rate in Fieldfares is density dependent, and since their use of ejected faeces in communal defence may be detrimental, even lethal, to avian but not mammalian predators, it is suggested that a high density of mustelids results in selection for solitary breeding, whilst a predominance of avian predation risk selects for colonial breeding by the Fieldfare. The physical condition (fat index) of the Fieldfares is apparently a contributing factor in determining their nest dispersion pattern. The proportion of colonial nesting pairs was negatively correlated with the Fieldfare density and indicated a distributional pattern in a patchy habitat in agreement with the ideal free distribution theory.     

Nest survival is influenced by parental behaviour and heterospecifics in a mixed‐species colony

Studies of avian nest success often focus on examining influences of variation in environmental and seasonal factors. However, in‐depth evaluations can also incorporate variation in individual incubation behaviour to further advance our understanding of avian reproductive ecology. We examined these relationships in colonially nesting Black‐crowned Night‐Herons Nycticorax nycticorax using intensive video‐monitoring methods to quantify incubation behaviours. We modelled nest survival as a function of both extrinsic factors and incubation behaviours over a 3‐year period (2010–12) on Alcatraz Island, USA. Model‐averaged parameter estimates indicated that nest survival increased as a function of greater incubation constancy (% of time spent incubating eggs within a 24‐h period), and average daily precipitation throughout the nesting stage. Common Ravens Corvus corax are the only known nest predator of Night‐Herons on Alcatraz Island, as on many other coastal Pacific islands. We also investigated the effects of heterospecific nesting of California Gulls Larus californicus and Western Gulls Larus occidentalis in a mixed‐species colony with Night‐Herons, based on nesting proximity data collected over a 2‐year period (2011–12). This second analysis indicated that, in addition to incubation behaviours, nesting heterospecifics are an important factor for explaining variation in Night‐Heron nest survival. However, contrary to our original expectation, we found that Night‐Herons experienced increased nest survival with increasing distance from gull colony boundaries. These results may apply to other areas with multiple colonial nesting species and similar predator communities and climatic patterns.     

Female choice and male competition in longear sunfish

Mating systems with spatial clumping of nests or display sitestheoretically can result from female preference for clumpedmales or from competitive interactions among males. We testedpredictions derived from these two types of models against observationsof nest dispersion, mating success, and alternative male matingtactics in a naturally occurring population of central longearsunfish (Lepomis megalotis megalotis). The data were consistentwith models for male-initiated spatial clumping of nest sites;no evidence of female preference for clumped nests was found.We observed that large males had greater mating success thansmall males and that solitarily nesting males were larger thancolonial males; the most successful males were solitary nesters.Mating success of large males did not increase with colony size.Furthermore, colonial males were often cuckolded by neighbors,whereas solitary males were not cuckolded. We propose that colonialnesting is maintained in longear sunfish because group nestingallows subordinate males to obtain access to females.     

Birds respond similarly to taxidermic models and live cuckoos <Emphasis Type="Italic">Cuculus canorus</Emphasis>

Stuffed birds are widely used in research for identifying effects of predators and nest parasites on bird behaviour, studying levels of aggression and the size of territories. However, the fact that these models do not move or vocalize may question the results of such studies and open them to criticism. One solution would be to determine how the results of research using stuffed dummies correlate with the response of wild animals to enemies under the same environmental conditions. In a first attempt, we examined the correlation between the intensity of mobbing of a dummy cuckoo Cuculus canorus and interactions with live cuckoos in the field during the breeding season in western Poland. A total of 39 bird species mobbed cuckoo dummies; all 39 were found to attack live cuckoos, while 24 species (61.5%) did so during experiments using a dummy. The number of individual birds involved in mobbing a dummy was positively correlated with the number of individuals attacking real cuckoos in the same areas, even when the most commonly mobbing species, the barn swallow Hirundo rustica, was excluded from the analyses. However, we did not find significant differences in frequency of mobbing behaviour depending on cuckoo behaviour described as flight or sitting, or calling rather than remaining quiet. Therefore, we conclude that the use of a dummy for studying mobbing of hosts and non-hosts of the cuckoo provide results that are similar to those made in response to the behaviour of live hosts.     

The nest defence by the red‐backed shrike Lanius collurio – support for the vulnerability hypothesis

The majority of altricial bird species defend their brood against predators more intensively in nestlings rather than eggs stage. Several hypotheses have been proposed to explain this difference. The majority of existing experimental studies have recorded a gradually increasing intensity of nest defence supporting the reproductive value hypothesis. We have compared nest defence in two nesting stages of the red‐backed shrike against two predators of adult birds and against two predators of nests. While the nests with nestlings were defended by parents against three out of four predators, nests with eggs were almost not defended at all. This rapid change in parent nest defence supports rather the vulnerability hypothesis, predicting that the threat to nests with nestlings increases rapidly after hatching, as they became more conspicuous due to their begging and parental provisioning. Unlike most of the species tested previously, the red‐backed shrike uses very vigorous mobbing towards predators. We suggest that the occurrence of this active mobbing (strikes, including physical contact) is a good proxy of the current threat to the nest.     

Biology of <Emphasis Type="Italic">Lasioglossum</Emphasis> (<Emphasis Type="Italic">L.</Emphasis>) <Emphasis Type="Italic">majus</Emphasis> (Hymenoptera: Halictidae), a largely solitary sweat bee with behavioural adaptations to communality

Within the bee family Halictidae there have been three origins of sociality. Although detection of origins and reversal from sociality requires phylogenetic studies, at a behavioural level a predisposition to sociality can be detected by analysis of intra-specific interactions. We studied aspects of nesting biology and behavioural interactions in Lasioglossum (Lasioglossum) majus, a poorly known halictine inhabiting temperate regions of Europe, which is suspected to be solitary. Nests were found to be largely used by one female, but some were shared by more than one individual. These few nests, whose entrances were very close to each other, were found to be connected underground. A few individuals were observed to enter in a nest where a female was waiting, behaving as a guard and allowing the incoming bee to enter the nest. By use of circle-tube experiments, the behavioural repertoire exhibited by females during encounters was assessed. Levels of withdrawal and cooperative events were comparable with those observed in other solitary nesting species, but aggressive events were very rare, as in several observed communal species. We conclude that L. (L.) majus females, despite general solitary nesting, possess behavioural components enabling them to adopt, probably in high nest-density areas, nest-sharing strategies. A similar kind of local social polymorphism has been observed in two other species of the subgenus Lasioglossum, but these are the first data available on a European species and the first record of subterranean connections among nests of halictid bees.     

Power lines,roads, and avian nest survival: effects on predator identity and predation intensity

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Birds, bugs and blood: avian parasitism and conservation

Parasitism has far-reaching implications not only for the ecology and evolution of species but also for conservation. The effects of blood-feeding ectoparasites on colonially nesting bird species have been wodely studied, but recent surprising reports show that solitarily nesting species are also commonly attacked, mainly by the larvae of flies. Most bird species are solitary nesters; as their habitats are increasingly fragmented, how will the potential for such parasitism be affected? One example is that of the endangered Puerto Rican parrot (Amazona vittata), in which habitat changes have introduced a deadly parasitic fly species in a complex and unpredicted manner. As theories on habitat fragmentation outpace the data, we need to carry out more field studies of the interactions between fragmentation and parasitism, and to include parasitism in species survival and recovery plans.