Availability Of Host Nests Research Articles

Great spotted cuckoos show dynamic patterns of host selection during the breeding season. The importance of laying stage and parasitism status of magpie nests

AbstractAvian brood parasites depend entirely on their hosts to raise their nestlings until independence. Thus, parasite females should select suitable host nests for egg laying according to traits that enhance offspring survival. The availability of nests of certain characteristics influencing the survival of parasitic offspring is, however, temporally dynamic and, thus, patterns of host selection should be evaluated considering characteristics of available host nests the day of parasitism. This allows detecting possible seasonal changes and, therefore, a more realistic picture of host selection by brood parasites. In this paper, we adopt such a new approach and consider daily availability of magpie (Pica pica) host nests at different breeding stage that were or were not parasitized by the great spotted cuckoo (Clamator glandarius). Theory predicts that cuckoos should select host nests at the laying stage. Accordingly, we detected that cuckoos preferred to parasitize magpie nests at the laying stage but, mainly, those that already harbored one or two cuckoo eggs, which may seem counterintuitive. We also showed that patterns of host selection by cuckoos varied during the breeding season, which implies that brood parasite–host interaction is dynamic depending on phenology. These patterns are hidden when not considering the temporally dynamic nature of the availability of host nests of characteristics of interest. We discuss the importance of such patterns and considering diary hosts nests availability for detecting them.

Egg-spot matching in common cuckoo parasitism of the oriental reed warbler: effects of host nest availability and egg rejection

The success of cuckoo parasitism is thought to depend largely on the extent of egg matching between cuckoo and host eggs, since poor-matching cuckoo egg would lead to more frequent egg rejection by the host. In this study, we investigated how egg-spot matching between the Common Cuckoo (Cuculus canorus) and its host, the Oriental Reed Warbler (Acrocephalus orientalis) is affected by the local parasitism rate, nest availability in breeding synchronization and egg rejection. We used the paired design of parasitized and their nearest non-parasitized nests where breeding occurred simultaneously to compare egg-spot matching. The image analysis was used to compare four eggshell pattern variables, namely spot size, density, coverage on the different areas of egg surface, and the distribution on the whole egg surface. Egg recognition experiments were conducted to test the effect of egg spots on egg rejection by the host. Our results show that much better matching in almost all spot parameters tested on the side of the egg and the spot distribution on the whole egg occurred in parasitized nests than in non-parasitized nests. Matching of spot density between cuckoo and host eggs in parasitized nests increased with the synchronization between temporal availability of nests and the egg-laying period of female cuckoos. Egg recognition experiments in which the warbler eggs were deliberately painted with extra spots led to a significantly higher egg rejection rate (78.3%) than of unpainted eggs. Our data suggest that both the high temporal encounter rate between cuckoo and warbler nests as well as the high egg rejection ability of the host are important factors for egg-spot matching of the cuckoos.

Criteria for host selection in a brood parasite vary depending on parasitism rate

Avian brood parasites leave parental care of their offspring to unrelated foster parents; therefore, their fitness will closely relate to their efficiency in selecting the best host. Empirical studies have shown that parasitism is not random, although it is yet unclear if this results from strategic choices of better quality hosts by brood parasites or can be a consequence of hosts and/or nests characteristics that make them more exposed to parasitism. Here, we hypothesize that the optimal strategy of host use for a brood parasite may switch depending on fluctuations in the relative abundance of parasites with respect to hosts and predict that parasites should more likely select phenotypic traits indicating host quality when this is relatively low (i.e., many available host nests for each parasite at a given time). In an 8-year study of magpie Pica pica hosts parasitized by great spotted cuckoos Clamator glandarius, we have found that in years with lower than average parasitism bigger magpie nests were more likely parasitized than smaller ones, whereas in years with higher than average parasitism big and small magpie nests had a similar chance of being parasitized. Because nest size is a postmating sexually selected signal revealing parental abilities in magpies that can be used as a target to choose profitable hosts by cuckoos, our findings support the hypothesis that active selection will become a more prevalent great spotted cuckoo laying strategy when cuckoos have a larger availability of host nests to choose among.

Nest predation risk, but not demography, drives dynamics of conspecific brood parasitism

Conspecific brood parasitism (CBP) is an alternative reproductive tactic in several animal taxa. Although various behavioral aspects related to CBP have been studied in several species, understanding spatial and temporal dynamics of CBP and its drivers is still limited. We studied roles of nest predation risk and demography as possible drivers of dynamics of CBP in common goldeneyes (Bucephala clangula), a cavity-nesting duck. We provided decoy nests for parasitic laying in an experimental setting of 15 lakes for 7 consecutive years irrespective of local nest predation, being thus able to control for effects of predation-determined host nest availability. Individual parasites were recognized using protein fingerprints from egg albumen of parasitic eggs laid in the decoy nests. We found considerable spatial and temporal variation in the frequency of CBP within the experimental setting. Variation in CBP was driven by nest predation risk: the rate of CBP tracked the number of nonpredated nesting attempts at the lakes during the previous year. Neither variation in lake-specific number of potential homing first-time breeding females (i.e., demography) nor variation in lake-specific number of nesting females present explained the variation in lake-specific frequency of CBP. Our findings provide evidence that parasitically laying females pursue a genuine and flexible safety-seeking tactic in nest selection and that nest predation risk drives spatial and temporal dynamics of CBP.

Nest relocation in the slavemaking ants Formica subintegra and Formica pergandei: a response to host nest availability that increases raiding success

Social insects typically occupy spatially fixed nests which may thus constrain their mobility. Nevertheless, colony movements are a frequent component of the life cycle of many social insects, particularly ants. Nest relocation in ants may be driven by a variety of factors, including nest deterioration, seasonality, disturbances, changes in microclimate, and local depletion of resources. The colony movements of slavemaking ants have been noted anecdotally, and in recent studies such relocations were primarily attributed to nest deterioration or shifts to overwintering locations. In this study we explore nest relocations in large colonies of formicine slavemakers which occupy stable and persistent earthen nest mounds. We investigate the hypothesis that colony relocations of these slavemakers are best explained by efforts to improve raiding success by seeking areas of higher host availability. Five summers of monitoring the raiding behavior of 11–14 colonies of the slavemakers Formica subintegra and Formica pergandei revealed relatively frequent nest relocations: of 14 colonies that have been tracked for at least three of 5 years, all but one moved at least once by invading existing host nests. Movements tended to occur in the middle of the raiding season and were typically followed by continued raiding of nearby host colonies. Spatial patterns of movements suggest that their purpose is to gain access to more host colonies to raid: the distance moved is typically farther than the mean raiding distance before the move, which may indicate an effort to escape their local neighborhood. Furthermore, the mean distance of raids after relocation is shorter than the distance before relocation. For many slavemaking ant colonies, particularly those on the verge of relocating, raiding distance increased as the raiding season progressed. In addition, movements tended to be toward areas of higher local host density. Nest relocation is likely an important component of the ecology of slavemaking ants that contributes to the dynamic nature of their interaction with the host ant population.

Common Cuckoos Cuculus canorus change their nest‐searching strategy according to the number of available host nests

In recent decades, numerous studies have examined factors affecting risk of host nest parasitism in well‐known avian host–parasite systems; however, little attention has been paid to the role of host nest availability. In accordance with other studies, we found that nest visibility, reed density and timing of breeding predicted brood parasitism of Great Reed Warblers Acrocephalus arundinaceus by the Common Cuckoo Cuculus canorus. More interestingly, hosts had a greater chance of escaping brood parasitism if nesting was synchronized. Cuckoo nest searching was governed primarily by nest visibility at high host‐nest density. However, even well‐concealed nests were likely to be parasitized during periods when just a few hosts were laying eggs, suggesting that Cuckoos adjust their nest‐searching strategy in relation to the availability of host nests. Our results demonstrate that host vulnerability to brood parasitism varies temporally and that Cuckoo females are able to optimize their nest‐searching strategy. Moreover, our study indicated that Cuckoos always manage to find at least some nests to parasitize. Thus, in this case, the co‐evolutionary arms race should take place mainly in the form of parasitic egg rejection rather than via frontline pre‐parasitism defence.

Australian cuckoos and their adaptations for brood parasitism

The strategies used by parasitic cuckoos to fool their hosts have intrigued naturalists and ornithologists for centuries. Here I review some of the tricks used by Australian parasitic cuckoos to increase host nest availability, access host nests, and fool their hosts into accepting their eggs and chicks. Some of these strategies are widely used by cuckoo species around the world, but other traits, such as cryptic eggs and mimetic chicks, appear to be largely restricted to the Australasian cuckoos. Generalist cuckoos face greater challenges than specialists if they must fool multiple host species, and this provides a possible explanation for why different species of cuckoos have evolved different strate- gies for host deception.

High levels of relatedness between Brown-headed Cowbird (Molothrus ater) nestmates in a heavily parasitized host community

Multiple parasitism of host nests by generalist brood parasites reflects the decisions of laying females and may influence the development and behavior of parasitic young. We used microsatellite and mtDNA control-region haplotype data to examine the relatedness of Brown-headed Cowbird (Molothrus ater) offspring in multiply parasitized nests sampled from a heavily parasitized host community in northeastern Kansas. We also examined how host nest availability influenced the degree of multiple parasitism, and used community-wide parasitism data to explore whether female cowbirds were constrained in their laying decisions. Relatedness estimates for all suitable pairwise comparisons (n = 94 from 41 multiply parasitized nests) found that the mean likelihood than an individual cowbird in a multiply parasitized nest shared its nest with a full sibling was 40.4% (95% confidence interval: 28.4–52.4%), indicating that many cowbird offspring were reared with full siblings. Extensive community-wide parasitism data revealed that most cowbird offspring shared the nest with ≥1 other conspecific. Additionally, we found that the proportion of available host nests increased steeply at the start of the breeding season and remained high for most of the breeding season, but that the degree of multiple parasitism was unrelated to the number of new nests. We found evidence that laying decisions of female cowbirds were constrained, which suggests that heavy parasitism levels were due to a high degree of competition for host nests. This intense competition for host nests, in turn, results in cowbird offspring often competing with conspecifics in our population, including full siblings, for host parental care.

EGG-LAYING BEHAVIOR IN SCREAMING COWBIRDS: WHY DOES A SPECIALIST BROOD PARASITE WASTE SO MANY EGGS?

Abstract Obligate brood parasites should synchronize parasitism with host laying to maximize egg hatchability and chick survival. While the generalist Shiny (Molothrus bonariensis), Brown-headed (M. ater), and Bronzed (M. aeneus) Cowbirds frequently synchronize parasitism with host laying, specialist Screaming Cowbirds (M. rufoaxillaris) very often fail to do so in nests of their main host, the Bay-winged Cowbird (Agelaioides badius). The poor synchronization of Screaming Cowbird parasitism may be the result of low availability of host nests at the time of laying, higher nest attentiveness by the host during laying, or unpredictable host laying behavior. We used a large set of observational data to test these hypotheses. The rate of Screaming Cowbird parasitism occurring during host prelaying was 31%, while during laying and incubation, it was 50% and 19%, respectively. Synchronization of parasitism was not associated with availability of host nests at laying or with changes in host nest attentiveness thr...

Vocal behaviour of the Common Koel, Eudynamys scolopacea, and implications for mating systems

The Common Koel, Eudynamys scolopacea, is a migratory cuckoo that occurs along the eastern coast of Australia. Its most conspicuous feature is the loud and persistent calling of males heard throughout the breeding season. Although the commonest vocalisation of the Koel, the Cooee call, is well known, other vocalisations have not been described in detail. Here we report on six vocalisations produced by adult birds, including duetting. The rate of calling of male Koels was investigated on two different scales: monthly over the breeding season, and hourly during the day and night. Calling peaked both in the early and late months of the breeding season, possibly associated with the availability of host nests. During the day, calling rates were significantly higher at dawn and dusk than at all other times of the day. Data collected on trees inhabited by Koels showed that calling males favoured trees with a particularly wide canopy and dense foliage; most often, these were species of Ficus. We speculate that the Koel shares with other cuckoos a basic breeding pattern based on male dominance interactions that lead to polygyny but that the discovery of duetting strongly suggests the possibility of short-term pair-bonding within this mating system.

Female spacing patterns in brown-headed cowbirds

Breeding female cowbirds at the Queen's University Biological Station are often aggressive when encountering other females within their ranges, but they do not defend exclusive territories. The likelihood of aggression appears to be a function of two factors. First, females are more aggressive near the centres of their ranges than around its periphery, suggesting a gradient of aggression based on location within the female's range. Second, females are most aggressive in woodland and swampy areas and least aggressive in grassy areas and at artificial feeding stations. We suggest this is related to the availability of host nests.