Brood Parasitism Research Articles

Physiological stress responses to nonmimetic model brood parasite eggs: Leukocyte profiles and heat-shock protein Hsp70 levels.

Obligate avian brood parasites lay their eggs in the nest of other bird species, known as hosts. Brood parasitism often imposes severe fitness costs on hosts, selecting for the evolution of effective antiparasitic defences, such as recognition and rejection of brood parasite eggs. Glucocorticoids have been recently found to mediate host physiological and behavioral adjustments in response to brood parasite eggs; however, it remains unclear whether brood parasitism triggers a general response involving multiple physiological elements. In this study, we experimentally investigated whether a salient brood parasitic stimulus (the presence of a nonmimetic model egg in the nest) causes physiological adjustments in adult Eurasian blackbirds (Turdus merula) at immune (leukocyte profiles) and cellular (heat-shock protein Hsp70 synthesis) level. Also, we explored whether these physiological changes are mediated by variations in corticosterone (CORT) levels. We found that experimental brood parasitism caused an increase in heterophils and a decrease in lymphocytes, leading to higher heterophils and lymphocytes ratios in parasitized birds. Nevertheless, we did not find tradeoffs between immune function and CORT levels. Hsp70 synthesis was not affected by our experimental manipulation. Our findings provide evidence that brood parasite eggs trigger a general stress response in egg-rejecter hosts, including changes in cellular immune profiles.

The Impact of Different Biotopes and Management Practices on the Burden of Parasites in Artificial Nests of Osmia spp. (Megachilidae) Bees

The decline in pollinator insect abundance and diversity is increasing on a global scale. Major threats are the byproducts of numerous negative environmental pressures acting individually or in combination. They vary throughout different geographical areas, affecting the solitary bees differently. One of the most important negative pressures are the many parasites, predators and pests representing a threat to the successful reproduction of solitary bees in artificial nests. Especially vulnerable are the managed Osmia spp. bee populations reared for commercialization and trade. The primary goals of our monitoring study were: (i) to examine the presence and the prevalence of brood parasites in the various types of bees’ nesting material and in semi-field rearing conditions using the nest section analyses; (ii) to determine the presence of Nosema spp. in samples of feces and homogenized bee abdomens using a multiplex PCR method; (iii) the evaluation of the survival success level and emergence mass of healthy bees at each of the four studied bee rearing locations separately, depending on different environments and on the implementation of different managing practices. We determined the presence and prevalence of nest destructor parasites and accompanying fauna. Their presence was positively correlated with bee rearing failures. The results of this study may be used as a baseline for further solitary bee nest parasites monitoring schemes.

Asymmetric sibling rivalry extends to hosts and brood parasites

Asymmetric sibling rivalry extends to hosts and brood parasites

Understanding hippocampal neural plasticity in captivity: Unique contributions of spatial specialists.

Neural plasticity in the hippocampus has been studied in a wide variety of model systems, including in avian species where the hippocampus underlies specialized spatial behaviours. Examples of such behaviours include navigating to a home roost over long distances by homing pigeons or returning to a potential nest site for egg deposit by brood parasites. The best studied example, however, is food storing in parids and the interaction between this behaviour and changes in hippocampus volume and neurogenesis. However, understanding the interaction between brain and behaviour necessitates research that includes studies with at least some form of captivity, which may itself affect hippocampal plasticity. Captivity might particularly affect spatial specialists where free-ranging movement on a large scale is especially important in daily, and seasonal, behaviours. This review examines how captivity might affect hippocampal plasticity in avian spatial specialists and specifically food-storing parids, and also considers how the effects of captivity may be mitigated by researchers studying hippocampal plasticity when the goal is understanding the relationship between behaviour and hippocampal change.

The Supercooling Responses of the Solitary Bee Osmia excavata (Hymenoptera: Megachilidae) under the Biological Stress of Its Brood Parasite, Sapyga coma (Hymenoptera: Sapygidae).

Simple SummaryInsects have different strategies to adapt to environment change and parasites, but the supercooling response of pollinator populations under the biological stress has not been sufficiently investigated. This study assessed the supercooling traits of the solitary bee and its brood parasite. We discovered significant differences in the supercooling points were found between the solitary bee and its brood parasite in the same sex, and also between sexes of same species. The supercooling traits (supercooling points, fresh weight, and fat content) of the two species were significantly positively correlated. Our results suggest that the supercooling points of the solitary bee increase under the biological stress of its brood parasite at a certain level. Overall, the supercooling of pollinator populations varies regularly under brood parasitism pressure.(1) Background: Many insects have evolved different strategies to adapt to subzero temperatures and parasites, but the supercooling response of pollinator populations under the brood parasitism pressure has not been sufficiently investigated. (2) Methods: This study assessed the supercooling traits (supercooling points, fresh weight and fat content) of the solitary bee Osmia excavata Alfken and its brood parasite, Sapyga coma Yasumatsu & Sugihara. We measured 4035 samples (3025 O. excavata and 1010 S. coma, one individual as one sample) and discovered the supercooling traits relations between solitary bee and brood parasite. (3) Results: Significant differences in the supercooling points were found between O. excavata (females: −24.18 (−26.02~−20.07) vs. males: −23.21 (−25.15~−18.65) °C) and S. coma (females: −22.19 (−25.46~−18.38) vs. males: −20.65 (−23.85~−16.15) °C, p < 0.0001) in the same sex, and also between sexes of same species. The two species’ supercooling traits (supercooling points, fresh weight, and fat content) were significantly positively correlated. The supercooling points of the solitary bee varies regularly under brood parasitism pressure. (4) Conclusions: Our study indicates the supercooling traits relationships between a solitary bee and its brood parasite and suggests that the supercooling points of the solitary bee increase under the biological stress of its brood parasite in a certain level.

Clutch Abandoning Parasitised Yellow Warblers Have Increased Circulating Corticosterone With No Effect of Past Corticosterone or Differences in Egg Maculation Characteristics

Parental care can be costly to parents’ fitness. As such, abandonment of the current reproductive attempt may benefit potential future opportunities, maximising lifetime reproductive success. Obligate brood parasitism, a reproductive strategy in which parasites lay their eggs in the nests of other species and rely solely on them to raise the parasitic young, is an ideal system to study brood abandonment. Some parasitised host species have evolved anti-parasitic defences, notably clutch abandonment (egg burial and nest desertion), that may mitigate negative consequences of parasitism. Abandonment of clutches due to parasitism is not unlike abandonment of reproduction in times of stress, suggesting that host responses to parasitism could be triggered at least partly by elevated stress hormones that mediate individual decisions. Yet, the mechanistic basis for clutch abandonment remains unclear. Here, we experimentally parasitised clutches of yellow warblers (Setophaga petechia), a common host of the brown-headed cowbird (Molothrus ater), with model cowbird eggs to examine whether host circulating corticosterone (CORT) differed among females that accepted parasitic eggs or rejected them through clutch abandonment. We also assessed whether feather CORT, a measure of past corticosterone exposure, differed between accepters and abandoners. Finally, we investigated whether egg visual signals, specifically differences in maculation characteristics between model cowbird and host eggs, predicted abandonment of experimentally parasitised clutches. Circulating CORT was higher in females who abandoned their parasitised clutches, but not in those who accepted, relative to controls with no egg addition. Past stress and differences in maculation characteristics did not predict whether individuals accepted or abandoned experimentally parasitised clutches. Moreover, differences in maculation characteristics between the host and model cowbird eggs did not predict CORT levels or nest abandonment. Thus, parasitism with subsequent clutch abandonment may be associated with elevated circulating CORT, but neither past stress nor differences in maculation characteristics influenced abandonment. The combination of these results contributes to our understanding of the roles of corticosterone and egg visual signals in the context of clutch abandonment in brood parasitism specifically, and of parental care more broadly.

Rejection of Conspecific Eggs Associated with the Appearance of Eggs, in the Azure-Winged Magpie Cyanopica cyanus in Korea

Avian brood parasitism is a reproductive strategy in which a parasitic species lays its eggs in the nests of a host. In response to parasitism, hosts have evolved various defence strategies. One of the host defences against intraspecific and interspecific brood parasitism is to distinguish parasitic eggs based on intraclutch variation in egg appearance. Hosts can improve their ability to discriminate parasitic eggs by lowering the degree of their intraclutch variation in egg appearance. Therefore, intraclutch variation may affect the egg rejection behaviour of hosts. In this study, we conducted experiments to study egg recognition and rejection behavior for mimetic eggs in Azure-winged Magpies Cyanopica cyanus in Korea. We also investigated the level of variation in egg appearance (egg color, spottiness and volume) in order to explore whether the degree of this variation is associated with the rejection decision. We found that there were no differences in egg coloration or spottiness between the rejecter and accepter. However, we found that intraclutch egg volume variation in rejecters was significantly lower than that in accepters, indicating that the Azure-winged Magpie is likely to recognize its own eggs by lowering its intraclutch variation in egg volume as a defensive strategy against brood parasitism. This study suggests that the Azure-winged Magpie use not the differences in egg coloration but egg volume to discriminate and reject closely mimetic conspecific eggs.

Do Attributes of Gray Vireo Nest Sites Influence Brown-headed Cowbird Brood Parasitism?

Brood parasitism can have major detrimental effects on the fitness of reproducing songbirds and often contributes to nest failure. As the Gray Vireo (Vireo vicinior) suffers high rates of brood parasitism by the Brown-headed Cowbird (Molothrus ater), we hypothesized that vireos might choose nest sites selectively to thwart cowbird parasitism. To investigate this question, we measured and compared vegetative and spatial attributes of nest sites in a known breeding population of the Gray Vireo on the Sevilleta National Wildlife Refuge, New Mexico, in 2017 and 2018. Specifically, we compared parasitized and unparasitized nests with respect to the nest’s height and the average height, diameter, and foliage density of the nest tree. We also compared the spatial attributes of the nearest neighboring nest, nearest parasitized nest, and the density of surrounding juniper trees within 50 m of a nest. Interestingly, among none of the variables measured did we find an association with the incidence of brood parasitism, suggesting that nest parasitism might be more strongly linked to other larger-scale ecological or behavioral variables.

Nest predation, brood parasitism and the reproductive success of the masked laughingthrush Garrulax perspicillatus in the rural habitat of central China

Knowledge of nest site selection and reproductive ecology is fundamental to understanding the evolution of life history traits and developing species conservation strategies. However, life history traits of species in the genus Garrulax are poorly known. Particularly, research on the breeding biology of Garrulax perspicillatus in their natural habitat and comparison between populations in different environments (rural vs urban) are lacking. We presented data of nest site selection and breeding ecology of Masked Laughingthrush in central China during 2021, and made a detailed investigation on nest predation and interspecific brood parasitism. The breeding season began from March and ended in August. Most nests were built on Sulphur Bamboo ( Phyllostachys sulphurea). First egg laying occurred between late March and late July. Incubation period lasted 13.9 days (±0.3 SE; 13–15) and nestling period of 13.1 days (±0.2 SE; 12–15). Average clutch size was 3.8 eggs (±0.1 SE; 3–7), and brood size at fledging was 2.7 young (±0.2 SE; 1–4). Overall, 36.2% of nesting attempts successfully fledged at least one young. Nest predation (0% in March, 38.2% in April, 30.0% in May, 20.0% in June and 27.3% in July) and interspecific brood parasitism (13.3% in May, 40.0% in June and 36.4% in July) were two main reasons for nest failure. This is the first study that provided detailed information of breeding ecology of Masked Laughingthrush in rural habitat, and we discussed the difference of life history traits between urban and rural habitats.

Announcing the 2021 Journal of Experimental Biology Outstanding Paper Prize shortlist and winner.

Announcing the 2021 Journal of Experimental Biology Outstanding Paper Prize shortlist and winner.

Predation, parasitism, and drought counteract the benefits of patch-burn grazing for the reproductive success of grassland songbirds

Abstract Intensification of livestock production has reduced heterogeneity in vegetative structure in managed grasslands, which has been linked to widespread declines in grassland songbird populations throughout North America. Patch-burn grazing management aims to restore some of that heterogeneity in vegetative structure by burning discrete pasture sections, so that cattle preferentially graze in recently burned areas. Although patch-burn grazing can increase reproductive success of grassland songbirds, we know little about possible interactions with regional variation in predator communities or brood parasite abundance, or annual variation in weather conditions. Using six years of data from two tallgrass prairie sites in eastern Kansas, USA, we tested effects of patch-burn grazing on the rates of brood parasitism, clutch size, nest survival, and fledging success of three common grassland songbirds, Dickcissels (Spiza americana), Eastern Meadowlarks (Sturnella magna), and Grasshopper Sparrows (Ammodramus savannarum), among pastures managed with patch-burn grazing versus pastures that were annually burned and either grazed or ungrazed. Dickcissel nests experienced lower parasitism (72.8 ± 4.6% SE vs. 89.1 ± 2.2%) and Eastern Meadowlarks had higher nest survival (63.2 ± 20.5% vs. 16.5 ± 3.5%) in annually burned and ungrazed pastures than pastures managed with patch-burn grazing. However, average number of host fledglings per nesting attempt did not differ among management treatments for any species. Annual variation in weather conditions had a large effect on vegetation structure, but not on reproductive success. Probability of brood parasitism was consistently high (25.5‒84.7%) and nest survival was consistently low (9.9–16.9%) for all species pooled across treatments, sites, and years, indicating that combined effects of predation, parasitism and drought can offset potential benefits of patch-burn grazing management previously found in tallgrass prairies. Although differences in reproductive success among management treatments were minimal, patch-burn grazing management could still benefit population dynamics of grassland songbirds in areas where nest predators and brood parasites are locally abundant by providing suitable nesting habitat for bird species that require greater amounts of vegetation cover and litter, generally not present in burned pastures.

Preferential Begging Responses of Shiny Cowbirds to the Conspecific Chatter Call

Avian brood parasites lay their eggs into the nests of other species, which incubate them and raise the chicks until their independence. Despite living their early weeks of life surrounded by heterospecifics, young brood parasites have the ability to recognize and associate to conspecifics after independence. It has been proposed that the initial conspecific recognition develops when a young parasite encounters a unique species-specific signal that triggers the learning of other aspects of the producer of the signal. For cowbirds (Molothrus spp.), this species-specific signal is hypothesized to be the chatter call. Young birds also could express auditory biases, which in some cases lead to discrimination in favor of conspecific songs. Therefore, the perceptual selectivity for chatters might be also present in nestlings. Our aim was to assess if nestlings of the shiny cowbird (M. bonariensis) present a preferential begging response to conspecific chatter calls. We evaluated if they respond more to the parasitic vocalization than host chicks and if they respond more to the chatter than to heterospecific nonhost calls. We tested shiny cowbird chicks reared by chalk-browed mockingbirds (Mimus saturninus) or house wrens (Troglodytes aedon) and host chicks, as control species. We randomly presented to 6-day-old chicks the following playback treatments: (1) conspecific chatter calls, (2) host calls, used as positive controls, and (3) nonhost calls, used as negative control. We measured if chicks begged during the playback treatments and the begging intensity. When responding to the playback of chatter calls, shiny cowbird chicks begged at a higher frequency and more intensively than host chicks. Shiny cowbird chicks reared by mockingbirds begged more intensively to playbacks of conspecific chatter calls than to host calls, while those reared by wrens begged with a similar intensity to playbacks of conspecific chatter and host calls. On the contrary, wren nestlings begged more intensively to playbacks of the wren call than to chatter calls. Mockingbird nestlings did not beg during any treatment. None of the three species begged during the playback of nonhost calls. Our results show that the chatter call produced a preferential begging response in cowbird nestlings, which may be the beginning of a process of conspecific recognition.

Interclutch variability in egg characteristics in two species of rail: Is maternal identity encoded in eggshell patterns?

Maternal signatures are present in the eggs of some birds, but quantifying interclutch variability within populations remains challenging. Maternal assignment of eggs with distinctive appearances could be used to non-invasively identify renesting females, including hens returning among years, as well as to identify cases of conspecific brood parasitism. We explored whether King Rail (Rallus elegans) eggs with shared maternity could be matched based on eggshell pattern. We used NaturePatternMatch (NPM) software to match egg images taken in the field in conjunction with spatial and temporal data on nests. Since we had only a small number of marked breeders, we analyzed similar clutch images from a study of Eurasian Common Moorhens (Gallinula chloropus chloropus) with color-banded breeders for which parentage at many nests had been verified genetically to validate the method. We ran 66 King Rail clutches (n = 338 eggs) and 58 Common Moorhen clutches (n = 364 eggs) through NPM. We performed non-metric multidimensional scaling and permutational analysis of variance using the best egg match output from NPM. We also explored whether eggs could be grouped by clutch using a combination of egg dimensions and pattern data derived from NPM using linear discriminant analyses. We then scrutinized specific matches returned by NPM for King Rail eggs to determine whether multiple matches between the same clutches might reveal maternity among nests and inform our understanding of female laying behavior. To do this, we ran separate NPM analyses for clutches photographed over several years from two spatially distant parts of the site. With these narrower datasets, we were able to identify four instances where hens likely returned to breed among years, four likely cases of conspecific brood parasitism, and a within-season re-nesting attempt. Thus, the matching output was helpful in identifying congruent egg patterns among clutches when used in conjunction with spatial and temporal data, revealing previously unrecognized site fidelity, within-season movements, and reproductive interference by breeding females. Egg pattern data in combination with nest mapping can be used to inform our understanding of female reproductive effort, success, and longevity in King Rails. These methods may also be applied to other secretive birds and species of conservation concern.

Integrating voice and phenotype in a revision of the brush cuckoo Cacomantis variolosus (Aves: Cuculidae) complex

Brush cuckoos of the Cacomantis variolosus complex, which range from Southeast Asia to Australia and the Solomon Islands, have undergone much taxonomic upheaval. Here we examine 389 vocal recordings, 832 skins, and records of brood parasitism and habitat partitioning to shed light on their species and subspecies taxonomy. Bioacoustic analysis revealed seven distinct vocal groups. Among morphological markers, shape and proportions of the tail were found to be supporting indicators, in addition to plumage tone and pattern. Integration of the resulting data set distinguished six species-level taxa within the complex: sepulcralis in the Philippines and Sundaland east to central Nusa Tenggara, virescens in Sulawesi and the Sula Archipelago, aeruginosus in the Moluccas, variolosus in east Nusa Tenggara, the Moluccas, north and east Australia, New Guinea and Bismarck Archipelago, blandus in the Admiralty Islands, and addendus in the Solomon Islands. Our review of infra-specific differentiation among species leads us to distinguish 13 subspecies. All taxa identified are listed in a summary classification of the complex. Taxon diversity is greatest in the Moluccas, where two habitat-partitioned species and five allopatric subspecies occur, of which one species and three subspecies are endemic to this region.

Notes from rusty patched bumble bee (Bombus affinis Cresson) nest observations

Abstract The rusty patched bumble bee, Bombus affinis, is federally endangered in the United States and Canada. Information on natural history is crucial to conservation planning, but little is known about B. affinis nesting biology, habitat, overwintering, and mating behaviours. We report observations on three B. affinis nests in Minnesota and Wisconsin found in 2020. Previous to this report, there were only four published descriptions of B. affinis nests, with the last nest recorded nearly 30 years ago. Here, we share findings on nesting habitat, nest size, mating behaviours, and nest parasites. The nests were located in between the foundation and a layer of insulation in an urban residence, in an urban backyard near a house foundation, and in a degraded semi‐wooded, riparian natural area. Colony size estimates ranged from 251 to 1341 bees. We observed males chasing gynes near a nest entrance and one mating event approximately 5 m from the nest. We documented the chalcid wasp, Melittobia acasta, as a new host association. These observations increased the known colony size range, documented a new host association, and indicate the potential importance of urban and degraded habitats for recovery of the endangered rusty patched bumble bee.

Is there an effect of fostering a brood parasite on the timing of host autumn migration?

Is there an effect of fostering a brood parasite on the timing of host autumn migration?

LOW INCIDENCE OF HELMINTH PARASITES IN BROWN-HEADED COWBIRDS (MOLOTHRUS ATER) FROM EAST TEXAS

LOW INCIDENCE OF HELMINTH PARASITES IN BROWN-HEADED COWBIRDS (<i>MOLOTHRUS ATER</i>) FROM EAST TEXAS

Twenty-two years of brood parasitism data do not support the mafia hypothesis in an accepter host of the Brown-headed Cowbird (Molothrus ater)

Most host species of the obligate brood parasitic Brown-headed Cowbird (<em>Molothrus ater</em>) accept foreign eggs and offspring despite the associated reproductive costs. One theoretical explanation for this host tolerance is the potential for mafia-like behavior by the brood parasite, which involves the retaliatory destruction of a host’s eggs and/or nestlings in response to that host’s rejection of the parasitic progeny. Here, we use a long-term dataset of an accepter cowbird host, the Dark-eyed Junco (<em>Junco hyemalis carolinensis</em>), where researchers opportunistically removed parasitic cowbird eggs from the clutch, to test critical assumptions and predictions of the mafia hypothesis in this cowbird-host system. For the mafia hypothesis to be supported, at least some junco nestlings should survive in cowbird parasitized nests. In turn, if cowbirds parasitizing juncos engage in mafia behavior, then nests where the parasitic egg was removed should have lower nest success than nests where the cowbird egg remained. We found no support for the mafia hypothesis, because fledgling success was higher in nests where the cowbird egg was removed compared to nests where the cowbird egg remained. If mafia behavior is present in this cowbird population, as suggested by anecdotal observations, it is likely inconsistent over time and space or localized to a small number of individual female parasites rather than a population-wide phenomenon. Further studies are needed to assess how widespread cowbird mafia behavior is across host species and populations and what its implications and impacts may be on host fitness.

Spatially structured brown-headed cowbird control measures and their effects on Kirtland’s warbler long-term population sustainability

Context Brown-headed cowbirds (Molothrus ater), through brood parasitism, can exert extrinsic population growth pressures on North American songbirds. Cowbird removal programs may reduce parasitism rates on host species but can be expensive and difficult to implement throughout a host species’ breeding range. Aim We estimated cowbird abundance and nest parasitism rates within Kirtland’s warbler (Setophaga kirtlandii) primary breeding range in Michigan, USA, and determined the maximum sustainable parasitism rate for Kirtland’s warblers under several spatially structured cowbird removal designs. Methods We conducted point counts to estimate cowbird abundance and monitored nests to quantify nest parasitism rates during 2019–2021. We used the modelling software STELLA to determine the maximum sustainable parasitism rate for Kirtland’s warblers under different spatially structured cowbird removal scenarios (complete, core-only, and no removal). Key results Cowbird abundance and parasitism rates remained low following cowbird trap closures in 2018. In the simulation study, complete removal was the most robust scenario with no replications having &lt;1000 Kirtland’s warbler males. The core-only removal scenario had a substantially higher sustainable parasitism rate in the peripheral breeding area than the no removal scenario. Assumed hatch-year dispersal distance had the greatest impact on the maximum sustainable parasitism rate in the core-only scenario. Conclusions Low cowbird abundance and nest parasitism following suspension of cowbird removal efforts showed resuming the removal program may not be required in the short-term. If cowbird abundance increases, however, adaptive cowbird removal programs can be used to sustain Kirtland’s warbler populations long-term. Implications Our results indicate that incorporating spatial structure of host species’ habitat into designing cowbird removal programs may minimise costs of cowbird management while sustaining populations of Kirtland’s warbler and possibly other host species that are affected by brood parasitism.

Light matters: Nest illumination alters egg rejection behavior in a cavity-nesting bird

Egg discrimination by cavity-nesting birds that build nests under dim light conditions was presumed to depend on nest luminance, although this hypothesis has rarely been tested. Tests of egg discrimination ability by cavity-nesting tits under dim light conditions may reveal the selection pressure from brood parasitism that they encounter under natural interactions. We manipulated the intensity of luminance of nests of the Green-backed Tit (Parus monticolus), a potential cuckoo host that possesses a strong discrimination ability of non-mimetic foreign eggs. We performed experiments to test their egg discrimination ability under different light conditions. Our results showed that Green-backed Tits discriminate against non-mimetic foreign eggs under normal light conditions in nest boxes, and this ability persisted at nest luminance as low as 4.78 ​± ​1.31 lux that is several times lower than normal luminance (38.11 ​± ​24.02 lux). However, egg discrimination by Green-backed Tits disappeared when nest luminance was reduced to a minimum of 0.35 ​± ​0.15 lux. The latter value represents total darkness for humans. The present study shows that nest luminance plays a key role in egg discrimination by Green-backed Tits that build nests under dim light conditions. This study provides strong experimental evidence for nest illumination altering egg rejection behavior in cavity-nesting birds.