Agelaioides Badius Research Articles

Behavioral and physiological changes in the passerine Agelaioides badius following the ingestion of coated seeds with imidacloprid in a 30-day experiment

The wide use of neonicotinoid seed treatment represents a hazard for farmland birds that feed on treated seeds. This study aimed to characterize the long-term effects of the neonicotinoid imidacloprid (IMI) in the passerine grayish baywing (Agelaioides badius). The birds were fed ad libitum for 32 days only with seeds treated with 53.1 (Low, 11 % of LD50) and 514 (High, (112 % of LD50) mg IMI/kg seed; these concentrations representing respectively, 1.8 and 17.1 % of 3 g IMI/kg, an average application rate used to treat crop seeds in Argentina. The effects exerted by IMI on birds were evaluated at behavioral, physiological, hematological, genotoxic, and biochemical levels. No differences in food consumption were observed between Control and Low treatments birds, indicating a lack of aversion to treated seeds. High treatment birds only decreased their food consumption by 20 % in the first 3 days of exposure. Birds from High treatment experienced an early loss of body weight, reduction in their mobility, lack of response to threats (i.e., predator call and approaching person), and altered their use of the cage. On the contrary, birds from Low treatment experienced a delay in the onset of effects like reduction in mobility, lack of response to threats, and a tendency to reduce their body weight. At the end of exposure, glutathione S transferase activity in the plasma of treated birds decreased, and cholinesterase activity increased in the liver of treated birds. This study highlights that consumption equivalent to 1.8 % of the daily diet of baywings as IMI-treated seeds, is sufficient to generate behavioral and physiological alterations and death. In the wild, these effects may have ecological consequences, by impairing the survival of birds, representing a risk to farmland bird populations.

Behavioral and physiological response of the passerine bird Agelaioides badius to seeds coated with imidacloprid.

Neonicotinoids are globally used insecticides, and there are increasing evidence on their negative effects on birds. This study is aimed at characterizing the behavioral and physiological effects of the neonicotinoid imidacloprid (IMI) in a songbird. Adults of Agelaioides badius were exposed for 7days to non-treated peeled millet and to peeled millet treated with nominal concentrations of 75 (IMI1) and 450 (IMI2) mg IMI/kg seed. On days 2 and 6 of the trial, the behavior of each bird was evaluated for 9min by measuring the time spent on the floor, the perch, or the feeder. Daily millet consumption, initial and final body weight, and physiological, hematological, genotoxic, and biochemical parameters at the end of exposure were also measured. Activity was greatest on the floor, followed by the perch and the feeder. On the second day, birds exposed to IMI1and IMI2 remained mostly on the perch and the feeder, respectively. On the sixth day, a transition occurred to sectors of greater activity, consistent with the disappearance of the intoxication signs: birds from IMI1 and IMI2 increased their time on the floor and the perch, respectively. Control birds always remained most of the time on the floor. IMI2 birds significantly decreased their feed intake by 31% the first 3days, compared to the other groups, and significantly decreased their body weight at the end of the exposure. From the set of hematological, genotoxic, and biochemical parameters, treated birds exhibited an alteration of glutathione-S-transferase activity (GST) in breast muscle; the minimal effects observed are probably related to the IMI administration regime. These results highlight that the consumption of less than 10% of the bird daily diet as IMI-treated seeds trigger effects at multiple levels that can impair bird survival.

Blood parasites of passerines in the Brazilian Pampas and their implications for a potential population supplementation program for the endangered Yellow Cardinal (Gubernatrix cristata).

Espinilho savanna ("seasonal steppe savanna") is a unique vegetation formation of the Pampas biome that is found near the tri-border of Brazil, Uruguay, and Argentina. The Yellow Cardinal (Gubernatrix cristata) is a flagship species of this ecosystem, but it is classified as "critically endangered" in Brazil due to habitat loss and poaching for the illegal trade. Population supplementation through the release of individuals that were captive-bred or apprehended by authorities from the illegal trade has been considered as a conservation strategy for this species; however, the risk of pathogen introduction is a critical concern. We used microscopy and molecular methods to investigate the occurrence of blood parasites in wild passerines (n = 64, including three Yellow Cardinals) at Espinilho State Park, Rio Grande do Sul, Brazil, and in captive Yellow Cardinals (n = 30) at three facilities in Brazil. Haemosporidian parasites were detected in the blood smears of 10.9% of the wild passerines, comprising the morphospecies Haemoproteus erythrogravidus in Rufous-collared Sparrow (Zonotrichia capensis), H. quiscalus in Grayish Baywing (Agelaioides badius), and H. tyranni in Great Kiskadee (Pitangus sulphuratus); these are the southernmost records for these morphospecies and their first record for the Pampas biome. No haemosporidian parasites were detected in the blood smears of the Yellow Cardinals, wild or captive. Microfilariae were detected in the blood smears of 14.1% of the wild passerines, including all wild Yellow Cardinals, and in 43.3% of captive Yellow Cardinals. Trypanosoma sp. was detected in the blood smear of one captive Yellow Cardinal. Nested PCR and gene sequencing of the cyt-b gene of Haemoproteus/Plasmodium was used to test a subset of wild passerines and captive Yellow Cardinals, allowing for the molecular barcoding of H. quiscalus lineage AGEBAD04 and H. tyranni lineage PITSUL01; additionally, DNA identical to that of lineage PITSUL01 was detected in the blood of one captive Yellow Cardinal. This study provides valuable data to support the conservation management of the Yellow Cardinal and other threatened passerines from the Pampas and highlights the need for further studies on the epidemiology and pathology of filarioid worms and trypanosomes in passerines from this biome.

Family ties in a neotropical cooperative breeder: within‐group relatedness and fine‐scale genetic structure in the greyish Baywing (Agelaioides badius)

Cooperative breeding is a reproductive system in which one or more adults (helpers) assist others in rearing their offspring. Cooperative breeding occurs in 9% of birds, encompassing remarkable variation in mating systems and patterns of social organization. Understanding how this diversity evolved requires assessing social and genetic relationships across a broad range of cooperative systems. Yet, for some geographical regions like the Neotropics, detailed genetic studies of cooperatively breeding birds are still comparatively scarce. We used double‐digest restriction‐site associated DNA sequencing to define the genetic relationships within and between cooperative groups in a Neotropical facultative cooperative breeder, the Greyish Baywing Agelaioides badius. Between 2015 and 2018, we banded and sampled adults and nestlings of 41 breeding groups from a population in the Province of Buenos Aires, Argentina. We found that helpers were primarily males, the majority of which were genetically related to the individuals they assisted, either as previous offspring of the breeding pair or as first‐ or second‐order relatives of the breeding male. However, we also observed unrelated male and female helpers. Parentage analysis indicates that reproduction was strongly skewed towards the dominant pair and helpers never gained paternity within and only once outside their social group. This scenario is consistent with helping behaviour being driven primarily by kin selection rather than by direct genetic benefits to helpers. However, the occasional occurrence of helpers unrelated to the breeding pair suggests that non‐reproductive direct benefits such as increased access to resources or future breeding opportunities may also influence helping decisions in this species. We found weak evidence consistent with male natal philopatry, and fine‐scale genetic structure, as adult males in our population showed higher relatedness at close geographical distances than females. Future studies that further examine the mechanisms behind group formation and the fitness pay‐offs of helping behaviour will increase our understanding of the complex cooperative system of the Greyish Baywing.

Automated radio tracking provides evidence for social pair bonds in an obligate brood parasite

Social monogamy predominates in avian mating systems, but this strategy seems unlikely among brood parasites, where the emancipation from parental care should lead to an increase in numbers of mates for both sexes. Despite this, there is great diversity in mating systems in brood parasitic birds. The Screaming CowbirdMolothrus rufoaxillarisis a brood parasite that specializes almost exclusively on one host, the Greyish BaywingAgelaioides badius. Field observations and a radio telemetry study have indicated that male–female pairs spend a great deal of time together through the day, suggesting that they may be socially monogamous. We tested the hypothesis of social monogamy by radio‐tracking male and female Screaming Cowbirds using an array of automated radiotracking receivers to collect data on spatial behaviour and social mating system. Monogamous pair bonds were recorded through social network analysis. These bonds endured throughout the entire breeding season, with males and females remaining associated throughout the day. In accordance with the hypothesis, paired Screaming Cowbirds spent significantly more time in proximity to their mates than to other conspecifics of the opposite sex, and had similar home‐ranges. Social monogamy in the Screaming Cowbird differed markedly from the social polygyny/promiscuity exhibited by the sympatric congener Shiny CowbirdMolothrus bonariensis, a generalist brood parasite.

Local and landscape features of wooded streets influenced bird taxonomic and functional diversity

Wooded streets diminish the negative consequences of urban growth on biodiversity. However, bird use of wooded streets has been little studied, in most cases analyzing bird species richness and abundance in developed countries. In this study, we analyzed the relationship between environmental variables of wooded streets of Buenos Aires City (Argentina) and bird taxonomic and functional diversity as well as species and functional trait composition. We placed 26 100m × 50m transects within the wooded streets of the urban center. Bird surveys were performed during the austral spring and summer. Species richness, Pielou’s evenness, Shannon index, Functional dispersion (FDis), and species and functional trait composition were analyzed. Taxonomic and functional diversity were negatively related to pedestrian and motorized vehicle traffic. On the other hand, taxonomic diversity was related positively to streets with varied tree heights. Native taxonomic diversity and functional diversity increased near green areas. The coverage of high buildings was negatively related to the native taxonomic diversity. Bird species associated with humans, such as the Rock Dove (Columba livia) and the Eared Dove (Zenaida auriculata) increased their abundances in sites with high pedestrian and motorized traffic. The House Wren (Troglodytes aedon), the Baywinged Cowbird (Agelaioides badius), and the Red-bellied Thrush (Turdus rufiventris) were positively related to varied tree heights. Birds that feed on the ground and the undergrowth were negatively associated with the coverage of high buildings. It is imperative to preserve green areas and to control motorized vehicle traffic in order to improve the environmental quality of wooded streets for supporting bird diversity.

Tissue distribution and sublethal effects of imidacloprid in the South American grayish baywing (Agelaioides badius)

The neonicotinoids are globally used insecticides, which have been shown to cause negative impacts on birds. The current study aimed to evaluate the distribution of the neonicotinoid imidacloprid (IMI) in the tissues of a songbird and identify related physiological effects. Adults of the grayish baywing (Agelaioides baduis) were administered with a single dose of 35 mg IMI/kg, and the IMI concentration was evaluated in liver, kidney and plasma at 4, 12, 24, and 48 h after dosing. At the same time points, effects on hematological, genetic and enzymatic parameters were assessed. Results showed that IMI was absorbed before 4 h, and eliminated at 48 h, in every tissue, and the highest concentrations were detected in plasma. Baywings showed intoxication signs and reduced mobility within the first 5 min post-dosing. Hematological parameters: red blood cells, packed cell volume, hemoglobin, and their derived indices exhibited a transient elevation 24 h after dosing, which coincided with maximum concentrations of IMI in the tissues. No effects were observed on the genotoxicity parameters evaluated: micronuclei and comet assay. Treated birds exhibited an alteration of cholinesterases activity in the muscle and plasma, and of glutathione-S-transferase (GST) activity in the plasma, brain, liver, and muscle. Based on the results obtained, the combined detection of IMI and inhibition of GST activity in the plasma is suggested as a non-lethal biomarker of IMI exposure in wild birds. As efficient field monitoring depends on the availability of proven biomarkers, the current study provides valuable tools for bird conservation in agroecosystems.

Imidacloprid seed coating poses a risk of acute toxicity to small farmland birds: A weight-of-evidence analysis using data from the grayish baywing Agelaioides badius

The aim of this study was to estimate the risk posed by imidacloprid (IMI) seed coating to passerine birds of the Pampa Region of Argentina using data specifically generated with the grayish baywing (Agelaioides badius). Median lethal dose (LD50) of the IMI-based formulation tested was 57.11 mg IMI/kg body weight (bw), with intoxication signs starting from 20.6 mg IMI/kg bw. The feed intake rate (FIR) was estimated experimentally as 4.895 g/day per bird, representing 12.43% of bw. It was calculated that the ingestion of 7–10% of the FIR as treated seeds would be enough to achieve the LD50 for sorghum, corn, sunflower, and alfalfa, whereas consumption of 31 and 54% of FIR was necessary for oat and wheat, respectively. Based on spill data values available in the literature, it was calculated that, for most crops, a baywing would have to forage an area of field corresponding to less than 60 m2 to obtain the number of seeds required to reach the LD50. It was also shown that this number of seeds is coherent with the amount of seeds ingested in a bout. In a pilot study, all grayish baywings fed with millet seeds treated with 3 g IMI/kg died within three to five days of exposure. In Tier I risk assessment, the trigger value was achieved for all crops except soybean and a weight-of-evidence risk assessment was performed. All lines of evidence examined are consistent with the view that grayish baywings, and probably other small farmland birds, are exposed to a risk of acute toxicity and mortality under both worst-case and mixed-ration exposure scenarios. The possible impacts on bird species calls for an urgent reconsideration of IMI seed coating practices currently approved in the Pampa Region of Argentina and the various parts of the world where this practice is still in use.

Genetic patterns of repeat and multiple parasitism by screaming cowbirds, a specialist brood parasite

Avian brood parasites lay their eggs in the nests of other species, leaving the hosts to care for the parasitic offspring. The bookkeeping hypothesis predicts that, in order to reduce competition between parasitic nestlings, female parasites should keep a mental inventory of host nests that they have already parasitized and avoid laying multiple eggs in the same host nest. However, selection against repeat parasitism should be weaker when host nests are limited, or when hosts are able to rear more than one parasitic nestling. Here we use microsatellite genotyping of parasitic eggs to test whether female screaming cowbirds, Molothrus rufoaxillaris, avoid repeatedly parasitizing nests of their primary host, the greyish baywing, Agelaioides badius, in Argentina. Parasitism rates were extremely high (96.5% of 57 host clutches were parasitized with an average of 5.7 cowbird eggs each), indicating that host nests are limited. Although eggs laid by the same female showed moderate spatiotemporal clustering, individual females rarely laid more than one egg in the same host clutch (2 of 57 clutches, 26 of which contained multiple genotyped cowbird eggs). Females were much more likely to lay subsequent eggs in different host nests than to return to the same host nest. We found no evidence for kin structure among female cowbirds parasitizing the same host nest, which were no more closely related than chance would predict. These results suggest that female screaming cowbirds frequently lay eggs in host nests that have already been parasitized by unrelated females. However, they typically lay just one egg per host clutch, even though greyish baywings are capable of rearing several nestlings. Since screaming cowbird laying is often poorly synchronized with that of their host, avoidance of repeat parasitism may be adaptive if it allows females to spread the risk of failure among multiple host nests.

Brood parasitic nestlings benefit from unusual host defenses against botfly larvae (Philornis spp.)

Brood parasitic birds lay their eggs into the nests of other birds, abandoning parental care of their nestlings to the unsuspecting hosts. Parasite and host nestlings may themselves be parasitized by botfly larvae (Philornis: Muscidae), which burrow under the nestlings’ skin and can seriously affect growth and survival. Here, we provide the first direct evidence that adult baywings (Agelaioides badius), the primary host of the specialist brood parasitic screaming cowbird (Molothrus rufoaxillaris), regularly remove botfly larvae from their own and parasitic nestlings by pulling them out of the nestlings’ skin. This is the only bird species known to remove botfly larvae. By combining nestling cross-fostering with video recording of baywing nests, we show that due to prompt removal, infection with botfly larvae had negligible effects on nestling growth and survival despite high prevalence. Our results provide the first direct observations for larva removal behavior in botfly hosts. Screaming cowbirds may benefit from using baywings as its main host, as larva removal by adult baywings reduces the costs of botfly parasitism. Infection by botfly larvae of the genus Philornis (Muscidae) causes nestling mortality in many Neotropical birds. Despite the lethal effects, most Philornis hosts studied so far lack specific defenses against these larvae. The grayish baywing (Agelaioides badius), primary host of the brood parasitic screaming cowbird (Molothrus rufoaxillaris), is the only species that, based on indirect evidence, would be able to remove Philornis larvae from infected nestlings. We provide the first direct evidence that adult baywings do indeed remove botfly larvae from their own nestlings as well as from parasitic cowbird nestlings and that this unusual defense may increase the survival of own and screaming cowbird nestlings at infected nests.

Non-mimetic shiny cowbird nestlings escape discrimination by baywings in absence of host nest mates

Nestlings of obligate brood parasites must obtain resources from heterospecific hosts that are attuned to the solicitation behaviours of their own progeny. Failing to match the appropriate stimuli may result in suboptimal provisioning or even the starvation of parasite young. Parasitic nestlings could overcome it by sharing the nest with host young, as long as they are able to compete efficiently for parental feedings. Here, we examined if non-mimetic shiny cowbird (Molothrus bonariensis) nestlings reared alone fail to elicit sufficient parental care from the grayish baywing (Agelaioides badius), a host that discriminates between their own and parasitic nestlings based on species-specific begging cues. We manipulated baywing broods to assess the ability of shiny cowbird nestlings to elicit parental provisioning and survive without host nest mates. Host provisioning rates and survival did not differ between shiny cowbirds reared alone and host nestlings in singleton broods. Also, growth patterns of experimental nestlings reared alone were similar to those reported for shiny cowbirds reared alongside baywing young. Hence, we did not find support for the hypothesis that non-mimetic nestlings require the assistance of host nest mates to elicit sufficient parental care from its baywing host. Furthermore, we found that shiny cowbirds that were reared alone continued receiving care from baywings after fledging, unlike shiny cowbirds from mixed broods. Our results add evidence to the idea of opposing selective pressures on the evolution of nest mate acceptance in cowbirds and suggest context-dependent host’s discrimination abilities that deserve further investigation. The evolution of nest mate killing versus tolerance strategies is a long-standing question in the study of brood parasitism. Parasitic nestlings may benefit from sharing the nest with host young if they collectively induce more parental provisioning and the parasite can benefit from it. Host nest mates could also confer protection against discrimination when hosts respond preferentially to stimuli of their own kind. We examined this idea in a generalist brood parasite, the shiny cowbird (Molothrus bonariensis), and a host able to discriminate species-specific begging cues. The results showed that shiny cowbirds reared alone performed well and circumvent host discrimination also after leaving the nest. Our study supports the existence of trade-offs on the evolution of nest mate killing behaviours and adds evidence that context-dependent host’s discrimination abilities similar to those observed towards parasitic eggs can be at play towards parasitic fledglings.

Coevolutionary arms race between a specialist brood parasite, the Screaming Cowbird, and its host, the Grayish Baywing

Interspecific brood parasites exploit the parental care of host species. This exploitation entails fitness costs for the hosts, which favor the evolution of antiparasitic defenses. Host defenses select for counter-defenses in the parasite, which in turn select for improved host defenses; this results in a coevolutionary arms race that may operate at each stage of the nesting cycle of the host. Most studied examples of the coevolutionary arms race in brood parasites are restricted to the egg stage, with relatively few studies showing coevolution between hosts and parasites at the nestling or fledgling stages; studies on the whole set of host defenses and potential parasite counter-defenses at each stage of the breeding cycle are still lacking. Systems in which parasites are host specialists are particularly well suited to an examination of the pairwise coevolutionary interactions before, during and after host egg-laying, and how these interactions have shaped host resistance or tolerance of parasitism. The Screaming Cowbird (Molothrus rufoaxillaris) is one of the most specialized brood parasites, and mainly parasitizes nests of a single host species, the Grayish Baywing (Agelaioides badius). Parasitism rates of Grayish Baywing nests are extremely high, with most nests parasitized several times. Several traits of this host-parasite system suggest ancient coevolutionary relationships encompassing the entire nesting cycle. In this paper we summarize the main results of a long-term study on the costs of Screaming Cowbird parasitism on the Grayish Baywing’s reproductive success and how these costs have favored reciprocal adaptations and counter-adaptations at each stage of the nesting cycle.

High Rates of Nest Usurpation by Grayish Baywings (Agelaioides badius) in Active Nests of House Wrens (Troglodytes aedon) in Central Andes

ABSTRACT Nest usurpation is a behavior where one individual takes over the active nest of another individual of the same or a different species. The Grayish Baywing (Agelaioides badius) has been reported as an occasional inter-specific nest usurper. In previous studies, researchers have reported usurpation of nests of House Wrens (Troglodytes aedon) by Grayish Baywings. In this paper, we report that nest usurpation by Grayish Baywings is the second cause of breeding failure in a population of House Wrens in the Central Andes.

Kinship and genetic mating system of the Grayish Baywing (Agelaioides badius), a cooperatively breeding Neotropical blackbird

ABSTRACT Kin selection theory predicts that extrapair mating should be rare in cooperatively breeding birds. However, most cooperative breeders are not genetically monogamous and the relationship between promiscuity and cooperative breeding remains unclear. This relationship is further complicated by a lack of data. The majority of cooperatively breeding birds live in the tropics, and their genetic mating systems are little known. Here we studied the genetic mating system of the Grayish Baywing (Agelaioides badius), a socially monogamous Neotropical blackbird in which most nesting pairs are assisted by helpers, previously assumed to be offspring of the breeding pair. Grayish Baywings are the primary host of the parasitic Screaming Cowbird (Molothrus rufoaxillaris), and previous studies have found a positive association between brood parasitism and helper recruitment in the last part of the nestling period. We used microsatellite markers to analyze the kinship of 192 individuals in 47 breeding groups, find...

New records of bird species from Ilha Grande, state of Rio de Janeiro, southeastern Brazil

We add 32 new records of species to the existing checklist of birds of the coastal island of Ilha Grande, state of Rio de Janeiro, Brazil. Notably, seven of these species are endemic to the Atlantic Forest. Sporophila falcirostris is globally Vulnerable and Haematopus palliatus is Near Threatened in Brazil. We also report the second record of Agelaioides badius from Rio de Janeiro state. We also compare our species list with lists of birds of Ilhabela and Anchieta islands. While some of the newly recorded species are probably non-resident to Ilha Grande or represent range expansions, most species occur in Rio de Janeiro throughout the year. Thus, our records may be a consequence of the surveying new sites on the island but also recent colonization. Our study increases the number of bird species known to occur on Ilha Grande from 222 to 254, which is one-third of the species reported from Rio de Janeiro state. We recorded 13 species threatened by extinction at regional, national or global levels.

Functional role of the invasive European Starling, Sturnus vulgaris, in Argentina

The introduction of exotic species may have severe effects on native ecosystems by disrupting communities and ecosystem services. Consequently, assessing the functional role of a species newly added to a community is an important task in order to identify native species at risk. In Argentina, the ecology of the invasive European Starling (Sturnus vulgaris) is poorly known and studies addressing its ecological role in bird communities are still lacking. We assessed the functional role of the European Starling by sampling bird communities across four vegetation types (Solanum grassland, Cynodon grassland, flood plain and forest patches) and making comparisons of body mass, and dietary and foraging traits of European Starling with native and other introduced bird species in east-central Argentina. The European Starling was functionally most similar to two widespread, generalist native passerines—the Bay-winged Cowbird (Agelaioides badius) and the Chalk-browed Mockingbird (Mimus saturninus)—and to the invasive House Sparrow (Passer domesticus), which together defined a functional group of terrestrial and foliage omnivores. European Starlings were more abundant in Solanum grasslands than in other vegetation types and showed significant vegetation-type overlap with functionally similar species. Moreover, abundance of European Starlings was positively correlated with bird abundance and diversity. Our results identify native species that are functionally equivalent to European Starlings, and, consequently, potentially subject to ecological impacts.

New data on the taxonomy and distribution of ten Neotropical chewing lice of the genus Myrsidea (Phthiraptera: Menoponidae), including the description of a new species.

The new species Myrsidea alexanderi is described and illustrated ex Pheugopedius maculipectus (Troglodytidae) from Honduras. Redescriptions and illustrations are given for both sexes of Myrsidea chiapensis ex Calocitta formosa from Costa Rica, and the male of M. dissimilis ex Progne chalybea from Brazil. Also, seven other previously known species or subspecies of the louse genus Myrsidea are recorded and discussed from passerine birds of the Neotropical Region, as follows: Myrsidea antiqua, Myrsidea balteri, Myrsidea diffusa, Myrsidea nesomimi borealis, Myrsidea paleno, Myrsidea psittaci and Myrsidea serini. Our data increase knowledge of intraspecific morphological variability within these species, and also of their host and geographical distribution. New host-louse associations are: Agelaioides badius for M. psittaci; Basileuterus culicivorus and Myiothlypis leucoblephara for M. paleno; Mimus saturninus for M. nesomimi borealis; and Icterus dominicensis and Molothrus rufoaxillaris for Myrsidea sp.

Reproductive success of the specialist brood parasite Screaming Cowbird in an alternative host, the Chopi Blackbird

ABSTRACT The Screaming Cowbird (Molothrus rufoaxillaris) is the most specialized brood-parasitic cowbird, relying almost entirely on the Bay-winged Cowbird (Agelaioides badius) as host. Recently, Screaming Cowbirds have expanded their range to areas where Bay-winged Cowbirds are absent, and they are exploiting the Chopi Blackbird (Gnorimopsar chopi). Interactions between Screaming Cowbirds and Chopi Blackbirds are largely unexplored, as is the reproductive success of the parasite in this host. Screaming Cowbirds, Chopi Blackbirds, and Bay-winged Cowbirds coexist in northeastern Argentina, providing an ideal system to explore interactions between a specialist brood parasite and an alternative host and to compare the reproductive success of the parasite in its main host and in an alternative host. Screaming Cowbirds parasitized both hosts throughout their breeding seasons (Chopi Blackbirds, mid-October to mid-January; Bay-winged Cowbirds, mid-November to mid-March). Frequency of parasitism was lower in Chop...

NOTES ON TAXONOMY AND DISTRIBUTION OF MYRSIDEA SERINI (SÉGUY, 1944) (PHTHIRAPTERA: AMBLYCERA: MENOPONIDAE) ON SOUTHERN SOUTH AMERICAN PASSERINE BIRDS (AVES: PASSERIFORMES)

Myrsidea serini (Seguy, 1944) is recorded from three different passerine hosts from Argentina and Chile: Carduelis barbata (Molina, 1782) (Fringillidae), Chrysomus thilius petersi (Laubmann, 1934) and Agelaioides badius badius (Vieillot, 1819) (Icteridae). Somatic features and body measurements from available specimens belonging to these host-populations are compared with those recorded from Old World hosts, finding only some slight differences in certain body measurements (here interpreted as correlated to differences in host sizes), but none in chaetotaxy. This species was synoxenic with Myrsidea psittaci Carriker, 1955 on C. t. petersi in at least two localities in Buenos Aires Province, Argentina. Comparative studies of external chorionic architecture of the eggs, preferential sites of oviposition, prevalence has been carried out for both species, along with some remarks concerning the still problematic species, Myrsidea argentina (Kellogg, 1906), originally recorded off Carduelis magellanica (Vieillot, 1805).

High frequency but low impact of brood parasitism by the specialist Screaming Cowbird on its primary host, the Baywing

Brood-parasitic cowbirds (Molothrus spp.) exploit the parental care of other species (hosts) that raise their offspring. Parasitism by cowbirds reduces host reproductive success in several ways and quantifying such costs is an important step to better understand evolutionary interactions in host-parasite associations. We estimated the costs of parasitism by the host-specialist Screaming Cowbird (M. rufoaxillaris) to the reproductive success of its primary host, the Baywing (Agelaioides badius). We tested the effect of Cowbird parasitism on egg survival, hatching success, nestling survival and body mass at fledging of Baywings in a population of eastern Argentina where the frequency of parasitism by Screaming Cowbirds exceeds 90% of Baywing nests. Egg survival decreased with the number of Screaming Cowbird eggs laid during the egg-stage and, on average, host clutch-size was reduced by 10% per parasitic event. However, contrary to our expectations, we did not find any clear effect of parasitism on hatching success, nestling survival and body mass at fledging of Baywings. Our results suggest that, despite its high frequency, parasitism by Screaming Cowbirds has a rather little effect on the viability of Baywing offspring. We discuss how clutch rejection behaviour and flexible nest-provisioning rules of the hosts might help to explain this paradoxical result.