Molothrus Bonariensis Research Articles

Pale-breasted thrush (Turdus leucomelas) feeds nestlings of the brood parasite shiny cowbird (Molothrus bonariensis) more and faster than its own nestlings

Pale-breasted thrush (Turdus leucomelas) feeds nestlings of the brood parasite shiny cowbird (Molothrus bonariensis) more and faster than its own nestlings

Lack of response to conspecific juvenile vocalizations in two avian brood parasites.

Juveniles of interspecific avian brood parasites need to locate and recognize conspecifics to continue their life cycle after being reared by individuals of another species. However, little is known about the recognition mechanisms and cues involved in this critical stage of their lives. It has been proposed that adult parasites could show some kind of parental behavior by actively searching and interacting with conspecific young, which in turn could serve the juveniles to learn and/or reinforce the learning of conspecific characteristics. Since acoustic communication is one of the main channels used by birds, if such form of parental behavior by adult avian brood parasites does exist, adult cowbirds should recognize and respond positively to vocalizations of conspecific juveniles. We experimentally tested whether adult shiny Molothrus bonariensis and screaming M. rufoaxillaris cowbirds respond positively towards acoustic signals of conspecific juveniles using two playback experiments, one conducted in semi-captivity and the other in the field. In both cases, we presented 3 types of playbacks to adults of both cowbird species: vocalizations of shiny cowbird juveniles, vocalizations of screaming cowbird juveniles, and white noise as a control. In the experiment in semi-captivity, no significant differences were found between treatments. In the field experiment, no conspecifics approached the playback area, but hosts of the species whose playback was played were attracted to the loudspeaker. In conclusion, our results do not support the predictions we tested from the parental behavior hypothesis and indicate that adult shiny and screaming cowbirds do not respond positively to acoustic signals of conspecific juveniles, at least not to the type of signals used in our experiments.

Horizontal transmission maintains host specificity and codiversification of symbionts in a brood parasitic host

In host-symbiont systems, interspecific transmissions create opportunities for host switches, potentially leading to cophylogenetic incongruence. In contrast, conspecific transmissions often result in high host specificity and congruent cophylogenies. In most bird-feather mite systems, conspecific transmission is considered dominant, while interspecific transmission is supposedly rare. However, while mites typically maintain high host specificity, incongruent cophylogenies are common. To explain this conundrum, we quantify the magnitude of conspecific vs. interspecific transmission in the brood parasitic shiny cowbird (Molothrus bonariensis). M. bonariensis lacks parental care, allowing the assessment of the role of horizontal transmission alone in maintaining host specificity. We found that despite frequent interspecific interactions via foster parental care, mite species dispersing via conspecific horizontal contacts are three times more likely to colonize M. bonariensis than mites transmitted vertically via foster parents. The results highlight the previously underappreciated rate of transmission via horizontal contacts in maintaining host specificity on a microevolutionary scale. On a macroevolutionary scale, however, host switches were estimated to have occurred as frequently as codivergences. This suggests that macroevolutionary patterns resulting from rare events cannot be easily generalized from short-term evolutionary trends.

Shiny Cowbird (Molothrus bonariensis) brood parasitism occurrence and impact increases with decreasing forest cover

ABSTRACT Cowbirds brood parasitism has a detrimental effect on the breeding success of their hosts. The occurrence of parasitism observed may be related to environmental features at landscape or nest-site scales. Such relationships have been assessed for the Brown-headed Cowbird (Molothrus ater) in the large forests of the northern hemisphere. Here, we present a study conducted on the Shiny Cowbird (M. bonariensis) in native forests of the southern hemisphere in Argentina. These forests are characterised as semi-open woodlands, with forest fragments of variable sizes immersed in native grasslands. We aimed to evaluate the effect of Shiny Cowbird brood parasitism on the breeding success of a native passerine, the Masked Gnatcatcher (Polioptila dumicola), and to assess the relationship of its occurrence with environmental features at landscape and nest-site scales. During three breeding seasons (2015–2018) we monitored 207 gnatcatcher nests of which 70 were parasitised. Brood parasitism was the cause of nest failure in 60% of the parasitised nests. In addition, breeding success measured by apparent nest success, egg survival, hatching success and nestling survival were significantly lower for parasitised nests than for non-parasitised nests. Brood parasitism occurrence was negatively associated with forest cover, where nests located in sites with less forest cover experienced a higher occurrence of parasitism than those with greater cover. As these native semi-open forests face a continuous decline, our results add to the evidence of negative impacts of deforestation.

Co-parasitism in the face of predation: Effects of natural enemies on a neotropical mockingbird.

Co-parasitism is ubiquitous and has important consequences for the ecology and evolution of wild host populations. Studies of parasite co-infections remain limited in scope, with few experimental tests of the fitness consequences of multiple parasites, especially in natural populations. We measured the separate and combined effects of Philornis seguyi nest flies and shiny cowbirds Molothrus bonariensis on the fitness of a shared host, the chalk-browed mockingbird (Mimus saturninus) in Argentina. Using a two-factor experimental approach, we manipulated the presence of nest flies and cowbirds in mockingbird nests and assessed their effects on mockingbird haemoglobin levels, begging and provisioning rates, body size, and fledging success. We also monitored rates of nest predation in relation to parasitism by flies and cowbirds. Nest flies reduced the haemoglobin concentration, body size, and fledging success of mockingbirds, likely because mockingbirds did not compensate for parasitism by begging more or feeding their nestlings more. Cowbirds also reduced the fledging success of mockingbirds, even though they had no detectable effect on haemoglobin or body size. Nests with cowbirds, which beg more than mockingbirds, attracted more nest predators. There was no significant interaction between the effects of flies and cowbirds on any component of mockingbird fitness. The combined effects of nest flies and cowbirds were strictly additive. In summary, we show that nest flies and cowbirds both reduce host fitness, but do not have interactive effects in co-parasitized nests. Our results further suggest that predators exacerbate the effects of nest flies and cowbirds on their hosts. Our study shows that the fitness consequences of co-parasitism are complex, especially in the context of community-level interactions.

Impacts of brood parasitism by shiny cowbird Molothrus bonariensis on the breeding success of a small host, the black-backed water tyrant Fluvicola albiventer.

The shiny cowbird Molothrus bonariensis parasitizes many species with different life-history traits and has a detrimental effect on the survival of the progeny of the hosts. In response, hosts have developed numerous antiparasitic defenses. Here, we examined the effects of brood parasitism by shiny cowbird on the clutch and brood sizes (83 nests) in a small host, the black-backed water tyrant Fluvicola albiventer. We also studied whether the death of parasite nestlings was related to the care of the foster parents and whether the host had any antiparasitic defense against the shiny cowbird. Our results indicate that brood parasitism significantly decreased the host hatching and fledging successes. The majority of nest failures (57%) were caused by brood parasitism. Shiny cowbird parasitism occurred in 52% of nests and the intensity of parasitism was 1.23 ± 0.53 eggs per parasitized nest. Of the total host eggs, 54% were damaged. During the incubation stage, 20 nests (47%) were abandoned because of egg punctures by shiny cowbirds females. Only two parasitic fledglings were recorded, while the remaining nestlings either died from starvation (n = 12) or predation (n = 3). Foster parents abandoned parasitic nestlings between 5 and 10 days old. Our findings demonstrate that the shiny cowbird has very low rates of fledging success when parasitizing black-backed water tyrant. Also, parasitism had a high reproductive cost in the black-backed water tyrant because a very low proportion (7%) of the parasitized nests (n = 43) were successful.

Highly Conserved Microchromosomal Organization in Passeriformes Birds Revealed via BAC-FISH Analysis

Passeriformes birds are widely recognized for their remarkable diversity, with over 5700 species described so far. Like most bird species, they possess a karyotype characteristic of modern birds, which includes a bimodal karyotype consisting of a few pairs of macrochromosomes and many pairs of microchromosomes. Although the karyotype is typically 2n = 80, the diploid number can atypically vary greatly, ranging from 56 to approximately 100 chromosomes. In this study, we aimed to understand the extent of conservation of the karyotype’s organizational structure within four species of this group using Bacterial Artificial Chromosomes via Fluorescence In Situ Hybridization (BAC-FISH) with microchromosome probes from Chicken (Gallus gallus) or Zebra Finch (Taeniopygia guttata) per microchromosomes (GGA10-28, except GGA16). By examining the chromosome complement of four passerine species—the Streaked Flycatcher (Myiodynastes maculatus), Shiny Cowbird (Molothrus bonariensis), Southern House Wren (Troglodytes aedon), and Double-collared Seedeater (Sporophila caerulescens)—we discovered a new chromosome number for Southern House Wren. Through FISH experiments, we were able to observe the same pattern of microchromosome organization as in the common ancestor of birds. As a result, we propose a new diploid number for Southern House Wren and confirm the conservation status of microchromosome organization, which may confer evolutionary advantages to this group.

Imprinting in an interspecific brood parasitic bird.

Many animals learn to recognize conspecifics after an early experience with them through sexual imprinting. For brood parasitic birds, it is not possible to develop conspecific recognition using cues provided by their foster parents. One solution is that a unique species-specific signal triggers the learning of additional aspects of the conspecific's phenotype. It has been proposed that for brood parasitic cowbirds, this signal is an innate vocalization, the chatter. This vocalization might act in a cross-modal learning process through which juveniles that listen to the song learn to recognize the visual characteristics of the song's producer. We trained two groups of juvenile shiny cowbirds (Molothrus bonariensis). In one group, individuals listened to the chatter or a heterospecific call while they observed a stuffed model of the corresponding species. In the other group, individuals listened to the call of one species (cowbird or heterospecific) while they observed the stuffed model of the other species. In the preference test, juveniles chose the model associated with the chatter, regardless of whether the model was a cowbird or a heterospecific. These results show how the auditory system through a species-specific signal can lead to cross-modal learning of visual cues allowing conspecific recognition in brood parasitic cowbirds.

Gradual changes in model shape affect egg-directed behaviours by parasitic shiny cowbirds Molothrus bonariensis in captivity.

Eggs are critically important for avian reproduction as all birds are oviparous. Accordingly, the recognition and care of own eggs represent the cornerstones of avian breeding, whereas the elimination of foreign objects, including brood-parasitic eggs and non-egg items from the nest are known to also increase fitness by refocusing incubation effort on the parents' own eggs. But egg recognition also plays a role in some avian obligate brood parasites' reproductive strategy through the pecking of already present eggs in the hosts' clutch to reduce nestmate competition with the parasite's own hatchling. Here we tested egg shape recognition in this parasitic egg-pecking context by exposing two different series of 3D printed models to captive obligate brood-parasitic shiny cowbirds (Molothrus bonariensis) in artificial nests. Natural egg-shaped models were pecked more often compared with increasingly thinner models, but there was no effect of increasing angularity on pecking rates, implying that a natural, rather than an artificial, range of variability elicited adaptive responses from parasitic cowbirds.

NOTES ABOUT THE PREDATION OF A SHINY COWBIRD Molothrus bonariensis (Icteridae) BY A COMMON BOA Boa constrictor (Boidae), IN MANABÍ, ECUADOR

We present a sightseen of a juvenile Common Boa Boa constrictor preying on an individual of Shiny Cowbird Molothrus bonariensis. The event occurred in Manabí, Ecuador and lasted almost two hours since the attack started until the prey was completely swallowed and the Boa started to move.

Detection of neutralizing antibodies against flaviviruses in free-ranging birds, Paraguay (2016-2018).

Saint Louis encephalitis virus (SLEV), West Nile virus (WNV) and Ilheus virus (ILHV) are flaviviruses maintained by enzootic transmission networks between mosquitoes and birds. They have been detected in South America, with no records for Paraguay. We detected the presence of neutralizing antibodies for SLEV, WNV and ILHV in free-ranging birds collected in Paraguay (2016-2018). Four positive samples were detected in resident birds: one SLEV (rufous-bellied thrush), one WNV (barred antshrike) and two ILHV (white-tipped dove and shiny cowbird). These results bring new information about enzootic activity of flaviviruses in Paraguay.

Modeling and estimating co-occurrence between the invasive Shiny Cowbird and its Puerto Rican hosts

Modeling and estimating co-occurrence between the invasive Shiny Cowbird and its Puerto Rican hosts

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.

The bird shiny cowbirds (Molothrus Bonariensis) in a relationship interesting of mycophagy with the mushroom Macrolepiota Bonaerensis in the brazilian pampa biome

Bird-fungi associations are ecologically important, and the species of these groups that occur in the Pampa biome region have different characteristics. The Shiny Cowbirds (Molothrus bonariensis – Icteridae) is a ground foraging bird that cohabits vegetation of grasslands. Some mushrooms of this biome have considerably large and edible basidiomes, such as species of genus Macrolepiota (Agaricaceae). Therefore, the objective of this study was to contribute to the first description of mycophagy for the Pampa biome, including the species Molothrus bonariensis and Macrolepiota bonariensis. Data were submitted to a test of variance ANOVA and Tukey test at a 5% significance level. For the quantitative multivariate data, the test of Kiviat was elaborated. The test of Schumacher and Eschmeyer was used to determine the degree of interaction of the birds with the mushrooms. 60 hours of observations were realized with a flock of bird containing approximately 76 individuals in the study area. 30 fresh scat samples and 10 mushrooms that showed pecks signals were collected from the area georeferenced. Microscopic analysis of scat of birds revealed basidiospores of mushroom. For the record of foraging events, the mycophagy of birds was higher in zones with more occurrence of mushrooms. The results assist in better understand this important mycophagy interaction between the Shiny Cowbird and the mushroom M. bonaerensis. The study confirms that bird-fungal mycophagy associations are more widespread than previously thought.

Nest, eggs, and nestlings of the Gray-headed Tanager (Eucometis penicillata albicollis) from São Paulo State, Brazil

The Gray-headed Tanager (Eucometis penicillata) has 7 subspecies widely distributed in Central and South America. Scattered reproductive data are available for most of them, but reproductive aspects were thoroughly documented only for E. p. stictothorax, from Costa Rica. Here, we provide detailed descriptions of nests, eggs, and nestlings of E. p. albicollis from southeastern Brazil, and compile nesting information available from this and other subspecies from the literature. During the 2019–2020 and 2020–2021 breeding seasons, we found 4 nests that were active from October to January. Nests were deep cups with 8.5–11.1 cm in outer diameter, constructed of loosely attached dry fibers and sticks, and could be supported at their rims, laterally, or from beneath. They were built in riparian forest understory, 1.1–1.5 m above ground, 1.0–10.5 m away from forest streams, and 72–100 m from the forest edge. Clutches consisted of 3 eggs. Eggs were brownish-gray in background color, with dark-brown blotches, measured 21.9 mm (±0.8) in length and 16.2 mm (±0.7) in width, and weighed 3.0 g (±0.3). The hatchlings had reddish skin, bright orange mouth lining, and white commissure. The pair shared nestling provisioning and we also document the first case of brood parasitism by Shiny Cowbird (Molothrus bonariensis) for the Gray-headed Tanager. Upon comparing our data with that of other subspecies, we observed differences in nest material, breeding phenology, clutch size, and eggs and nestling characteristics, which could be attributed to local adaptations of geographically distinct subspecies or to phylogenetic divergences between still unsplit species.

The location of thrush nests on buildings affects the chance of cowbird parasitism

Nest site placement is a critical choice among passerines, being an important factor that affects their breeding success. In urban areas, human buildings offer suitable nesting sites usually less exposed to predators and brood parasitic birds and readily available to be reused for several breeding seasons. However, the extent to which the features of nest placement sites in buildings contribute to reduce nest detectability by predators and brood parasites is still unknown. Here, we tested whether the features of the nesting site (i.e., lateral concealment, distance to the building ceiling, and height above ground) affect the chance of brood parasitism by Shiny Cowbirds (Molothrus bonariensis) in Pale-breasted Thrushes (Turdus leucomelas) nests placed on buildings in a Brazilian suburban area from 2013 to 2019. Cowbird parasitism increased throughout the study years, and nests closer to ceilings, supposedly better concealed, were more likely to be parasitized. Laying date, height above ground, and lateral concealment were not related to the probability of cowbird parasitism. We suggest that less concealed nests enhance vicinity monitoring by parents, allowing a faster agonistic response to the presence of cowbirds near the nest. Our results indicate that nest site location in cities may have consequences for the breeding success of cowbird hosts.

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.

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

FEEDING HABITS OF THE STYGIAN OWL (ASIO STYGIUS) AND THE SHORT-EARED OWL (A. FLAMMEUS) IN THE SOUTHWEST OF BOGOTÁ SAVANNA, CUNDINAMARCA, COLOMBIA

This study quantitively compares the diets of the Stygian Owl (Asio stygius) and the Short-eared Owl (A. flammeus) in the south-west of the Bogotá Savanna, Colombia. We identified 130 prey items from 111 A. stygius pellets and 579 prey items from 149 A. flammeus pellets. In terms of the numbers of preys, the diet of A. stygius consisted of the following: 88.1% birds, mainly pigeons, rails and cuckoos; and a smaller proportion of beetles (11.4%). In the diet of A. flammeus, insects were the most frequent prey item (59.8%), followed by rodents (39.8%), and birds (0.5%). In terms of biomass contribution, the main preys in the diet of A. stygius were Eared Doves (Zenaida auriculata) (54%) and Purple Gallinules (Porphyrio martinica) (19.3%), while the diet of A. flammeus consisted mainly of House Mice (Mus musculus) (65.2%). Diet diversity varied between the owl species: A. flammeus was more selective in its hunting habits, while A. stygius was more of an opportunistic predator. It is important to quantify the ecosystem services these owls provide not only by controlling M. musculus, Z. auriculata, and Shiny Cowbird (Molothrus bonariensis) populations, which can affect human well-being and threatened species populations, but also through secondary seed dispersion and birdwatching opportunities.

Imposter eggs of pecking cowbirds have stronger shells for protection

When Alfred, Lord Tennyson, described, ‘Nature, red in tooth and claw’, he should probably have thrown in beaks too. Cowbirds that inveigle their eggs into the nests of others often pierce the resident eggs to give their impostors the best chance of a future. But there is nothing to prevent subsequent intruders from meting out the same fate to the eggs of previous interlopers. Analía López from the Universidad de Buenos Aires, Argentina, explains that birds like cuckoos, which lay their eggs in others’ nests, tend to have thicker eggshells. But she and her colleagues from Argentina and the USA, knew that other aspects of the eggshell's construction also contribute to its strength. They decided to take a closer look at the eggs from screaming cowbirds and shiny cowbirds – which puncture resident eggs to rid their young of competition – and compared them with the eggs of brown-headed cowbirds – which toss out the eggs of the species upon which they prey – to find out how the arms race between the eggshells of hard-working foster parents and their lackadaisical imposters has played out.‘We spent countless hours in the field looking for hidden bird nests to collect a few eggs’, says López, who sometimes used an extendable ladder – and even free climbed a few trees – to locate the eggs. Then, she and Lía Gerschenson (Universidad de Buenos Aires) tested how strong the shells were by recording the force required to puncture the eggs at the widest point, which is usually targeted by the pecking parasites. Sure enough, the shells of the egg puncturing screaming cowbirds and shiny cowbirds were up to 3.2 times stronger than the shells of their unwitting hosts; they were also 2.2 times stronger than brown-headed cowbirds’ shells. And when López checked how much energy it took to form the cracks that shatter the shells, the screaming and shiny cowbird's eggs were 1.5 times tougher.Next López teamed up with Raúl Bolmaro (Instituto Física Rosario, Argentina) and colleagues to compare the microscopic structures of the eggshells, and discovered that the external layer of the shell – known as the palisade layer, which provides the shell's strength – is thicker in screaming and shiny cowbirds than in brown-headed cowbirds. Also, the mammillary cones, which provide calcium for shell development, are packed more densely into the lower layer of the eggshell. And when López compared how calcium carbonate crystals are arranged in the shell, she found that the packing is far more complex in screaming and shiny cowbird eggs than in the shells of the other species, making them more difficult to crack open.Screaming and shiny cowbirds have evolved eggshells that are far more resistant to pernicious pecks than the eggs they usurp, providing their developing chicks with the best protection for a safe start in life. But López, Mark Hauber (University of Illinois at Urbana-Champagne, USA) and Juan Reboreda (Universidad de Buenos Aires) also point out that the eggshells can't be so tough that the tiny inhabitants within are unable to liberate themselves. Fortunately, it seems that toward the end of incubation the shells are less resistant to the chick's frail pecks from within. ‘As the chick tries to break the shell it does so by imposing expansion forces through internal shell pressures, which tend to open the small cracks produced by the beak's pressure points’, says López, explaining that this is how the imposter can break free of a shell that likely withstood the pounding of an adult cowbird's beak intent upon its destruction.