Molothrus Bonariensis Research Articles

Parasitismo de cría: nuevos eventos para el vaquero brilloso Molothrus bonariensis

Brood parasites lay their eggs in the nests of other species, thereby imposing on them the cost of parental care. In the Neotropics, the Shiny Cowbird Molothrus bonariensis is an obligate, generalist and opportunistic brood parasite with a wide and expanding range. This has led to an increase in the number of host species and potentially to fresh conservation problems. We searched for parasitic interactions in the Shiny Cowbird in Ecuador and documented 28 such events with 11 species. We added the Grey-browed Brush-finch Arremon assimilis and the Golden Grosbeak Pheucticus chrysogaster to the catalogue of previously known hosts (i.e., species that successfully raise the parasitic young). Additionally, we present here evidence of parasitism with the Eared Dove Zenaida auriculata, Fasciated Wren Campylorhynchus fasciatus, Thrush-like Wren C. turdinus and Tropical Mockingbird Mimus gilvus, which were previously listed only as victims (i.e., with no evidence of having successfully raised the parasitic young). We also increased the number of records of parasitism with the Peruvian Meadowlark Leistes bellicosus as a victim, and the Rufous-collared Sparrow Zonotrichia capensis, the Yellow-tailed Oriole Icterus mesomelas, the Scrub Blackbird Dives warczewiczi and the Silver-beaked Tanager Ramphocelus carbo as hosts. The Rufous-collared Sparrow seems to be the most commonly selected host in the Andean region of Ecuador. Although previously frequently recorded, many aspects of the natural history of this parasitic bird still need further research to preclude potential conservation problems in their host species.

Egg-puncturing behaviour by shiny cowbirds increases nest desertion in chalk-browed mockingbirds

Egg-puncturing behaviour by shiny cowbirds increases nest desertion in chalk-browed mockingbirds

Behavior and survival of parasitic Shiny Cowbird (Molothrus bonariensis) fledglings

Abstract For songbirds, the post-fledging period is critical for development and survival, as young must learn to get food, practice flying, and identify predators to become independent from their parents and disperse or migrate. Obligate avian brood parasites, like cuckoos and cowbirds, lay eggs in nests of other bird species that provide parental care until the parasite’s young become independent. The information on the post-fledging period in songbirds is limited due to the difficulty in following and observing fledglings and it is even scarcer for brood parasites. We studied the behavior, survival, and age of independence of Shiny Cowbird (Molothrus bonariensis) fledglings raised by two hosts that differ markedly in body size: the House Wren (Troglodytes aedon) and the Chalk-Browed Mockingbird (Mimus saturninus). We radio-tracked individuals from a few days before they left the nest until they disappeared from the natal territory. We found: 1) chicks left the nest when they were 11-15 days of age and the age of fledgling did not differ between the two host species, 2); after leaving the nest, they spent most of the time perched in a hidden place without begging but as they grew, the proportion of time perched without begging decreased and begging in hidden and exposed places increased, 3) we observed approaches between adult parasitic females and young in host territories, 4) young abandoned the host territory and joined conspecific flocks when they were 35-39 days of age, and 5) the estimated post-fledging survival was between 12.5% and 20.8%.

Anthropogenic nesting substrates increase parental fitness in a Neotropical songbird, the pale‐breasted thrush Turdus leucomelas

The failure of breeding attempts is a major hindrance to bird reproduction, making nest site choice under strong selective pressure. Urbanization may offer lower risk of nest predation to certain bird species, but the impact of using anthropogenic structures as nesting sites on parental fitness is seldom studied. We studied the effect of anthropogenic substrates and brood parasitism by the shiny cowbird Molothrus bonariensis on the nest success of a Neotropical songbird, the pale‐breasted thrush Turdus leucomelas. We monitored 263 nesting attempts between 2017 and 2020 to estimate daily survival rate (DSR), which represents the probability of a given nest surviving until the next day. DSR was modelled as a response variable in function of substrate type (plants as ‘natural' or human buildings as ‘artificial') and brood parasitism as fixed factors, using as covariates year, a linear and a quadratic seasonal trends. Additionally, we tested the effect of these same explanatory variables on the number of fledglings per nest using a generalized linear mixed‐effects model. Most nests (78.7%) were placed in artificial substrates and apparent nest success (i.e. the percentage of nesting attempts that produced at least one thrush fledgling) was higher in artificial (50.2%) than in natural substrates (37.5%). DSR was higher for nests in artificial than in natural substrates regardless of cowbird parasitism, whereas the number of fledglings per nest was higher both in artificial substrates and for nests without cowbird parasitism. We highlight that nesting in buildings significantly increases parental fitness in pale‐breasted thrushes, which may favor their settlement in cities and potentially drive the evolution of this breeding behavior in urban birds.

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).

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

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.

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.