Red-winged Blackbirds Agelaius Phoeniceus Research Articles

Functional neurogenomic responses to acoustic threats, including a heterospecific referential alarm call and its referent, in the auditory forebrain of red-winged blackbirds

In animal communication, functionally referential alarm calls elicit the same behavioral responses as their referents, despite their typically distinct bioacoustic traits. Yet the auditory forebrain in at least one songbird species, the black-capped chickadee Poecile atricapillus, responds similarly to threat calls and their referent predatory owl calls, as assessed by immediate early gene responses in the secondary auditory forebrain nuclei. Whether and where in the brain such perceptual and cognitive equivalence is processed remains to be understood in most other avian systems. Here, we studied the functional neurogenomic (non-) equivalence of acoustic threat stimuli perception by the red-winged blackbird Agelaius phoeniceus in response to the actual calls of the obligate brood parasitic brown-headed cowbird Molothrus ater and the referential anti-parasitic alarm calls of the yellow warbler Setophaga petechia, upon which the blackbird is known to eavesdrop. Using RNA-sequencing from neural tissue in the auditory lobule (primary and secondary auditory nuclei combined), in contrast to previous findings, we found significant differences in the gene expression profiles of both an immediate early gene, ZENK (egr-1), and other song-system relevant gene-products in blackbirds responding to cowbird vs. warbler calls. In turn, direct cues of threats (including conspecific intruder calls and nest-predator calls) elicited higher ZENK and other differential gene expression patterns compared to harmless heterospecific calls. These patterns are consistent with a perceptual non-equivalence in the auditory forebrain of adult male red-winged blackbirds in response to referential calls and the calls of their referents.

Attempted forced copulation by an immature Red-winged Blackbird male: Video evidence from the Grand River Grasslands of Iowa and potential explanations

Forced copulations are a type of sexual coercion that typically occurs when the fitness interests of males and females are in conflict. Forced copulations are rare in most species of birds, and there are only a few reports in passerine species. Here we report the first published observation of an immature Red-winged Blackbird Agelaius phoeniceus male attempting a forced copulation on a nesting Red-winged Blackbird female. We describe the behaviour and discuss potential explanations and implications for our observations.

Male Red-winged Blackbirds (Agelaius phoeniceus) respond with greater intensity to epaulets with UV reflectance

ABSTRACT Male Red-winged Blackbirds (Agelaius phoeniceus) have red epaulets that are used as badges for intrasexual competition for territory acquisition and defense. Red epaulets reflect very litt...

Shared transcriptional responses to con- and heterospecific behavioral antagonists in a wild songbird

The recognition of and differential responses to salient stimuli are among the main drivers of behavioral plasticity, yet, how animals evolve and modulate functional responses to novel classes of antagonistic stimuli remain poorly understood. We studied free-living male red-winged blackbirds (Agelaius phoeniceus) to test whether gene expression responses in blood are distinct or shared between patterns of aggressive behavioral responses directed at simulated conspecific versus heterospecific intruders. In this species, males defend territories against conspecific males and respond aggressively to female brown-headed cowbirds (Molothrus ater), a brood parasite that commonly lays eggs in blackbird nests. Both conspecific songs and parasitic calls elicited aggressive responses from focal subjects and caused a downregulation in genes associated with immune system response, relative to control calls of a second, harmless heterospecific species. In turn, only the conspecific song treatment elicited an increase in singing behavior and an upregulation of genes associated with metabolic processes relative to the two heterospecific calls. Our results suggest that aspects of antagonistic behaviors to both conspecifics and brood parasites can be mediated by similar physiological responses, suggestive of shared molecular and behavioral pathways involved in the recognition and reaction to both evolutionarily old and new enemies.

Calling in the face of danger: Do nestling Red-winged Blackbirds (Agelaius phoeniceus) suppress begging in response to predator playbacks?

AbstractNest predation is the most frequent cause of nest failure in birds such as the Red-winged Blackbird (Agelaius phoeniceus) that nest on or near the substrate. Nestlings should therefore exhibit adaptations to reduce the risk of nest predation. We tested the nestling antipredator hypothesis by examining the begging responses of Red-winged Blackbird nestlings to vocalizations of (1) an important nest predator (American Crow, Corvus brachyrhynchos), (2) a predator that rarely preys on nestlings (Cooper’s Hawk, Accipiter cooperii), and (3) a nonpredator (Northern Flicker, Colaptes auratus). We performed playbacks with (1) both parents present at the nest, (2) male at the nest, and (3) neither parent present. Following playback, we measured duration of nestling begging after the parent departed (begging persistence), bouts of otherwise normal begging when no parent was present (parent-absent begging), and calling without postural components of begging (nonpostural begging). When the male or both parents were present during playback, adults responded with alarm calls and nestlings significantly reduced parent-absent begging following American Crow and Cooper’s Hawk playbacks. Nonpostural begging was significantly reduced following Cooper’s Hawk playback, but there were no significant differences in the other begging variables. When neither parent was present, we found no significant differences in nonpostural begging in response to the 3 playback types, but parent-absent begging was significantly reduced following American Crow and Cooper’s Hawk playbacks when compared to Northern Flicker playbacks. These results show that nestlings suppress their vocal begging in response to calls of predators including Cooper’s Hawks even though they are not common nest predators.

Antipredator Behavior of Adult and Nestling Red-winged Blackbirds (Agelaius phoeniceus)

ABSTRACT Red-winged Blackbirds (Agelaius phoeniceus) experience high rates of nest predation and are therefore expected to exhibit adaptations to reduce the risk of eavesdropping by predators. We used a simulated predator and observations of adult and nestling behavior to test predictions of the predator eavesdropping hypothesis. Females (n = 42) delayed their feeding visits significantly longer and took significantly longer to complete their round trips when a plastic American crow (Corvus brachyrhynchos) was 20 m from their nests than when a black wood block was at the same location, but time spent off territory foraging did not differ significantly. Nestlings (n = 35 broods) begged appropriately (in response to a female at the nest) significantly less and at significantly lower intensity when the plastic crow was 20 m from their nests than when the wood block was at the same location, but the crow had no significant effect on the amount or intensity of inappropriate (no female present) begging. These a...

Nest Defense by Male Red-Winged Blackbirds (Agelaius phoeniceus) Improves Survival of Broods They Provision

ABSTRACT I observed male Red-winged Blackbirds (Agelaius phoeniceus) defend and provision nests, and I documented survival of pair-fed and female-fed broods to determine whether male parental behavior affects nestling survival and nest success. Broods provisioned by both males and females (n = 208) had significantly higher daily survival and were significantly more likely to produce fledglings than those fed only by females (n = 268). Examination of male responses to a crow model during incubation (n = 114) showed that males were more aggressive towards the simulated predator at nests they would later provision than at nests fed only by females. These results show that male provisioning is associated with more aggressive nest defense and increased nestling and nest survival, and suggest that parental behavior of male Red-winged Blackbirds is both plastic and adaptive.

Do Begging Calls From Nestling Red-Winged Blackbirds (Agelaius phoeniceus) Increase Nest Predation?

ABSTRACT I used 20 years of nest records and predation at silent control and begging-call playback nests to determine whether begging calls of Red-winged Blackbirds (Agelaius phoeniceus) attract predators. Survival analysis provided no evidence that vocal begging affected nest predation. Survival schedules during egg and nestling periods were not significantly different, and vocal begging activity was not significantly correlated with daily nest survival. I found that predation at 35 no-longer-active nests at which begging calls were played at natural volume, at a typical rate, and following a normal schedule was slightly but not significantly higher than at 35 silent control nests. Selection may have favored adaptations of nestling Red-winged Blackbirds' begging calls that reduce the risk of predation.

Mercury Concentrations in Eggs of Red-Winged Blackbirds and Tree Swallows Breeding in Voyageurs National Park, Minnesota.

Most investigations of the environmental effects of mercury (Hg) have focused on aquatic food webs that include piscivorous fish or wildlife. However, recent investigations have shown that other species, including passerine songbirds, may also be at risk from exposure to methylmercury (MeHg). We quantified Hg concentrations in eggs of two species of songbirds, red-winged blackbirds (Agelaius phoeniceus) and tree swallows (Tachycineta bicolor), nesting in Voyageurs National Park, Minnesota, USA. Geometric mean concentrations of total Hg (THg) were lower in red-winged blackbird eggs [218 and 107ng/g dry weight (dw) for 2012 and 2013, respectively] than in tree swallow eggs (228 and 300ng/g dw for 2012 and 2013, respectively), presumably reflecting differences in the trophic positionsof these two species. Concentrations of MeHg averaged 98.4% of THg in red-winged blackbird eggs. Levels of THg observed in this study were well below critical toxicological benchmarks commonly applied to eggs of avian species, suggesting these breeding populations were not adversely affected by exposure to MeHg. In red-winged blackbirds, concentrations of THg in eggs collected in 2012 were twice those in eggs collected in 2013. Hg levels in eggs of both species increased with date of clutch initiation. In red-winged blackbirds, for example, temporal patterns showed that a 3-week delay in clutch initiation increased egg THg by 60%. These observations indicate that in ovo exposure of wetland birds to MeHg can vary significantly within nesting season as well as between years.

Mismatched begging displays between foreign and host offspring reduce brood parasite fitness

Obligate brood parasites must obtain food from unrelated host parents during the developmental period, and this may be especially difficult when parasitic nestlings are raised alone. Unlike specialist brood parasites, generalist brood parasites use a single begging display for a range of host species. In this study, we 1) tested whether the begging display of the generalist brown-headed cowbird (Molothrus ater) was more exaggerated than the closely related, nonparasitic red-winged blackbird (Agelaius phoeniceus) and 2) examined how begging displays were linked to food provisioning when both foreign species were raised by the Bell’s vireo (Vireo bellii), a small cowbird host. We also quantified parental provisioning to unparasitized broods containing 1–4 vireo nestlings to provide a reference provisioning curve to provide context for assessing the feeding rate to foreign offspring. We found blackbirds begged as intensely as (or more intensely than) cowbird nestlings, vireo parents provisioned both species similarly, and the amount of food provisioned to unparasitized broods increased with brood size and maintained per-capita vireo growth. However, feeding of a single foreign nestling was significantly less than that of a modal brood of 4 vireos, indicating parents fed foreign nestlings at submaximal rates. Vireos did not respond to begging of foreign nestlings in the same manner as their own offspring, and this led to significant fitness costs for foreign nestlings. We conclude that a single foreign nestling provided an inadequate stimulus for vireos, probably because of a mismatch between the begging displays of foreign and host offspring.

Video Evidence of Infanticide by a Female Red-winged Blackbird

Abstract Several hypotheses have been proposed to explain infanticide in animals, but the behavior has only been observed in a few bird species. I describe video evidence of infanticide by a female Red-winged Blackbird (Agelaius phoeniceus) at a nest in Valley Forge National Historical Park in Pennsylvania. A female Red-winged Blackbird was seen pecking and pulling at the sole remaining 5-day-old nestling and eventually pulled the nestling from the nest until it fell to the ground. A female Red-winged Blackbird later returned to the nest with food 1 hour after the infanticide and made several visits with food in its bill. The last visit to the empty nest occurred 7 hours after the infanticide occurred. There were not sufficient plumage differences between the feeding and attacking bird to determine conclusively that they were different birds. The occurrence of infanticide could be explained by several hypotheses and might be more common in Red-winged Blackbirds than has been reported. For example, infant...

Immune Function in an Avian Brood Parasite and Its Nonparasitic Relative

Organisms that breed multiple times must trade off resources between current and future reproduction. In many species, sexual selection can lead to reduced levels of immune function in males because they invest heavily in current reproduction at the expense of self-maintenance. Much less is known about whether the same trend is seen in species such as the brood-parasitic brown-headed cowbird Molothrus ater (hereafter "cowbird"), in which females invest heavily in current reproduction. We examined two measures of immune function (bactericidal capacity of the plasma and the phytohemagglutinin swelling response) and baseline levels of corticosterone in both sexes of the cowbird and its nonparasitic relative the red-winged blackbird Agelaius phoeniceus (hereafter "redwing") during the breeding and subsequent nonbreeding seasons. We found that female cowbirds exhibited significantly lower levels of both measures of immune function than did male cowbirds and female redwings during the breeding season but had comparable levels during the nonbreeding season. Female redwings, in contrast, exhibited higher or comparable levels of immune function when compared with male redwings during the breeding season. In conjunction with published accounts documenting significantly higher rates of mortality for female cowbirds compared with male cowbirds and the fact that female cowbirds produce very high numbers of eggs (25-65) in a single breeding season, our results suggest that female cowbirds invest heavily in current reproduction at the expense of self-maintenance.

Do Sora Nests Protect Red-winged Blackbirds from Marsh Wren Predation?

Abstract We report an apparent protective effect of neighboring Sora (Porzana carolina) nests on Red-winged Blackbird (Agelaius phoeniceus) nests in an experimental study. We suggest that quail eggs used in Sora nests acted as a supernormal stimulus drawing Marsh Wrens (Cistothorus palustris), the main predator in the system, from Red-winged Blackbird nests.

Late pleistocene passerine birds from Sonora, Mexico

Songbirds (Passeriformes) have a very limited fossil record in spite of making up more than one-half of the world's 10,000 living species of birds. From the late Pleistocene fossil site of Térapa in east-central Sonora, Mexico, the identifiable fossils of songbirds consist exclusively of species of Icteridae. The seven extant species (Red-winged Blackbird Agelaius phoeniceus, Yellow-headed Blackbird Xanthocephalus xanthocephalus, Brewer's Blackbird Euphagus cyanocephalus, Great-tailed Grackle Quiscalus mexicanus, Bronzed Cowbird Molothrus aeneus, Brown-headed Cowbird M. ater, and Orchard Oriole Icterus spurius) still occur in Sonora, either as residents or migrants. The eighth fossil icterid from Térapa is an extinct genus and species of cowbird, Pandanaris convexa. The genus Pandanaris was known formerly only from late Pleistocene sites in southern California ( P. convexa A. H. Miller) and Florida ( P. floridana Brodkorb). We synonymize P. floridana with P. convexa because their supposed differences either cannot be substantiated or can be attributed to sexual dimorphism in size within a single species. Among the few Pleistocene sites from Mexico or the United States with well-studied and substantial assemblages of fossil passerines, Térapa is unique in its dominance of icterids (which may be common elsewhere but not dominant) and in its absence of corvids. Today, tropical “foothills thornscrub” is the vegetation type at Térapa except for riparian forest along the río Moctezuma. The icterid fossils are compatible with previous evidence (from plant, invertebrate, and other vertebrate fossils) that tropical/subtropical marsh, savanna, and riparian forest existed at Térapa during the late Pleistocene. Just as the two extant species of cowbirds associate today with large grazing mammals, the extinct Pandanaris convexa may have foraged in association with Pleistocene mammals whose extinction led to the demise of P. convexa as well.

Yellow-billed Cuckoo Hatched and Fed by a Red-winged Blackbird

Abstract I observed a Red-winged Blackbird (Agelaius phoeniceus) nest in southcentral Wisconsin, USA that received a Yellow-billed Cuckoo (Coccyzus americanus) egg. The cuckoo egg was laid after the blackbird clutch was complete and the female had begun incubation. The parasitic egg was considerably different in size and color, but was accepted by the female Red-winged Blackbird. The female, but not the male, also cared for the nestling, which was strikingly different in plumage, gape markings, and begging behavior, and which grew despite its 3–4 day hatching delay relative to its nest mates. Rapid development and exaggerated begging behavior of the Yellow-billed Cuckoo nestling may enable a parasitic cuckoo nestling to compete successfully with host nestlings for food.

Epaulet Color and Sexual Selection in the Red-Winged Blackbird: A Field Experiment

Abstract. The epaulets of male Red-winged Blackbirds (Agelaius phoeniceus) function in both intersexual and intrasexual contexts, but there is little evidence that they covary with reproductive success in this well-studied species. We used path analysis of male/territory traits, mating success, and reproductive success of unmanipulated males to estimate current directional selection. Territory size had a positive effect on number of within-pair mates. Number of extra-pair mates had a positive effect on number of extra-pair fledglings, and number of within-pair and extra-pair fledglings had positive effects on total number of fledglings. We also reddened epaulets of free-living territorial males to determine whether manipulated and control males differ in territorial behavior, mating success, or reproductive success. Compared with control males, males with reddened epaulets incurred elevated rates of trespassing and territorial challenges, lost their territories more often, and were unable to produce extra...

Family structure and variation in reproductive success in blackbirds

In avian families, some offspring are rendered unequal by parental fiat. By imposing phenotypic handicaps (e.g., via asynchronous hatching) upon certain of their offspring and not others, parents structure the sibship into castes of advantaged “core” offspring and disadvantaged “marginal” offspring that results in an asymmetric sibling rivalry. Here, I show how this family structure scales up to population level reproductive consequences. In a 17-year study of red-winged blackbirds (Agelaius phoeniceus), I show that year-to-year variation in the number of surviving offspring is driven primarily by variation in the number of marginal offspring at hatching and their posthatching survival. Clutch size, core brood at hatching, and fledging varied little from year to year and had little direct effect on year-to-year variation in total brood size at fledging; conversely, variation in the size of the marginal brood at hatching and at fledging was much greater. Marginal but not core brood size at hatching rose with mean clutch size; in years where parents laid larger average clutches they did so by adding marginal progeny. The mean posthatching survival of marginal offspring was always lower than that of core offspring in a given year, and there was no overlap in the distributions. The highest mean survival of marginal offspring across years fell below the lowest mean survival of core offspring; broods were deeply structured. There was an overall female bias among fledglings, and the sex ratio varied across years, with a higher proportion of the smaller female nestlings in years of below average reproductive success. Such variation was especially pronounced in the marginal brood where a higher incidence of brood reduction allowed greater potential for sex-biased nestling mortality. In years of the highest average reproductive success, the sex ratio in the marginal brood approached equality, whereas in years of the lowest average reproductive success, more than two thirds of 8-day-old nestlings were female. Structuring the brood into core and marginal elements allowed parents to modulate both offspring number and sex under ecological uncertainty with direct consequences for population-level reproductive success. They produced fewer and less expensive fledglings in below average years and more and more expensive fledglings in above average years.

Dispersal of viable row-crop seeds of commercial agriculture by farmland birds: implication for genetically modified crops

To address some concerns about the expansion of genetically engineered pharmaceutical and industrial crops to outdoor plantings and potential impacts on the human food supply, we determined whether commercial agriculture seeds of maize or corn Zea mays L., barley Hordeum vulgare L., safflower Carthamus tinctorius L. and rice Oryza sativa L. are digested or pass viably through the digestive tract, or are transported externally, by captive mallard ducks Anas platyrhynchos L., ring-necked pheasants Phasianus colchicus L., red-winged blackbirds Agelaius phoeniceus (L.) and rock pigeons Columba livia Gmelin (with the exception of whole maize seeds which were too large to feed to the blackbirds). These crop seeds, whether free-fed or force-fed, did not pass through the digestive tract of these bird species. The birds nonetheless did retain viable seeds in the esophagus/crop and gizzard for several hours. For example, after foraging for 6 h, mallards had retained an average of 228 +/- 112 barley seeds and pheasants 192 +/- 78 in the esophagus/crop, and their germination rates were 93 and 50%, respectively. Birds externally transported seeds away from the feeding location, but in only four instances were seeds found attached to their muddy feet or legs and in no case to feathers. Risk of such crop seeds germinating, establishing and reproducing off site after transport by a bird (externally or internally) or movement of a carcass by a predator, will depend greatly on the crop and bird species, location, environmental conditions (including soil characteristics), timing, and seed condition.

TERRITORY SELECTION BY UPLAND RED-WINGED BLACKBIRDS IN EXPERIMENTAL RESTORATION PLOTS

Abstract We examined territory selection of Red-winged Blackbirds (Agelaius phoeniceus) in experimental treatments with varied groundcovers and densities of planted and naturally occurring oaks (Quercus spp.) used by blackbirds for perching. We also compared vegetation parameters between blackbird territories and unused (i.e., unoccupied by Red-winged Blackbirds) areas. Although perch densities were greater in blackbird territories in unplanted controls and oak-planted treatments without redtop grass (Agrostis gigantea) than they were in unused areas, the low densities of perches in territories planted with redtop grass indicate that perch density is not limiting above some lower threshold. Territories, particularly in treatments with no redtop, tended to have greater mean grass cover and taller grass heights than unused areas. Our results are consistent with other studies in finding that Red-winged Blackbirds prefer areas having tall vegetation and dense grass.

Generalizability of artificial neural network models in ecological applications: Predicting nest occurrence and breeding success of the red-winged blackbird Agelaius phoeniceus

Separate artificial neural network (ANN) models were developed from data in two geographical regions and years apart for a marsh-nesting bird, the red-winged blackbird Agelaius phoeniceus. Each model was independently tested on the spatially and temporally distinct data from the other region to determine how generalizable it was. The first model was developed to predict occurrence of nests in two wetlands on Lake Erie, Ohio in 1995 and 1996. The second model was developed to predict breeding success in two marshes in Connecticut, USA in 1969 and 1970. Independent variables were vegetation durability, stem density, stem/nest height, distance to open water, distance to edge, and water depth. The nest occurrence model performance on the training data were at an average cross entropy, or concordance index ( c-index), of 0.75. Within geographical region testing in two different wetlands resulted in c-indices of 0.66 and 0.53. The breeding success model performance was at a c-index of 0.75 on the training data and at c-indices of 0.47 and 0.53 for within region testing. When we tested the nest occurrence model on fledged nestling data we obtained c-indices of 0.69 and 0.47 in Clarkes Pond in 1969 and 1970, respectively, and 0.43 and 0.52 in All Saints Marsh in 1969 and 1970, respectively. When we tested the fledged nestling model on the nest occurrence data, we obtained c-indices of 0.70 and 0.41 in Stubble Patch in 1995 and 1996, respectively, and 0.54 and 0.55 for Darr in 1995 and 1996, respectively. With input variable relevances, sensitivity analyses and neural interpretation diagrams we were able to understand how the different models predicted nest occurrence and breeding success and compare their differences and similarities. Important variables for predicting nest site selection/breeding success in both models were vegetation durability and distance to open water. Both models also predicted increasing nest occurrence/breeding success with increasing water depth under the nest and increasing distance to edge. However, relationships for prediction differed in the models. Generalizability of the models was poor except when the marshes had similar values of important variables in the model, for example water depth. ANN models performed better than generalized linear models (GLM) on marshes with similar structures. Generalizability of the models did not differ in nest occurrence and breeding success data. Extensive testing also showed that the GLMs were not necessarily more generalizable than ANNs. The results from this study suggest that ANN models make good definitions of a study system but are too specific to generalize well to other ecologically complex systems unless input variable distributions are very similar.