Turdus Migratorius Research Articles

WINTERING LAND BIRDS IN RUSSIAN OLIVE IN SOUTHERN IDAHO

Point counts of wintering land birds using Russian Olive (Elaeagnus angustifolia) stands were conducted in 2000 and 2005 on the Snake River Plain, Idaho. The 14 most common species of the 28 recorded were found in both years, and most common species were recorded with similar frequencies between years. Thirteen bird species were observed foraging on Russian Olive fruits. Increases in recent decades in both area occupied by Russian Olive and in counts of Yellow-rumped Warblers (Setophaga coronata) and American Robins (Turdus migratorius) on Christmas Bird Counts suggest that there may be a relationship between Russian Olive expansion and abundance of these species.

Aggressive responses of Eastern Phoebes (Sayornis phoebe) and American Robins (Turdus migratorius) toward brood parasites and nest predators: A model presentation experiment

Brood parasites reduce the reproductive success of many bird species by laying eggs in their nests. Hosts that reject parasitic eggs (“rejecters”) avoid most costs of brood parasitism altogether by physically ejecting eggs from nests or abandoning parasitized nesting attempts. Species that accept parasitic eggs once these are laid (“accepters”) may reduce or eliminate costs by aggressively responding to brood parasites at their nests to prevent parasitism from taking place. Accordingly, accepters should recognize brood parasites and nest predators as different nest threats with different levels of aggression, whereas rejecters may not. We exposed active Eastern Phoebe (Sayornis phoebe, an accepter host) and American Robin (Turdus migratorius, a rejecter host) nests to models of a female brood parasitic Brown-headed Cowbird (Molothrus ater), an eastern chipmunk (Tamias striatus, nest predator), and a European Starling (Sturnus vulgaris, nonthreatening control) during the incubation stage. Phoebes alarm-called equally toward the nest predator and brood parasite models, but attacked the nest predator model more than the brood parasite model. Robins, in contrast, alarm-called toward and attacked all 3 models equally. Interpreting these results is challenging due to experimental design elements, specifically small sample sizes and restricting the experiment to the incubation stage. Nonetheless, our experiment contributes to the paucity of comparative studies on accepter versus rejecter nest defense behavior in response to both nest parasites versus predators, and adds a new tested accepter species to the literature.

The limits of egg recognition: testing acceptance thresholds of American robins in response to decreasingly egg-shaped objects in the nest.

Some hosts of avian brood parasites reduce or eliminate the costs of parasitism by removing foreign eggs from the nest (rejecter hosts). In turn, even acceptor hosts typically remove most non-egg-shaped objects from the nest, including broken shells, fallen leaves and other detritus. In search for the evolutionary origins and sensory mechanisms of egg rejection, we assessed where the potential threshold between egg recognition and nest hygiene may lie when it comes to stimulus shape. Most previous studies applied comparisons of egg-sized objects with non-continuous variation in shape. Here, instead, we used two series of three-dimensional-printed objects, designed a priori to increasingly diverge from natural eggs along two axes (width or angularity) of shape variation. As predicted, we detected transitions from mostly acceptance to mostly rejection in the nests of American robins Turdus migratorius along each of the two axes. Our methods parallel previous innovations in egg-rejection studies through the use of continuous variation in egg coloration and maculation contrast, to better understand the sensory limits and thresholds of variation in egg recognition and rejection in diverse hosts of avian brood parasites.

The blunt pole is not a source of more salient recognition cues than the sharp pole for the rejection of model eggs by American robins (Turdus migratorius)

Hosts of obligate avian brood parasites can reduce the costs of raising parasitic offspring by rejecting foreign eggs from their nests. Rejecter hosts use various visual and tactile cues to discriminate between own and foreign eggs. The blunt pole hypothesis specifically states that avian-perceivable visual information at and around the broader pole of the eggshell contains more salient recognition cues than does the sharp pole of the same egg. The directional prediction is, therefore, that eggs painted non-mimetically on their blunt pole should more likely be rejected relative to those similarly painted on their sharp pole. This hypothesis had been experimentally tested and its predictions supported solely in mimetic avian host-parasite systems, with hosts producing denser and more variable eggshell maculation patterns at the blunt pole, and in one species with immaculate eggs but still with distinctly discernible blunt-pole specific colouration. Here we aimed to expand upon these previous works and assessed whether the blunt pole of model eggs contains more salient egg rejection cues, relative to the sharp pole, for the American robin (Turdus migratorius), a robust rejecter of non-mimetic brown-headed cowbird (Molothrus ater) eggs. In this system host eggs are uniformly immaculate whereas the brood parasitic shell is maculated. We painted model cowbird-sized eggs on either the blunt or the sharp half to mimic the immaculate robin egg colours and the other half to resemble non-mimetic egg colours and patterns. There was no statistical support for the predicted outcomes of the blunt pole hypothesis in our trials as rejection rates were similar regardless of whether eggs were painted with non-mimetic colours on the blunt or sharp poles. Future work should test the role of asymmetrical signalling content for anti-parasitic rejection of eggs in additional host species, especially those with both immaculate own and mimetic parasitic eggs.

Pre-existing Microfilarial Infections of American Robins (Passeriformes: Turdidae) and Common Grackles (Passeriformes: Icteridae) Have Limited Impact on Enhancing Dissemination of West Nile Virus in Culex pipiens Mosquitoes (Diptera: Culicidae).

Microfilariae (MF) are the immature stages of filarial nematode parasites and inhabit the blood and dermis of all classes of vertebrates, except fish. Concurrent ingestion of MF and arboviruses by mosquitoes can enhance mosquito transmission of virus compared to when virus is ingested alone. Shortly after being ingested, MF penetrate the mosquito's midgut and may introduce virus into the mosquito's hemocoel, creating a disseminated viral infection much sooner than normal. This phenomenon is known as microfilarial enhancement. Both American Robins and Common Grackles harbor MF-that is, Eufilaria sp. and Chandlerella quiscali von Linstow (Spirurida: Onchocercidae), respectively. We compared infection and dissemination rates in Culex pipiens L. mosquitoes that fed on birds with and without MF infections that had been infected with West Nile virus (WNV). At moderate viremias, about 107 plaque-forming units (pfu)/ml of blood, there were no differences in infection or dissemination rates among mosquitoes that ingested viremic blood from a bird with or without microfilaremia. At high viremias, >108.5 pfu/ml, mosquitoes feeding on a microfilaremic Grackle with concurrent viremia had significantly higher infection and dissemination rates than mosquitoes fed on viremic Grackles without microfilaremia. Microfilarial enhancement depends on the specific virus, MF, and mosquito species examined. How virus is introduced into the hemocoel by MF differs between the avian/WNV systems described here (i.e., leakage) and various arboviruses with MF of the human filarid, Brugia malayi (Brug) (Spirurida: Onchocercidae) (i.e., cotransport). Additional studies are needed to determine if other avian species and their MF are involved in the microfilarial enhancement of WNV in nature.

Proximate predictors of variation in egg rejection behavior by hosts of avian brood parasites.

The rejection of parasitic eggs by hosts of avian brood parasites is one of the most common and effective defenses against parasitism. Despite its adaptive significance, egg rejection often shows substantial intraspecific variation: some individuals are more likely to remove or abandon parasitic eggs than others. Understanding variation in egg rejection requires that we study factors linked to the ability to perceive parasitic eggs as well as factors that may influence the rejection of a foreign egg once it has been recognized. Here, we asked what cognitive, physiological, and life-history factors explained variation in the rejection of model eggs by American robin (Turdus migratorius) females. We found that the probability of egg rejection was related to the clutch size at the time of parasitism: In support of Weber's law, females with fewer eggs were more likely to reject the model eggs. In turn, females with greater mass and higher corticosterone levels were less likely to reject eggs, and egg rejection probability was negatively related to incubation progress. Our data thus suggest that proximate predictors of an individual's egg rejection behavior include the cognitive environment of the nest, life-history factors, as well as the physiological state of the subject. However, much of the statistical variation in the egg rejection responses of robins to the model eggs remained unexplained. Future experiments should aim to test the causal roles of these and other factors in generating within- and among-individual variation in the rejection of parasitic eggs. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Natural and artificial scents do not increase egg rejection rates of model brood parasitic eggs by American robins (Turdus migratorius)

Hosts of obligate avian brood parasites can diminish or eliminate the costs of parasitism by rejecting foreign eggs from the nests. A vast literature demonstrates that visual and/or tactile cues can be used to recognize and reject natural or model eggs from the nests of diverse host species. However, data on olfaction-based potential egg recognition cues are both sparse and equivocal: experimentally-applied, naturally-relevant (heterospecific, including parasitic) scents do not appear to increase egg rejection rates in two host species, whereas unnatural scents (human and tobacco scents) do so in one host species. Here I assessed the predictions that (i) human handling of mimetically-painted model eggs would increase rejection rates, and (ii) applying unnatural or natural scents to mimetically or non-mimetically painted model eggs alters these eggs’ respective rejection rates relative to controls. I studied wild American Robins (Turdus migratorius), a robust rejecter species of the eggs of obligate brood parasitic Brown-headed Cowbirds (Molothrus ater). There was no statistical evidence to support either prediction, whereas poorer color-mimicry was still a predicted cause of greater egg rejection in this data set. Nonetheless, future studies could focus on this and other host species and using these and different methods to apply and maintain the scenting of model eggs to more directly test hosts’ use of potential olfactory cues in the foreign-egg rejection process.

Detection of Babesia odocoilei in Ixodes scapularis Ticks Collected from Songbirds in Ontario and Quebec, Canada.

Songbirds widely disperse ticks that carry a diversity of pathogens, some of which are pathogenic to humans. Among ticks commonly removed from songbirds, the blacklegged tick, Ixodes scapularis, can harbor any combination of nine zoonotic pathogens, including Babesia species. From May through September 2019, a total 157 ticks were collected from 93 songbirds of 29 species in the Canadian provinces of Ontario and Québec. PCR testing for the 18S gene of Babesia species detected Babesia odocoilei in 12.63% of I. scapularis nymphs parasitizing songbirds in Ontario and Québec; none of the relatively small numbers of Ixodes muris, Ixodes brunneus, or Haemaphysalis leporispalustris were PCR-positive. For ticks at each site, the prevalence of B. odocoilei was 16.67% in Ontario and 8.89% and 5.26% in Québec. Of 31 live, engorged I. scapularis larvae and nymphs held to molt, 25 ticks completed the molt; five of these molted ticks were positive for B. odocoilei. PCR-positive ticks were collected from six bird species—namely, Common Yellowthroat, Swainson’s Thrush, Veery, House Wren, Baltimore Oriole, and American Robin. Phylogenetic analysis documented the close relationship of B. odocoilei to Babesia canis canis and Babesia divergens, the latter a known pathogen to humans. For the first time in Canada, we confirm the transstadial passage of B. odocoilei in I. scapularis molting from larvae to nymphs. A novel host record reveals I. scapularis on a Palm Warbler. Our findings show that B. odocoilei is present in all mobile life stages of I. scapularis, and it is widely dispersed by songbirds in Ontario and Québec.

Kestrel nest box occupancy and fledging rates and the effect of kestrel presence and absence on bird abundance and activity in fruiting crops in the Niagara Region and Norfolk County

Frugivory by birds has been well documented and can have significant economic impacts globally. Invasive or pest species such as European starlings (Sturnus vulgaris) and American robins (Turdus migratorius) have been most frequently implicated and are omnivorous, adaptable, and opportunistic. Reducing their impact on ripening fruit crops is a constant topic of research in crop protection. Often, deterrents are installed at time of ripening but are unsuccessful if overused, as their continued presence at a single location allows for habituation by frugivorous species. American kestrels (Falco sparverius) are currently in decline in Southern Ontario. Habitat fragmentation, urbanization, climate change and invasive species have all contributed to this phenomenon. Kestrels, being cavity nesting birds, can be attracted to nest or roost in areas by installing kestrel nest boxes. Although not present during the ripening period of the fruiting crops studied, kestrels significantly reduced overall bird activity and abundance, and the abundance of thrush species (American robins) during their use of nest boxes in sensitive crops in the Niagara Region, while also promoting the continued presence of an at-risk species. Facilitating the presence of kestrels using nest boxes, or promoting the presence of birds of prey in general, can therefore be an effective bird deterrent mechanism. However, competition for the use of nest boxes from invasive species such European starlings decreased the successful occupancy rate of installed nest boxes by either kestrels or other beneficial species. Therefore, the monitoring, management, and maintenance of installed boxes is integral to their success as a deterrent mechanism and should be considered before their installation.

Self‐referent phenotype matching is a poor predictor of egg rejection by American Robins

Self‐referent phenotype matching is a poor predictor of egg rejection by American Robins

Facultative brood parasitism by an American Robin (Turdus migratorius) in the nest of a Gray Catbird (Dumetella carolinensis)

Avian brood parasites can be classified as either obligate or facultative. Obligate brood parasites, such as Brown-headed Cowbirds (Molothrus ater), must lay their eggs in the nests of other species because they exhibit no parental care. Although facultative brood parasitism, when species that would normally lay eggs in their own nests dump eggs in the nest of another individual, may occur frequently among conspecifics, facultative interspecific brood parasitism is relatively rare. Here I report on observations made during the breeding season of 2018 of an example of facultative brood parasitism by an American Robin (Turdus migratorius) in the nest of a Gray Catbird (Dumetella carolinensis). Two robin eggs were laid in the nest of the catbird and were successfully raised by the catbird to fledging age. Although the young of obligate brood parasitic cowbirds are rarely raised successfully by catbirds, this is the first documented example, of which I am aware, of a Gray Catbird successfully raising the young of a facultative brood parasite.

Morphological and molecular data reveal a new species of Lueheia (Acanthocephala: Plagiorhynchidae) from Turdus migratorius (Turdidae) in central Mexico and its phylogenetic implications within the family.

Members of the genus Lueheia Travassos, 1919, are endoparasites of birds, particularly passerines, throughout the Americas. Adults of Lueheia sp., (Plagiorhynchidae Golvan, 1960; Porrorchinae Golvan, 1956) were recovered from the intestine of the American robin (Turdus migratorius phillipsi Bangs) in Mexico City, and two other species of acanthocephalans identified as Porrorchis nickoli, (Plagiorhynchidae: Porrorchinae) Salgado-Maldonado and Cruz-Reyes, 2002 and Centrorhynchus microcephalus (Bravo-Hollis, 1947) Golvan, 1956 (Centrorhynchidae Van Cleave, 1916), were recovered from the Virginia opossum (Didelphis virginiana Allen) and groove-billed ani (Crotophaga sulcirostris Swainson), respectively in southeastern Mexico. Specimens of three species were sequenced at two molecular markers, the small subunit (SSU) and large subunit (LSU) of the nuclear rDNA and compared with other sequences available in GenBank. Maximum likelihood and Bayesian inference analyses of the combined (LSU + SSU) dataset and each individual dataset revealed that the specimens of Lueheia sp. formed an independent lineage, which is recognized herein as a new species, Lueheia aztecae n. sp., representing the fifth species of the genus in the Americas, and the second in the Nearctic region. The new species can be morphologically distinguished from the other five species in the genus by having a cylindrical proboscis, armed with 24-26 longitudinal rows with 9-10 hooks each. Phylogenetic inference performed with the combined dataset consisting of two genes (LSU + SSU) revealed that Lueheia aztecae n. sp. and P. nickoli belonging to subfamily Porrorchinae, formed two independent lineages, indicating that the subfamily is paraphyletic. Porrorchis nickoli and C. microcephalus formed a clade with other species of the genus Centrorhynchus, suggesting that P. nickoli should be transferred to genus Centrorhynchus, to form C. nickoli n. comb. In addition, we briefly discuss the ecological associations between the members of the families Plagiorhynchidae and Centrorhynchidae.

All in the timing: how fruit nutritional content influences the timing of fruit consumption of two invasive shrubs

The functional role that invasive species occupy within their new range is of significant interest for those concerned about invasive species management. Of particular importance is the distribution mechanisms of invasive plants. Viburnum dilatatum and Viburnum sieboldii are considered invasive species in New Jersey forest understories. We have observed that while the fruit of both species ripens at the same time, there is a difference in how long fruit persists. To better understand the temporal pattern, we examine fruit phenology and consumption, as well as energy density, percentage crude fat, and antioxidant capacity. We hypothesized that the difference in the timing of fruit consumption in these species is largely driven by nutritional content and that fruit with higher energy and fat content are eaten during migration. Our results indicate that V. sieboldii fruit is depleted in the fall, while V. dilatatum fruit persists into winter. In addition, we found that V. sieboldii fruit had higher energy density and 4.4 times as much crude fat compared to that of V. dilatatum fruit. However, V. dilatatum fruit had 9.5 times greater antioxidant capacity than V. sieboldii fruit. We also found that V. sieboldii fruit is mainly consumed by gray catbirds (Dumetella carolinensis) during the fall migration and the primary avian consumer of V. dilatatum fruit are American robins (Turdus migratorius) in the winter when birds are more sedentary. We suspect a mutualistic relationship has developed between these two invasive viburnum species and native avian frugivores. What remains to be seen is what effect different fruiting strategies have on seed dispersal.

Bird Species Involved in West Nile Virus Epidemiological Cycle in Southern Québec.

Despite many studies on West Nile Virus (WNV) in the US, including the reservoir role of bird species and the summer shifts of the Culex mosquito, feeding from birds to mammals, there have been few equivalent studies in the neighboring regions of Canada where WNV is endemic. Here, a priority list of bird species likely involved in WNV transmission in the greater Montréal area is constructed by combining three sources of data: (i) from WNV surveillance in wild birds (2002–2015); (ii) blood meal analysis of Culex pipiens–restuans (CPR), the primary enzootic vectors of WNV in the region, collected from surveillance in 2008 and 2014; (iii) literature review on the sero-prevalence/host competence of resident birds. Each of these data sources yielded 18, 23 and 53 species, and overall, 67 different bird species were identified as potential WNV amplifiers/reservoirs. Of those identified from CPR blood meals, Common starlings, American robins, Song sparrows and House sparrows ranked the highest and blood meal analysis demonstrated a seasonal shift in feed preference from birds to mammals by CPR. Our study indicates that there are broad similarities in the ecology of WNV between our region and the northeastern US, although the relative importance of bird species varies somewhat between regions.

The ecological context and fitness impact of categorical perception: a comment on Green et al.

Animals, including humans, must make sense of information, bombarding them from the enviroment, quickly and effectively. Categorical perception is one such process, and the evidence for it is increasing. We argue that the next step in the research of category-based decision making should be to study wild animals in the field and in behavioral contexts that have strong fitness-relevant impacts. We illustrate this point by the promise of categorical perception in the rejection of foreign egg colors by American robins (Turdus migratorius).

A successfully breeding, partially leucistic American Robin (<i>Turdus migratorius</i>)

American Robin (Turdus migratorius) is the most abundant and broadly distributed thrush in North America. Both sexes likely engage in mate choice, and there is some evidence of assortative mating based on breast colour in this species. Over two breeding seasons, we documented a case of partial leucism, primarily of the breast feathers, in a male American Robin in London, Ontario, Canada. We report evidence that the leucistic robin was capable of successful breeding. How the fitness of leucistic versus normal robins compares and how leucism influences mate choice in this and other species remain to be explored.

Behavioral responses to spring snow conditions contribute to long-term shift in migration phenology in American robins

Migratory birds have the capacity to shift their migration phenology in response to climatic change. Yet the mechanistic underpinning of changes in migratory timing remain poorly understood. We employed newly developed global positioning system (GPS) tracking devices and long-term dataset of migration passage timing to investigate how behavioral responses to environmental conditions relate to phenological shifts in American robins (Turdus migratorius) during spring migration to Arctic-boreal breeding grounds. We found that over the past quarter-century (1994–2018), robins have migrated ca. 5 d/decade earlier. Based on GPS data collected for 55 robins over three springs (2016–2018), we found the arrival timing and likelihood of stopovers, and timing of arrival to breeding grounds, were strongly influenced by dynamics in snow conditions along migratory paths. These findings suggest plasticity in migratory behavior may be an important mechanism for how long-distance migrants adjust their breeding phenology to keep pace with advancement of spring on breeding grounds.

Egg Incubation Temperature Affects Development of Innate Immune Function in Nestling American Robins (Turdus migratorius).

The innate immune system provides important first-line defenses against invading pathogens and is considered especially important for developing organisms. However, we know little about how early-life conditions influence these defenses in wild animals. For oviparous species such as birds, embryonic development occurs in the egg, which can be subject to variation in thermal conditions. There is evidence from cavity-nesting species and species with precocial young that reduced incubation temperatures can result in reduced measures of innate immunity. Whether and how this thermal variation impacts innate immunity for open-cup-nesting species with altricial offspring has not been examined. In this study, we experimentally manipulated egg incubation temperature for American robins (Turdus migratorius) and compared the bacteria-killing ability (BKA) of the nestlings' blood plasma. We collected baseline and poststressor samples on day 7 and day 10 after hatch to gain additional insights into the ontogeny of this immune measure, as well as into whether any changes were linked to levels of the glucocorticoid hormone corticosterone (CORT). We found that nestlings incubated at the low treatment (36.1°C) had significantly reduced BKA compared with nestlings incubated at the high treatment (37.8°C) when controlling for the posthatch nest environment. We also documented a significant reduction in poststressor levels of BKA, as well as an increase in BKA from day 7 to day 10. We found a weak inverse association between CORT and BKA but no other indications that BKA was mediated via treatment-induced variation in CORT. Our results suggest that incubation temperature can affect development of innate immunity in open-cup-nesting passerines.

Visual acuity and egg spatial chromatic contrast predict egg rejection behavior of American robins.

Color and spatial vision is critical for recognition and discrimination tasks affecting fitness, including finding food and mates, and recognizing offspring. For example, as a counter defense to avoid the cost of raising the unrelated offspring of obligate interspecific avian brood parasites, many host species routinely view, recognize and remove the foreign egg(s) from their nests. Recent research has shown that host species visually attend to both chromatic and spatial pattern features of eggs; yet how hosts simultaneously integrate these features together when recognizing eggs remains an open question. Here, we tested egg rejection responses of American robins (Turdus migratorius) using a range of 3D-printed model eggs covered with blue and yellow checkered patterns differing in relative square sizes. We predicted that robins would reject a model egg if they could visually resolve the blue and yellow squares as separate features, or accept it if the squares blended together and appeared similar in color to the natural blue-green color of robin eggs as perceived by the avian visual system. As predicted, the probability of robins rejecting a model egg increased with greater sizes of its blue and yellow squares. Our results suggest that chromatic visual acuity and viewing distance have the potential to limit the ability of a bird to recognize a foreign egg in its nest, thus providing a limitation to host egg recognition that obligate interspecific avian brood parasites may exploit.

Inter-Individual Variation in Anti-Parasitic Egg Rejection Behavior: A Test of the Maternal Investment Hypothesis.

SynopsisHosts of avian brood parasites may reduce or forego the costs of caring for foreign young by rejecting parasitic eggs from the nest. Yet, many host species accept parasitic eggs and, even among rejecter species, some individuals go on to incubate and hatch them. The factors explaining the variation in egg rejection between species have received much theoretical and empirical attention, but the causes of intraspecific variation in different individuals’ propensity for accepting parasitic eggs are less well understood. Here we tested the maternal investment hypothesis, which predicts that hosts with costlier clutches will be more likely to reject parasitic eggs from their nest. We studied variation in the egg rejection responses of American robins (Turdus migratorius), a robust egg-rejecter host of the brood parasitic brown-headed cowbird (Molothrus ater), to 3D-printed cowbird-sized eggs which were painted dark blue, a color known to induce variable and repeatable egg rejection responses in individual robins. Costlier clutch investment was estimated by earlier laying date, larger clutch size, heavier unincubated yolk mass, and variable yolk steroid hormone concentrations. There was no statistical support for most of our predictions. However, we detected more concentrated and greater overall amount of deoxycorticosterone deposited in egg yolks of rejecters relative to acceptors, although this accounted for no more than 14% of variance in the data. Future work should test experimentally the potential physiological linkage between maternal egg yolk steroid investment and egg rejection propensity in this and other host species of avian brood parasites.