Quiscalus Lugubris Research Articles

Spermatid differentiation, with particular reference to acrosomogenesis, in the passeridan bird, Carib grackle (Quiscalus lugubris)

Only a few studies on the development of the passerine spermatozoon are available, yet species variations in the conformation as well as structure of the generally helical acrosome have been reported. This study of spermiogenesis in the Carib grackle (Quiscalus lugubris) intended to provide a deeper understanding of the development of the sperm, and in particular to investigate the bi-partite nature and development of the acrosome as well as its relationship with the nucleus, in the absence of a perforatorium that is found in most non-passerine birds. The acrosomal vesicle already displays a bi-partite nature in the acrosomal granule within the Golgi complex, and the attachment of the dense granule (future acrosomal core) within the crest part (future acrosomal crest) establishes polarity as it approaches and attaches to the nucleus. Thereafter, they develop variably. The acrosomal crest leads the elongation and spiraling of the acrosome, and the core portion contributes significantly to the formation of the keel of the crest part. The rounded, core-bearing part of the base of the acrosome progressively indents and fits into the concavity, thus formed, at the anterior part of the nucleus. The possible homology of the acrosomal complex (including the perforatorium) and the nucleus between non-passerine and passerine birds was discussed. The centriolar complex comprises both the proximal and distal centrioles in all spermatids and spermatozoa. The mitochondria undergo a number of morphological changes, including size and electron-density, from the round spermatid through to the mature spermatid; changes that are probably influenced by their functional states in the different evolving phases of the spermatids.

Speed-accuracy trade-off, detour reaching and response to PHA in Carib grackles.

Performance on different cognitive tasks varies between individuals within species. Recent evidence suggests that, in some species, this variation reflects the existence of coherent cognitive strategies bringing together positive and negative relationships between tasks. For example, Carib grackles show a speed-accuracy trade-off, where individuals that are fast at solving novel problems make more errors at discrimination learning than individuals that are slow solvers. Pathogens are thought to play a major role in shaping variation in cognition, either because different cognitive strategies lead to differential exposure to pathogens, or because investment in cognitive abilities is costly, limiting the ability to invest in anti-pathogen responses. In both cases, immunocompetence is expected to co-vary with cognition. Here, using wild-caught Carib grackles, we tested whether performance on reversal learning and detour-reaching tasks is associated with the speed-accuracy trade-off found in a previous study. In parallel, we measured the response of individuals to a phytohemagglutinin (PHA) injection, an immunoecological technique that assesses general immunity. Performance on two problem-solving tasks and two learning tasks was characterized by a speed-accuracy trade-off, reversal learning and discrimination learning performance being better in individuals with slower problem-solving performance. Detour-reaching performance was independent from this trade-off. Finally, our results show that PHA response was higher in accurate but slow grackles, and higher in grackles with better detour-reaching performance. Investigating the emergence and maintenance of variation in cognition in a framework integrating variation in physiology and life history is likely a major step towards a better understanding of the evolution of cognition.

Ocurrencia de Enteroparásitos en Poblaciones de Quiscalus lugubris (Aves: Passeriformes, Icteridae) del Semiárido Urbano del Estado Falcón, Venezuela

Los parásitos intestinales patógenos de aves paseriformes pueden potencialmente tener importancia zoonótica. Se realizó un estudio para determinar la ocurrencia de parásitos intestinales en heces de poblaciones de Quiscalus lugubris («torditos negros») (Aves, Passeriformes: Icteridae) en la ciudad de Coro, estado Falcón, Venezuela. El diagnóstico parasitológico de las muestras (n=156) se hizo mediante los métodos directo, flotación de Willis-Molloy y Faust, sedimentación en tubo y coloración de Kinyoun. Se detectaron hasta tres taxones de protozoarios, helmintos y acantocéfalos en 109 muestras (69.9%). Isospora spp (59.0%), Criptosporidium spp (37.8%) y el acantocéfalo Mediorhynchus spp (6.4%) fueron los enteroparásitos más frecuentes. Todos los parásitos encontrados representan nuevos registros para Q. lugubris en Venezuela.

Structural features of the spermatozoon of a passeridan bird, the Carib grackle, Quiscalus lugubris.

The spermatozoon of the Carib grackle, Quiscalus lugubris, a member of the family Icteridae, is generally similar in organization to the passerine-type of spermatozoon, in being highly elongated and displaying a helical structure of the acrosome, nucleus and principal piece of the tail. There are subtle variations in acrosomal structural features between this organelle in the grackle and that in some of the very few passerine species of birds in which the spermatozoon has been studied. The proximal centriole is present, and, thus, the Carib grackle is the third passeridan bird in which this organelle, hitherto regarded as absent in passerine birds, has been described in the spermatozoon. The spermatozoon of this bird also possesses a granular helix, which feature has been found variably even in the scanty available reports on passerine spermatozoa. It is advocated that the spermatozoon be studied in many more species of this large clade of birds. This report provides a basis for the study of spermiogenesis in the Carib grackle, with the aim of exposing, inter alia, a number of developmental features and processes of certain organelles that have received attention, recently, in the spermatozoa of passerine birds.

Bajan Birds Pull Strings: Two Wild Antillean Species Enter the Select Club of String-Pullers.

String-pulling is one of the most popular tests in animal cognition because of its apparent complexity, and of its potential to be applied to very different taxa. In birds, the basic procedure involves a food reward, suspended from a perch by a string, which can be reached by a series of coordinated pulling actions with the beak and holding actions of the pulled lengths of string with the foot. The taxonomic distribution of species that pass the test includes several corvids, parrots and parids, but in other families, data are much spottier and the number of individuals per species that succeed is often low. To date, the association between string-pulling ability and other cognitive traits was never tested. It is generally assumed that string-pulling is a complex form of problem-solving, suggesting that performance on string-pulling and other problem-solving tasks should be correlated. Here, we show that individuals of two innovative species from Barbados, the bullfinch Loxigilla barbadensis and the Carib grackle Quiscalus lugubris fortirostris, pass the string-pulling test. Eighteen of the 42 bullfinches tested succeeded, allowing us to correlate performance on this test to that on several other behavioral measurements. Surprisingly, string-pulling in bullfinches was unrelated to shyness, neophobia, problem-solving, discrimination and reversal learning performance. Only two of 31 grackles tested succeeded, precluding correlational analyses with other measures but still, the two successful birds largely differed in their other behavioral traits.

Feeding innovations in a nested phylogeny of Neotropical passerines.

Several studies on cognition, molecular phylogenetics and taxonomic diversity independently suggest that Darwin's finches are part of a larger clade of speciose, flexible birds, the family Thraupidae, a member of the New World nine-primaried oscine superfamily Emberizoidea. Here, we first present a new, previously unpublished, dataset of feeding innovations covering the Neotropical region and compare the stem clades of Darwin's finches to other neotropical clades at the levels of the subfamily, family and superfamily/order. Both in terms of raw frequency as well as rates corrected for research effort and phylogeny, the family Thraupidae and superfamily Emberizoidea show high levels of innovation, supporting the idea that adaptive radiations are favoured when the ancestral stem species were flexible. Second, we discuss examples of innovation and problem-solving in two opportunistic and tame Emberizoid species, the Barbados bullfinch Loxigilla barbadensis and the Carib grackle Quiscalus lugubris fortirostris in Barbados. We review studies on these two species and argue that a comparison of L. barbadensis with its closest, but very shy and conservative local relative, the black-faced grassquit Tiaris bicolor, might provide key insights into the evolutionary divergence of cognition.

Problem-solving and learning in Carib grackles: individuals show a consistent speed-accuracy trade-off.

The generation and maintenance of within-population variation in cognitive abilities remain poorly understood. Recent theories propose that this variation might reflect the existence of consistent cognitive strategies distributed along a slow-fast continuum influenced by shyness. The slow-fast continuum might be reflected in the well-known speed-accuracy trade-off, where animals cannot simultaneously maximise the speed and the accuracy with which they perform a task. We test this idea on 49 wild-caught Carib grackles (Quiscalus lugubris), a tame opportunistic generalist Icterid bird in Barbados. Grackles that are fast at solving novel problems involving obstacle removal to reach visible food perform consistently over two different tasks, spend more time per trial attending to both tasks, and are those that show more shyness in a pretest. However, they are also the individuals that make more errors in a colour discrimination task requiring no new motor act. Our data reconcile some of the mixed positive and negative correlations reported in the comparative literature on cognitive tasks, suggesting that a speed-accuracy trade-off could lead to negative correlations between tasks favouring speed and tasks favouring accuracy, but still reveal consistent strategies based on stable individual differences.

Cruzando o desviando los Andes: un comentario sobre extensiones de distribución recientes de aves cis-Andinas al oeste de los Andes de Colombia.

Título en ingles: Crossing or bypassing the Andes: a commentary on recent range extensions of cis-Andean birds to the West of the Andes of Colombia Titulo en Español: Cruzando o desviando los Andes: un comentario sobre extensiones de distribución recientes de aves cis-Andinas al oeste de los Andes de Colombia.titulo en Portugues: Cruzando ou desviando os Andes: um comentário sobre extensões de distrubuição recentes de aves cis-Andinas ao oeste dos Andes da Colômbia.Resumen: Varias especies de aves cis-Andinas (i.e. Orinoco-Amazonas) han sido reportadas recientemente en la ver- tiente occidental de la Cordillera Oriental y el valle medio del Magdalena de Colombia (i.e. trans-Andes). En este artículo presentamos los registros adicionales para tres de estas especies. El Colibrí Llanero (Polytmus guainumbi), la Mirla Caripelada (Turdus nudigenis) y el Chango Llanero (Quiscalus lugubris). Reportamos por primera vez el Moriche Blanco (Cissopis leverianus) en la región trans-Andina. También discutimos algunas hipótesis que explicarían estos registros trans-Andinos con base en la ecología de estas especies y las caracte- rísticas del paisaje. Dada la acelerada tasa de pérdida de hábitat y fragmentación a lo largo de las laderas An- dinas y tierras bajas circundantes, en conjunto con el efecto del calentamiento global sobre los rangos de las especies, sugerimos que las expansiones a través y alrededor de los Andes podrían ser más comunes durante las próximas décadas. Las especies generalistas podrían liderar las expansiones, mientras que las especies especialistas podrían enfrentar reducciones poblacionales debido a sus limitadas habilidades de dispersión. Estos registros evidencian la necesidad de monitorear la transformación del paisaje, la colonización y viabili- dad de las poblaciones de aves, así como la necesidad de continuar el trabajo de campo, incluso en regiones consideradas relativamente bien muestreadas en el país.Palabras clave: Dispersión, extensión de distribución, levantamiento de los Andes, pasos de montaña, trans-Andino, transformación del paisaje.Abstract: Several cis-Andean (i.e. Orinoco-Amazon) bird species have been recently recorded on the west slope of the Cordillera Oriental and the middle Magdalena valley, in Colombia (i.e. trans-Andes). Here, we provide additional records for three of these species. White-tailed Goldenthroat (Polytmus guainumbi), Spectacled Thrush (Turdus nudigenis) and Carib Grackle (Quiscalus lugubris). We report Magpie Tanager (Cissopis leverianus) for the first time in the trans-Andean region. We also discuss some hypotheses explaining these trans-Andean records based on the ecology of these species and landscape characteristics. Given the accelerated rate of habitat loss and fragmentation along the Andean slopes and adjacent lowlands, coupled with the effect of global warming on species’ ranges, we suggest that cross- and bypass-Andean expansions could become more common in the next decades. Generalist species could lead those expansions, whereas specialist species could face population reductions due to their limited dispersal abilities. These records show the necessity of monitoring the dynamics between landscape transformation, colonization and population viability of birds, and continuing fieldwork, even in areas considered relatively well sampled in the country.Key words: Andean uplift, dispersal, landscape transformation, mountain passes, range extension, trans-Andean.Resumo: Várias espécies de aves cis-Andinas (ex. Orinoco-Amazonas) têm sido reportadas recentemente na vertente ocidental da cordilheira Oriental e o vale Meio do Magdalena, em Colômbia (ex. trans-Andes). Nesse artigo apresentamos registros adicionais para três dessas espécies. Beija-flor-de-bico-curvo (Polytmus guainumbi), Caraxué (Turdus nudigenis) e Iraúna-do-norte (Quiscalus lugubris).Reportamos pela primeira vez a Tietinga (Cissopis leverianus) na região trans-Andina. Também discutimos algumas hipóteses que explicariam esses re- gistros trans-Andinos com base na ecologia dessas espécies e características da paisagem. Devido à acelerada taxa de perda de habitat e fragmentação ao longo das encostas Andinas e terras baixas ao redor, em conjunto como efeito do aquecimento global sobre o território das espécies, sugerimos que as expansões através e ao redor dos Andes poderiam ser mais comuns durante as próximas décadas; As espécies generalistas liderar as expansões, enquanto que as espécies especialistas poderiam enfrentar reduções populacionais por causa de suas limitadas habilidades de dispersão. Esses registros mostram a necessidade de monitorar a transformação da paisagem, a colonização e a viabilidade das populações de aves, assim como continuar o trabalho de campo, incluso nas regiões consideradas relativamente bem amostradas no país.Palavras chaves: Dispersão, extensão de distribuição, levantamento dos Andes, passagem de montanha, trans- Andino, transformação da paisagem.

Innovative foraging behaviour in birds: What characterizes an innovator?

Innovative foraging behaviour has been observed in many species, but little is known about how novel behaviour emerges or why individuals differ in their propensity to innovate. Here, we investigate these questions by presenting 36 wild-caught adult male Carib grackles (Quiscalus lugubris) with a novel problem-solving task. Twenty birds solved the task ("innovators") while 16 did not ("non-innovators"). We compared innovators to non-innovators and explored variation in latency to innovate to determine the characteristics of an innovative bird. Innovativeness was not predicted by any morphological trait, but innovators had higher exploration scores and lower object neophobia scores than non-innovators. Within the innovators, latency to innovate was positively correlated with learning speed. Video analysis also revealed a marked difference in the way individuals interacted with the novel apparatus: when innovators contacted the correct part of the apparatus, they continued to do so until they solved the problem. Non-innovators often contacted the correct part of the apparatus, but did not persist in doing so. The importance of obstacle movement cues was confirmed by an experiment where they were manipulated.

Innovation in groups: does the proximity of others facilitate or inhibit performance?

AbstractForaging innovation, in which an individual eats a novel food or uses a novel foraging technique, has been observed in a wide range of species. If other individuals are nearby, they may adopt the innovation, thus spreading it through the population. Much research has focused on this social transmission of behaviour, but the effect of social context on the emergence of novel behaviour is unclear. Here, we examine the effect of social context on innovative feeding behaviour in the Carib grackle (Quiscalus lugubris), an opportunistic, gregarious bird. We test the effect of the proximity of conspecifics, while eliminating the direct effects of interference, scrounging, or aggression. Using a repeated-measures design, we found that birds took significantly longer to contact novel foraging tasks when in the presence of others vs. alone, and during playbacks of alarm calls vs. a control sound. Further, performance of a food-processing behaviour decreased when birds were with others, and individuals adjusted their behaviour depending on their distance from conspecifics. Our results suggest that feeding in groups may slow down or inhibit innovative foraging behaviour in this species. We discuss the implications of a trade-off between feeding in groups and taking advantage of new feeding opportunities.

Kleptoparasitism by Grey Kingbirds (Tyrannus dominicensis) in Barbados

We observed Grey Kingbirds (Tyrannus dominicensis) from late February to May 2007 stealing food items from the bills of Carib Grackles (Quiscalus lugubris). This behavior occurred at two baited walk-in bird traps on the grounds of Bellairs Research Institute of McGill University in St James, Barbados. Grey Kingbirds were not seen entering traps, but were regularly observed in tree branches near traps, often chasing Carib Grackles and Zenaida Doves (Zenaida aurita) as they exited the traps with food. We describe six instances of kleptoparasitism by Grey Kingbirds from Carib Grackles. To our knowledge, this is the first report of kleptoparasitism for this species.

Wild Carib grackles play a producer scrounger game

Producer-scrounger (PS) game-theoretical foraging models make predictions about the decision of group-feeding animals either to look for food (produce) or for opportunities to exploit the discoveries of other foragers (scrounge). We report the most complete demonstration to date of the applicability of the PS foraging game in a free-living animal, the Carib grackle (Quiscalus lugubris) of Barbados. As assumed by PS games, the payoffs obtained by scroungers were negatively frequency dependent. Experimentally, increasing the cost of scrounging led to a decrease in the observed proportion of scroungers, whereas raising the cost of producing increased the proportion of scroungers. Observations of marked birds revealed that group-level changes could be brought about by individual flexibility in tactic use. Despite consistent individual differences in tactic use, most birds used both tactics and could alter their use of producing and scrounging when conditions changed. We found no difference in the payoffs obtained by producers and scroungers, suggesting a symmetrical game equilibrium. Our results call for testing the PS foraging game in a broader range of biological systems that include different types of scrounging behavior (e.g., scramble, stealthful, or aggressive scrounging) as well as the exploitation of different phases of food production (e.g., searching, handling).

Flexible expression of a food-processing behaviour: Determinants of dunking rates in wild Carib grackles of Barbados

Dunking, the softening of dry food in water to speed up consumption time, is normally a very rare behaviour in wild Carib grackles (Quiscalus lugubris) of Barbados. Its frequency can be experimentally increased when large numbers of dry items are repeatedly placed near a standing source of water in conditions that minimize intraspecific competition and risk of theft. To reconcile the normally low frequency of the behaviour in the wild with the high rates obtained in previous experiments, we tested three conditions where dunking varied between 0 and 70%. Dunking was very rare when it had been made unnecessary by pre-soaking the food, water was far from the dry items offered and only one food item was given, focusing all competitive interactions and theft attempts on a single individual. In contrast, dunking rate was high when food was not pre-soaked, water was close to dry food and more than one item (and hence target for competition and theft) was given. These experiments confirm that dunking rates, like other proto-tool-like food-processing techniques, depend on the costs and benefits of the situation where they are used.

Stealing of dunked food in Carib grackles (Quiscalus lugubris)

The use of tool or tool-like food processing behaviours can render animals vulnerable to theft (kleptoparasitism) because (1) large, nutritious items are usually involved, (2) value is added to the food due to long and/or complex handling, and (3) physical control of items is often temporarily lost during handling. In Barbados, Carib grackles (Quiscalus lugubris) immersing items in water before consumption (a behaviour known as food dunking) lose a larger proportion of items to conspecific food thieves than grackles that do not dunk. In this paper, we first show that dunking in Carib grackles functions as a proto-tool food-processing technique that speeds up ingestion. We then examine five potential predictors of kleptoparasitism: only conspecific density and loss of physical control on food were found to influence the probability that birds would be attacked and successfully robbed of food by conspecifics. Grackles could reduce the probability of kleptoparasitism by holding items in the bill while dunking and engaging in head-up displays. These behaviours were used flexibly depending on variation in the risk of kleptoparasitism. We suggest that costs like the ones incurred from theft might limit the profitability and frequency of tool and proto-tool food processing behaviours, creating a context where counter-strategies might be selected.

Mixed-species aggregations in birds: zenaida doves, Zenaida aurita, respond to the alarm calls of carib grackles, Quiscalus lugubris

Aggregating with heterospecifics may be particularly beneficial for a species that is able to exploit the antipredator behaviour of another. Territorial zenaida doves vigorously exclude conspecific intruders from their territory, but forage with, and acquire novel foraging techniques from, carib grackles. Given that doves associate with no other conspecific than their mate and they have no vocal alarm signals of their own, they might benefit from attending to the conspicuous alarm calls of carib grackles. In the present study, we found that zenaida doves suppressed foraging both in response to a model predator and in response to the sound of grackle alarm vocalizations. Although doves' responses to the predator model also involved moving away from the immediate vicinity, their responses to grackle alarm vocalizations consisted of remaining alert and tail flicking. Together, these results strongly suggest that doves attend to the antipredator behaviour of carib grackles. These findings extend earlier work demonstrating that doves obtain foraging benefits from their association with grackles, to show that they may also obtain predator avoidance benefits.

Social learning about predators: does timing matter?

In Pavlovian conditioning, animals acquire a response to a previously neutral stimulus (conditioned stimulus, CS), such as a light, if that stimulus predicts a biologically important event (unconditioned stimulus, US), such as delivery of food. Learning typically occurs when the CS precedes the US (forward conditioning), and not when the CS follows the US (backward conditioning). In social learning about predators, the predator stimulus is considered to be the CS to which observers acquire avoidance responses after the stimulus has been presented in contiguity with an alarmed demonstrator, the US. We tested the prediction that social learning of response to a predator would occur even if the social alarm cues (the US) appeared before the predatory stimulus (the CS). Carib grackles, Quiscalus lugubris , responded to a familiar predator presented at close range by suppressing alarm calls. Presentation of an unfamiliar avian model (black-and-yellow pigeon) also decreased calling, and this inhibition of calling was enhanced following a training session in which the model stimulus was presented in association with grackle alarm calls. Acquired inhibition of calling was independent of the order of presentation of the model and an alarm chorus. These are the first results to indicate that social acquisition of predator avoidance is not dependent upon a particular temporal relationship between predators and social alarm cues. Evolution may have modified some properties of Pavlovian conditioning to accommodate social learning about potentially dangerous stimuli.

Dunking behaviour in Carib grackles

Dunking behaviour, the dipping of food in water, has been anecdotally observed in more than 25 species of birds in the wild, but its function and ecology have not been systematically studied. In experiments conducted in the field and in captivity on Carib grackles, Quiscalus lugubris, in Barbados, we showed that: (1) dunking rate in the field was influenced by food type and that moistening dry food seems to be one of the major benefits of dunking; (2) most dunking observed in the field was performed by a minority of individuals, but the vast majority (86%) of grackles tested in captivity were capable of dunking; (3) a higher density of conspecifics at a water source was associated with a lower dunking rate and an increased risk of kleptoparasitism when dunking; and (4) there were consistent individual differences in dunking and stealing frequency. We conclude that dunking is part of the normal behavioural repertoire of Carib grackles in Barbados, and that the low frequency of the behaviour in the field did not result from the inability of some individuals to perform the technique, but more likely from the balance of costs and benefits affecting its expression.

Problem solving and neophobia in a columbiform–passeriform assemblage in Barbados

Previous research suggests a link between innovation rate, neophobia and behavioural flexibility in the field and in captivity. In this paper we examine three correlates of flexibility in five opportunistic avian species that feed together in Barbados: three Passeriformes (the Carib grackle, Quiscalus lugubris, the Lesser Antillean bullfinch,Loxigilla noctis , and the shiny cowbird, Molothrus bonariensis) and two Columbiformes (the zenaida dove,Zenaida aurita and the common ground dove, Columbina passerina). The flexibility measures are habituation to a new food patch, willingness to feed near a novel object (neophobia) and ability to obtain food from a new apparatus (problem solving). Passeriformes (in particular grackles and bullfinches), as predicted from their high innovation rate in anecdotal data, outperformed Columbiformes on all three measures. The three tests yielded similar results in the field and in captivity. Grackles, which are members of the most innovative passeriform genus in North America after Corvus, were by far the most successful species on the problem solving test. Individual variation in attempts to obtain food from the new apparatus was predicted by latency to approach it, which was in turn predicted by latency to feed near novel objects. This study provides experimental evidence, both in the field and in captivity, for the taxonomic differences in innovative flexibility seen in anecdotal data and suggests that neophobia is an important intervening variable in response to new feeding problems.

Ecological Differences in Social Learning between Adjacent, Mixing, Populations of Zenaida Doves

AbstractIn Zenaida doves, Zenaida aurita, of Barbados, previous work has shown that social learning is associated with foraging ecology in the field: in captive experiments, group‐foraging birds learn more readily from a conspecific tutor, while territorial birds learn from the heterospecific they most often feed with in mixed‐species aggregations, the Carib grackle, Quiscalus lugubris. This study examines foraging ecology and social learning in a dove population that experiences both territorial defence and occasional group feeding, Brandon's Beach. In part I, we document the dual foraging pattern seen in this population, which lives only a few hundred metres from the group‐foraging harbour population studied in previous work. In part II, we show that doves from Brandon's Beach, consistent with their dual foraging experience, learn as readily from a conspecific as they do from a heterospecific tutor; control doves from the adjacent harbour site learn primarily from a conspecific tutor. Field sightings of banded individuals caught at the harbour and Brandon's show strong site fidelity, but sufficient movement between areas (4%) to make reproductive divergence between the two neighbouring populations highly unlikely, suggesting that social learning differences between them are non‐genetic.

Carib Grackles Imitate Conspecific and Zenaida Dove Tutors

Abstract In Barbados, Carib grackles (Quiscalus lugubris) forage in opportunistic aggregations that include territorial Zenaida doves (Zenaida aurita) and flocks of conspecifics. In searching for and handling food, grackles use complex beak movements and modulate priority of access with a mixture of postural signals and intra- and interspecific scramble (unaggressive) competition. We show in two experiments that wild-caught grackles learn as readily from a Zenaida dove as they do from a conspecific tutor, whether tutors use similar or different food-finding techniques. Grackles also imitate the technical variant that the hetero- and conspecific tutors were shaped to demonstrate: those who observed a Zenaida dove used the dove's closed beak pecking technique, while those who observed a conspecific used the grackle's open beak pulling, probing or prying. Our findings suggest that imitation, like other forms of social learning, is strongly influenced by a species' foraging ecology. In particular, the ability to imitate novel motor skills should be favored in opportunistic species which exhibit scramble competition and which use complex searching and handling techniques to forage on embedded foods.