Maternal vocalizations of mallard ducks (Anas platyrhynchos)

Vocalizations of the Pekin duck (Anas platyrhynchos domesticus): how stimuli, sex, and social groups affect their vocal repertoire

Pekin ducks are exposed to stressors such as heat stress, enteric pathogens, mycotoxins, and other environmental stressors. We know from wild bird literature that birds communicate through vocalizations. We hypothesized that Pekin ducks would have a diverse repertoire that is affected by the sex, social group, and specific stimuli. We utilized adult Pekin ducks to develop a vocal repertoire. We placed 1 to 4 ducks of varying sexes into a sound chamber with various stimuli used to encourage new vocalizations. Birds were recorded for 20 min with several variations of number and sexes of ducks. Once the ducks were recorded each vocalization that was clipped was named based on a predetermined naming system. We characterized the vocal system of the ducks under each stimulus and social treatment in 4 ways: overall call rates, call diversity, call repertoire, and call spectral properties. In all cases, normality of residuals and homogeneity of variances for GLM and ANOVA models were confirmed using Proc Univariate (SAS v9.4) where a p ≤ 0.05 was considered significant. We found that Pekin ducks produce up to 16 different vocalizations. The treatments had a significant effect on the overall rate of calls given by the ducks (ANOVA: F6,31 = 8.55, p < 0.0001). Ducks produced the most calls by far when someone was sitting in the chamber with them (30.04 ± 4.45 calls/min). For call diversity, we found that there was a significant main effect of hen number (F218 = 12.21, p = 0.0004) but no main effect of drake number (F3,18 = 3.04, p = 0.0555). Cluster analyses indicated that certain types of calls were given under specific conditions. There were generally 6 major clusters of vocal repertoires (R-square = 0.899, Cubic Clustering Criterion = 9.30). Our results suggest that Pekin ducks are affected by the types of stimuli and social environment in how much they vocalize and in the properties of the calls they use. In addition, males and females differ somewhat in the repertoire of the calls they use, and in the spectral properties of their calls.

The Biology of Bird-Song Dialects

No single theory so far proposed gives a wholly satisfactory account of the origin and maintenance of bird-song dialects. This failure is the consequence of a weak comparative literature that precludes careful comparisons among species or studies, and of the complexity of the issues involved. Complexity arises because dialects seem to bear upon a wide range of features in the life history of bird species. We give an account of the principal issues in bird-song dialects: evolution of vocal learning, experimental findings on song ontogeny, dialect descriptions, female and male reactions to differences in dialect, and population genetics and dispersal.

We present a synthetic theory of the origin and maintenance of song dialects, one that accommodates most of the different systems reported in the literature. The few data available suggest that large, regional dialect populations are genetically differentiated; this pattern is correlated with reduced dispersal between dialects, assortative mating by females, and male-male exclusion. At the same time, “subdialects” may be formed within regional dialects. Subdialect clusters are usually small and may represent vocal mimicry among a few adjacent territorial males. The relative importance of genetic and social adaptation may contribute to the emergence of subdialects; their distinctiveness may be correlated with the degree of polygyny, for example. Thus, subdialect formation is linked to one theory of the evolution of repertoire size, but data are too fragmentary to examine this idea critically.

Contrasting approaches to a theory of learning

The general process view of learning, which guided research into learning for the first half of this century, has come under attack in recent years from several quarters. One form of criticism has come from proponents of the so-called biological boundaries approach to learning. These theorists have presented a variety of data showing that supposedly general laws of learning may in fact be limited in their applicability to different species and learning tasks, and they argue that the limitations are drawn by the nature of each species' adaptation to the particular requirements of its natural environment. The biological boundaries approach has served an important critical function in the move away from general process learning theory, but it is limited in its ability to provide an alternative to the general process approach. In particular, the biological boundaries approach lacks generality, it is in some respects subservient to the general process tradition, and its ecological content is in too many cases limited to ex post facto adaptive explanations of learning skills. A contrasting, ecological approach to learning, which can provide a true alternative to general process theory, is presented. The ecological approach begins by providing an ecological task description for naturally occurring instances of learning; this step answers the question: What does this animal learn to do? The next step is an analysis of the means by which learning occurs in the course of development, answering the question: How does the animal learn to do this? On the basis of such analyses, local principles of adaptation are formulated to account for the learning abilities of individual species. More global principles are sought by generalization among these local principles and may form the basis for a general ecological theory of learning.

Intersensory functioning in bobwhite quail chicks: early sensory dominance

Two sensory systems known to be important for the control of early filial behavior in precocial avian neonates are the auditory and visual modalities. This study examined the interaction between naturally occurring auditory and visual stimulation in the control of filial behavior in bobwhite quail (Colinus virginianus) during the first four days of postnatal development. Results revealed a hierarchy in the functional priority of the auditory and visual systems in the days immediately following hatchling. At one and two days of age, species identification in quail hatchlings was found to depend on the auditory component of maternal stimulation. Later in development (at three and four days of age), combined auditory-visual stimulation was necessary to control species-specific filial behavior. Even at these later stages of development, however, the auditory modality remained dominant over the visual in eliciting responsiveness to the maternal hen. These findings conform well to what is known about the neuroembryological development of the sensory systems, in that the auditory system of birds (and mammals) develops in advance of the visual system. This prenatal sequence of sensory system development appears to influence the nature of early postnatal perceptual preferences and serves to question several traditional assumptions regarding the imprinting process.

Maternal and peer imprinting in mallard ducklings under experimentally simulated natural social conditions

Previous studies revealed that if socially reared mallard ducklings actively follow a stuffed mallard (Anas platyrhynchos) hen, they later show a visual preference for the familiar mallard hen over an unfamiliar redhead (Aythya americana) hen. The present study determined that the experience of actively following the hen is essential to the induction of a visually controlled, species-typical, maternal preference. Domestic mallard ducklings that had not been given the opportunity to follow the mallard hen were "passively" reared in social groups consisting of a stuffed mallard hen and seven same-aged siblings for either 24, 48, or 72 hr after hatching. These birds were largely unresponsive to the hen in a later choice test, even when they were passively exposed to the mallard hen for as long as 72 hr prior to testing. The question arose as to whether passive exposure to the ducklings induced a preference for them that interfered with establishment of maternal imprinting under these simulated natural nest conditions. Results indicated that socially reared ducklings do prefer stuffed ducklings to a stuffed mallard hen in a simultaneous choice test even when the hen is present and vocalizing during social rearing. Further, even ducklings reared individually with the mallard hen were unresponsive to her in the later choice test. That there is something special about the stimulation provided by ducklings was further demonstrated by the finding that stuffed ducklings were preferred over the mallard hen (1) when the social rearing situation precluded active physical interaction with live ducklings and (2) when reared with inanimate stuffed ducklings. Thus, the ineffectiveness of the stuffed mallard hen in inducing visual imprinting under simulated nesting conditions cannot be attributed to the fact that she was not alive or reciprocally interactive. The present results suggest that mallard ducklings do not become visually imprinted to their hen until after departure from the nest, that the visual component of maternal imprinting likely involves active following subsequent to nest departure, and that early in postnatal development siblings are more visually attractive than is the hen.

Alarm call responsivity of mallard ducklings: VIII. Interaction between developmental history and behavioral context

Mallard ducklings (Anas platyrhynchos) inhibit their vocal behavior upon hearing the maternal alarm call of their species. The present study assesses the interaction of the ducklings' experiential history with the environment in which they are tested. If ducklings are reared and tested to the alarm call in small social groups, they respond by dramatically inhibiting their vocalizations. If, however, socially reared ducklings are tested to the alarm call individually in an open field, responsiveness drops precipitously. In addition, individually reared ducklings respond at a far greater level to the alarm call when tested individually, not in groups. Thus, there is an interaction between the rearing history and the testing environment such that the same rearing history leads to different behavioral outcomes depending on the context in which the ducklings are observed. This demonstrates the importance of behavioral context, in addition to developmental history, as one of the determinants of behavior.

Development of species identification in ducklings: XV. Individual auditory recognition

The present experiments examined the ability of domestic mallard ducklings (Anas platyrhynchos) to learn individual mallard maternal calls by either repetition-rate differences or spectral (Hz) differences, both of which are present in such calls recorded in nature. The ducklings could learn both kinds of differences within the first 24 hr after hatching, corresponding to the period prior to the exodus from the nest in nature. The hatchlings were able to learn these differences based upon only 12 min of exposure to the maternal calls during the first day after hatching. They were also able to retain (remember) the familiar call for an additional day after exposure. Embryos, on the other hand, could learn the spectral differences after either 12 or 24 min of exposure but could not retain the information under either exposure condition. An additional difference between the auditory learning competence of hatchlings and embryos was that the hatchlings were capable of learning the spectral features of a maternal call even if it was pulsed at different repetition rates during exposure (familiarization) and the subsequent test for recognition. The evolutionary significance of the results was discussed in terms of the general importance of familiarization as a basic behavioral mechanism underlying not only parental attachment but dietary and habitat preferences and the like.

Social specificity: interaction with own species is necessary to foster species-specific maternal preference in ducklings

Previous studies have shown that if domestic mallard ducklings are allowed social interaction with broodmates after their initial exposure to a stuffed mallard (Anas platyrhynchos) hen, they later show a visual preference for the familiar mallard over an unfamiliar redhead (Aythya americana) hen. Birds kept in social isolation do not make this difficult discrimination. In the present study, we examined whether this social enhancement of imprintability to a natural maternal model is merely the result of social stimulation in its most general sense, or if its effects are specific to social interaction for 30 min (training). This experience resulted in visual preference for the familiar mallard hen over the unfamiliar redhead hen in simultaneous choices tests at 48 hr and 72 hr after hatching only if the birds were allowed social experience with a group of same-age undomesticated mallard hatchings. No visual preference for the familiar mallard hen was found if the ducklings were permitted social experience with a group of same-age chick (Gallus domesticus) hatchlings or muscovy (Cairina moschata) ducklings. Thus, it appears that for ducklings to show a visually imprinted preference for a natural maternal model, they must be allowed social interaction with broodmates of their own species. Social rearing with other precocial bird hatchlings, even other ducklings, is without apparent effect. These results provide further evidence of the importance of nonobvious experimental factors in the development of species-typical behavior. They also suggest that in the evolution of the species-specific learning underlying early species identification, natural selection has operated on the entire (organism-environment) developmental manifold and not merely on genetic, organic, or organismic aspects of that system.

Alarm call responsivity of mallard ducklings: V. Age-related changes in repetition rate specificity and behavioral inhibition

Twenty-four-hour-old mallard ducklings (Anas platyrhynchos) exhibit a high degree of behavioral freezing (i.e., vocal and locomotor inhibition) upon hearing the maternal alarm call, which the hen utters when potential predators are near the nest. In this study, we assessed age-related changes in alarm call responsivity between 12 and 72 hr after hatching. Experiment 1 revealed that, although a significant reduction in vocal activity occurred upon exposure to the alarm call at all ages tested (12, 24, 36, 48, 60, 72 hr), birds older than 48 hr exhibited lower levels of freezing than younger birds. Furthermore, 12-hr-old ducklings exhibited the greatest level of freezing among the younger-aged groups. In Experiment 2, 12-, and 72-hr-old ducklings were tested to variations of the alarm call that differed in repetition rate (0.2 to 2.6 notes/sec, in increments of 2/10 of a second) to ascertain whether there are age-related changes in perceptual specificity and whether ducklings exhibit perceptual sharpening. Although older ducklings exhibited a slight shift in perceptual specificity toward faster repetition rates, they froze significantly less than younger ducklings at all repetition rates. Therefore, there was no evidence of perceptual sharpening. These data suggest that alarm call responsivity may represent an adaptation that appears to be associated with the timing of the nest exodus.

Training ducklings in broods interferes with maternal imprinting

Under natural conditions, if maternal imprinting is to occur it must occur in a social situation which includes the presence of broodmates. In the laboratory it has been shown that social rearing with siblings prior to maternal imprinting interferes with the establishment of maternal imprinting, whereas social experience with siblings after maternal imprinting enhances the imprinting experience. The present study examined the influence of social experience with broodmates during an imprinting trial on the establishment of a visually imprinted maternal preference in domestic mallard ducklings (Anas platyrhynchos). Twenty-four-hour-old ducklings were allowed to follow a stuffed mallard hen for 30 min either individually or in a brood of four same-aged ducklings. The birds trained alone subsequently showed an imprinted preference for the familiar mallard hen over an unfamiliar pintail hen or four stuffed ducklings in simultaneous choice tests at 48 and 72 hr after hatching. Ducklings trained with broodmates did not show a preference for the familiar mallard hen over the unfamiliar pintail hen and displayed a preference for the stuffed ducklings over the mallard hen at 48 and 72 hr choice tests. These results demonstrate that even brief (30 min) experience with siblings during a maternal imprinting trial results in peer imprinting that interferes with the establishment of maternal imprinting. These and other results of a similar sort render dubious the significance of most laboratory studies of imprinting for an understanding of such events in nature.

Visually imprinted maternal preference in ducklings is redirected by social interaction with siblings

This study examined the influence of social interaction with broodmates on a visually imprinted maternal preference in domestic mallard ducklings (Anas platyrhynchos) during the first three days of postnatal life. Twenty-four-hour-old ducklings were allowed to follow a stuffed mallard hen for 30 min. This experience resulted in a visually imprinted preference for the familiar stuffed hen over 4 stuffed ducklings in simultaneous choice tests at 48 and 72 hr after hatching, but only if the imprinted birds were kept in social isolation. Imprinted ducklings reared in a social group containing either same-age siblings or the stuffed mallard hen and same-age siblings displayed a visual preference for the stuffed ducklings over the familiar mallard hen at 48 and 72 hr tests. As a first step in the analysis of the features of the social exposure to siblings that are necessary for the redirection of the visually imprinted maternal preference, it was found that direct social interaction is essential to establish the preference for ducklings, but even mere visual exposure to siblings does away with the imprinted maternal preference. These results provide striking evidence of the ready redirection of a species-specific maternal preference in otherwise imprinted ducklings.

Effects of social experience on visually imprinted maternal preferences in Peking ducklings

If Peking ducklings are given social experience with agemates after their initial exposure to a maternal imprinting model (a stuffed mallard hen) their subsequent maternal preferences in simultaneous choice tests are different from those of isolate-reared ducklings. Early in development (at 48 hr after hatching), they show a visual preference for the mallard over a redhead model, a difficult discrimination that isolated birds do not make (Experiment I). However, later in development (at 72 hr after hatching) the social experience interferes with the birds' maternal preferences, in that socially reared birds do not show a visual preference for the mallard over a pintail model, a preference that isolated birds do show at that age (Experiment II). It was found that it is the later social experience with agemates (between 48 and 72 hr) that actively interferes with the preference for the mallard model, because birds that have had only early social experience with agemates (between 24 and 48 hr) prefer the familiar mallard to the pintail model at both 48 and 72 hr (Experiment III). The conventional view of visual imprinting is that it serves to establish a maternal bond that does not require further experience with the mother to be maintained. Our results suggest that in the natural situation, where potentially interfering social stimulation is provided by siblings, continual exposure to the mother may be necessary to maintain the maternal bond even after it has been established.