Prion Remains Infectious after Passage through Digestive System of American Crows (Corvus brachyrhynchos)

Avian scavengers, such as American crows (Corvus brachyrhynchos), have potential to translocate infectious agents (prions) of transmissible spongiform encephalopathy (TSE) diseases including chronic wasting disease, scrapie, and bovine spongiform encephalopathy. We inoculated mice with fecal extracts obtained from 20 American crows that were force-fed material infected with RML-strain scrapie prions. These mice all evinced severe neurological dysfunction 196–231 d postinoculation ( = 198; 95% CI: 210–216) and tested positive for prion disease. Our results suggest a large proportion of crows that consume prion-positive tissue are capable of passing infectious prions in their feces ( = 1.0; 95% CI: 0.8–1.0). Therefore, this common, migratory North American scavenger could play a role in the geographic spread of TSE diseases.     

Foraging Decision Rules and Prey Species Preferences of Northwestern Crows (Corvus caurinus)

Categorization of similar prey types and the application of decision rules by dietary generalists can enhance the efficiency of foraging decisions and facilitate the inclusion of novel prey types in the diet. While considerable research attention has been directed toward investigation of these concepts in invertebrates, few have assessed categorization and decision rules used by generalist vertebrate predators. In this study, we experimentally investigated decision rules and prey preferences of northwestern crows (Corvus caurinus) feeding on littleneck clams (Tapes philippinarum) and whelks (Nucella lamellosa). We presented crows with three species‐size combinations: small clams (2.0–2.9 cm length) paired with large whelks (4.0–4.9 cm), small clams paired with medium whelks (3.0–3.9 cm), and large clams (4.0–4.9 cm) with large whelks. Profitability estimates based on observations of crows feeding on these prey species indicated that clams were always the more energetically profitable option; however, in prey choice trials crows consistently selected the heavier prey species, regardless of differences in profitability. These results show that crows apply a general decision rule according to which they select heavier prey items when feeding on hard‐shelled prey requiring similar handling techniques, and that while such decision rules may approximate optimal choices they may not always follow predictions based solely on prey profitability. We discuss these results in the context of behavioural flexibility of generalist predators, and predicting impacts of intertidal avian predators on prey populations.     

Behavioural Type Affects Space Use in a Wild Population of Crows (Corvus corone)

While personality‐dependent dispersal is well studied, local space use has received surprisingly little attention in this context, despite the multiple consequences on survival and fitness. Regarding the coping style of individuals, recent studies on personality‐dependent space use within a habitat indicate that ‘proactive’ individuals are wider ranging than ‘reactive’ ones. However, such studies are still scarce and cover limited taxonomic diversity, and thus, more research is needed to explore whether this pattern generalises across species. We examined the link between coping style and space use in a population of crows (Corvus corone) freely inhabiting the urban zoo of Vienna, Austria. We used a binary docility rating (struggle during handling vs. no struggle) and a tonic immobility test to quantify individual coping style. Individual space use was quantified as the number of different sites at which each crow was observed, and we controlled for different number of sightings per individual by creating a space use index. Only the binary docility rating showed repeatability over time, and significantly predicted space use. In contrast to previous studies, we found that reactive crows (no struggle during handling) showed wider ranging space use within the study site than proactive individuals (who struggled during handling). The discrepancy from previous results suggests that the relationship between behavioural type and space use may vary between species, potentially reflecting differences in socioecology.     

Age Differences in the Responses to Adult and Juvenile Alarm Calls by Bonnet Macaques (Macaca radiata)

This study examined the differential responses to alarm calls from juvenile and adult wild bonnet macaques ( Macaca radiata ) in two parks in southern India. Field studies of several mammalian species have reported that the alarm vocalizations of immature individuals are often treated by perceivers as less provocative than those of adults. This study documents such differences in response using field-recorded playbacks of juvenile and adult alarm vocalizations. To validate the use of playback vocalizations as proxies of natural calls, we compared the responses of bonnet macaques to playbacks of alarm vocalizations with responses engendered by natural alarm vocalizations. We found that the frequency of flight, latency to flee, and the frequency of scanning to vocalization playbacks and natural vocalizations were comparable, thus supporting the use of playbacks to compare the effects of adult and juvenile calls. Our results showed that adult alarm calls were more provocative than juvenile alarm calls, inducing greater frequencies of flight with faster reaction times. Conversely, juvenile alarm calls were more likely to engender scanning by adults, a result interpreted as reflecting the lack of reliability of juvenile calls. Finally, we found age differences in flight behavior to juvenile alarm calls and to playbacks of motorcycle engine sounds, with juveniles and subadults more likely to flee than adults after hearing such sounds. These findings might reflect an increased vulnerability to predators or a lack of experience in young bonnet macaques.     

Filarioid nematodes (Filarioidea: Onchocercidae) of Corvus brachyrhynchos brachyrhynchos Brehm in southern Ontario,Canada and a consideration of the epizootiology of avian filariasis

Summary Chandlerella chitwoodae Anderson, 1961 (prevalence 65%), Splendidofilaria caperata Hibler, 1964 (21%), Eufilaria longicaudata Hibler, 1964 (15.5%), C. quiscali (von Linstow, 1904) Robinson, 1971 (1.9%), Cardiofilaria pavlovskyi Strom, 1937 (0.4%) and Splendidofilaria wehri (0.3%) were found in crows (Corvus brachyrhynchos brachyrhynchos Brehm) wintering in southern Ontario, Canada. S. caperata, E. longicaudata, Cardiofilaria pavlovskyi and S. wehri are reported for the first time from this host.Infection with Chandlerella chitwoodae and E. longicaudata produced microfilaraemias and these two common species apparently are maintained in the crow population. Infection with S. caperata was amicrofilaraemic (occult) and this common species cannot, therefore, be maintained in the crow population. C. quiscali, Cardiofilaria pavlovskyi and S. wehri occurred infrequently and must be common parasites of other woodland bird species. The presence of both common and sporadic infections in crows suggests that some avian filarioids parasitize numerous birds sharing a particular habitat. However, some host species are probably more important than others in maintaining infections within an avian community.The hosts of each species in Chandlerella, Splendidofilaria, Cardiofilaria and Eufilaria are listed. Chandlerella flexivaginalis (Jones, 1961) Sultana, 1962 and C. hispanica López-Caballero, 1974 are placed in synonymy with C. chitwoodae. Splendidofilarioides Freitas & Ibáñez, 1968 is made a synonym of Splendidofilaria and the type species becomes Splendidofilaria pachacuteci (Freitas & Ibáñez, 1968) n. comb. S. passerina Koch & Huizinga, 1971 is synonymized with S. algonquinensis (Anderson, 1955) Anderson, 1961. Pseudaproctella andersoni var. major Chabaud, Brygoo & Richard, 1964 and Cardiofilaria chabaudi Dissanaike & Fernando, 1965 are placed in synonymy with C. major Dissanaike & Fernando, 1965. Eufilaria cypseli (Annett, Dutton & Elliot, 1901) Nelson, 1966 is transferred to Lemdana as L. cypseli (Annett, Dutton & Elliot, 1901) n. comb. E. buckleyi (Desmukh, 1968) n. comb. is designated for Neofilaria buckleyi Desmukh, 1968 (= Eufilaria utae Anderson & Bain, 1976). ac]19800116Addendum: Since this paper went to press the following article has come to our attention: Olsen, O.W. & Braun, C.E. (1976) New species of Splendidofilaria and Chandlerella (Filarioidea: Nematoda), with keys to the species, from the band-tailed pigeon (Columba fasciata fasciata) in the Rocky Mountain region. Great Basin Naturalist, 36, 445–457. In their paper the authors describe the new species Splendidofilaria columbensis, S. hibleri and Chandlerella robinsoni. S. columbensis and S. hibleri are known from males only and their validity requires further study. C. robinsoni will also require further study.     

Breeding biology of House Crows (Corvus splendens) in Durban,South Africa

Nesting House Crows Corvus splendens were studied in the suburb of Merewent, Durban, South Africa, during the summer breeding season of 1999–2000. The c. 1km² study area supported 52–62 pairs. Breeding dispersal was clumped, suggesting a level of colonial breeding, but pairs were apparently intolerant of conspecifics nesting in the same tree. The two closest simultaneously active nests were 30m apart in adjacent trees. Details of nest locations, trees, heights, structure, dimensions and weights are provided. Egg-laying occurred October–January, mainly mid October to end November. Clutch size, egg dimensions and weights are given. Apparent repeat clutches were found but there was no evidence of double brooding. Details of nestling growth, and fledging and post-fledging dependence periods, are provided. Breeding success was relatively poor. Early breeding attempts were more successful than late breeding attempts. Breeding failure was suspected, or known, to be associated with observer disturbance, egg breakage, failure of eggs to hatch, starvation of chicks, nest collapse and independent control measures.     

Isolation and characterization of microsatellite loci in a cooperatively breeding corvid,the American crow (Corvus brachyrhynchos)

We describe 11 microsatellite loci isolated from the American crow (Corvus brachyrhynchos), the most wide‐spread cooperatively breeding bird in North America. Polymorphism at these loci ranged from four to 43 alleles, and observed heterozygosities from 0.53 to 0.92. Genetic parentage analyses using these markers will allow us to describe the mating system of this common but socially complex species, and to interpret their behavioural interactions in light of relatedness.     

Alarm Calls of Marmosets (Callithrix geoffroyi) to Snakes and Perched Raptors

Communication about the presence of predators is an important benefit of group living. Critical information about the nature of danger can be conveyed through referential alarm calls. Raptors pose a significant predatory threat to callitrichid species. Unlike a raptor in flight, a perched raptor cannot attack suddenly at great speed, and it can be monitored from a safe distance. In this sense a perched bird may pose a threat more similar to that of a terrestrial predator such as a snake. Here we compare predatory contexts by addressing these two questions: 1) Do marmosets produce acoustically distinct alarm calls to snake models and perched raptor models? 2) Do the visual responses of the marmosets to the playbacks of perched raptor–elicited calls differ from those given to the playbacks of calls given in response to snakes? We recorded alarm calls from two groups of outdoor-housed Geoffroy’s marmosets (Callithrix geoffroyi) in response to predator models. Later, we played back stimuli created from these recordings to the marmosets and scored their gaze direction. Results show that calls given to models of perched raptors are acoustically distinct from those given to models of snakes. Further, the relative number of upward to downward looks while listening to the playbacks of perched raptor–elicited calls was significantly greater than it was for snake-elicited calls. Reactions to airborne raptors are known to elicit freezing or rapid flight, neither of which occurred in response to our playbacks. Our data suggest a greater complexity in the alarm call repertoire of marmosets than previously demonstrated.     

Attitudes toward and Acceptability of Management Strategies for a Population of Hooded Crows (Corvus cornix) in Slovenia

Recently, the number of hooded crows (Corvus cornix) in Slovenia has increased, which has resulted in a higher number of situations perceived as human–wildlife conflicts. The purpose of our survey was to provide a basis for population management measures of hooded crows that would be both feasible and acceptable to the public. An online survey based on snowball sampling received 1,042 responses, representing about 0.05% of the total and 0.13% of the active human population of the Republic of Slovenia. The major findings are that the majority of respondents were interested in learning more about problems caused by crows and think that crow numbers should be reduced, but by measures that would not cause their death. About one-third of respondents would be willing to participate in measures directed to controlling the crow population; however, about one-third would actively oppose such measures. They would even sign a petition regarding control measures. From the results, we conclude that the most suitable strategies in terms of acceptability would be passive, by educating people about how to avoid conflict with crows, and by better management of the resources affecting their foraging success.     

Distress Calls of a Fast-Flying Bat (Molossus molossus) Provoke Inspection Flights but Not Cooperative Mobbing

Many birds and mammals produce distress calls when captured. Bats often approach speakers playing conspecific distress calls, which has led to the hypothesis that bat distress calls promote cooperative mobbing. An alternative explanation is that approaching bats are selfishly assessing predation risk. Previous playback studies on bat distress calls involved species with highly maneuverable flight, capable of making close passes and tight circles around speakers, which can look like mobbing. We broadcast distress calls recorded from the velvety free-tailed bat, Molossus molossus, a fast-flying aerial-hawker with relatively poor maneuverability. Based on their flight behavior, we predicted that, in response to distress call playbacks, M. molossus would make individual passing inspection flights but would not approach in groups or approach within a meter of the distress call source. By recording responses via ultrasonic recording and infrared video, we found that M. molossus, and to a lesser extent Saccopteryx bilineata, made more flight passes during distress call playbacks compared to noise. However, only the more maneuverable S. bilineata made close approaches to the speaker, and we found no evidence of mobbing in groups. Instead, our findings are consistent with the hypothesis that single bats approached distress calls simply to investigate the situation. These results suggest that approaches by bats to distress calls should not suffice as clear evidence for mobbing.     

Alarm Calls of California Ground Squirrels (Spermophilus beecheyi)

California ground squirrel alarm vocalizations were recorded in field and laboratory, and sonagraphically analysed. The contexts of both naturally occurring and experimentally elicited calls were noted in the field. The components of this graded system are chatters, chats and whistles. Chatters and chats are often elicited by terrestrial predators, whistles commonly by low flying raptors. Whistles are more commonly associated with cryptic behavior and flight than chatter-chats, but both call types usually elicit bipedal alert postures. These calls grade along a number of dimensions which may signal redundantly the level of excitation of the caller. We propose that the chatter-chat calls of highly aroused squirrels are composed of more and longer notes, occur at a higher rate, are less noisy and contain more frequency modulation. Whistles, however, are single-note calls that contain no frequency modulation, even though they are emitted by highly aroused squirrels and are long and noise free. Preliminary data suggest that: 1) chats are easier for a human ♀ to localize than whistles; 2) elevation of the head, by adopting bipedal postures and mounting promontories, enhances the audibility of alarms.     

Behavioural and Hormonal Stress Responses to Social Separation in Ravens,Corvus corax

Social life is profitable, but it facilitates conflicts over resources and creates interdependence between individuals. Separating highly social animals triggers intense reactions aimed at re‐establishing lost connections. Less is known, however, about behavioural and physiological responses to separation in socially facultative species, where individuals temporarily form groups and may subsequently leave them. Non‐breeding common ravens (Corvus corax) gather in large numbers at feeding and roosting sites, but otherwise spend time seemingly solitary or in small subgroups. We here studied how ravens cope with being socially isolated, and investigated the life characteristics that might explain potential individual differences. For this, we individually separated captive subadult ravens (n = 25) and housed them in physical and visual isolation from their group members across 4 d. During the separation period, we collected behavioural data and measured the amount of immunoreactive corticosterone metabolites from bird droppings to assess the ravens’ physiological stress response. We found behavioural indicators of stress at the start of the separation, when ravens showed higher levels of tension than of comfort – a pattern that reversed at the end of the separation. Furthermore, we found that the upbringing of ravens affected their behaviour during separation. Hand‐raised birds produced more vocalisations in the beginning of the separation, and were less active at the end, while the reverse pattern occurred with parent‐raised ravens. Contrary to our predictions, we did not find differences in hormonal responses between the beginning and end of the separation period or any link between hormonal responses and behaviours. Ravens’ behavioural responses to social separation stress seem to be dependent on their arousal states, although possible links with hormonal reactions remain unclear. Our results show that behavioural reactions are not always linked with hormonal responses to stress, and further emphasise the importance of investigating effects of early‐life experiences.     

Interspecific Responses of Ringtailed Lemurs to Playback of Antipredator Alarm Calls Given by Verreaux's Sifakas

The ringtailed lemur, Lemur catta, and Verreaux's sifaka, Propithecus verreauxi verreauxi, are diurnal prosimians living sympatrically in Madagascar. Species-specific alarm calls emitted by each of these two species in response to aerial and terrestrial predators differ acoustically. Behavioural responses of ringtailed lemurs evoked by playbacks of conspecific alarm calls differ when the vocalizations were produced in response to aerial predators as opposed to terrestrial predators. We conducted playback experiments on two populations of ringtailed lemurs, using two types of sifaka alarm calls. One population consisted of free-ranging groups which lived sympatrically with sifakas, the other was a colony group which had no contact with sifakas. The results illustrate that the former group of lemurs can perceive what type of predators the sifaka calls refer to, whereas the latter group was not able to recognize the difference in the calls.     

Variation in and Meaning of Alarm Calls in a Social Desert Rodent Rhombomys opimus

The great gerbil (Rhombomys opimus), a social rodent that lives in family groups, emits three different alarm vocalizations in the presence of predators: a rhythmic call; a faster more intense call; and a single whistle. We tested the hypothesis that the alarm calls communicate risk of predation. We quantified the relationship between predator distance and type of alarm call via human approaches to gerbils. We also tested responses of focal adults in family groups to playback broadcasts of the different calls and controls of bird song and tape noise. Results showed that alarm calls were related to distance from a predator. Gerbils gave the rhythmic call when the predator was farthest away, the more intense call as the predator moved closer; and a short whistle when startled by a close approach of the predator. Gerbils stopped feeding and stood vigilant in a frozen alert posture in response to playbacks of all three alarm calls. They decreased non‐vigilant behavior to the alarm vocalizations more than to the controls and decreased non‐vigilant behavior significantly more in response to the intense alarm and whistle compared with the rhythmic alarm. We conclude that one function of gerbil alarm calls is to communicate response urgency to family members. The rhythmic alarm communicates danger at a distance, whereas the intense alarm and whistle signal the close approach of a predator.     

Red Squirrels (Sciurus vulgaris) Respond to Alarm Calls of Eurasian Jays (Garrulus glandarius)

Recognition of heterospecific (interspecific) alarm calls has been demonstrated in birds and mammals, but bird–mammal interactions have rarely been studied. Here, I tested the hypothesis that red squirrels (Sciurus vulgaris) are able to recognize alarm calls of a sympatric bird species, the Eurasian jay (Garrulus glandarius), and respond adequately with anti‐predator behaviour. Both animals are preyed upon by the same predators. To test whether squirrels would react to heterospecific alarm calls, I recorded squirrels behaviour during playbacks of jay alarm calls, control playbacks (territorial songs of sympatric songbirds) and during silence. Differences between the control treatment (songbirds) and silence were not significant. Seven of the 13 squirrels responded with escape after broadcasting alarm calls of jays. Further, squirrels spent less time in the patch, expressed a higher vigilance, and showed more rapid head and body movements. These results suggest that squirrels recognize heterospecific alarm vocalizations of jays and discriminate them from equally loud non‐threatening sounds.     

Early Ontogeny of the Behavior of Young in Large-Billed Crows (Corvus macrorhynchos) in Their Natural Habitat

Biology Bulletin - The early ontogeny of behavior of corvid juveniles in their natural habitat was studied, and the large-billed crow (Corvus macrorhynchos) taken as an example. Research was...     

Responses of Redfronted Lemurs to Experimentally Modified Alarm Calls: Evidence for Urgency-Based Changes in Call Structure

Abstract The aim of this study was to investigate how information about the affective state is expressed in vocalizations. Alarm calls can serve as model systems with which to study this general question. Therefore, we examined the information content of terrestrial predator alarm calls of redfronted lemurs ( Eulemur fulvus rufus ), group-living Malagasy primates. Redfronted lemurs give specific alarm calls only towards raptors, whereas calls given in response to terrestrial predators (woofs) are also used in other situations characterized by high arousal. Woofs may therefore have the potential to express the perceived risk of a given threat. In order to examine whether different levels of arousal are expressed in call structure, we analysed woofs given during inter-group encounters or in response to playbacks of a barking dog, assuming that animals engaged in inter-group encounters experience higher arousal than during the playbacks of dog barks. A multivariate acoustic analysis revealed that calls given during group encounters were characterized by higher frequencies than calls given in response to playbacks of dog barks. In order to examine whether this change in call structure is salient to conspecifics, we conducted playback experiments with woofs, modified in either amplitude or frequencies. Playbacks of calls with increased frequency or amplitude elicited a longer orienting response, suggesting that different levels of arousal are expressed in call structure and provide meaningful information for listeners. In conclusion, the results of our study indicate that the information about the sender's affective state is expressed in the structure of vocalizations.     

Age Differences in the Response of Willow Tits (Parus montanus) to Conspecific Alarm Calls

Predation is an important mortality factor in wintering birds. To counter this, birds produce alarm calls in the presence of predators which serve to warn conspecifics. In social hierarchical bird flocks, adults survive the winter better than juveniles and therefore survival strategies probably vary with social status. This study examined the differential responses to alarm calls by free-living willow tits, Parus montanus, in dominance-structured winter flocks in Finland. To explore the age-dependent differences in response to conspecific alarm calls, a series with three alarm calls was played to focal adults and juveniles while they sat in the middle section of a spruce branch. Immediately after the playback, juvenile willow tits moved more often, flew longer distances and changed branches more often than did adults. Previous mammal studies have shown that juveniles are more likely to flee than adults after hearing conspecific alarm calls. The current study demonstrates that similar age-dependent responses to conspecific alarm calls occur in birds also. These findings reflect an increased vulnerability to predators or lack of experience of young birds.