Captive Brown-headed Cowbirds Research Articles

Speed kills: ineffective avian escape responses to oncoming vehicles.

Animal-vehicle collisions cause high levels of vertebrate mortality worldwide, and what goes wrong when animals fail to escape and ultimately collide with vehicles is not well understood. We investigated alert and escape behaviours of captive brown-headed cowbirds (Molothrus ater) in response to virtual vehicle approaches of different sizes and at speeds ranging from 60 to 360 km h(-1). Alert and flight initiation distances remained similar across vehicle speeds, and accordingly, alert and flight initiation times decreased at higher vehicle speeds. Thus, avoidance behaviours in cowbirds appeared to be based on distance rather than time available for escape, particularly at 60-150 km h(-1); however, at higher speeds (more than or equal to 180 km h(-1)) no trend in response behaviour was discernible. As vehicle speed increased, cowbirds did not have enough time to assess the approaching vehicle, and cowbirds generally did not initiate flight with enough time to avoid collision when vehicle speed exceeded 120 km h(-1). Although potentially effective for evading predators, the decision-making process used by cowbirds in our study appears maladaptive in the context of avoiding fast-moving vehicles. Our methodological approach and findings provide a framework to assess how novel management strategies could affect escape rules, and the sensory and cognitive abilities animals use to avoid vehicle collisions.

Behavioral compatibility and reproductive outcomes in two distant populations of captive brown-headed cowbirds (Molothrus ater).

Increased understanding of geographic variation in courtship behavior in animal species can provide insight into the ways behavior may influence evolutionary change. Here, the relationship of geographic variation in courtship behavior to reproductive outcomes was tested in two distant and behaviorally distinct populations of brown-headed cowbirds, Molothrus ater, by comparing rates of copulation and egg production. Females from an Indiana (IN) population and a South Dakota (SD) population were housed in aviaries with males from either their own population (INsame and SDsame) or the other population (INmix and SDmix). Over the breeding season, INsame females exhibited higher rates of copulation and egg production compared with INmix females, but no differences were detected between SDsame and SDmix females. The data suggest that behavioral differences between IN and SD cowbirds are the likely cause of lower egg production in the INmix females.

EFFICACY OF AIRCRAFT LANDING LIGHTS IN STIMULATING AVOIDANCE BEHAVIOR IN BIRDS

Abstract Aircraft collisions with wildlife (primarily birds) are costly in terms of injury or loss of human life, loss of the animals involved, damage to property and business, and the use of lethal control of wildlife at airports worldwide. One potential nonlethal technique to reduce bird–aircraft collisions—pulsed white and wavelength-specific aircraft-mounted light—has been considered for nearly 3 decades, but the efficacy of the technique has not been evaluated quantitatively. We tested the hypothesis that during daylight, captive birds exposed to an approaching ground-based vehicle exhibiting pulsing 250-W white aircraft landing lights would initiate avoidance behavior more quickly than birds experiencing an oncoming vehicle with nonpulsing (steady) or no lights (control). In experiments involving captive brown-headed cowbirds (Molothrus ater), Canada geese (Branta canadensis), European starlings (Sturnis vulgaris), herring gulls (Larus argentatus), and mourning doves (Zenaida macroura), only cow-bir...

BROWN-HEADED COWBIRDS IN EASTERN AND WESTERN NORTH AMERICA SHOW SIMILAR USE OF COURTSHIP SONGS IN COPULATION CONTEXTS

Abstract Past work with captive Brown-headed Cowbirds (Molothrus ater) has suggested geographic variation in the relative importance females place on the two categories of male courtship song, flight whistles and perched songs. However, audio-recorded copulation sequences showed that western M. a. obscurus (California) and eastern M. a. ater (Maryland, Oklahoma and Missouri) males gave both song categories immediately before and during most sequences in nature, matching previously reported data for the third subspecies, M. a. artemisiae. Thus field data provide no evidence for geographic variation in song use during mating. Because female lordosis responses to flight whistles in captivity can be negated by certain research methodologies, unlike perched song responses, flight whistle responsiveness appears to be more dependent on experience. In all regions, males sang at higher rates prior to and during copulation than in other contexts, a distinctive manner of vocalization that may influence female mating...

Factors Limiting Fecundity of Captive Brown-Headed Cowbirds

Factors Limiting Fecundity of Captive Brown-Headed Cowbirds

Sampling Blood from Birds: A Technique and an Assessment of Its Effect

We describe a technique and apparatus for extracting blood samples from birds in the field. We tested the effect of our technique on the health and behavior of captive Brown-headed Cowbirds (Molothrus ater) and free-living Red-winged Blackbirds (Agelaius phoeniceus). We found that captive Brown-headed Cowbirds that had been bled did not lose any more weight than birds that had not been bled. Territory loss by male Red-winged Blackbirds was not affected by taking blood samples, nor was annual return rate. Female Red-winged Blackbirds that were bled did not differ significantly in their rate of nest abandonment, nest success, fledging rate or annual return relative to females that were not bled. We conclude that blood sampling is not obviously harmful to wild birds as long as proper precautions are taken. Given the ease of the field technique and the vast potential for information to be gained, field ornithologists should not preclude adding laboratory blood analyses to their research program because of concerns about the technique negatively affecting the birds' health or behavior.

Endocrine Response of Captive Male Brown-Headed Cowbirds to Intrasexual Social Cues

The hormonal response to a spectrum of intrasexual social stimuli was studied in captive Brown-headed Cowbirds (Molothrus ater). Males were housed in individual cages in one of four conditions: (1) in a semicircle with other males (= visual + vocal stimuli), (2) in acoustic chambers with visual access to a devocalized companion (= visual stimuli only), (3) in chambers in which a tutor tape was played daily (= vocal stimuli only), and (4) in acoustic chambers with no other input (neither visual nor social stimuli). Blood samples were taken at 2-week intervals throughout the spring and early summer and assayed for testosterone. The results indicate that the greatest increase in testosterone was in the birds receiving visual plus vocal stimuli and in those receiving only visual stimuli; males receiving only vocal stimuli had a muted endocrine response, and those receiving no social stimulation exhibited the briefest response. The relatively small response to vocal stimulation is consistent with the absence of a behavioral response to simulated territorial intrusions (i.e., song playbacks) that has been shown in previous studies in male cowbirds.

Singing and the establishment and maintenance of dominance hierarchies in captive brown-headed cowbirds

The importance of singing in the establishment and maintenance of dominance rank was investigated in captive flocks of brown-headed cowbirds (Molothrus ater). Each flock consisted of 3 males and 1 female. In one experiment the two largest males in each of 4 flocks were temporarily devocalized by puncturing the interclavicular air sac just before group formation. The third male in each group was sham-operated. There was a significant tendency for the non-devocalized birds to become the dominant member of their group. Only sham-operated males sang immediately after the operation. In a second experiment, dominant males from flocks with established hierarchies were temporarily devocalized. None of these males lost their dominant positions, despite their inability to sing. These results suggest that song is important in the establishment of dominance rank; however, once established, social hierarchies may be maintained by non-vocal means, such as social inertia or individual recognition.

A guide to the literature on aggressive behavior

A guide to the literature on aggressive behavior