Number Of Crows Research Articles

Determining the cause of the hen harrier decline on the Orkney Islands: an experimental test of two hypotheses

A supplementary feeding and predator removal experiment was conducted on the hen harrier population on West Mainland, Orkney, to test whether increased predation pressure or shortage of food was responsible for the poor breeding success and potentially the decline of this population. Although numbers of crows appeared to have increased since 1983, the removal of hooded crows from breeding territories of male harriers had no detectable effect on any of the breeding parameters measured. The provision of supplementary food to male harriers significantly increased their numbers of breeding females, but had no detectable effect on either lay date, clutch size or hatching success. Results suggest that the current low levels of polygyny are a consequence of a shortage of food during the pre-lay period. Conservation management for this species should therefore be directed towards increasing the harriers' food supply, especially during the pre-lay period.

Sound levels of broadcast calls and responses by American crows

Bird control often entails the use of sound to disperse birds from croplands or other sites. Little information is available concerning the sound levels produced by noise-making devices or the effective area of coverage. In 1998 and 1999 we measured the sound levels of American crow (Corvus brachyrhynchos) distress calls produced by 2 models of a commercially available broadcast unit. With the units set up at different heights (0.9 to 4.9 m) in an open area or in an almond orchard, we used a sound meter to measure sound levels at distances of 1 m and 15 m, and then at 15-m intervals out to a distance of 90 m from the speakers. Sound levels decreased from about 102 dB at 1 m down to or nearly to background noise levels at a distance of 90 m. Sound levels from a unit set up to broadcast at a 4.9-m height through the orchard canopy were lower than for a unit set up at a 0.9-m height broadcasting under the canopy. Sound levels from a unit set at the 0.9-m height in the open were greater than those from the 0.9-m setup under the canopy only at a distance of 90 m. We set up a broadcast unit at various roadside locations in Yolo County, California, to determine the distance over which crows heard and reacted to the broadcast calls. Upon activation of the unit, we scanned the surrounding area for any crows flying from their perches. When crows reacted to the call we recorded the distance to the site of origin with a laser rangefinder and the number of crows. We also recorded the distance and number as above for any 2nd or 3rd flocks responding. We broadcast the calls on 11 days and on 27 occasions crows responded, typically by flying up from their perches, sometimes flying overhead, and then flying away. The average distance for the 1st flocks was 142 m + 73 SD (range 22 - 275 m). On 7 occasions 2nd flocks responded from an average distance of 174 m + 110 SD (range 71 - 312 m). On all but one occasion the 2nd flocks originated from a more distant location than the associated primary responders. We observed one instance of a 3rd flock responding. Fourteen (51.8%) of the 27 primary responses were from distances >122 m, about the distance at which the sound levels from the broadcast unit drop to background levels. These data indicate crows detected sounds from the broadcast units at distances greater than suggested by the sound meter. Using the average distance of 142 m for the 1st flocks responding, we calculated crows in a 6.3 ha open area could hear the broadcast calls. Using the maximum distances we observed of 275 m for 1st flocks and 312 m for 2nd flocks, we suggest that under some conditions crows within open areas of nearly 24.3 ha and 30.4 ha, respectively, heard the calls or responded to other crows hearing the calls.

Evaluation of lasers to disperse American crows, Corvus brachyrhynchos, from urban night roosts

American crows ( Corvus brachyrhynchos ) have a long history of causing agricultural damage in North America. Shooting and bombing at crow night roosts have been employed to reduce such damage. Most roosts were located in rural locations, but in the latter half of the 1900s crows began to roost in urban locations. Urban crow roosts are presently a nationwide problem in the United States. Thousands of crows at a roost create problems for businesses and residents. Improved control techniques are needed. Lasers have been used in Europe to scare and disperse birds but the technique has only recently received formal testing. We treated urban roosts with lasers to determine if crows react to laser light, can be dispersed from roosts, and whether lasers are effective for eliciting roost abandonment. We treated 63 roosts in Woodland, California and recorded the immediate and short-term reactions of crows. We counted crows at five roosts in Davis, California during an 8-day pre-treatment period and then again during a 4-day treatment period to evaluate crow response to laser treatment. Crows reacted to the laser beam. In Woodland 100% of the crows flew immediately away from 49% of the treated roosts. Between 50% to 99% of all crows flew immediately away at 44% of the treated roosts. At 84% of the roosts crows left without vocalizing and at 95% of the roosts flew directly away without circling overhead. Crows returned to all roosts within 15 min. In Davis there was no difference in the number of crows using roosts during the pre-treatment versus treatment periods. Despite initial dispersal upon treatment, crows reoccupied all treated roosts the same night after treatment. No roosts were abandoned. Therefore, we do not recommend lasers as a stand-alone dispersal tool at urban crow roosts.

Preroosting behaviour of hooded crows (Corvus corone cornix)

Gatherings of birds at preroosts before departure to nocturnal roosts have rarely been studied and their function is poorly understood. We recorded preroosting behaviour of hooded crows, Corvus corone cornix, in a mixed farmland-forest landscape in southeastern Norway during fall and winter, by selecting gatherings attended by at least one radio-tagged crow for observation. The preroosting crows perched in a highly aggregated and exposed group and did not forage. As the amount of snowfall during the preceding 24 h increased, an indication of sudden difficulty in finding food, the maximum number of crows that gathered increased, the duration of the gathering increased, and the straight-line distance covered by the radio-tagged crows from preroost to roost increased. The crows flew conspicuously in formation more often and for a longer time when on their way from preroost to roost on days with stronger winds. The results suggest that, in hooded crows, a preroost gathering is not simply a consequence of many individuals approaching the same roosting area but has some function, presumably that of maximizing the probability of finding rewarding food sites the next day by finding is a communal roost where information on the location of these sites may be obtained.

Beach-Foraging Behavior of Northwestern Crows as a Function of Tide Height

From 8 February to 8 June 1995, we investigated aspects of the foraging behavior of northwestern crows (Corvus caurinus) in the intertidal zone relative to various tide heights and invertebrate availability along an urban beach in Seattle, Washington. We directly sampled the density and diversity of invertebrates in the upper, middle, and lower littoral zones to assess their distribution. We recorded the number of steps taken and amount of time spent foraging by crows by tidal zone and tide direction. Worms, crabs, and snails were expected to be exposed to predation at lower tide heights, and some species of worms were only found at low tides (<0.36 m). There was no significant difference in the number of bivalves found in relationship to tide height. Among the crows observed, the number of steps and search times were greater during rising than falling tides, but the number of probes was not significantly different be- tween tide directions. In addition, the number of steps between probes and the amount of time between probes decreased during rising tides. The number of crows foraging in the intertidal zone did not appear to be related to tide height. Results of this study suggest that tidal zone and direction influences prey availability and thus certain aspects of the foraging behavior of northwestern crows.

Nest predation and numbers of Golden PloversPluvialis apricariaand other moorland waders

The recovery of a declining population of Golden Plovers may have been prevented by high nest predation from Carrion Crows Corvus corone and Common Gulls Larus canus. In order to test this hypothesis predators were experimentally removed from Kerloch moor in NE Scotland during 1986–89. Although the numbers of crows and gulls were significantly reduced, no young Golden Plover hatched at Kerloch and breeding numbers continued to decline. Numbers also declined on a less intensive study area 50 km further away where predators were not removed and where hatching success was poor (except in 1986). Hatching success of other moorland waders was generally higher during the experiment than before it, but breeding numbers did not increase. The removal of crows and gulls did not lead to increases in the breeding populations of Golden Plovers and other waders, although the outcome of the experiment was complicated by rising nest predation from foxes Vulpes vulpes whic¸ may have masked any benefits from the removal of other predators.

Genetic Variation in a Wintering Flock of the American Crow (Corvus brachyrhynchos)

Genetic Variation in a Wintering Flock of the American Crow (Corvus brachyrhynchos)

Ecology of a marginal Carrion Crow population. I. — Distribution and abundance

A low density population of the Carrion Crow Corvus c. corone was censused in the Camargue delta region, southern France. Three methods were used : (A) a line transect along 45 km roadside, (B) mapping of the crows on a 16 km² study plot by car, and (C) a complete survey revealing all resident crows during the breeding season on the same plot. Accuracy of the two estimates (A) and (B) was checked with those of method (C). This revealed that 7 censues gave accurate results for both method (B) and for the main belt census sector for method (A). Fortnightly counts using methods (A) and (B) served to monitor number, group size and habitat use of the crows during one whole annual cycle. Size and composition of the population of the study plot, which lays entirely in marshland did not show significant differences between seasons, while a significant increase in number of crows in winter and larger group size and a preference of open cultivated land during the moult/dispersal period, was found along the roadside circuit. Extrapolation of crow distribution and density for the whole Camargue region (750 km²) revealed to be difficult because neither methods (A) and (B) gave results about the population structure and percentage of non-breeders. It is concluded that only repeated surveys (C) in different habitat could provide accurate results.

A signal detection problem and possible solution in Japanese quail ( Coturnix coturnix japonica)

The ambient noise level in the environment of most species varies and consequently many animals that use acoustic signals are faced with a potential signal detection problem. A male Japanese quail emits separation crowing when separated from a female with which it has paired. These separation crows tend to be emitted in temporal groups or bouts. This study demonstrates that the ambient noise level affects the emission of separation crowing. The two related changes in emission of separation crowing found in this study were: (a) increasing the frequency of separation crowing; and (b) increasing the number of crows per bout. These related changes should help to increase the detectability of the signal and the localizability of the transmitter.

OBSERVATIONS ON THE AUTUMN MIGRATION IN THE AREA BETWEEN THE SEA OF AZOV AND THE CASPIAN

Summary.Bird‐migration was observed 5 October‐14 November 1942 along 150 km. of railway line between Salsk and Stalingrad (between the Sea of Azov and the Lower Volga). The typical steppe‐birds of South Russia were recorded—larks, harriers, bustards etc.—and also astonishing numbers of crows, starlings, finches, thrushes, pigeons and others. Magpies, Yellow Buntings (many), sparrows, Crested Larks, Great Tits and Partridges also appeared as migrants.Most birds were travelling southwest or south but the geese were going west (except for one flock), as were Redwings and part of the Great Bustards and Yellow Buntings. Eastward movement was rare.The immediate destination of the birds observed can only be presumed, but those flying west would reach the coasts of the Sea of Azov and very likely continue further. Birds flying southwest and south were headed for the eastern half of the Black Sea, or the Caucasus. This range, which forms a very pronounced barrier, is well known to be crossed by migrants.After the autumn sojourn another period of observation followed, 1–18 January 1943 (mostly between Proletarskaja and Salsk).In all, 45 species were observed alive, and under telegraph wires birds of 25 species were found dead, including 10 not otherwise recorded.

CROW EATING SERICA BEETLES (COLEOPTERA, SCARABAEIDAE)

On July 6, 1946, Game Warden, J. P. C. Atwood, of Vernon, B. C., saw a number of crows (Corvus brachyrhynchos hesperis) in coniferous trees adjacent to the highway, near where the Monte Creck road meets the Vernon-Kamloops road. He shot one on the wing, killing it in the air. The bird must have landed on its crop, for on reaching it he found its beak held wide open by a mass of beetles which also filled its throat and spilled out onto the ground.

Crowing and Vitality Observations

July 24, 1914, the writer observed a number of male birds from 5 a. m. to 8 p. m., or from daylight until dark, to register the number of crows by each, bird. The results are reported in the Journal as a matter of record.The work was conducted at the poultry plant of the Oklahoma Agricultural and Mechanical College, Stillwater, Okla. The day was cloudy and cool, with a minimum temperature of 69° F.and a maximum of 91° F. Observations were made from the roof of a building overlooking the yards, but not close enough to interfere with the normal activities of the birds.Eight males were studied: Rose Comb Rhode Island Reds, Barred Plymouth Rocks, White Orpington and a mongrel. They were in adjoining pens, 20x100 feet, some of which were occupied by hens and others by half-grown chickens. The crowing started before the birds left the roost .