Diet Of Owls Research Articles

Diet and ecology of Short-eared OwlsAsio flammeusbreeding on heather moor

Observations were made of the diet and breeding biology of a small population of Short-eared Owls Asio flammeus breeding on a Welsh heather moor during 1971–¸84. Of 694 vertebrate prey items, Pigmy Shrews Sorex minutus were dominant numerically (43% of prey), Wood Mice Apodemus in biomass (18%). Significant numbers of Common Shrews Sorex araneus, birds, Short-tailed Voles Microtus agrestis and Bank Voles Clethrionomys glareolus were noted. Proportions of prey species in diets varied between. sites, probably in relation to differences in vegetation between hunting ranges. The birds were generally inconspicuous and their population density was low; numbers, time of breeding, clutch-size, and breeding success were fairly uniform. This breeding ecology is contrasted with that reported for Shorteared Owls breeding in grassland and feeding on Microtus voles.

Common Barn Owl Diet in Northeastern Oregon

Common Barn Owl Diet in Northeastern Oregon

Feeding ecology of breeding Long-eared Owls in southwestern Idaho

Feeding ecology of Long-eared Owls (Asio otus) was investigated in the Snake River Birds of Prey Area, southwestern Idaho, during the breeding seasons of 1980 and 1981. The owls preyed mainly on five genera of small mammals: Peromyscus, Perognathus, Dipodomys, Microtus, and Reithrodontomys. There was considerable variation in prey composition among sites but not between years. In both years the proportion of Perognathus in the diet increased after the young owls fledged. Compared with other North American studies, Long-eared Owls in the Snake River Birds of Prey Area had a wider feeding niche and preyed more extensively on nonmicrotines. The range of prey sizes in Long-eared Owl diets was similar to that in other areas, with most prey weighing less than 100 g. Interlocality differences in the Long-eared Owl feeding niche probably reflect differences in the composition of small mammal faunas. Long-eared Owls in the Snake River Birds of Prey Area appeared to feed opportunistically on a diversity of available small mammals; prey size, rather than prey type, was the most important factor in food selection.

Feeding Ecology of Sympatric Barn Owls and Long-Eared Owls in Idaho

The diets of Barn Owls and Long-eared Owls were compared during two consecutive nesting seasons in the Snake River Birds of Prey Area in southwestern Idaho, U.S.A. Over 12800 prey items were identified. Both species fed almost exclusively on small mammals. Microtus were the most important Barn Owl prey, while Long-eared Owls fed primarily on Peromyscus and heteromyid rodents. Nesting Barn Owls were more closely associated with irrigated agriculture than were Long-eared Owls. The feeding niche of Barn Owls was narrower than that of Long-eared Owls the first year but wider the next. Dietary overlap was 48.4% the first year and 60.9% the next. In comparison with other North American studies of sympatric Barn Owls and Longeared Owls, the owls in our study had wider feeding niches and a reduced dietary overlap. Mean weights of Barn Owl prey were significantly heavier than those of Long-eared Owl prey thus Barn Owl prey weight distributions were shifted towards heavier prey than were those of Long-eared Owls. Differences in habitat use, food niche breadth and prey size are potentially important coexistence mechanisms.

Evaluation of the potential hazard to barn owls of talon (brodifacoum bait) used to control rats and house mice

AbstractDuring 1980, a radiotelemetry study on barn owls (Tyto alba) was conducted to evaluate the secondary hazards of the anticoagulant rodenticide TALON® (containing 0.005% brodifacoum) when it was used for controlling rats (Rattus spp.) and house mice (Mus musculus) on farms. Thirty‐five active nests were located in about 1,100 km2 (430 mi2) in southwestern New Jersey. Starting on June 9, 1980, radio transmitters with tail clips were attached to 26 adult nesting barn owls and 8 fledged young of the year. In one 20‐km2 (about 8 mi2) area, which was the most intensively searched, 12 active barn owl nests were located. Of all 35 active nests, 66% were in trees, 11% in barns, 8.5% in silos, 8.5% in chimneys and 6% in miscellaneous locations. Analysis of regurgitated pellets showed that meadow voles (Microtus pennsylvanicus) were the most common prey at all sites. Although Norway rats (Rattus norvegicus) and house mice occurred in some pellet collections, they made up only a small part of the diet (3.9% rats and 2% mice) of barn owls in the study area. Baiting at farms with TALON was begun on July 24, and ended on September 29, 1980. TALON was not observed to cause or implicated in barn owl mortality during the study. However, trace residues (< 0.05 ppm, the limit of determination) of brodifacoum were found in one electrocuted barn owl. Young barn owls were fledged from at least eight sites where poisoned rodents were available on the farms for at least part of the nesting and feeding period (including pre‐ and postfledging). Furthermore, radiotelemetry confirmed that at least 9, and possibly 12, of the radio‐equipped owls were present on sites posttreatment, when census evaluations showed commensal rodents were present and consuming TALON bait.

EVALUATION OF THE POTENTIAL HAZARD TO BARN OWLS OF TALON (BRODIFACOUM BAIT) USED TO CONTROL RATS AND HOUSE MICE

During 1980, a radiotelemetry study on barn owls (Tyto alba) was conducted to evaluate the secondary hazards of the anticoagulant rodenticide TALON® (containing 0.005% brodifacoum) when it was used for controlling rats (Rattus spp.) and house mice (Mus musculus) on farms. Thirty-five active nests were located in about 1,100 km2 (430 mi2) in southwestern New Jersey. Starting on June 9, 1980, radio transmitters with tail clips were attached to 26 adult nesting barn owls and 8 fledged young of the year. In one 20-km2 (about 8 mi2) area, which was the most intensively searched, 12 active barn owl nests were located. Of all 35 active nests, 66% were in trees, 11% in barns, 8.5% in silos, 8.5% in chimneys and 6% in miscellaneous locations. Analysis of regurgitated pellets showed that meadow voles (Microtus pennsylvanicus) were the most common prey at all sites. Although Norway rats (Rattus norvegicus) and house mice occurred in some pellet collections, they made up only a small part of the diet (3.9% rats and 2% mice) of barn owls in the study area. Baiting at farms with TALON was begun on July 24, and ended on September 29, 1980. TALON was not observed to cause or implicated in barn owl mortality during the study. However, trace residues (< 0.05 ppm, the limit of determination) of brodifacoum were found in one electrocuted barn owl. Young barn owls were fledged from at least eight sites where poisoned rodents were available on the farms for at least part of the nesting and feeding period (including pre- and postfledging). Furthermore, radiotelemetry confirmed that at least 9, and possibly 12, of the radio-equipped owls were present on sites posttreatment, when census evaluations showed commensal rodents were present and consuming TALON bait.

The diet and breeding of Long-eared Owls in relation to vole numbers

It is well known that owls achieve better breeding results in good rodent years than in poor ones. This study found that the difference in breeding success between good versus poor years was apparent mainly in the degree of non-breeding and in clutch size. Desertion of eggs or young was not correlated with prey abundance; possibly only the 'fitter' pairs breed in poor rodent years.

Diet of the Snowy Owl in the Absence of Small Mammals

Snowy Owls (Nyctea scandiaca) prey mostly on small mammals (Pitelka et al. 1955, Watson 1957, Taylor 1974), though they are known to eat birds (Murie 1929, Gross 1944, Wiggins 1953, Campbell and MacColl 1978). On Agattu Island in the Near Island group of the western Aleutian Islands, the owls occur in the absence of small mammals and subsist entirely on a diet of birds. From June to August 1975 one of us (LGF) collected 141 pellets which were analyzed to determine the Snowy Owl diet in this unusual ecological situation. Snowy Owls have been seen sporadically throughout the Aleutians and are found consistently on Agattu, Buldir, and Attu (Turner 1886, Murie 1959). While they are known to breed on the Commander Islands (Murie 1959) and on Attu where Norway rats (Rattus norvegicus) are present, they did not appear to breed on Agattu in 1974-77 (J. L. Trapp, pers. comm.). We saw no evidence of nesting, breeding displays, or territorial behavior in 14 h of observation in June 1975. No immatures were seen on Agattu, although they have been seen on Buldir.

Predation on Small Mammals by Tawny Owl and Comparison with Barn Owl in the Farma Valley (Central Italy)

Abstract The diet of the tawny owl and the barn owl's, both dwelling in the Farma Valley (Tuscany) has been studied. These two strigiformes prey upon about the same micromammal species (which make up over 95% of their diets), although in different proportions. The barn owl is more microphagous than the tawny owl. Comparison with the barn owl's diet in other sites in Central Italy brings to light that the tawny owl's trophic niche, generally, is quite different from the born owl's, however two niches may in some way overlap, when the barn owl is roosting near wooded areas, thereby further substantiating the euryphagy of the barn owl. During winter, the tawny owl's diet is characterized by the crocidurinae shortage and the abundance in typically sylvan preys (Sorex minutus, Clethrionomys glareolus); during late spring sylvan preys, may be on account of the forest lesser accessibility, decrease in number, whereby the tawny owl's trophic niche appears to converge towards the usual barn owl's niche. In summer,...

Response of Great Horned Owl Populations to Changing Prey Densities

From 1966 through 1969, we measured ie numbers, productivity, and food habits of great horned owls (Bubo virginianus) on an area of 62 square miles near Rochester, Alberta. During these years, there were sevenfold, twofold, and threefold increases in the numbers of snowshoe hares ( Lepus americanus), ruffed grouse (Bonasa umbellus), and sharp-tailed grouse (Pedioecetes phasianellus) re- spectively. The owls responded to these chzanges in numbers of prey by an increase in numbers from io to 18, by an increase from 20 to 100 percent in the proportion nesting, and by an increase in the percentage of snowshoe hare biomass in the diet from 23 percent in 1966 to 50 percent in 1969. The proportion of sharp-tailed grouse in the owl diet also increased from none in 1966 to 10 percent in 1968 but decreased to 3 percent in 1969. The proportion of ruffed grouse in the diet decreased each year, from 23 percent in 1966 to none in 1969. The diets of owl families were related to the vegetative cover surrounding the nests and presumably to the composittion o£ the prey base. Snowshoe hares, waterfowl, and pocket gophers (Thomomys talpoides) were the pnncipal components of the os^71 diet. The quantitative impact of owl predation on spring populations of snowshoe hares and ruffed grouse appeared to be low ( between 0 and 7 percent). Although 60 percent of the hares alive in spring were young-of-the-year, 97 percent of the hares in ie owl diet were adults. Similarly, only 3 of 26 grouse in the owl diet were females, despite balanced sex ratios in the spring grouse populations. The continued increase in numbers of snowshoe hares coincided with decreased predation rates on ruffed grouse and decreased incidence of sharp-tailed grouse in the owl diet, as owls consumed relatively more snowshoe hares. Abstract: From 1966 through 1969, we measured ie numbers, productivity, and food habits of great horned owls (Bubo virginianus) on an area of 62 square miles near Rochester, Alberta. During these years, there were sevenfold, twofold, and threefold increases in the numbers of snowshoe hares ( Lepus americanus), ruffed grouse (Bonasa umbellus), and sharp-tailed grouse (Pedioecetes phasianellus) re- spectively. The owls responded to these chzanges in numbers of prey by an increase in numbers from io to 18, by an increase from 20 to 100 percent in the proportion nesting, and by an increase in the percentage of snowshoe hare biomass in the diet from 23 percent in 1966 to 50 percent in 1969. The proportion of sharp-tailed grouse in the owl diet also increased from none in 1966 to 10 percent in 1968 but decreased to 3 percent in 1969. The proportion of ruffed grouse in the diet decreased each year, from 23 percent in 1966 to none in 1969. The diets of owl families were related to the vegetative cover surrounding the nests and presumably to the composittion o£ the prey base. Snowshoe hares, waterfowl, and pocket gophers (Thomomys talpoides) were the pnncipal components of the os^71 diet. The quantitative impact of owl predation on spring populations of snowshoe hares and ruffed grouse appeared to be low ( between 0 and 7 percent). Although 60 percent of the hares alive in spring were young-of-the-year, 97 percent of the hares in ie owl diet were adults. Similarly, only 3 of 26 grouse in the owl diet were females, despite balanced sex ratios in the spring grouse populations. The continued increase in numbers of snowshoe hares coincided with decreased predation rates on ruffed grouse and decreased incidence of sharp-tailed grouse in the owl diet, as owls consumed relatively more snowshoe hares.