Treesearch

Three Strix species breed sympatrically in Belarus. The Tawny Owl (Strix aluco) is one of two commonest owl species in the country, and is distributed throughout the whole territory. Its' range overlaps widely with two other species, the Ural Owl (S. uralensis) which is common in the forests of the northern part and the Great Gray Owl (S. nebulosa) which occurs in a rather limited area in the southern region. The diet of all three species was studied from 1986-1996 by the analysis of pellets collected mainly near nests. All owls preyed mainly on voles and shrews, but niche differences...

This workshop was convened to review the current status of the Western Burrowing Owl (Speotyto cunicularia hypugaea) in North America, to discuss means by which we can improve our knowledge of this owl, and to initiate conservation action to benefit the species.

The Northern Saw-whet Owl of the Queen Charlotte Islands, British Columbia is recognized as a distinct subspecies Aegolius acadicus brooksi. Little is known of the biology of this subspecies, and no nests have ever been found. We surveyed for Northern Saw-whet Owls on the Queen Charlotte Islands between 4 May and 28 May, 1996 establishing 10 survey routes comprising a total of 238 survey stations on Graham and Moresby Islands. Routes were chosen to maximize coverage of different forest types. We detected 61 owls and identified five trees used by singing owls. No nests were found. We used...

A nearly isolated Great Gray Owl (Strix nebulosa Forster) population of 50-100 breeding pairs exists in southwestern and south-central Belarus and northern Ukraine. It exhibits rather high nesting density in particular forest tracts and is separated from populations in northwestern Russia by several hundred kilometers. No reliable data on residency, postbreeding movements and wintering strategies are available. Twig nests are used for nesting almost exclusively; the proportion of other nest sites was ca. 10 per cent. Mean clutch size was 3.4, with 1.3 young produced per breeding attempt....

We studied movements and breeding success of resident Great Horned Owls (Bubo virginianus) at the Rocky Mountain Arsenal National Wildlife Refuge from 1994-1996. We captured adult owls prior to nest initiation and outfitted them with radio transmitters. Twelve, 5, and 11 pairs nested each year, respectively. Eleven nests successfully hatched and produced 24 owlets in 1994, 3 nests produced 6 owlets in 1995, and 10 nests produced 29 owlets in 1996. We documented three cases in which a single parent successfully fledged owlets. We recorded three cases of nest site reuse. Ninety-five percent...

Demographic characteristics of the Northern Spotted Owl (Strix occidentalis caurina) were studied on the Eugene District Bureau of Land Management, central Oregon Coast Ranges from 1989-1995. Survival rates were estimated from capture histories of banded owls using Cormack-Jolly-Seber open population models. We banded 233 owls, including 119 that were ≥ 3 years old, 15 that were 1 or 2 years old, and 99 juveniles. Among year variation in the proportion of pairs nesting and fecundity of females was significant ( P < 0.001). Estimates of apparent annual survival from the selected capture-reca...

Tropical owls, being poorly studied, have been excluded from discussions of reversed size dimorphism. As part of a breeding and food habits study, we weighed and measured 20 Mottled Owls (Ciccaba virgata) and a mated pair of Black-and-white Owls (C. nigrolineata) in northern Guatemala. Mottled Owls exhibited pronounced dimorphism with respect to body mass, wing chord, and tail length. A mated pair of Black-and-white Owls was also quite dimorphic with respect to body mass. Mate choice in six pairs of Mottled Owls was not correlated with size (mass or wing chord). Since both species are...

Practitioners have been using numerous methods to protect Burrowing Owls (Speotyto cunicularia hypugaea) affected by human activities. Primary approaches include protecting birds and burrows in place, allowing birds to relocate within their nesting territory, allowing birds to colonize new patches, moving birds within the geographic region and moving birds outside the geographic region. Very little data are readily available on most of these. Preliminary information indicates that methods which keep birds near nest burrows may be more successful than those in which birds are relocated...

We studied the intra- and interspecific responses to playback of pre-recorded calls by five tropical humid forest owl species at La Selva preserve in northeastern Costa Rica from April to September 1995. Response to conspecific broadcast calls differed among species (X² = 24.4; df = 1; P < 0.001): vermiculated screech-owls (Otus guatemalae) responded to 47.6 per cent of broadcasts, followed by Crested Owls (Lophostrix cristata, 45 percent), Mottled Owls (Ciccaba virgata, 18.3 per cent), and Black-and-white Owls (C. nigrolineata, 9 percent). Crested Owls (x = 16.37, sd = 2.6), Mottled Owls...

Northern Saw-whet Owls (Aegolius acadicus) were once considered a "rare" bird in Wisconsin. In the 1960's mist netting at bird-banding stations revealed Saw-whets to be a regular, uncommon migrant. Passive mist netting was initiated at the Little Suamico Ornithological Station in 1971. Our Saw-whet Owl experiences were similar to other banding stations until 1986, when we developed an "audiolure". This technique, utilizing an amplified Saw-whet "solicitation" courtship call increased our annual catch more than tenfold. Now in use at major banding stations in the western Great Lakes area,...