| General Species Description: |
Length 29 cm. Typical owl with large black eyes in mainywhite, heart-shaped facial mask. No ear tufs. Underparts white or buffish; upperparts minutely marmorated golden-brown, grey, and white. Long, brisled legs and toes. In sleeping pose, Facial disc is contractd and eyes are mere slits; whole bids look then unnaturally slim and unatrractive. Reproduction Comments:Nests in late winter, spring, and/or early summer in most of North America. Breeds throughout year in Texas. Nests with eggs or young have been found in the northeastern U.S. during every month of the year (Poole 1930; Bent 1938; Scott 1950; Stewart 1952; C. Rosenburg, unpubl. Data), but peak egg laying occurs during mid-April (Colvin 1984, Byrd and Rosenburg 1986). Second clutches are typically laid between June and September (Wallace 1948, Keith 1964, Reese 1972, Soucy 1979). As many three broods per year; some California birds attempt two broods per year; one brood per year in most of the range. Clutch size ranges between one to 13 eggs (Bent 1938, Parker and Castrale 1990) with the mean clutch size ranging between four to six eggs (Otteni et al. 1972, Reese 1972, Smith et al. 1974). Clutch size depends on condition; increases with food supply and after mild winters in some areas. Eggs are usually laid two days apart and hatch asynchronously since incubation starts after the laying of the first egg (Wallace 1948, Smith et al. 1974). Incubation by female, 21-24 days for single egg, 29-34 days for full clutch (Smith et al. 1974, Marshall et al. 1986). The peak of hatching in the Northeast occurs in mid-May (Colvin 1984; Byrd and Rosenburg 1986; S. Smith, pers. Comm.). Female broods and feeds young, male brings food. Young reportedly fly at 50-55 days in England; young fledge at 8-10 weeks in U.S. (Pickwell 1948, Reese 1972, Smith et al. 1974). Peak fledging occurs in mid to late July (Colvin 1984, Byrd and Rosenburg 1986). Juveniles may remain in the vicinity of the nest site for several weeks before dispersing (Otteni et al. 1972, Smith et al. 1974, Marti 1990). Male may care for fledged young as female begins second clutch. In northern Utah, 71% of all nesting attempts yielded at least one fledgling; reproductive success and productivity were reduced following winters with particularly low temperatures and long periods of deep snow cover (Marti 1994). Breeding density depends on availability of nest sites and on food supply. See Marti (1989) for information on breeding phenology in different areas.
Matures and breeds within its first year (Stewart 1952, Maestrelli 1973, Marti 1990) and sometimes as early as seven months of age (B. Colvin, pers. Comm.). It is typically monogamous, but Colvin and Hegdal (1989) reported that as many as 10% of the adult males in their New Jersey study area may be polygynous.
Ecology Comments:Individuals range over large areas; mean home range size (based on the minimum home range method (Mohr and Stumpf 1966)) has been reported as 355 ha in southern Texas (Byrd 1982), 757 ha and 921 ha in southwestern New Jersey (Colvin 1984, Hegdal and Blaskiewicz 1984), 414 ha in eastern Virginia (Rosenburg 1986), 850 ha in Virginia (Byrd and Johnston 1991), and 198 ha in western Nebraska (Gubanyi 1989). As much as 5.6 km may be traveled between a nest site and foraging areas, although distances within 1.6 km are more usual (Colvin 1984, Hegdal and Blaskiewicz 1984, Rosenburg 1986). Overlap of individual home ranges is common, particularly where nest sites and prey are abundant. (Smith et al. 1974, Colvin 1984, Rosenburg 1986).
Young disperse widely from natal area, commonly more than 80 km, up to hundreds or 1900 km documented; wide dispersal facilitates colonization of new areas. Hatching-year barn owls have been recovered great distances from natal areas (commonly > 80 km and as much as 1800 km) (Stewart 1952; Soucy 1980, 1985). Although juveniles have been recovered from essentially every compass direction from their natal area, most had traveled in a southerly direction (Stewart 1952). Juveniles in the northern U.S. migrate south but return to nest somewhere within 320 km of their natal sites (Stewart 1952). Most individuals banded as nestlings and later found breeding did so at distances of about 50 km from their natal areas (Marti 1990). Cases of dispersal > 320 km have also been documented. An individual banded as a nestling in southwestern Iowa was recovered as a breeding adult 419 km to the east (Ehresman et al. 1989). A nestling banded in central New Jersey was found nesting in Ohio (B. Colvin, pers. Comm.). Extensive banding of nestlings and capture of adults in southwest New Jersey reveals that only a small percentage of nestlings banded within the study area enter the adult population there: 5% of 181 nestlings banded in 1988 were found in the adult population in 1989 (Colvin and Hegdal 1989). Although they may return to breed relatively close to their natal area, individuals frequently become established great distances away. Very successful at colonizing new areas because of this broad dispersal behavior.
Susceptible to starvation during prolonged low temperatures and snow cover (Marti and Wagner 1985). In Utah, most adults survived only 1 breeding season (Marti 1989). Disease, parasites, and predation are natural factors that may in part limit populations. Appears to be resistant to many diseases that infect other raptors (Schulz 1986). In California, diseases documented include tuberculosis, aspergillosis, and trichomoniasis (Schulz 1986). Toxoplasmosis and eastern equine encephalitis have been detected in New Jersey, although no impact to the birds was apparent (Colvin and Hegdal 1986, 1987). Salmonellosis has been recorded in Pennsylvania (Locke and Newman 1970) and New Jersey (Kirkpatrick and Colvin 1986). Kirkpatrick and Colvin (1986) found SALMONELLA-positive nestlings at five of the 25 New Jersey nest sites examined, and reported that all infected young apparently fledged.
Dipteran ectoparasites and lice have been found on owls (Schulz 1986, Kirkpatrick and Colvin 1989). The endoparasites TRYPANOSOMA, CAPILLARIA, and PORROCAECUM have been identified from the feces of New Jersey owls (Colvin and Hegdal 1986).
NON-BREEDING: solitary or in pairs. |
