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The Screech Owl: Its Life History and Population Ecology in Northern Ohio

North American Fauna No. 71

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Abstract

1. The life history and population ecology of the screech owl was studied in northern Ohio between 1944 and 1973. The owls nested in boxes established for wood ducks. The birds were banded and periodically recaptured. Food habits, productivity information, and color phase of the parent birds and offspring were recorded. 2. The screech owl is an opportunistic feeder. The diet changes with the seasons of the year, i.e., during the nesting season migrant birds replace mammals in importance, and during the late summer insects become important. 3. There is no evidence from banding data to suggest that screech owls in the northeastern United States migrate. 4. Young screech owls begin dispersing from their natal areas in late summer or early fall, with only about one-fourth of the young birds remaining within 10 km (6 mi) of the banding site. On the contrary, adult birds remain close to the area where they previously nested. 5. The hypothesis of random dispersal distance in young screech owls was rejected. There appear to be two groups in the population: (1) a group showing little dispersal, and (2) a group wandering considerable distances. 6. The directional pattern of dispersal was random. 7. Pairs of screech owls were noted in the nest boxes in early February, but egg laying did not peak until about 15 March. Hatching takes place in mid-April to early May and most of the young leave the nest the last week of May or the first week in June. 8. The mean clutch size was 4.43 with a mean of 3.80 young fledged per successful nest. An estimated 69.2% of the nesting attempts were successful. Including unsuccessful nesting attempts, an estimated 2.55 to 2.63 young were fledged per breeding pair. 9. Annual variation in the number of young fledged per successful nest was small. The lack of variability was probably due to the predictable food source of passerine birds that migrated through the area each spring when young were in the nest. This contrasts with the highly variable productivity reported for owls dependent upon local cyclic rodent populations. 10. Raccoon predation was implicated in a number of unsuccessful nesting attempts, but the overall effect of the raccoon on the screech owl population was not fully assessed. 11. The sex ratio in the population did not differ significantly from a 50:50 ratio. 12. The first year mortality rate ofthe screech owl was estimated at 69.5%; adult mortality was estimated at 33.9%. 13. Male and female screech owls banded as nestlings were known to nest successfully at the end of their first year of life (as 1-yr olds). Two estimates of the average proportion of 1-yr-olds nesting ranged from 77 to 83%, but the percentage may be lower. 14. No significant eggshell thinning was detected in the population in 1973, and residue levels of DDE and PCB's were low. 15. In northern Ohio, the screech owl population consists mainly of a gray- and red-phased birds, but about 2 to 3% of the birds are intermediate in color. 16. A significant change in the ratio of red- to gray-phased birds occurred in December 1951. This change coincided with the lowest temperatures during the 30-yr study and the heaviest snowfall. The red-phased birds decreased from 23.3% of the population to 14.7%. Additional evidence from retrap information suggests that the grays survived much better than the reds during the stressful period. The ratio of reds in the population failed to increase to pre-1951 levels during the next 20 yr. 17. No significant relationship existed between sex and color phase in our sample of 760 nesting screech owls. 18. The following hypotheses of gene action remain: (1) If the intermediate phenotype is assumed to be due to genetic modifiers, the difference between red and gray is due to one pair of alleles, the gene for red exhibiting dominance over its allele for gray; or (2) if all three colors are considered, the colors are inherited on the basis of a series of three alleles with

Additional Publication Details

Publication type:
Report
Publication Subtype:
Federal Government Series
Title:
The Screech Owl: Its Life History and Population Ecology in Northern Ohio
Series title:
North American Fauna
Series number:
No. 71
Year Published:
1975
Language:
English
Publisher:
U.S. Fish and Wildlife Service
Contributing office(s):
Patuxent Wildlife Research Center
Description:
v, 65