, Raptm-Res. 30(4):194-197 J. © 1996 The Raptor Research Foundation, Inc. A BANDING STUDY OF CINCINNATI AREA GREAT HORNED OWLS John B. Holt, Jr. MA 833Johnson Street, North Andover, 01843-3313 U.S.A. — Abstract. From 1964-92, 1570 nestling great horned owls {Bubo virginianus) were banded at 906 successful nests within 80 km of Cincinnati, Ohio. One nest contained four young, 40 nests three young, 581 two young, and 284 one young. Mean annual productivity was remarkably constant at 1.7 young per successful nest and 1.3 young per breeding attempt. An average of 15% of breeding pairs failed to raise young and 38% of the pairs did not attempt to nest; the number ofyoung per occupied territory was variable but averaged 0.80 young. From 1236 nesting attempts, 533 occurred in nests built in pre- vious years by red-tailed hawks {Buteojamaicensis) 527 were in broken-off snags, and 125 were on man- made platforms. Most band recoveries occurred within the 80-km radius study area but six dead owls were found in Michigan as old as nine years of age. Key Words: Bubo virginianus; bird banding, breeding success] brood size, nest sites', unhatched eggs] Ohio] Kentucky] Indiana. Estudio de marcaje de Bubo virginianus en el area de Cincinnati — Resumen. Desde 1964 a 1992, 1570 polluelos de Bubo virginianus fueron marcados en 906 nidos exi- tosos a 80 km de Cincinnati, Ohio. Un nido tuvo cuatro juveniles, 40 nidos tres juveniles, 581 dos juveniles y 284 un juvenil. La productividad media anual fue marcadamente constante de 1.7juveniles por nido exitoso y 1.3juveniles por pareja reproductiva. Un promedio de 15% de parejas reproductivas fallo en criarjuveniles, el 38% no intento reproducirse; el numero dejuveniles por territorio ocupado fue variable pero en promedio era de 0.80. De 1236 intentos reproductivos, 533 ocurrieron en nidos construidos en anos previos por Buteojamaicensis, 527 fueron en ramas quebradas y 125 fueron construi- dos sobre plataformas artificiales. [Traduccion de Ivan Lazo] I studied nest-site selection and reproductive I classified a breeding attempt by a horned owl “suc- success of great horned owls {Bubo virginianus) cessful” if one or more young survived to banding age, or “failed” if incubation was begun but no young were within an 80-km radius of Cincinnati, Ohio from A produced. territory was considered to be “occupied” 1964—92. Here, I report the results of this lifelong if a pair of horned owls was present, regardless of their study. breeding status. StudyArea and Methods Results and Discussion Most of the 20000 km^ study area was in Ohio and ranged from hilly, wooded areas to moderately settled I climbed into 1236 nests from 1964r-92 and river bottoms of the Ohio River and its tributaries, and banded 1570 nestling great horned owls in 906 suc- from urban and suburban backyards, parks, cemeteries cessful nests; 1193 were banded in Ohio, 324 in and golf courses, to fairly flat and sparsely wooded areas to the north and west of the city. The Indiana portion Indiana, and 53 in Kentucky (Table 1). More than was hilly and heavily wooded to the south, changing to half of the owlets were banded before they were flat and sparsely settled agricultural areas to the north. three weeks of age. Of 1777 instances where owls The Kentucky segment was hilly throughout and ranged occupied territories, 841 (47.3%) bred successfully, from heavily wooded in the north to sparsely wooded ar- 266 failed (15%), and 670 (37.7%) made no at- eas in the south. The most intensive nest searching and banding oc- tempt to breed (Table 2). curred from 1964-77. From 1980-92, I covered only the I found a total of 97 unhatched eggs or 5.8% of parks of the Hamilton County Park District with a total the 1667 eggs observed. Seventy-six of these were area of 49.8 km^. My experiences during the first two years of this study were described in Austing and Holt in nests that contained no young, 19 in nests with (1966). one young, and two were in nests with two young. 194 6 , December 1996 Banding oe Great Horned Owls 195 The Ratcliffe eggshell thickness index (Ratcliffe Table 1 Numbers ofnestling greathorned owls banded . 1967) was determined in 1969 for 18 unhatched near Cincinnati, Ohio from 1964—92. eggs collected in 13 nests and averaged 1.822 (Range = 1.442-2.274). This average was 8% thin- Year Ohio Indiana Kentucky Total ner than the index of 2-01 for pre-1947 eggs from 1964 42 15 57 the Midwest (Anderson and Hickey 1972). 1965 51 14 65 Brood size at the time of banding in 802 nests 1966 37 8 45 was: one young in 248 (31%) nests, two young in 1967 51 13 64 515 (64%) nests, three young in 38 (5%) nests, 1968 62 17 2 81 and four young in one (0.1%) nest (Table 2). 1969 84 31 1 116 There was an attrition of 101 (6.7%) young owlets 1970 106 27 3 136 which died or disappeared prior to banding visits. 1971 68 17 1 86 The only brood of four young was encountered in 1972 115 35 4 154 1973 87 20 9 116 1970 when productivity reached an all-time peak. 1974 87 34 5 126 In that year, there were eight broods ofthree, over 1975 59 13 8 80 twice the norm, in what was called “the year ofthe 1976 110 40 6 156 rat.” Norway rats {Rattus norvegicus) were almost 1977 77 26 11 114 everywhere, either killed on roads, scurrying 1978 12 3 3 18 around in cornfields and farm buildings, or even 1979 0 0 0 0 out in broad daylight. Owl nests had as many as six 1980 12 12 rats piled in them. In other years, three or four 1981 25 25 rats would have been an expected number found 1982 2 2 among prey remains in an entire nesting season. 1983 9 9 1984 8 8 Mean productivity per successful nest was re- 1985 10 3 13 markably constant throughout the study at 1.7 1986 9 5 14 young per successful nest (Table 2), roughly equiv- 1987 12 12 alent to the success of great horned owls in Sas- 1988 13 2 15 katchewan after a population crash of snowshoe 1989 12 12 hares {Lepus americanus) but far below the 2.5-2. 1990 14 1 15 young per successful nest at the peak of the hare 1991 10 10 cycle (Houston 1987, Houston and Francis 1995). 1992 9 9 The number of young per occupied territory var- Total 1193 324 53 1570 ied considerably between years but averaged 0.80, excluding from this calculation 39 successful nests in which young were found too late to be banded. in the hayloft of a barn (Table 3). Many pairs re- This productivity was well below the 1.47young per nested in the same territory for two or more years. nesting attempt suggested by Henny (1972) as nec- Of 21 territories observed for 15 years, two were essary to maintain a stable population, but these occupied by pairs of breeding great horned owls calculations based on early banding recoveries may for 14 years and another two were occupied for 13 A have overestimated annual adult mortality (Hous- years. total of 54 territories were used for only ton and Francis 1995). The number of young per one year. occupied territory varied considerably by year with Owls began nesting tbe second week ofJanuary the number of pairs reaching a peak in 1970, the and continued until the first week of March. Of year of highest prey abundance. 903 broods which could be back-dated, 519 were Of 1236 breeding attempts, 585 pairs used nests initiated inJanuary, 379 in February, and only 5 in built in previous years by other birds or mammals; March. Of these, 329 were initiated during the last 533 used nests built by red-tailed hawks {Buteo ja- 10 days ofJanuary and 222 were initiated in the maicensis) and almost an equal number (527) made first week ofFebruary. Early breeding pairs tended use ofhollows, broken-offsnags and rotted-out cav- to reoccupy known sites and to raise more young ities in overmature beech (Fagus spp.) and maple than pairs that nested later. Some ofthe later nests (Acer spp.) trees. Artificial platforms which I con- may have been renesting attempts. A structed were used 125 times and owls nested once total of 151 banded great horned owls were 196 HoltJr. VoL. 30, No. 4 J. Table 2. Brood size and productivity of great horned owl nests near Cincinnati, Ohio from 1964-92. Total Total Total Brood Size Total Young Successful Occupied Year 1 yg- 2 yg- 3 yg. 4yg- Nests Banded Nests Nests 1964 15 18 2 35 57 1.6 1.14 1965 12 25 1 38 65 1.7 0.88 1966 8 17 1 26 45 1.7 0.63 1967 17 22 1 40 64 1.6 0.71 1968 17 29 2 48 81 1.7 0.75 1969 11 48 3 62 116 1.9 0.96 1970 18 45 8 1 72 136 1.9 1.12 1971 17 30 3 50 86 1.7 0.67 1972 23 61 3 87 154 1.8 0.99 1973 24 40 4 68 116 1.7 0.70 1974 21 48 3 72 126 1.8 0.80 1975 12 34 46 80 1.7 0.51 1976 23 59 5 87 156 1.8 0.94 1977 30 39 2 71 114 1.6 0.66 1978 6 9 12 18 1.5 1980-92 30 60 2 90 156 1.7 Total 284 584 40 1 906 1570 1.7 recovered dead. About 42% (64) were reported as night and kept him awake with their food begging. code “00” or found dead, another 15 were “04” Another farmer did likewise claiming that the owls or caught in traps (five of which were caught in were bothering his pigs. illegal pole traps and destroyed), 14 were “14” and Due to the nonmigratory nature of these great “45” or killed on highways, 10 were code “01” or horned owls, most (141 of 151) were recovered shot, six were captured alive and released, five were dead within the 80-km radius of the study area. Six captured and kept in captivity, and the status of recoveries were of special interest; all were report- four was uncertain. Owls were found dead ed from Michigan and two of the owls were 1-yr throughout the year and only 16 were found dead old, two were 2-yr old, one was 6-yr old and one during the fall hunting season. None of the owls was 9-yr of age. reported shot were shot during the hunting sea- Acknowledgments son. A farmer shot both nestling owls I banded on I wish to thank C.S. Houston for writing and editorial bis property because they sat on his barn roof at suggestions and with helpful comparisons with Saskatch- Table 3. Nests used by great horned owls near Cincinnati, Ohio from 1964—92. Total Number of Years Used Total Nest- 1 2 3 4 5 6 7 8 9 Nests lings Red-tailed hawk'^ 263 77 24 6 1 1 1 373 533 Cavity/snag 136 63 29 18 6 5 3 2 1 263 527 Platform 22 9 11 4 6 1 53 125 E. fox squirrel’’ 17 1 18 19 American crow^ 13 13 13 Red-shouldered hawk'* 11 11 11 Cooper’s hawk*’ 5 5 5 Green heron^ 1 1 1 Barn loft 1 1 2 Buteojamaicensis; Sciurus niger, Corvus brachyrhynchos; Buteo lineatus; Accipiter cooperir, ^Butorides striatus. December 1996 Banding of Great Horned Owls 197 ewan horned owls. FrankJoy, Sergej Postupalsky, Dwight modern pesticide era. Wildlife Research Report 1, Smith, Robert K, Murphy, and Marc J. Bechard offered U.S. Fish and Wildlife Service, Washington, DC U.S.A valuable constructive criticism, while S. Postupalsky mea- Houston, C.S. 1987. Nearly synchronous cycles of the sured eggshell thickness. Ron Austing, Traman Burk, great horned owl and snowshoe hare in Saskatche- David Tepe, George Terlinden, and Tom Wilmers helped with banding. wan. Pp. 56-58 in R.W. Nero, R.J. Clark, R.J. Knapton, and R.H. Hamre [Eds.], Biology and conservation of Literature Cited northern forest owls: symposium proceedings. Gen. Anderson, D.W. AND Hickey. 1972. Eggshell changes Tech. Rep. RM-142, U.S. Dept. Agric., Forest Service, JJ. CO in certain North American birds. Proc. Int. Ornithol. Fort Collins, U.S.A. Congr. 15:514-540. Houston, C.S. and C.M. Francis. 1995. Survival ofgreat Austing, G.R. andJ.B. Holt,Jr. 1966. The world ofthe horned owls in relation to the snowshoe hare cycle. great horned owl. J.B. Lippincott, Philadelphia, PA Auk 112:44-59. U.S.A. Ratcliffe, D.A. 1967. Decrease in eggshell weight in cer- Henny, G.J. 1972. Great horned owl. Pp. 11-16 in An tain birds of prey. Nature 215:208-210. analysis of the population dynamics of selected avian species with special reference to changes during the Received 24 August 1995; accepted 16 August 1996.