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Double Brooding in the Long-Eared Owl

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Double Brooding in the Long-Eared Owl SHORT COMMUNICATIONS 273 Strix use buildings, especially barns, as nest HOUSTON, C. S. 1959. First records of the Barred Owl sites. The Tawny Owl (Strix &co) uses build- in Saskatchewan. Blue Jay 17:94. HOUSTON, C. S. 1961. First Saskatchewan nest of ings as nest sites 15% of the time, similarly, Barred Owl. Blue Jay 19:114-l 15. the Ural Owl (Strix urulensis) nests in build- JOHNSON,D. H. AND D. G. FOLLEN. 1984. Barred owls ings 2-4% of the time (Mikkola 1983). and nest boxes. Raptor Res. 18:34-35. MAZUR, K. M., I? C. JAMES, AND S. D. FRITH. 1997. ACKNOWLEDGMENTS Barred Owl (Strix maria) nest site characteristics I thank M. Belcher, J. S. Marks, J. E Roy, and four in the boreal forest of Saskatchewan, Canada. U.S. anonymous reviewers for constructive criticism. Forest Service General Technical Report NC-190: 267-27 1. LITERATURE CITED MIKKOLA, H. 1983. Owls of Europe. Buteo Books, BENT, A. C. 1938. Life histories of North American Vermillion, South Dakota. birds of prey. U.S. Nat. Mus. Bull. 170:182-201. Wilson Bull., 11 l(2), 1999, pp. 273-276 Double Brooding in the Long-eared Owl Jeffrey S. Marks,2’ and Alison E. H. Perkins ’ ABSTRACT.-Owls in the family Strigidae typi- fecundity of the adults and their young from cally raise no more than one brood per year. We doc- the first brood. The occurrence of double umented what apparently is the first unequivocal case brooding may be influenced by factors such of double brooding in Long-eared Owls (Ash otus). A as length of the breeding season, food avail- banded female raised 12 young in two nesting attempts compared with a mean of 5.3 young for three single- ability, growth rates of the young, and the du- brooded females that nested in the same grove. Two ration and quality of parental care (e.g., Drent factors may have influenced the occurrence of double and Daan 1980, Askenmo and Unger 1986, brooding: the first nest was initiated unusually early in Tinbergen and van Balen 1988). the year (mid-February) and food availability (in the Double brooding is relatively rare in rap- form of voles) was high. The rare description of double tors, presumably because the length of the brooding in Long-eared Owls may be due to the dif- ficulty of detecting it. Alternatively, double brooding breeding cycle and extended postfledging care may be uncommon because it is seldom an economi- preclude its occurrence (Newton 1979, Mor- cally viable strategy. Factors that would select against rison 1998). Among nocturnal raptors, double double brooding include low probability of recruitment brooding occurs regularly in Barn Owls (Tyto of the first-brood young, and reduced survival and fe- alba; Marti 1992, 1997) and occasionally in cundity of the adults. Received17 Sept. 1998, accepted Florida Burrowing Owls (Athene cuniczhria 29 Dec. 1998. JEoridunu; Millsap and Bear 1990) and Boreal Owls (Aegolius funereus; Kellom&i et al. 1977, Solheim 1983). During a study of The number of young raised per year is an breeding Long-eared Owls (Ask otus), we important component of an individuals’ life- documented a female that raised two broods time reproductive success. Double brooding, during the same nesting season. Here, we de- in which a second brood is attempted after a scribe the event and discuss factors that may successful first attempt, is a viable strategy if have influenced its occurrence. the increase in fitness that results outweighs the cost of any reduction in future survival or STUDY AREA AND METHODS The study area is a small grove (ca 2 ha) of quaking ’ ’ Montana Cooperative Wildlife Research Unit, aspens (Populus tremuloides) and black hawthorns Univ. of Montana, Missoula, MT 59812. (Crataegus douglasii) located about 16 km west of Z Corresponding author; Poison, Lake County, Montana (47” 40’ N, 114” 20’ E-mail: [email protected] W). The elevation at the site is 888 m, and the nesting 274 THE WILSON BULLETIN l Vol. 111, No. 2, June 1999 grove is surrounded by grasslands and agricultural note her pattern of flight-feather molt that we fields (mostly hay). The 11 Long-eared Owl nests that had confirmed in the hand the previous night occurred in the grove in 1997 and 1998 were in old (4 primaries and 2 secondaries growing on nests of Black-billed Magpies (Pica pica) and Amer- ican Crows (Corvus bruchyrhynchos). each wing). Also at this time, we noticed that Adults were captured at night in mist nests placed her mate was banded. After several attempts, near the nest or at dusk with the aid of a plastic decoy we succeeded in capturing the male on the of a Great Horned Owl (Bubo virginianus). Captured evening of 13 July, at which time the oldest adults were classified as after hatching year (AHY) or chicks were capable of short flights from tree after second year (ASY) based on the absence or pres- to tree. The male proved to be no. 914, the ence of two generations of secondaries, respectively same male that had nested at this site in 1997. (see Pyle 1997). During the breeding season, the sex of most adults can be determined in the field by dif- Female 951 was still present, and both adults ferences in plumage coloration and in the hand by presumably were provisioning their fledglings. presence or absence of an incubation patch (Marks et Interestingly, male 914 had not started flight- al. 1994). feather molt. Female 951 fledged 12 young (defining RESULTS “fledging” as capable of sustained flight; On 16 February 1998, we observed a fe- Marks 1986) in two nesting attempts com- male Long-eared Owl incubating at a nest pared with a mean of 5.3 young (range 5 to (PSNII) about 25 m north of a nest that had 6) produced by the other three pairs that nest- produced young the previous year. The male ed in the grove in 1998. The estimated time was roosting nearby, but we could not deter- between the initiation of 95 ls’ two nesting at- mine whether he was banded. Three of the tempts was 90 days (i.e., 12 February and 12 five Long-eared Owl nests that occurred in the May). At the time 951 initiated her second grove in 1998 were initiated in February; clutch, the oldest offspring from her first PSNII appeared to be the earliest of these brood would have been about 6 weeks old. nests. On 2 April, JSM captured the adult (AHY) female (band no. 951) by hand at DISCUSSION PSNII as she was brooding seven young that Several records of double brooding by ranged in age from about 1 to 3 weeks old. Long-eared Owls have been reported in Eu- Based on the estimated age of the chicks and rope (Reinsch and Wamcke 1968, Rinne 1981, an incubation period of 28 days (Marks et al. Scott 1997), but in each case the evidence was 1994), female 951 would have initiated egg circumstantial. To our knowledge, ours is the laying on 12 February, and the oldest chick first report of double brooding in Long-eared would have hatched on 12 March. Other du- Owls based on a banded individual. ties prevented us from catching the mate of We suspect that weather and food avail- female 951 during this nesting attempt. ability played a major role in this case of dou- During a visit to the nesting grove on 25 ble brooding. The winter of 1998 was unusu- June, we found a new Long-eared Owl nest at ally mild in western Montana. The ground at the northern edge of the grove 28 m from nest the study area was virtually free of snow from PSNII. A female was brooding small chicks January onward (pers. obs.), and the mean that appeared to be about 2 weeks old, and a temperature in February was 2.1” C above male was flushed from the same roost site typ- normal at the Kerr Dam weather station 13 km ically used by the PSNII male earlier that from the study area (data obtained from the spring. We returned to the nest on the evening National Climatic Data Center). In addition, of 30 June and captured the female in a mist voles (Microtus spp.) were abundant in winter net placed directly in front of the nest. She and spring; we saw many during the day, and proved to be 951, the same female that had other vole-eating raptors [i.e., Northern Har- fledged seven chicks earlier in the spring. The rier (Circus cyaneus), Rough-legged Hawk next morning we banded her five chicks, (Buteo Zagopus), and Short-eared Owl (Ado which were about 2 to 3 weeks old. Female jkzmmeus)] were numerous in the study area. 951 was very aggressive as we handled her The mild weather and abundant food probably chicks, diving and perching within 1 m of us induced Long-eared Owls to nest in February, and enabling us to observe her band and to which is very early for this species (see Marks SHORT COMMUNICATIONS 275 et al. 1994). The continued high numbers of received a normal amount of parental care (the voles in summer provided an opportunity for second clutch was started when the oldest double brooding, at least for one of the three chicks from the first nest were 6 weeks old) pairs that began nesting in February. only if the female changed mates between In general, the incidence of second nesting nesting attempts (and the male continued to attempts in facultatively double-brooded spe- care for the young), or if one or both parents cies is negatively correlated with the laying continued to provision the first brood while date of the first clutch (e.g., Smith et al.
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