Brian D. Linkhart

RETURN RATE, FIDELITY, AND DISPERSAL IN A BREEDING POPULATION OF FLAMMULATED OWLS (OTUS FLAMMEOLUS)

Abstract We estimated annual return rate, fidelity, and breeding dispersal in a migratory population of Flammulated Owls (Otus flammeolus) in central Colorado. Return rates, based on capture-recapture histories of 39 males and 52 females from 1981 to 2003, were higher for males (84%) than for females (45%). Annual recapture probability was higher for females, because breeders are easier to capture than nonbreeders and females always attempted to nest, whereas some males were unpaired (did not nest) for up to four years. Territory fidelity was male biased (92%, vs. 56% for females, adjusted for undetected emigration), and mean tenure on territories was more than twice as long for males as for females. Females, but not males, had lower return rates to territories in the year following nesting failure compared with females whose nests were successful. Most males appeared to occupy one territory their entire reproductive lives, countering predictions of habitat-selection models that individuals should move to higher-quality habitats when they become available. We estimated that 74% of pairs retained the same mate in consecutive nesting attempts, but mates that bred together for multiple years had no reproductive advantages over mates that bred together for the first time. In most cases, females dispersed from territories if their mates did not return. When females dispersed, they went to territories where total productivity over the study and lifetime reproductive success of new mates were higher than on original territories, which supports the hypothesis that dispersal by females increases individual fitness. Tasa de Retorno, Fidelidad y Dispersión en una Población Reproductiva de Otus flammeolus

Extra-pair copulation and extra-range movements in flammulated owls

We report an extra-pair copulation (EPC) in the Flammulated Owl (Otus flammeolus), the first in strigiforms, and document 21 cases of extra-range movements (ERMs) in this species. Extra-range movements occurred throughout nesting with both sexes participating: males anytime during nesting and females only after their young fledged. Males appear to make ERMs to gain EPCs and later to evaluate resources and the status of males in other areas, whereas females may be assessing the success of nests in adjacent ranges to judge the quality of potential future mates.

Lifetime Reproduction of Flammulated Owls in Colorado

ABSTRACT We investigated lifetime reproductive success (LRS) of 22 male and 46 female adult Flammulated Owls (Otus flammeolus) in Colorado from 1981–2003. Sexual differences in LRS were at least partially attributable to incomplete breeding histories of females, due to females having a higher estimated emigration rate from the study area than males. The mean number of lifetime breeding attempts for males was 3.4 ± 0.6 (SE; range  =  1–12), and for females it was 1.9 ± 0.3 (range  =  1–8). Adjusted for emigration beyond the study area, the estimated mean number of lifetime breeding attempts was 3.6 for males and 2.5 for females. The mean number of lifetime successful breeding attempts (fledging at least one owlet) was similar to lifetime breeding attempts for each sex, reflecting the fact that 84% (85 of 101) of all breeding attempts were successful. Breeding lifespan was correlated with lifetime reproduction for both sexes. Males tended nests that produced 6.9 ± 1.2 fledglings over 4.3 ± 0.8 yr, while females produced 4.0 ± 0.6 fledglings over 2.0 ± 0.3 yr; adjusted for emigration beyond the study area, males tended nests that produced 7.2 fledglings over 4.5 yr, while females produced 5.2 fledglings over 2.6 yr. Relatively few individuals of each sex produced most of the offspring, as 18% of females and 24% of males produced 50% of total owlets. Our finding that relatively few adults accounted for most offspring appears to be associated with habitat quality in territories. Flammulated Owls tend to have a life-history strategy similar to larger raptors by having a relatively low annual reproductive rate and a relatively long lifespan.

Longevity of Flammulated Owls: additional records and comparisons to other North American strigiforms

Abstract A male Flammulated Owl (Otus flammeolus), banded as a breeding adult (age unknown) on 8 July 1988 in central Colorado, was last recaptured on 8 July 2001. On the same study area, a female Flammulated Owl was banded as a breeding adult (age unknown) on 7 July 1988 and was last recaptured on 22 June 1995. These data establish longevity at a minimum 14 yrs for males and 8 yrs for females. The data suggest that Flammulated Owls may be relatively long-lived, and support evidence that this species has a life history strategy similar to larger raptors.

First observed instance of polygyny in Flammulated Owls

Abstract We document the first observed instance of polygyny in Flammulated Owls (Otus flammeolus) and the first among insectivorous raptors. Chronologies of the males two nests, which were 510 m apart, were separated by nearly 2 weeks. Each brood initially consisted of three owlets, similar to the mean brood size in monogamous pairs. The male delivered considerably fewer prey to the secondary nest, compared with prey-delivery rates at nests of monogamous males during the nestling period. Evidence suggested that all owlets fledged from the primary brood, but only one fledged from the secondary brood. We were uncertain of the cause of polygyny, but a possible explanation is the Hayman Fire shifted the operational sex ratio of the owls in favor of females. The extent of polygyny in Flammulated Owls may be limited by costs to the reproductive success of secondary females.