Food Habits. Feeding. Home Species Subscribe News & Info FAQ

Transcription

1 Page 1 of 5 From the CORNELL LAB OF ORNITHOLOGY and the AMERICAN ORNITHOLOGISTS' UNION. species or keywords Search Home Species Subscribe News & Info FAQ Flammulated Owl Psiloscops flammeolus Order STRIGIFORMES Family STRIGIDAE Issue No. 093 Revised: May 21, 2013 Authors: Mccallum, D. Archibald Revisors: Linkhart, Brian D. Articles Multimedia References Access provided by US Forest Service Have a personal subscription? Sign in Articles Introduction Distinguishing Characteristics Food Habits Distribution Systematics Migration Habitat Food Habits Sounds Behavior Breeding Demography and Populations Conservation and Management Appearance Measurements Priorities for Future Research Acknowledgments About the Author Owl with prey, Chimney Beach, NV, 1 August. Feeding Flammulated Main Foods Taken Nocturnal arthropods, especially owlet and geometrid moths (Noctuidae and Geometridae), crickets and grasshoppers (Orthoptera), and beetles (Coleoptera). Food Capture And Consumption Hunts exclusively at night. Feeding visits to nest (see Breeding: parental care) indicate peak activity occurs within ~ 1 h after sunset and before sunrise, but this pattern not tested for non-nesting birds. Locates prey from perch visually, apparently judging distance by bobbing head vertically and horizontally. In Colorado, foraging males typically assume perches within crowns of large conifers and make short flights to glean insects from the needles, limbs, and trunks (while hovering), and occasionally hawk flying insects between tree crowns, or drop from lower crown branches to capture arthropods on the ground (the latter generally later in the nesting season; Linkhart 1984, Linkhart et al. 1998). Marshall (1939) described hawkers as returning to the same perch, Marshall (1957) and Reynolds and Linkhart (1987b) as landing on new perch. Single-prey loaders, delivering only one prey item per trip to nests (Reynolds and Linkhart 1987b, Linkhart et al. 1998). Captive fledglings use feet to capture prey, including moths taken in upside-down position from ceiling. Captive nestlings swallow soft-bodied prey whole, but large grasshoppers held in feet and torn apart with bill (Richmond et al. 1980).

2 Page 2 of 5 Legs of jumping orthopterans apparently a hazard (choking; Kenyon 1947). Prey carried to nest in bill. Acuity of senses not tested, but hearing may not be as important as for carnivorous owls, in that flight is not silent and combs on leading edges of wings not as well developed. Karalus and Eckert (1974) reported direct attack by an owl sitting 0.25 miles away after squeak of mouse was simulated, but their description suggests another owl species was under observation. (Several observations by Karalus and Eckert [1974] severely strain credulity of observers experienced with Flammulated Owl, so their entire account of this species must therefore be used with caution.) Foraging Habitat And Microsites Eighty-one percent of male foraging in the breeding season in Colorado was concentrated in small (0.5 ha) intensive foraging areas (IFAs), 80% of which in south-facing ponderosa pine/douglas-fir forest on ridgetops and slopes representing nonrandom selection of this forest type and underuse of young Douglas-fir/blue spruce stands (Linkhart et al. 1998). Nests in most territories occurred in IFAs; most males foraged in nest IFAs or in IFAs closest to nests early in the evening, when prey delivery rates to nests highest, and some foraged in more distant IFAs later at night when prey delivery rates lower (Linkhart et al. 1998). In Oregon, adults forage more than expected by chance in stands with low to medium stem density; also favor ponderosa pine and Douglas-fir over mixed conifers and grassland, but edge most preferred of all (Goggans 1986). Prey items captured from foliage of canopy and understory shrubs, airspace (mostly between crowns), and ground of conifer forests, associated broadleaf forests, and grassland edge. During nesting season, arthropods captured mostly from needles and bark of large tree crowns in Colorado, where foraging trees average 199 yr in age (vs. 111 yr for random sample in study area; Linkhart et al. 1998). Old forests also contain numerous openings, which facilitate hawking and especially ground foraging by fledged owlets and molting adults in late summer (Reynolds and Linkhart 1987b; see also Behavior: locomotion). Diet Major Foods Taken In North America during summer, crickets and grasshoppers (Orthoptera), moths (Lepidoptera), beetles (Coleoptera), or true bugs (Hemiptera) predominate, depending upon availability (Table 1). Noctuid [owlet] and geometrid moths appear to be the only flying prey available to the owls during the cold spring nights; frequently seen in May moving about the forest canopy when temperatures were below freezing (Reynolds and Linkhart 1987b). As breeding season progresses and nights become warmer, breadth of available arthropod taxa at blacklights greatly increases (Reynolds and Linkhart 1987b), Numerous arthropod taxa taken during the nestling period (Table 1). Anecdotal reports of food do not enlarge list in Table 1. Assertion that small vertebrates were taken during late 1800s and 1900s had little convincing documentation. Smith (1891) collected female whose stomach contained the remains of some small rodents. On the basis of this report and the assumption of similarity to species of Megascops, Bendire (1892) concluded that smaller mammals were major part of diet. Bent (1938) concluded species was largely, if not wholly, insectivorous, though it may occasionally capture a small mammal or bird. Bent s statement has been repeated in several uncritical compendia. Karalus and Eckert (1974) went further in asserting that this owl will eat mice of many varieties, shrews, moles, and, during nesting season only, a few small birds. It appears that the food habits, as well as the weights, Karulus and Eckert (1974) report may be those of Eastern Screech-Owl complex.

3 Page 3 of 5 In Oregon, Bull and Anderson (1978) found a pellet containing remains of red-backed vole (Clethrionomys gapperi) below a nest tree, and Dark-eyed Junco (Junco hyemalis) feathers in another nest, but the previous occupant, e.g., Northern Saw-whet Owl (Aegolius acadicus), may have taken these prey (E. Bull pers. comm.). Legs (with bands) of juvenile Mountain Chickadee (Poecile gambeli) in nest in New Mexico; chickadee had been banded as a nestling 30 m away (McCallum et al. 1995). Cannings (1994) removed a shrew (Sorex monticolus) from the stomach of an apparently healthy (mass = 60 g) owl that struck a window 15 Nov 1988 in Kelowna, BC. The validity of two sightings in Montana in 1981, one of owl perched in tree with vole in talons on 21 Nov and another of owl chasing passerines at bird feeder on 20 Dec (Holt et al. 1987), have been debated (Holt 1996, McCallum 1996). More recently, Oleyar et al. (2003) reported 13 instances of vertebrate prey in nest boxes of 10 different owl pairs in Utah from , including several bats (Family Vespertilionidae and Myotis sp.), unidentified songbirds, and Peromyscus sp. Tail and hind feet of one Peromyscus mouse were observed hanging from an owlet s mouth during one nest visit, and was subsequently swallowed. Videotaping prey deliveries at the Utah nests over two years documented one male delivering a rodent, probably Peromyscus sp., to the nest, the only vertebrate prey observed in 1,875 prey deliveries (0.053%; Oleyar et al. 2003). No vertebrate prey observed delivered to nests during 141 h at 4 nests in New Mexico (DAM unpubl. data). Observations of contents of > 300 nests in Colorado from documented a total of three vertebrate prey in three different nests; two nests each contained a Peromyscus mouse carcass (one with puncture marks near the head that penetrated the pelage, another that appeared unscathed) that was never consumed by owlets, and one nest contained legs of an unidentified songbird (Linkhart and Reynolds 1994, BDL unpubl. data). Over the 30- year period, observations of prey deliveries during > 2000 h at nests documented delivery of just one vertebrate prey, a Peromyscus sp. carcass by a female. With exception of one observed Peromyscus sp. in a nest, all other observations of vertebrate prey noted in Colorado study occurred in two of driest Jan to Jul periods (2006 and 2011), one period of which (2006) resulted in the highest annual rate of reproductive failure noted over the study (BDL unpubl. data). Also in 2006, two instances of apparent cannibalism documented, consisting of partial remains of two Flammulated Owl nestlings in separate nests (one banded leg recovered in one nest, one side of body in other nest). Unknown whether the two owlets, which had been in poor body condition prior to recovery in the late nestling period, had died on their own or were killed by siblings or adults. Taken collectively, these observations indicate Flammulated Owls rarely eat small vertebrate prey and then primarily during periods of environmental stress. Documentation of capturing and killing vertebrate prey, rather than simply scavenging, still is lacking. These observations also leave little doubt the owl is highly adapted as an insectivore. The possibility that Flammulated Owls may overwinter in northern areas by subsisting on vertebrates, however, cannot be completely discounted. Quantitative Analysis In Colorado, prey deliveries at nests consisted principally of Lepidoptera during courtship (May), incubation (May-June), and nestling phases (June-July), although diet breadth expanded to include other insect taxa during the nestling phase; these patterns generally followed the availability of arthropod taxa in blacklight samples (Reynolds and Linkhart 1987b). In Idaho, Lepidoptera was the predominant taxon observed in prey deliveries at three nests during July, which mirrored the pattern observed in blacklight sampling, while prey deliveries at one nest were dominated by orthopteran prey (Table 1; Powers et al. 1996). In Utah, lepidopteran prey accounted for 60% of 199 prey deliveries at 28 nests, and orthopterans accounted for 15% (Table 1; Mika unpubl. data.). In Oregon, no difference between proportions of arthropod taxa in traps (pit and aerial) and those brought to nestlings

4 Page 4 of 5 during Jul/Aug (Table 1; Goggans 1986). Orthopterans were the most available and most commonly delivered prey to nestlings (Table 1), and this taxon was 2.2 times more abundant in contiguous grassland than in pine forest where nests were located (Goggans 1986). Orthopteran prey also commonly observed in prey deliveries at nests in British Columbia (van Woudenberg 1999). Oleyar et al. (2003) and the author s (BDL) work are the only studies to date that observed delivery of vertebrate prey at nests (see above). Nutrition And Energetics A pair captured by Johnson (1965) died in an emaciated condition after several days in captivity despite nightly consumption of bird carcasses placed in their cage. Captives can be maintained indefinitely on diet of mealworms and neonatal mice ( pinkies ) but apparently cannot process bone of mature vertebrates (M. Altenbach pers. comm.). Captives eat juvenile mice (< 9 g; K. McKeever in Cannings 1994). Richmond et al. (1980) hand-raised 2 nestlings on a diet of grasshoppers. Metabolism And Temperature Regulation No data. Ligon (1969) studied 6 other species of small North American owls, including 3 Megascops species (Whiskered, Western, and Eastern screech-owls) and a small, migratory insectivore (Elf Owl; Micrathene whitneyi). His metabolism-mass curve (kcal d-1= 45.6* kg0.71) yields estimate of 5.82 kcal d-1(24.35 kj d-1) for 55-g Flammulated Owl. Whiskered and Western screech-owls and Elf Owl (from Arizona) are all able to maintain body temperatures below rising ambient temperatures when relative humidity is low. As ambient temperatures rose, activity ceased and plumage compressed, wings held away from body, and eyes closed. Panting ensued, often with conspicuous movements of abdomen, followed by gular fluttering. Megascops species appeared to flutter more efficiently and effectively than other owl species. They also survived elevation of body temperature to over 42 C, whereas 2 Northern Saw-whet Owl and Elf Owl did not. In Ligon s (1969) study, lower critical temperature (LCT) of Eastern and Western screechowls about 19 C, whereas Whiskered Screech-Owl expended energy on thermoregulation below 28 C. Smaller Flammulated Owl may have even higher LCT. Nonmigratory Eastern and Western screech-owls (Ligon 1969) and migratory Flammulated (Banks 1964, J. D. Ligon in Winter 1974) have resisted attempts to induce torpor with low ambient temperatures and food deprivation (but ability to enter torpor may be sensitive to photoperiod, which was not necessarily appropriate in these tests). Such birds do tolerate up to 25% mass losses when starved at low temperatures. Mass lability is characteristic of Flammulated Owls, as indicated by enlargement of breeding females and significant mass loss of individuals found starved in spring snowstorms (Ligon 1968a, Kingery 1979). These starving birds were not torpid. Taken collectively, these data suggest Flammulated Owl must produce metabolic heat for thermoregulation (when immobile) at rather mild temperatures. But greatest cold stress occurs in the early breeding season, particularly during courtship, when males are actively foraging for females generating egg mass. Females remain in cavities once egg-laying begins, which may reduce their energy needs for thermoregulation. May be able to tolerate warmer temperatures than some other small owls, as long as humidity is low. These speculations are consistent with the tropical affinities of Megascops and with open pine forests inhabited by Flammulated Owls. Drinking, Pellet-Casting, And Defecation Drinking not described. Captives maintained on grasshoppers produce dry, chitinous pellets (Richmond et al. 1980), fitting description by Karalus and Eckert (1974). Few or no pellets found beneath nests in Colorado (Webb 1982, BDL pers. obs.) and New Mexico (DAM pers.

5 Page 5 of 5 obs.), but chitinous pellets found in nest boxes in British Columbia (R. J. Cannings pers. comm.). Adults and young may produce almost black, fetid fecal material when handled. Sounds Habitat Recommended Citation Linkhart, Brian D. and D. Archibald Mccallum Flammulated Owl (Psiloscops flammeolus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: doi: /bna.93 Home Contact Us Terms of Service 2015 by Cornell Lab of Ornithology