Breeding

Pair Formation

Begins mid-Feb, continues through Jun (Urner 1923, 1925, DuBois 1924, Pitelka 1955b, Hamerstrom et al. 1961, Beske and Champion 1971, Trann 1974, Clark 1975, Holt 1992). Communal winter roosts may turn into local breeding territories (Clark 1975, Wilson 1995, DWH). Thought to be a colonial nester, but probably dependent on prey, nesting cover, and area; thus facultative more appropriate. In n. Europe, mid-Apr to Jun (Mikkola 1983, Cramp 1985).

First Brood Per Season

Figure 6 . Occasionally late Mar, but mostly Apr; Jun in high arctic (Pitelka 1955b). Extreme cases include breeding autumn/winter in Rumania, Dec in Netherlands (Mikkola 1983), and Dec/Jan in Russia (Mikkola 1983) – probably related to high prey densities. In Southern Hemisphere (Colombia), breeding begins Sep (Borrero 1962).

In British Columbia, 32 clutches found 24 Mar to 9 Jul, most (51%) between 20 Apr and 15 May (Campbell et al. 1990). In Yukon, clutches found as early as May, but most in Jun (Sinclair et al. 2003).  In N. Dakota, 26 clutches found 4 Apr - 1 Aug, peak in May and Jun (Stewart 1975). Ontario egg dates range from 14 Apr to 1 Aug (James 1991).

Historical egg-laying data (Bent 1938): Alaska and Arctic Canada – Jun 10-30 (n = 8); Alberta and Manitoba – May 5- Jun 20 (n = 9); Dakotas and Minnesota – Mar 20-Jun 12 (n = 17), with peak (n = 9) May 12-23.

Second Brood Per Season

Reported to raise second brood (Mikkola 1983). Need data with marked individuals to comfirm this.

Selection Process

Males sky dance over territory to attract females, but not known which sex selects nest site (Holt 1992).

Microhabitat

Mean vegetation height at 9 nests in Massachusetts 45.1 cm, SD = 5.0, range 35.5 to 53.3; > 90.0% beach grass (Ammophila breviliqulata; Holt 1992). Within 1 m line-intercepts of the four cardinal compass directions surrounding 28 nests, 79.0% of the nest cover was grasses, 17.0% herbaceous, and 4.0% herb/grass, respectively. Of this, 80.0% of the vegetation was < 0.5 m height, 12.0% between 0.5–1.0 m, and 8.0% > 1.0 m (DWH and SML). In Montana, nests located in patches of relatively dense grassland, with high visual obstruction readings (Fondell and Ball 2004).

Nest Building

Nests on ground and may construct conspicuous nests. Nest bowls scraped out by female and lined with grasses (Clark 1975) and downy feathers (Holt 1992) - one of the few owls to construct its own nest. In Europe, females reported to build nests (Mikkola 1983). One nest on bare soil with no nest material (Holt 1992).

Site Characteristics

Nests selected when previous year’s residual vegetation dead and often matted down (Holt 1992). Usually nest on dry sites, often small knolls, ridges, or hummocks; wet areas used less frequently. Of 63 nests (North America), 55.0% in grasslands; 24.0% grain stubble; 14.0% hayland; 6.0% low perennials (Clark 1975). Of 28 nests in Montana, 15 m line-intercepts from the nest center in four cardinal compass directions showed 85.0% grasses, 8.0% herbs, and 7.0% herb/grass composition. Of these, 90.0% of the vegetation was < 0.5 m height, 9.0% 0.5–1.0 m, and 1.0% > 1.0 m (DWH and SML). Nests difficult to locate; females reluctant to flush until humans/predator? are just a few meters from nest. Atypical nests reported in burrow and clump of low bushes (Bent 1938). In Europe, on a ledge, a stump 3 m above ground, and a tree (Mikkola 1983). Other tree nesting questionable, more likely Long-eared Owl. See also: http://www.on.ec.gc.ca/wildlife/wildspace/life.cfm?ID=SEOW%Page=Nest%Lang=e

Dimensions

More data needed; Urner (1923) reports 23–25 cm diameter (n = 2), 4–5 cm high. In Europe, average nest mass 74 g (n = 6). In Montana mean length and width 19.0 x 19.0 cm (n = 28; DWH and SML).

Reuse Of Nests

Urner (1923) found a new nest constructed over previous year’s nest with old eggs. In Montana, one nest built on top of previous year’s nest with 5 old eggs (B. Swaney pers. comm., DWH; see also Eggs: interspecific egg dumping, and Parental Care). In Europe, Schuster (in Mikkola 1983) found new nest with eggs presumably built over last year’s nest with 4 old eggs.

Nonbreeding Nests

Unoccupied nests found near active nests, (Holt 1992) and females flushed from scrapes (Pitelka 1955a, Clark 1975); suggests several sites tried before one selected.

Shape

Short elliptical.

Size And Mass

Length x breadth (mm): In North America, 39 x 31, n = 56 (Bent 1938);  Europe, 37-45 x 30-34, n = 100 (Cramp 1985); Chile, 43 x 35 (see Voous 1988). In Manitoba, mean egg mass 22 g (20.7-23.7 g, n = 6; Clark 1975).

Color

Non-glossy to glossy cream/white becoming darker with age from wear and stained from debris in nest. Photos at: http://www.on.ec.gc.ca/wildlife/wildspace/life.cfm?ID=SEOW%Page=Nest%Lang=e

Surface Texture

Smooth.

Egg Laying

1–2 d between eggs (DWH). In Finland, Gronlund and Mikkola (1969) reported laying intervals of 26 h.

Interspecific Egg Dumping

In Montana, a Mallard (Anas platyrhynchos) dumped one egg in an active Short-eared Owl nest with 3 eggs (B. Swaney pers. comm., DWH; see Reuse of nests, above; also Parental Care, below).

Onset Of Broodiness And Incubation In Relation To Laying

Incubation by female only, begins with first egg (DWH). Foster (1955), however, stated both sexes incubate.

Incubation Patch

Single large patch on female only (DWH).

Incubation Period

21 d (Bent 1938); 26–37 d, Alaska (Pitelka 1955b); 3 eggs from 3 different nests 29, 30, 31 d, Massachusetts (Tate 1992); 24–29 d, Finland (Gronlund and Mikkola 1969); 24–28 d, Europe (see Millola 1983), and in England, prolonged incubation of at least 42 d on clutch of 6 addled eggs (Goddard 1935a).

Parental Behavior

From Mikkola 1983; DWH. Male feeds incubating and brooding female; defends nest with distraction displays and vocalizations, rarely attacking humans. Some males aggressive, most generally not. Eggs sometimes flipped out of nest by female when flushed. Female may retrieve eggs that roll out of nest by hooking bill under egg and rolling it back in nest . Females on nests reluctant to flush and often defecate on eggs if flushed. Smell of defecation generally thought to mask scent of nest, or the putrid smell may redirect path of predator. Needs study.

Asynchronous and in order of laying; usually over 1–2 d intervals. One exception, 2nd egg laid, hatched 1 d before 1st egg (DWH). In US (Massachusetts and Montana), (5.6%) and 19 (8.1%) of 235 eggs laid were infertile or abandoned, respectively (DWH and SML). Nestlings vocalize from within egg; break shell from within using egg tooth on maxilla, striking upward on inside shell.  See also: http://www.on.ec.gc.ca/wildlife/wildspace/life.cfm?ID=SEOW%Page=Nest%Lang=e

Condition At Hatching

Semi-altricial and nidicolous. Body mass at hatching from incubator, 16, 18 g (n = 2; Clark 1975); in the wild, 16 g (n = 8; Holt et al. 1992). In Finland, 15.4 g (range 14–17, n = 5; Gronlund and Mikkola 1969). Hatch wet, eyes closed, egg tooth present. Natal down (neoptile) buff colored on upperparts (darker zone bordering mantle), white with buff tinge on underparts; down covers body except bill, cere, talons, and soles (see illustration in Baicich and Harrison 1997 .

Growth And Development

Models used by Holt et al. (1992) report gains of about 8 g body mass/d for first 1–5 d of life, 19 g/d at 6–10 d, 21 g/d at 11–15 d, and 12 g/d at 16–20 d of age. Most rapid growth at 11–15 d, at which time nestlings gain almost three times the body mass as in period 1–5. These gains coincide with pre-fledging dispersal from nest—dispersal on foot, by nestlings not yet old enough to fly. Young disperse from nests when about 14–17 d.

As a ground nester, vulnerable to mammalian predation. Selective pressure may favor rapid growth, development, and pre-fledging dispersal as anti-predator adaptation to ground nesting, because it (1) minimizes the amount of time predators have to locate nests, and (2) asynchronous dispersal can ensure successful reproduction even if a predator finds nests after some young have dispersed. Pre-fledging dispersal may also act to reduce sibling brood cannibalism (Holt et al. 1992); such dispersers have moved up to 55 m from the nest.

Descriptive Sequence Of Development

(Fig. 7): Day 1–3: First natal down (neoptile) buff colored, eyes closed, egg tooth present. Day 5: Second natal down (mesoptile) beginning, eyes open to slits (often one at a time), egg tooth present. Day 7: Mesoptile tan colored with dark bands, eyes half open and foggy, egg tooth present. Day 9: Down becoming darker, eyes open on most and clearing, egg tooth present or gone on some, contour feathers visibly erupting from feather tracts (pterylae). Day 11: Down dark rust, eyes open and clear, egg tooth gone on most, fascial disk developing and interior turning black around orbits. Primaries and tail feathers visible as Juvenal plumage progresses. Day 13: Juvenal plumage developing with flight and body contour feathers, fascial disk almost entirely black, posture upright, alert and around edge of nests. Rarely an egg tooth. Day 15: Similar to above, ear-tufts erupting, mobile and ready to disperse from nest.

Control Of Body Temperature

Not known for young birds. However, 7 captive adults housed outdoors in Barrow, AK, with ambient temperatures -11° to -23°C, had a mean body temperature of 41.2°C (range 39.2°–42.2°C; Irving and Krog 1954).

Behavior

Little known within nest. Two captive birds cast first pellets when 8 and 9 d old (Clark 1975). In Scotland, cast pellets at about 12 d old (Lockie 1955). In nest huddle together under females body until about 9 d old, then sit upright on edge of nest during day. Probably thermoregulate at this age. Sibling scavenging (nestling feeding on its nest mate) occurs (Ingram 1962, Holt 1992), but the actual killing and consumption (cannibalism) of nest mates not observed. Holt (1992) reported 5 nestlings from 2 nests eaten by siblings; not known if they were already dead or killed and then eaten by nest mates.

Brooding And Feeding

Only female broods and feeds nestlings; male provides food. In large broods, female may or may not brood youngest after oldest have dispersed (DWH). Female feeds nestlings whose eyes are still closed by touching mouth gape with small pieces of food (Gerber in Voous 1988). Clark (1975) reported 3–4 d old nestlings in upright posture give food begging call Pssssss-sip, flap wings, and gape for food. Female protects nestlings from some weather conditions by brooding when young, mantling when larger (DWH). Both sexes may defend young in nest and as pre-fledged dispersers, but this behavior varies among individuals (DWH). Not known how long adults feed and protect pre-fledged dispersers and fledglings. In an unusual case, a clutch was replaced with 3 domestic chicken eggs, which the female owl hatched, brooded, and attempted to feed (DuBois 1923). The chickens’ precocial behavior eventually led to their death. In Montana, a female Short-eared Owl hatched a Mallard egg which was dumped in her nest of 3 eggs; Mallard chick seen day of hatching only, brooded by the owl (B. Swaney pers. comm., DWH, see also interspecific egg dumping, above).

Nest Sanitation

Behavior unknown. Lack of eggshell debris suggest it is trampled, eaten, or carried away. Clark (1975) reports that nestlings withdraw 1 m off nest to defecate. Nests generally clean, but dead uneaten prey, feathers, and feet of avian prey often found (DWH). Nestling pellets and fecal waste accumulate toward end of nestling period (DWH).

Nidicolous parasitic and commensal microarthropods in Massachusetts nests (n = 7) included: 79.0% mites (Gamasida, Actenidida, Acaridida, Oribatida) and insects (Philips et al. 1988). Mesostigmatid mites were most abundant. Mammal associated mites and a deer tick (Ixodes dammini) recorded at one nest. Commensal arthropods included those which feed on nest material, owl prey remains, fecal waste, other arthropods. Other ectoparasites on adults and young include Philopterus syrnii (Peters 1936). Hematozoa include Haemoproteus and Leucocytozoon (Stabler and Holt 1965).

Parent Carrying Of Young

Urner (1923) suggested adults may move eggs and nestlings, but this needs corroborating. No other reports of this behavior.

Not known (but see Behavior: sexual).

Not known (but see Interspecific egg dumping, above).

Departure From Nest

Around 12–18 d (see growth and development, above). Wander on foot until fledging (first flight) at 27 d of age(Clark 1975); 28–35 d (Holt 1992); in Europe, 24–27 d (Voous 1988).

Association With Parents Or Other Young

Poorly known. Once fledged, young form communal family group and roost together during the day; adults may participate at first, but not known how long or sex role partitioning (DWH). Brood mingling may also occur. Independent at 1–2 wk after fledging (Urner 1923); but needs further study. In Europe, young successfully begged food 25 d after fledging (Cramp 1985), not independent of parents until 50 d (Voous 1988).

Not known.