BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Asio flammeus | Short-Eared Owl 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Age at sexual maturity - 1 year [27]

Courtship and breeding - Short-eared owl form pair bonds; whether the
pairing lasts past the breeding season is unknown [27].  Depending upon
latitude, courtship begins in mid-winter or early spring, and breeding
is completed by late winter or late spring.  In Idaho and Massachusetts,
courtship begins in March and the female lays eggs by May [2,24].  In
Illinois, courtship begins in late April and egg-laying is complete by
early May [28].

Nesting and incubation - Most North American populations are
single-brooded, although short-eared owls in the South are sometimes
double-brooded.  Clutch size varies from 2 to 14 eggs, with 5 to 7 eggs
being the norm [28].  The female tends to lay more eggs when prey
populations are high [13].  Murray [37] found that clutch sizes were
significantly larger with increasing latitude; he attributed this to
larger rodent populations in the North.  The female lays her eggs
asynchronously, from 2 to 7 days apart.  Regional egg-laying dates are
given below [28].

Alaska and arctic Canada:  June 5-July 2; usually June 10-June 25
southern Canada:  April 30-June 22; usually May 4-June 17
northern United States:  April 14-June 15; usually April 23-June 10
Midwest:  April 4-June 8; usually April 16-May 25
southern California:  March 20-May 18; usually March 26-April 26

Destroyed clutches are usually replaced within 2 weeks; second clutch
sizes are smaller [12,28].

The female is the sole incubator; the male supplies her with food during
incubation.  Incubation time is 21 to 29 days per egg.  The eggs hatch
asynchronously, about one every 3 days.  The brood therefore consists of
different-aged sibs.  The female does all brooding; the male hunts to
feed the young and his mate [12,16,24,28].

Fledging - Young leave the nest on foot about 16 days after hatching and
fledge at approximately 29 days of age [24,25].  The brood is dependent
on the parents for food "for a period of time" after fledging [13].
After all young have fledged, parents lead the brood to a new area if
prey is scarce on the nesting grounds [34].

Clark [12] reported a mean clutch size of 8.6 for short-eared owl nests
in a Massachusetts freshwater marsh.  An average of 7.0 young per nest
hatched, and an average of 4.0 young per nest fledged.  On Nantucket
maritime heath, Tate and others [45] found a mean clutch size of 5.7 in
1985.  An average of 3.4 eggs hatched, and 2.0 young per nest fledged.  In
1986, mean clutch size was 7.7, with an average of 7.0 eggs hatching and
3.4 young per nest fledging.

Migration - Much remains to be discovered about short-eared owl
migration dates and routes.  The short-eared owl is well adapted to heat
and cold.  As a result, it is appearently only weakly migratory [28].
Short-eared owl populations at the edge of the species' northern
distribution move south in late summer or early fall, but it is unclear
whether more southerly populations migrate or remain in an area as
permanent residents.  Banding records are few, but limited studies show
that some individuals in populations south of taiga are regular
migrants.  Others are irregular migrants, leaving in some years but not
others.  Some owls probably migrate to new areas as young adults, then
become permanent residents.  Migration routes are generally north-south,
but not always.  Some migrants, for example, move back and forth from
North Dakota and eastern Oregon [12].

Except for populations at climatic extremes, when entire populations
migrate it is usually in response to depletion of the prey base rather
than seasonal climate changes.  Short-eared owl rapidly move out of an
area bereft of prey, and rapidly move into areas where rodent
populations are rising [12,29,34].

Longevity - Captive birds have lived to age 15.  It is unknown how long
short-eared owl usually survive in the wild [28].


PREFERRED HABITAT : 
Short-eared owl occupy a variety of open habitats within their wide
geographical distribution.  Preferred habitats include fresh- and
saltwater marshes [6,7,12,21], coastal plains [24], tamarack (Larix
laricina)-black spruce (Picea mariana) bogs [8], old fields [14,18],
prairies [30], sagebrush (Artemisia spp.) steppes [38,40,42], wet
meadows, grasslands, open shrublands, and montane parklands [21,22].

Since the species is only weakly migratory, nesting, hunting, and
wintering habitats are generally the same [12,28].  In Massachusetts,
short-eared owl in maritime heath occupied a home range of 63 to 198
acres (25-79 ha) [45].  In freshwater marsh, the home range was 184.8 to
303.5 acres (73.9-121.4 ha) [12].

Nesting habitat - Short-eared owl nest on dry ground in open areas with
dense herbaceous cover.  Even in wetlands, dry microsites are selected
for nesting [13].  Taiga and tundra are poor nesting habitat [12].

Hunting habitat - The owl uses open ground where prey is available [7,33].


COVER REQUIREMENTS : 
Nesting cover - Short-eared owl require open areas with dense, tall
herbs for nesting.  They are the only North American owl that habitually
build their own nest each year.  Nesting short-eared owl build the nest
with sticks and rotting vegetation; they approach it through a short
tunnel in the thick grass [28].  Duebbert and Lokemoen [15] found that
in North Dakota rangeland planted to smooth brome (Bromus inermis),
intermediate wheatgrass (Thinopyrum intermedium), and tall wheatgrass
(Elytrigia elongata), owls selected sites where grass cover was 12 to 24
inches (30-60 cm) tall.  Seventy-five percent of nests were
three-fourths concealed from the sides; tops were mostly open.  Evrard
and others [18] found that in a Wisconsin old field, nesting cover was
mostly 3-foot (90-cm) quackgrass (Elytrigia repens).

Hunting cover - Short-eared owl require open landscapes for hunting.
They generally hunt on the wing, flying low [28], but occasionally hunt
from low perches such as saplings and fenceposts [7].

Roosting cover - Short-eared owl usually roost on the ground or on grass
tussocks, although they occasionally use low brush [28], fenceposts, and
telephone poles [9].  During winter in snow country, they often roost
communally in low-growing conifers [12,28,33,39].  Observers in New
Jersey saw short-eared owl flocking together and roosting in short
conifers whenever snow cover was greater than 30 inches (75 cm) [9].


FOOD HABITS : 
Unlike most owls, short-eared owl hunt both day and at night until
sufficient prey are taken [12,28].  Throughout most of North America,
the meadow vole (Microtus pennsylvanicus) is selectively hunted and
comprises at least 90 percent of the short-eared owl's diet
[5,12,14,26,28].  Clark [12] speculated that on this continent,
short-eared owl cannot reproduce unless sufficient meadow vole are
taken.  Current knowledge of short-eared owl food habits and nutritional
requirements is insufficient to determine whether this is true, however
[50].  Minor items in the short-eared owl diet include other voles
(Microtus spp.), deer mouse (Peromyscus maniculatus), shrews
(Soricidae), and small birds [9,46,48].  In Hawaii, the house mouse (Mus
musculus) and the Polynesian rat (Rattus exulans) are primary prey
[22,42].


PREDATORS : 
Large avain predators such as great horned owl (Bubo virginianus) [4],
snowy owl (Nyctea scandiaca) [33], and rough-legged hawk (Buteo lagopus)
[36] occasionally prey upon both juvenile and adult short-eared owl.
Ground-nest predators such as American badger (Taxidea taxus) [47] and
gulls (Larus spp.) [12] eat the eggs.


MANAGEMENT CONSIDERATIONS : 
Short-eared owl populations have declined over most of their former
North American range due to habitat loss [24].  By 1986, they were
widely reported as declining in the Hudson-Delaware region, the Midwest,
and the Southern Great Plains; in severe decline in central-southern,
prairie, and mid-Pacific coast regions; and long since extirpated from
southern California [17].  In the Midwest, short-eared owl are currently
reported only from remnant prairie [44].  Baldner [2] and Sinclair [43]
attributed the species' rarity in Iowa to loss of tallgrass prairie.
Urbanization of coastlands has decimated populations in Massachusetts
[12,45].  Central California populations have been reduced by
agricultural and urban development [21].  Marti and Marks [35] have
listed populations as stable in Oregon and Colorado and fluctuating but
stable in Montana.

Short-eared owl often persist near farmland borders where agriculture is
not intensive.  Intensive agriculture or conversion of meadows,
wetlands, or other short-eared owl habitat to cropland, however, results
in short-eared owl decline [24,29].

Overgrazing removes cover needed for nesting and brooding [21,35].  In
Idaho, short-eared owl were present in ungrazed big sagebrush-standard
wheatgrass (Artemisia tridentata-Agropyron desertorum), but not in areas
grazed by sheep [40,41].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Asio flammeus | Short-Eared Owl