Elf owls are often found in the upland deserts of Arizona and Sonora, Mexico, their range also spreads into parts of California, New Mexico and Texas. Most are members of three populations that breed in the area of the United States-Mexico border and spend the winter in southern Mexico. Three other distinct populations exist in southern Baja California and Puebla, Mexico; these populations are nonmigratory.

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Breeding

Global Range: BREEDING: Extreme southern Nevada, southeastern California, central Arizona, southwestern New Mexico, western and southern Texas, Coahuila, and Nuevo Leon south to Sonora, Guanajuato, and Puebla; also southern Baja California (AOU 1998). Formerly more widespread and abundant along the Colorado River of California/Arizona (Henry and Gehlbach 1999). NON-BREEDING: southern Sinaloa, Michoacan, Morelos, and southern Texas south to Guerrero, Puebla, and northwestern Oaxaca (AOU 1998, Henry and Gehlbach 1999). RESIDENT: Socorro Island and Baja California Sur (AOU 1998, Henry and Gehlbach 1999).

Elf owls are the smallest owls in the world; the total length of an adult is 12.4 to 14.2 cm. Adults weigh 35 to 55 grams. Males and females resemble each other, but the total length of the female is 3% larger than the male, and the female is 6% larger in mass. Elf owls have short tails, yellow irises, conspicuous white eyebrow marks and two rows of white spots on the wings. Their backs are grayish-brown with buff mottling; cinnamon-brown blurry vertical streaks occur on the breast. Their bills are greenish yellow and their legs and feet are tan to dull yellow.

Range mass: 35 to 55 g.

Range length: 12.4 to 14.2 cm.

Sexual Dimorphism: sexes alike; female larger

Average basal metabolic rate: 0.259435 W.

Length: 15 cm

Weight: 41 grams

• Terrestrial
• Freshwater

Elf owls live in a wide variety of habitats, including upland deserts, subtropical thorn woodlands, montane evergreen woodlands and canyon riparian forests, as well as in partially urbanized areas. Elf owls nest in old woodpecker holes in columnar cacti, such as the saguaro (Carnegiea gigantea), trees, such as the Arizona sycamore (Platanus wrightii) and agave and yucca flowering stalks. Sometimes they nest in deciduous foliage. The alligator juniper (Juniperus deppeana) is commonly used for nest cavities in canyon riparian and evergreen woodlands. In suburbs and agricultural areas bordered by woods they use fence posts, utility poles and nest-boxes.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: desert or dune ; forest ; scrub forest ; mountains

Other Habitat Features: urban ; suburban ; agricultural

Comments: BREEDING: In California, nests in POPULUS-SALIX-PROSOPIS riparian forest (Halterman et al. 1989); in southern Arizona, southwestern New Mexico, and Sonora nests in OLNEYA-CERCIDEUM-PROSOPIS desert-wash woodland, POPULUS-SALIX-CELTIS riparian forest, CEREUS-CERCIDEUM-PROSOPIS upland desert, PLANTANUS-JUGLANS-FRAXINUS-ACER canyon riparian forest, and evergreen woodland; in SW Texas and Coahuila, Mexico, nests in AGAVE-ACACIA-LEUCOPHYLLUM lowland desert, PROSOPIS-ACACIA-CELTIS-CHILOPSIS desert-wash woodland, POPULUS-SALIX-FRAXINUS-JUGLANS-ACER canyon riparian forest, and QUERCUS-PINUS-JUNIPERUS evergreen woodland; and in the lower Rio Grande valley of Texas and Tamaulipas and Nuevo Leon, Mexico, nests in ACACIA-PROSOPIS-CELTIS-DIOSPYRUS-BUMELIA subtropical thorn woodland and PITHECELLOBIUM-EHRETIA-ULMUS-LEUCAENA riparian woodland (Henry and Gehlbach 1999).

In the Sonoran region, nests most often in saguaro (Cereus giganteus) and columnar cacti, fremont cottonwood (Populus fremontii), honey mesquite (Prosopis glandulosa), and gooding willow (SALIX GOODINGII; Goad and Mannan 1987, Halterman et al. 1987, Henry and Gehlbach 1999). In riparian habitats, nests principally in Arizona sycamore (PLANTANUS WRIGHTII), fremont cottonwood, velvet ash (Fraxinus pennsylvanica var. Velutina), Arizona walnut (Juglans major), Chihuahua pine (Pinus leiophylla), and various evergreen oaks (Quercus arizonica, Q. EMORYI, Q. HYPOLEUCOIDES; Henry and Gehlbach 1999, Ligon 1968, Marshall 1957).

In the Chihuahuan region of Texas, nests in yucca (Yucca faxoniana, Y. ROSTRATA), agave (Agave havardiana, A. PARRYI), Rio Grande cottonwood (POPULUS WISLIZENII), black willow (Salix nigra), evergreen oaks (Quercus emoryi, Q. GRISEA) and deciduous oaks (Q. MUHLENBERGII). In the Rio Grande Valley, Texas, nests most often in eastern cottonwood (Populus deltoides), black willow (Salix nigra), mesquite (Prosopis spp.) and anacua (Ehretia anacua; Henry and Gehlbach 1999).

In western Arizona, most frequently encountered in riparian forests (45-88 percent of survey sites) and least frequently in pine-oak montane forest (8 percent) or oak chaparral (9 percent; Millsap 1988). Nests in cavities in trees, cacti, flowering stalks of agave and yucca, fence posts, and utility poles created by ladder-backed woodpecker (Picoides scalaris), golden-fronted woodpecker (Melanerpes aurifrons), acorn woodpecker, Strickland's woodpecker (Picoides stricklandi), gila woodpecker (Melanerpes uropygialis), and gilded flicker (Colaptes chrysoides), as well as in bird boxes (Henry and Gehlbach 1999, Johnsgard 1988, McKinney 1996). When woodpecker cavities are randomly oriented, select nesting cavities randomly (Goad and Mannan 1987, Korol and Hutto 1984).

In Arizona, nest height averages 6.3 meters (range = 3.4-10.9 meters) above the ground in saguaro cacti and 10.3 meters (range = 5.3-18.4 meters) above the ground in riparian canyon habitat (Goad and Mannan 1987, Ligon 1968).

NON-BREEDING: In winter, may roost in bush or shrubby tree. In SENOCEREUS-NEOBUXBAUMIA tropical deciduous forest and Lemaireocereus semi-arid grassy savanna in Mexico (Henry and Gehlbach 1999).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

The populations inhabiting the U.S.-Mexican border are migratory and winter in the Sierra Madre region of western Mexico. Generally returns to breeding habitat in March and leaves for wintering habitat between late September and early October. In some years early spring migrants arrive in mid-February (Henry and Gehlbach 1999, Phillips 1942). Individuals breeding at higher elevations in Arizona do not return until mid-April. Migration in flocks is suggested by observations of groups of birds in late summer and in March. Males apparently migrate before females (Henry 1998, Henry and Gehlbach 1999, Ligon 1968). Migration distances, routes and stopover sites are unknown. Non-migratory populations inhabit Baja California Sur and Puebla, Mexico (Henry and Gehlbach 1999). Reportedly present year-round in Texas, though some researchers did not find this species during February searches (Johnsgard 1988).

Elf owls primarily eat insects — especially moths, beetles, and crickets — but occasionally they eat small mammals and reptiles, like spiny lizards, earless lizards, blind snakes and kangaroo rats. In southeastern Arizona, elf owls change their diet based on the weather. They eat mainly moths and crickets until the summer rainy season begins, then they switch to scarab beetles. Elf owls employ a sit-and-wait strategy when foraging. They search for food on the ground, in the air, and in lower to mid-level vegetation. In urbanized areas, they forage by outdoor lights, lighted windows and at hummingbird feeders. They can catch insects in flight, capturing them with their feet or beak. Sometimes elf owls chase insects on the ground and beat them from plants. Elf owls move their food back and forth between their feet and beak in order to kill, pluck, and/or eat it. They avoid consuming dangerous body parts of prey; they remove the stingers of scorpions before eating them. Elf owls cache large prey in cavities in order to eat them at a later time.

Animal Foods: mammals; reptiles; insects

Foraging Behavior: stores or caches food

Primary Diet: carnivore (Insectivore )

Comments: A sit-and-wait predator, hunts from low perches which it changes frequently. Prey captured with feet or beak in the air or on the ground. Also chases prey on the ground, and probes flowers and foliage for prey (Henry and Gehlbach 1999, Ligon 1968, Marshall 1957). Water is obtained principally through prey (Ligon 1968). Feeds primarily on invertebrates, especially insects (moths [Lepidoptera], beetles [Coleoptera], and crickets [Orthoptera] predominate), but also whip scorpions (Uropygi), scorpions (Scorpionida), and spiders (Araneae). Occasionally preys on lizards (Sceloporus and Cophosaurus spp.), small snakes (Leptotyphlops spp.), and young kangaroo rats (Dipodomys spp.; Earhart and Johnson 1970, Henry and Gehlbach 1999, Ligon 1968). Caches large prey items in the nest cavity.

Elf owls eat insects and small mammals and are eaten by larger raptors and snakes. While they have an important place in the food chain, they are not keystone or indicator species.

Elf owls may have a symbiotic relationship with both blind snakes (Leptotyphlops dulcis and Leptotyphlops humilis) and tree ants (genus Crematogaster). Blind snakes put in the nest to feed the nestlings may occasionally escape, remain in the nest debris, and consume ants and fly maggots that eat part of the food caches meant for the nestlings. Tree ants are symbiotic with whiskered screech-owls, and they may have a similar relationship with elf owls, in which they attack intruders but leave the owls alone.

Mutualist Species:

• blind snakes (Leptotyphlops dulcis, Leptotyphlops humilis)
• tree ants (genus Crematogaster)

Adult and fledgling elf owls face predation by great horned owls (Bubo virginianus), mexican jays (Aphelocoma ultramarina), and probably by Cooper’s hawks (Accipiter cooperii). Eggs and hatchlings are exposed to predation by gopher snakes (Pituophis melanoleucus), green rat snakes (Senticolis triaspis), and maybe ringtails (Bassariscus astutus). In response to the presence of a predator in the area of the nest, the nesting pair of elf owls as well as 1 to 4 neighboring elf owls will cooperatively mob the predator by directing physical assaults on its head.

Known Predators:

• great horned owls (Bubo virginianus)
• mexican jays (Aphelocoma ultramarina)
• Cooper's hawks (Accipiter cooperii)
• gopher snakes (Pituophis melanoleucus)
• green rat snakes (Senticolis triaspis)
• ringtails (Bassariscus astutus)

Breeding density averages 2.2-8.3 nesting pairs per square kilometer for established populations and 0.3 pairs for colonizing populations (Henry and Gehlbach 1999). Territorial during the nesting season; multiple cavities are defended against conspecifics (Goad and Mannan 1987, Ligon 1968). Nine individuals radio-tracked in the lower Rio Grande Valley, Texas, ranged over an average of 1.0 hectare (range = 0.2-2.6 hectares) of subtropical woodland (Gamel 1997 cited in Henry and Gehlbach 1999). In Arizona, two nesting pairs used 0.2 and 0.4 hectare of canyon riparian forest, respectively (Henry and Gehlbach 1999).

Site fidelity is illustrated by the return of six nesting females to the same Chihuahuan Desert site the year following banding, the return of two after two years, and the return of one after three years (Henry and Gehlbach 1999). Maximum known age for a wild bird is 4 years, 11 months; can live up to 14 years in captivity (Henry and Gehlbach 1999).

Hungry nestlings peep or squeak softly, twitter, and rasp at a rate of up to 48 times a minute. The rate and volume of their vocalizations indicate how hungry they are. They trill at high pitches when fed. Males have a song type that both claims their territory and advertises themselves to females. Males sing a variant of that song that includes more notes and rises and falls in volume. The male sings continuously from a possible nest cavity. As a female nears, the male goes into the nest cavity while still singing. This advertises the potential nest cavity and incites the female to accept it. Males also have distinct songs for use in flight and before copulation. Females make unique sounds during copulation and when being fed by males. Both sexes make a short, single, soft whistle to communicate during nesting, typically when the pair is feeding their young. This strengthens the pair bond. Elf owls bark as they face intruders or mob predators. In such a situation, they flip their tails quickly back and forth. Elf owls also clap their bills during threatening situations.

Communication Channels: visual ; acoustic

Comments: Peak feeding periods (at least while young being fed): around dusk and dawn, with some foraging throughout the night (Ligon 1968).

At hatching, Elf Owls are covered with thick white down to the base of the claws and have large feet and bare heel pads. In 5-6 days their eyes open. Within 9-12 days they can observe, sit up, snap their beaks and rear back. After 21-22 days, the Elf Owl is active and might try ineffectively to fly. Fledging occurs 28-33 days after hatching. To incite them to leave the nest, parents may refuse to bring food to the nest cavity. Fledglings are adult size and can fly weakly upon leaving the nest. Parents continue to feed the fledglings for an unknown period of time, although the fledglings are able to catch crickets by themselves almost directly after fledging. About four months after hatching, juveniles molt to resemble adults (Henry 1999; Ligon 1968a).

The maximum age of elf owls is about five years in the wild, although they can reach 14 years in captivity. Causes of mortality among elf owls include: predation, competition with other species, competition between nestlings, and exposure.

Range lifespan

Status: captivity: 14 (high) years.

Typical lifespan

Status: wild: 5 (high) years.

Elf owls are usually monogamous. They may be serially monogamous (pairs remain together for the length of a breeding season but may choose a new mate for the next breeding season) or remain with the same mate for life.

Males are polyterritorial; they defend more than one nest cavity. The alternative cavities are places of roosting or of renesting if the first nest fails. The location of a roosting site seems to be based on behavioral thermoregulation.

Mating System: monogamous

Elf owls breed annually from April to July. Females begin breeding their first year following hatching. Elf owls raise only a single brood per year, but they do replace lost clutches and may replace lost broods. Clutches usually contain three eggs, but clutch size ranges from one to five eggs. Clutches in deserts are larger than in other habitats, probably because nesting begins earlier in deserts since food is more abundant early in the season in warmer, lower-elevation areas. Young fledge 28 to 33 days after hatching.

Breeding interval: Elf owls breed once yearly.

Breeding season: April to July

Range eggs per season: 1 to 5.

Range fledging age: 28 to 33 days.

Average age at sexual or reproductive maturity (female): 1 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization (Internal )

Average time to hatching: 24 days.

Average eggs per season: 2.

The male captures the majority of the food for the altricial young. Often he will give the food to the female, and she will feed the chicks. After the nestlings are 2 to 3 weeks old, the female also helps to collect food.

Parental Investment: no parental involvement; altricial ; pre-fertilization; pre-hatching/birth (Protecting); pre-weaning/fledging (Provisioning: Male, Female)

Eggs are laid once every other day on the bare floor of cavities from early May through early June; most in late May. Occasionally, egg laying begins the last week of April, especially during years of warmer temperatures and greater rainfall. The range-wide clutch-size mode is three eggs. Desert populations have larger clutches (mean = 3.4 eggs, range = 2-5, in Chihuahuan upland desert; mean = 3.2 eggs, range = 2-5 in Sonoran upland desert) than higher elevation populations (mean = 2.6 eggs, range = 1-4, in Arizona canyon riparian forest). Eggs are incubated only by the female after the second egg is laid; the male assists in feeding the nestlings (Henry 1998, Henry and Gehlbach 1999). Incubation lasts 21-24 days (Ligon 1968, Muller 1970).

Hatching success of eggs varies from 95 percent in canyon riparian habitat in Arizona to 38-85 percent in Chihuahuan upland desert. One clutch is produced annually, but depredated eggs are replaced. Fledging success in natural nests ranges from 94 percent in Arizona canyon riparian habitat to 78-97 percent (mean 90 percent) in Chihuahuan upland desert (Henry and Gehlbach 1999). In Texas, fledging success ranges from 96-100 percent in nest boxes (McKinney 1996). Fledglings generally leave the nest 28-33 days after hatching. Females reproduce annually beginning the year after hatching. Reproductive productivity is enhanced during years of higher rainfall and warmer temperatures due to an increased prey base (Henry and Gehlbach 1999).

Elf owls are classified as endangered in California. In some areas where deforestation is occurring, elf owls face losses of breeding habitat due to the destruction of the woodpecker holes they use as nest cavities. Attempts at conservation have generally been unsuccessful up to this point. For example, a 1983 endeavor to bring back native riparian woodland along the Lower Colorado River had mixed results because the salinity content of the soil was too high and irrigation of the native trees proved difficult. Another attempt at conservation occurred in 1994 at the Black Gap Wildlife Management Area in Trans-Pecos, Texas. Nest-boxes modeled after disappearing ladder-backed woodpecker holes were set up. The effectiveness of the attempt is unknown because no studies were conducted before the nest-boxes were set up, and there were no control groups. Conservation efforts that should continue include: field experiments that assess the habitat and populations of elf owls before the introduction of nest-boxes, the result of introducing nest-boxes into the elf owl’s habitat, and a continuous censusing of elf owl populations, which are subject to natural cycles of population increases and declines.

Elf owls are protected under the US MBTA and are listed under Appendix II by CITES, but are not listed by the IUCN or US ESA.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: appendix ii

IUCN Red List of Threatened Species: least concern

United States

Rounded National Status Rank: N5B - Secure

Rounded Global Status Rank: G5 - Secure

Comments: HABITAT: Major threats are loss of riparian habitat due to invasion of salt cedar (Tamarix chinensis), agricultural clearing, flood control, de-watering, overgrazing, and bank stabilization projects. Also loss of desert scrub habitat due to agricultural conversion and urbanization (e.g., Tucson and Phoenix areas; Alcorn 1988, Haltermann et al. 1989, Henry 1998, Millsap 1988). Invasion by salt cedar has been enhanced by hydrological alterations and frequent wildfires (S. Henry, pers. comm.). PREDATION: Great horned owls (Bubo virginianus) prey on fledglings and adults, and Mexican jays (Aphelocoma ultramarina) will attack fledglings. Suspected predators include Cooper's hawk (ACCIPITER COOPERI), gopher snake (Pituophis melanoleucus), green ratsnake (Senticolis triaspis), and ringtail (Bassariscus astutus). COMPETITION: Western screech owls (Otus kennicottii) and acorn woodpeckers (Melanerpes FORMICIVOROUS) sometimes displace elf owls from cavities, and European starlings (STURNA VULGARIS) and house sparrows (Passer domesticus) may usurp cavities. However, because nesting cavities do not appear to be a limiting resource in the habitats studied thus far, competition with other cavity nesting species is not considered to be an important threat. HUMAN DISTURBANCE: In their quest to see an elf owl, some birders will drive owls from their cavity by pounding or rubbing on trees, playing or imitating owl vocalizations, or shining lights into nest cavities. Such disturbances may be detrimental during incubation and brooding (Henry 1998, Henry and Gehlbach 1999). PARASITES: Fly larvae (Calliphoridae) sometimes parasitize nestlings between their toes and on their body (Ligon 1968).

Restoration Potential: In the early 1980s, 12 young were released into Piaute Canyon, San Bernardino County, California (Cade and Dague 1983, Henry 1998). Birds, however, were not detected during a 1987 survey (S. Henry, pers. comm.). Reintroduction efforts along lower Colorado River also have shown little success due to lack of available habitat (California Department of Fish and Game 1990). Reintroduction should be preceded by habitat restoration (S. Henry, pers. comm.).

Preserve Selection and Design Considerations: Suitable nest cavities are an essential component of the breeding habitat. A preserve less than 2.6 square kilometers is unlikely to be suitable over the long-term in the breeding range (S. Henry, pers. comm.).

Management Requirements: Maintain, restore, and manage riparian habitats in breeding range (Millsap 1988). Tolerates low-density development when native vegetation is left relatively intact; therefore, an effort should be made to incorporate native vegetation in housing developments (S. Henry, pers. comm.).

Management Research Needs: Need long-term monitoring to assess natural variations in population size. Studies are needed to assess wintering habitat requirements, winter diets, and winter interactions with other species. Migration distances, routes and stopover points need to be determined. The extent to which owls can co-exist with humans in urbanized areas needs study. Interactions with sympatric cavity-nesting birds, particularly competition for cavities, needs additional study (Henry and Gehlbach 1999).

Biological Research Needs: Ecological factors limiting populations at the northern and western limits of the range need to be determined (Millsap 1988).

Needs: See Millsap (1988) and California Department of Fish and Game (1990) for habitat protection recommendations (e.g., protection and restoration of riparian woodlands, protecting blocks of natural habitat in conjunction with development of desert scrub).

There are no known adverse affects of elf owls on humans.

We do not have information on economic importance for humans for this species at this time.

Stewardship Overview: Declining in California and Baja California, and to a lesser extent in Arizona. Principal threat is habitat loss, particularly of riparian forests due to habitat/hydrological alterations and subsequent invasion by salt cedar (Tamarix chinensis). Habitat preservation/restoration is the best form of management. Nest boxes can be used to supplement natural cavities when cavity density is low. Best monitored by imitating vocalizations or playing taped vocalizations from mid- to late-April during the first quarter through full moon.

Comments: The generic name Micropallas is a junior synonym of Micrathene (Banks and Browning 1995).