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Micrathene whitneyielf owl

By Kathryn Sterling

Geographic Range

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. (Henry and Gehlbach, 1999)

Habitat

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. (Brandt, 1951; Gehlbach, 1994; Henry and Gehlbach, 1999; Ligon, 1968; McKinney, 1996)

Physical Description

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. (Henry and Gehlbach, 1999; Howell and Webb, 1995)

  • Sexual Dimorphism
  • sexes alike
  • female larger
  • Range mass
    35 to 55 g
    1.23 to 1.94 oz
  • Range length
    12.4 to 14.2 cm
    4.88 to 5.59 in
  • Average basal metabolic rate
    0.259435 W
    AnAge

Development

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).

Reproduction

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. (Brandt, 1951; Gehlbach, 1981; Hardy, 1997; Henry and Gehlbach, 1999; Ligon, 1968; McKinney, 1996)

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. (Henry and Gehlbach, 1999; Ligon, 1968)

  • Breeding interval
    Elf owls breed once yearly.
  • Breeding season
    April to July
  • Range eggs per season
    1 to 5
  • Average eggs per season
    2
    AnAge
  • Average time to hatching
    24 days
    AnAge
  • Range fledging age
    28 to 33 days
  • Average age at sexual or reproductive maturity (female)
    1 years

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. (Henry and Gehlbach, 1999; Ligon, 1968)

  • Parental Investment
  • no parental involvement
  • altricial
  • pre-fertilization
  • pre-hatching/birth
    • protecting
  • pre-weaning/fledging
    • provisioning
      • male
      • female

Lifespan/Longevity

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. (Henry and Gehlbach, 1999; Klimkiewicz and Futcher, 1989; Ligon, 1968)

  • Range lifespan
    Status: captivity
    14 (high) years
  • Typical lifespan
    Status: wild
    5 (high) years

Behavior

Elf owls are nocturnal; most of their activity occurs at dusk and before dawn. They move by walking and hopping, and they can climb like parrots. When elf owls hunt, they strike in a straight line. They also fly in U-shaped arcs between perches and sometimes they glide and hover. Some populations are migratory, others sedentary. (Gehlbach, 1994; Henry and Gehlbach, 1999; Ligon, 1968; Marshall, 1957)

Home Range

We do not have information on home range for this species at this time.

Communication and Perception

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. (Boal, et al., 1997; Henry and Gehlbach, 1999; Ligon, 1968; Miller, 1946)

Food Habits

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. (Gehlbach, 1981; Henry and Gehlbach, 1999; Howell and Webb, 1995; Ligon, 1968)

  • Animal Foods
  • mammals
  • reptiles
  • insects

Predation

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. (Boal, et al., 1997; Henry and Gehlbach, 1999; Ligon, 1968)

Ecosystem Roles

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. (Gehlbach, 1994; Henry and Gehlbach, 1999; Ligon, 1968)

Mutualist Species

Economic Importance for Humans: Positive

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

Economic Importance for Humans: Negative

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

Conservation Status

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. (Henry, 1998; Henry and Gehlbach, 1999; McKinney, 1996; White Jehl, 1994)

Other Comments

Elf owls struggle to regulate their body temperatures when humidity is low. As the temperature of the surrounding environment increases, elf owls cease activity, compress their feathers, hold their wings away from their bodies, close their eyes and start panting. They also practice gular fluttering. Because elf owls have difficulty keeping cool, it has been suggested that the desert is a secondary habitat for them. Desert vegetation arrived in the Sonoran Region around 8,000 ago. Elf owls probably originally inhabited evergreen woodlands and riparian forests in the area where the Sonoran Desert is now located. (Henry and Gehlbach, 1999; Ligon, 1968; Lowe and Steenbergh, 1981)

Contributors

Alaine Camfield (editor), Animal Diversity Web.

Kathryn Sterling (author), University of Arizona, Todd McWhorter (editor), University of Arizona.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

Boal, C., B. Bibles, R. Mannan. 1997. Nest defense and mobbing behavior of Elf Owls. Journal of Raptor Research, 31(3): 286-287.

Brandt, H. 1951. Arizona and its bird life. Cleveland, Ohio: Bird Research Foundation.

Gehlbach, F. 1981. Mountain islands and desert seas: a natural history of the U.S.-Mexican borderlands. College Station: Texas A&M University Press.

Gehlbach, F. 1994. The Eastern Screech-Owl: life history, ecology, and behavior in the suburbs and countryside. College Station: Texas A&M University Press.

Hardy, P. 1997. Habitat selection by Elf Owls and Western Screech-Owls in the Sonoran Desert. Tucson: M.S. thesis, University of Arizona.

Henry, S. 1998. Elf Owl. Pp. 162-164 in R Glinski, ed. The raptors of Arizona. Tucson: University of Arizona Press.

Henry, S., F. Gehlbach. 1999. Elf Owl: Micrathene whitneyi. Pp. 1-19 in A Poole, F Gill, A Poole, F Gill, eds. The Birds of North America, Vol. 412. The Academy of Natural Sciences, Philadelphia, and The American Ornithologist's Union, Washington, D.C.

Howell, S., S. Webb. 1995. A guide to the birds of Mexico and northern central America. New York: Oxford University Press.

Klimkiewicz, M., A. Futcher. 1989. Longevity records of North American birds Supplement-1. Journal of Field Ornithology, 60 (4): 469-494.

Ligon, J. 1968. The biology of the Elf Owl, Micrathene Whitneyi. Miscellaneous Publications of the University of Michigan Museum of Zoology, 136.

Lowe, C., W. Steenbergh. 1981. On the Cenozoic ecology and evolution of the Sahuaro (Carnegia gigantea). Desert Plants, 3: 83-86.

Marshall, J. 1957. Birds of the pine-oak woodland in southern Arizona and adjacent Mexico. Pacific Coast Avifauna, 32: 5-122.

McKinney, B. 1996. The use of artificial nest boxes by Elf Owls in western Texas. Wildlife research highlights: 38-39.

Miller, L. 1946. The elf owl moves west. The Condor, 48: 284-285.

White Jehl, C. 1994. Population trends and current status of selected western raptors. Pp. 161-172 in J Jehl, Jr., N Johnson, eds. A century of avifaunal change in western North America. Stud. Avian Biol. no. 15.

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