Account prepared by Jeffrey Moore, Humboldt State University

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Section 1: Species Account Outline

Species: White-tailed kite (Elanus leucurus)
 

Subspecies status: Only one subspecies in North America, E. l. majusculus. E. l. leucurus is a smaller subspecies that occurs in South America. From 1981 to 1994, AOU considered the white-tailed kite to be a subspecies of the black-shouldered kite (E. caerulus) (Dunk 1995).
 

Management status: Given fully protected status in California in 1957 (Waian and Stendell 1970).
 

Range maps: www.mbr.nbs.gov/bbs/htm96/map617/ra3280.html (BBS summer range map) (Sauer, et al. 1999)
 

        I.  Historical references

At the turn of this century, the white-tailed kite may have been widespread throughout the lowlands of California, but during the early 1900s, the population severely declined and its range was reduced to western California, from the Sacramento Valley to San Diego (May 1935). Causes of this decline were likely habitat loss, shooting, and possible egg collecting (Pickwell 1930, Waian and Stendell 1970). During the 1930s, extinction was predicted for this species in California (Pickwell 1930). From the 1940s to the 1970s, populations and distribution increased (Fry 1966, Waian and Stendall 1970, Eisenmann 1971), due to protection from shooting and an increase in agricultural development, which may have increased rodent habitat (Eisenmann 1971, Small 1994).

II.  Current breeding distribution in California

I.  Average territory size: 1.6 – 21.5 ha (Dunk and Cooper 1994), 19 - 52 ha with a mean of 29 ha (Waian 1973), 17 - 120 ha (Henry 1983). Territory size is regulated ultimately by prey abundance, though kites may respond more directly to the abundance of interspecific and intraspecific competitors (Dunk 1995). Some ranges may overlap, and foraging may be limited to a small portion of the total area (Henry 1983). Home range for non-breeders is difficult to determine since communal roosts may be tens of kilometers away (Dunk 1995).
 

II.  Time of occurrence and seasonal movements:

A.  Arrival date and departure date on breeding grounds: This kite is probably not migratory. Stendell (1972) believed it to be resident, becoming nomadic during periods of low prey abundance. Nest-building occurs January through August (Dunk 1995). Egg laying begins in February and probably peaks in March and April. Peak fledging probably occurs in May and June with most fledging complete by October (Erichsen 1995).
 

B.  Extent of winter range in CA: Although probably resident through most of its breeding range, dispersal occurs during the non-breeding season, leading to range expansion that includes most of CA (Small 1994, Dunk 1995, also see CBC data at www.mbr.nbs.gov/bbs/cbcra/h3280ra.html (Sauer, et al. 1999).
 

A.  Stop-over period: No information

B.  Habitat use: No information

C.  Routes: No information
 

V.  Foraging strategy: Forages almost exclusively by hovering 5-25m high, facing the wind and scanning the ground. When attacking prey, wings are put nearly vertical and the kite drops feet first. Hunting occurs during the first and last hours of the day, but may occur longer if temperatures are below 20 degrees C. It is not known if this pattern is directly related to the temperature or the activity patterns of prey (Dunk 1995).
 

VI.  Displays

A.  Agonistic: Tail bob display – birds cock tail up over back and then back down in response to intrusion (Dunk 1995).

B.  Courtship
 

1) Both sexes engage in flutter flights, where wings are held at a shallow angle and flapped with quick short strokes (Dunk 1995)

2) Males offer prey to females, prior to egg laying in an acrobatic aerial exchange (Dunk 1995).


C.  Leg hanging (legs held down during flight) occurs during all flutter flights and when approaching another conspecific’s territory
 

A.  Typical breeding densities: No data exists for mean inter-nest distance within a population. However, the distance recorded between 8 observed nests ranged from 153 to 370 meters (Pickwell 1930, Hawbecker 1942, Dixon et al. 1957).

B.  Mating system: Monogamous (Dunk 1995)

C.  Delayed breeding: No information

D.  Post fledging biology of offspring: In years when adults have a second brood, juveniles of first broods roost communally during the parents’ second nesting period, possibly with non-breeders in the population (Wright 1978, Waian and Stendall 1970). Erichsen (1995) reported that males attend communal night roosts during the nesting period as well. Immatures associate more with adult males than females during the post-fledgling period, following them to hunting grounds and communal roosts (Erichsen 1995). Total dependency on parents as fledglings is about 1-2 months (Dunk 1995).

E.  Post fledging dispersal: Little information exists on juvenile dispersal. No evidence for natal philopatry exists (Dunk 1995). A few banded nestlings have been resighted at 1.6km to 160km from natal sites (Dixon et al. 1957, Stendell 1972). One individual established a territory adjacent to its natal site within 2 months of fledging (Dunk 1995).

F.  Post breeding social behavior: Kites attend night-roosts communally in the post-fledging period and through the winter, though daytime feeding territories are still maintained (Bamman 1975, Dunk and Cooper 1994, Dunk 1995).

IX.  Incubating sex: Female only (Dunk 1995)
 

X.  Incubation period: 28-32 days (Dunk 1995, Erichsen 1995)
 

XI.  Nestling period: 4-5 weeks (Dunk 1995)
 

XII.  Development at hatching: Altricial (Dunk 1995)
 

XIII.  Number of broods: Typically 1, though 2 are fairly common in years of high prey abundance. Kites will often reattempt to nest after an unsuccessful first attempt (Dunk 1995).
 

XIV.  Who tends the young: Females attend the nest from incubation until fledging (Dixon et al. 1957, Dunk 1995). Males provide all food to the female during this time (Dixon et al. 1957, Erichsen 1995), though it is the female that actually feeds the chicks (Dixon 1957).
 

XV.  Diet
 

A.  Major food items: Well studied. Year-round diet consists of >95% small mammals, based on pellet analysis. Primary prey genera in California are Microtus, Mus, and Reithrodontomys (Erichsen 1995, also see Dunk 1995 for summary of food habit studies in California).

B.  Drinking: No information

XVI.  Wintering ground needs and distribution: Winter habitat similar to breeding habitat (see Breeding habitat below), but without need for nest trees (Dunk 1995). In winter, uplands and wetlands, riparian zones, fallow and natural vegetation, and sugarbeet crops were preferred (Erichsen 1995). Note that with respect to agriculture, different types are preferred in spring and winter. Important features of roost sites (typically small stands of trees) are unknown, though kites don’t seem to associate with particular tree species (Dunk 1995).
 

BREEDING HABITAT AND NEST SITE CHARACTERISTICS

I.  Overview of breeding habitat: White-tailed kites breed in lowland grasslands, agriculture, wetlands, oak-woodland and savannah habitats, and riparian areas associated with open areas. Precipitation is highly variable among kite habitats, though kites are uncommon in areas with extensive winter freezes. Kites do not seem to associate with particular plant species, but are more tied to prey abundance and vegetation structure (see Landscape factors below). Those habitats supporting larger prey populations are more suitable; ungrazed lands support higher prey populations than grazed lands. Alfalfa and sugarbeets support the highest vole populations, relative to other agriculture. Erichsen (1995) found summer habitat preferences to include riparian zones, dry pastures, alfalfa, orchards, and rice stubble fields. Plowed field were avoided in both winter and summer. Nest trees range from single isolated trees to being within large stands (Dunk 1995).
 

II.  Nest site

A.  Substrate (species): Kites nest in shrubs and trees of various species (Dunk 1995).

B.  Height of nest: In upper third of trees (Dunk 1995).

C.  Height of plant: In shrubs from <3m tall to trees >50m tall (Dunk 1995).

D.  Nest concealment: Kites often nest on tree branches that conceal the nest well from the ground, however the nest may be shaded or fully exposed from above (Pickwell 1930, Hawbecker 1940).

A.  Canopy cover: No information, but this will vary with whether the nest tree is isolated or within a large stand, and how exposed the nest is at the top of the tree (see Overview of breeding habitat, and Nest concealment above).

B.  Dominant plant species in canopy: Highly variable

C.  Shrub cover: No information

D.  Dominant shrub species: Variable

E.  Average forb cover: No information, but probably unimportant.

F.  Dominant forb species: No information, but probably unimportant

G.  Ground cover: No information

H.  Slope: No information

I.  Aspect: No information

J.  Tree DBH: No information

K.  Snags: No information.

L.  Distance to water: Little information. However, in Erichsen’s study of kites in the Sacramento valley (1995), all successful nests (n=9) were <1.5km from water.

A.  Elevation: No information

B.  Fragmentation: No information

C.  Patch size: Nest trees may be isolated in the landscape or within larger forest stands. No information for required patch sizes for feeding, but see Average territory size (above).

D.  Disturbance: Little information. Communal roost disturbance has caused abandonment (Dunk 1995). Successful nests in the Sacramento valley were all >100m from a road and were surrounded by natural vegetation and non-urban human development (Erichsen 1995).

E.  Adjacent land use: Erichsen (1995) compared land use characteristics surrounding successful and unsuccessful nests in the Sacramento Valley. There were no differences in land use within a 1.6km radius surrounding successful vs. unsuccessful nests, however there were differences within 0.8km, suggesting that habitat characteristics within the immediate nest area may be important. Successful nests were surrounded by more natural, fallow and riparian vegetation, as well as non-urban human development. In this study, male kites frequently fed <0.5km and out to 1.6km from the nest. Thus it is probably important that nest sites be located within adequate foraging habitat.

I.  Brood Parasitism: Unknown
 

II.  Dietary: No information
 

III.  Sensitivity to human-induced disturbance: Sensitivity unknown, but see Landscape factors (above).
 

IV.  Pesticide use: No information
 

V.  Predators: Probable predators of adults and immatures included Red-tailed hawks, Peregrine falcons, Prarie falcons, and Great Horned owls. Probable egg and nestling predators include American crows, Common ravens, and small to medium sized carnivores (Dunk 1995).
 

VI.  Exotic species invasion / encroachment: No information
 

VII.  Other: Competition. Erichsen (1995) found that riparian corridors represent preferred nesting sites for kites. As preferred kite habitats (riparian woodlands, wetlands and native wooded grasslands) have diminished, kites must compete with larger raptors for nesting sites in remaining woodlands and agricultural settings. Such nest site competitors include Great Horned owls, Red-tailed hawks, Red-shouldered hawks, and Swainson’s hawks. Indeed, 6 of 13 failed nests were due to displacement by nesting Swainson’s hawks, all of which occurred along riparian corridors (Erichsen 1995).
 

POPULATION TREND: According to BBC trend data (www.mbr.nbs.gov/cgi-bin/atlasa98.pl?03280) (Sauer et al. 1999), populations have been decreasing in some areas since the 1980’s, including the Central valley, southern California grasslands and southern Pacific rainforests, while overall numbers in California have continued to increase. However, none of these trends are statistically significant. Possible declines may be due to conversion of agricultural lands to urban areas and clean farming techniques that reduce prey populations, increased interspecific nest-site competition, and human disturbance at nests (Dunk 1995).
 

DEMOGRAPHICS
 

I.  Age and sex ratios: No information

II.  Productivity measures: Stendell’s study (1972) yields the following nesting estimates in 3 different years:
 

Year	# pairs	# nests	% nest success	# fledged / successful nest
1969	10	12	50	2.50
1970	28	48	58	2.93
1971	12	13	31	3.75

Other studies (cited in Dunk 1995) yield the following estimates of # fledged / successful nest: 1.63 in San Francisco Bay area (n=49), 1.6 in Santa Cruz (n=8), 3.2 in San Diego (n=23). No information on fledgling survival, lifetime reproductive success or population recruitment rate.
 

III.  Survivorship: No information. Maximum recorded lifespan is 5 yr 11 mo.

IV.  Dispersal: See Post-fledging dispersal (above)

Long-term data on population numbers at a regional scale is lacking. Since kite numbers are largely dependent on cycling prey numbers, short term fluctuations in kite numbers over local areas are expected. To understand population trends, monitoring needs to be conducted over long time periods and large geographical areas.
 

Demographic information is essentially unavailable, e.g. sex ratio, age of first breeding, breeding frequency, lifetime reproductive success, juvenile survival, juvenile dispersal, philopatry, etc. Long-term studies of marked birds would provide this information, which is needed in order to predict reproductive response to changes in population size, habitat losses, land use practices, and management strategies.
 

Little is known about the breeding requirements of White-tailed kites. No studies have quantified microsite characteristics around successful nests. Only one study (Erichsen 1995) has quantified surrounding habitat characteristics. Sensitivity of nesting kites to human disturbance is unknown.
 

Riparian corridors represent a preferred landscape characteristic for kites in both the breeding and non-breeding season (Erichsen 1995). California has lost over 90% of its original riparian and wetland habitats, the remaining of which may be highly competed for by several species. The importance of remaining riparian habitat to kites, and the extent to which they are able to successfully breed within these fragments, should be investigated.
 

Today, kites live largely in a highly managed landscape (e.g. agriculture and pastureland) and therefore must respond to various land use practices. Practices supporting abundant prey populations may benefit kites, while those that reduce prey populations may represent habitat loss to kites. Similarly, land use practices that remove nest trees may be detrimental to kite reproduction. The potential effects of pesticide use on kites, either directly (e.g. reduced egg viability) or indirectly (e.g. reduced prey populations) have not been studied.
 

ASSOCIATED SPECIES: Literature typically mentions associated raptor species. Those known to co-occur in much of the kite’s range include Red-tailed hawks, Peregrine falcons, Prarie falcons, Red-shouldered hawks, Swainson’s hawks, Northern harriers, Rough-legged hawks, American kestrels, Great Horned owls, Short-eared owls, Barn owls, and probably others. Great Horned owls, Red-tailed hawks, Red-shouldered hawks, and Swainson’s hawks (threatened) in particular, are known to compete for nest sites in riparian woodlands, and would probably benefit from riparian habitat management for kites. In addition, other taxa associated with riparian corridors, ungrazed grasslands, and agriculture, would likely benefit from management for kites.
 
 

MONITORING METHODS AND RESEARCH NEEDS
 

I.  Conduct an accurate assessment of population trends over large geographic areas (Dunk 1995). Most studies of population trends have been short term and are vulnerable to confounding effects of cycling prey abundance.
 

II.  Examine nest-site selection, habitat requirements for successful nesting, and the effects of interspecific nest competition with corvids and other raptors (Dunk 1995).
 

III.  Determine the extent to which White-tailed kites are nest site limited. This would be important in open grasslands with few trees and in riparian areas where interspecific competition may be high. Dunk (1995) suggests that adding nest trees may be useful in such situations.
 

IV.  Data on demographic parameters are needed, e.g. survivorship, lifetime reproductive success, dispersal, etc. This information could be learned via intensive banding and monitoring programs (Dunk 1995).
 

V.  Identify specific land use practices that are either beneficial or harmful to kites, e.g. crop types, harvest methods, and determine the effects, if any, of pesticide use on kite populations.
 

VI.  Determine the function and importance of communal roosts (Dunk 1995).

STATUS: A fully protected species in California, White-tailed kites have recovered from near extinction in the 1930’s to being common throughout most of California today. Possible declines in some areas since the 1980s is a concern.
 

HABITAT NEEDS: Kites occur in nearly all lowlands in CA, except the southeast deserts. They require relatively open habitat for foraging, and trees (isolated or within stands) for nesting and roosting. Habitats favoring prey populations (ungrazed or little grazed grasslands, agriculture, and grass dominated wetlands) support more kites. It may be important that adequate foraging habitat be adjacent to nest sites. Distance to water may also be important.
 

CONCERNS: Primary concerns include the response of White-tailed kites to reduced foraging and nesting opportunities as prey habitats are urbanized (e.g. conversion of agricultural lands), and as nest site competition increases with the loss of nesting habitats (e.g. riparian corridors and wooded grasslands).
 

OBJECTIVES: Identify demographic parameters driving population dynamics of this species. Identify kite-friendly land use practices and similarly, habitat requirements of their prey populations. Determine habitat characteristics required for successful reproduction, and the impacts of human disturbance and interspecific competition on breeding success. Develop open-area and riparian management strategies that may benefit both kites and other raptor species, e.g. the threatened Swainson’s hawk.
 

ACTIONS: Initiate studies to address the above research needs. Initiate long-term banding and monitoring programs at a regional scale in order to gain demographic information and follow long-term population trends. In areas where kites may be nest site limited, add nesting trees. Land acquisition and restoration of wooded areas adjacent to open foraging areas will likely benefit kites. Manage for high prey populations.
 

Literature Cited:

Bammann, A. R. 1975. Ecology of predation and social interactions of wintering White-tailed kites. Thesis. Humboldt State University, Arcata, California.

Dixon, J. B., R. E. Dixon, and J. E. Dixon. 1957. Natural history of the White-tailed kite in San Diego, California. Condor 59:156-165.

Dunk, J. R. 1995. White-tailed kite (Elanus leucurus). In The Birds of North America, No. 178 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, and The American Ornithologists’ Union, Washington, D.C.

Dunk, J. R. and R. J. Cooper. 1994. Territory-size regulation in Black-shouldered kites. Auk 111:588-595.

Eisenmann, E. 1971. Range expansion and population increase in North and Middle America of the White- tailed kite (Elanus leucurus). American Birds 25:529-536.

Erichsen, A. L. 1995. The White-tailed kite (Elanus leucurus): nesting success and seasonal habitat selection in an agricultural landscape. Thesis. University of California at Davis, Davis, California.

Fry, D. H., Jr. 1966. Recovery of the White-tailed kite. Pacific Discovery 19:27-30.

Hawbecker, A. C. 1940. The nesting of the White-tailed kite in southern Santa Cruz county, California. Condor 42:106-111.

Henry, M. E. 1983. Home range and territoriality in breeding White-tailed kites. Thesis. San Diego State University, San Diego, California.

May, J. B. 1935. The Hawks of North America. National Association of Audubon Societies, New York.

Pickwell, G. 1930. The White-tailed kite. Condor 32:221-239.

Sauer, J. R., J. E. Hines, I. Thomas, J. Fallon, and G. Gough. 1999. The North American breeding bird survey, results and analysis 1996-1998. Version 98.1. USGS Patuxent.

Small, A. 1994. California birds: their status and distribution. Ibis Publishing Co., Vista, California.

Stendell, R. C. 1972. The occurrence, food habits, and nesting strategy of White-tailed kites in relation to a fluctuating vole population. Dissertation. University of California at Berkeley, Berkeley, California.

Waian, L. B. 1973. The behavioral ecology of the North American White-tailed kite (Elanus leucurus majusculus) of the Santa Barbara coastal plain. Dissertation. University of California at Santa Barbara, Santa Barbara, California.

Waian, L. B. and R. C. Stendell. 1970. The White-tailed kite in California with observations of the Santa Barbara population. California Fish and Game 56:188-198.

Wright, B. A. 1978. Ecology of the White-tailed kite in San Diego county. Thesis. San Diego State University, San Diego, California.
 

OTHER RELATED REFERENCES NOT CITED IN THIS ACCOUNT

Erichsen, A. L., A. M. Commandatore, and D. M. Fry. 1995.  Communal roosts: seasonal dynamics of a White-tailed kite population in the Sacramento Valley, California. J. Raptor Res.; 29:70. Abstract only.

Erichsen, A. L., S. K. Smallwood, A. M. Commandatore, B. W. Wilson, and M. D. Fry. 1996. White-tailed kite movement and nesting patterns in an agricultural landscape. Pages 165-176 in Bird, D. M., D. E. Varland, and J. J. Negro (editors). Raptors in Human Landscapes. Adaptations to built and cultivated environments. Academic Press, London.

Erichsen, A. L.; S. Smallwood; N. D. Ottum and D. M. Fry. 1994. The White-tailed kite: GIS analysis of habitat selection in the Sacramento Valley, California, with implications for conservation of wildlife in agricultural landscapes. J. Raptor Res.; 28:46. Abstract only.