White-Tailed Kite (Elanus leucurus)

Transcription

1 White-Tailed Kite (Elanus leucurus) Legal Status [Species photo to come] Taxonomy Distribution General State: Fully Protected Federal: None Critical Habitat: N/A Recovery Planning: N/A There are currently two recognized subspecies of white-tailed kite (Elanus leucurus): E. l. majusculus in North America and E. l. leucurus in South America. The Integrated Taxonomic Information System (2011) recognizes Elanus leucurus as a separate species from Elanus caeruleus (black-shouldered kite), which occurs in southwest Europe, Africa, and South Asia east to China and the Malay Peninsula. However, until biochemical analyses are conducted on Elanus kites, the taxonomy will likely remain in flux (Dunk 1995). A description of the species physical characteristics can be found in Dunk (1995). The white-tailed kite s breeding range stronghold in North America is California, with nearly all areas up to the western Sierra Nevada foothills and southeast deserts occupied (Dunk 1995). It is common in the Central Valley of California and along the entire length of the coast, possibly breeding in more arid regions of Southern California (Inyo and Kern Counties), with documented breeding in Imperial County (Small 1994; Patten et al. 2003), western Riverside County (County of Riverside 2003), and eastern San Diego County (Unitt undated). Coachella, Imperial, and Mexicali Valleys have records of white-tailed kites mostly from fall and winter (Patten et al. 2003). In the Sacramento Valley, kite populations have predominantly increased in irrigated agricultural areas where the California vole (Microtus californicus) often occurs (Warner and Rudd 1975). White- 1 March 2012

2 tailed kite also breeds in other parts of North America, such as western Oregon, southwest Washington, south Texas, and south Florida, as well as Baja California, Mexico, into Central America, and in South America from Colombia south to Buenos Aires (Figure SP-B18; Dunk 1995; County of Riverside 2003). Distribution and Occurrences within the Plan Area Historical In 1923, Van Rossem noted a white-tailed kite flying up and down the Mojave River, near Victorville, San Bernardino County (Pickwell 1930). A white-tailed kite was recorded in the Coachella Valley, near Mecca, in 1965, and again in the summer of 1984 (Patten et al. 2003). In the Imperial Valley, a pair bred in 1975 near Brawley (Patten et al. 2003). Records also exist for Finney Lake (north of Brawley) from 1984 and 1985 (Patten et al. 2003). Recent A number of nesting records occur in the Imperial Valley and the white-tailed kite may now be continuously resident there (Patten et al. 2003). In 1993, a pair nested in the valley near the mouth of the New River and produced at least one young, while two pairs were suspected of nesting along the New River in 2000: one east of Fig Lagoon and the other southwest of Brawley (Patten et al. 2003). Also, a pair definitely nested near the south end of the Salton Sea in 1995 and 1996 (Patten et al. 2003). Finally, at least 12 individuals were recorded during the winter of in the Imperial Valley (Patten et al. 2003). Based on 1990 and newer sightings from March through July in ebird (2011), white-tailed kite have been observed at the following locations in the Antelope Valley: Holiday Lake (observed May 9, 1994, near the community of Neenach), Piute Ponds (observed most recently on July 7, 2006, north of Lancaster), 60th Street East at East Avenue H and East Avenue G (observed in May 1993 in Lancaster), 110th Street East at East Avenue J (observed on May 5, 1996), and Lake Palmdale (observed on April 24, 2007, in Palmdale). In Morongo Valley, white-tailed kite was observed near Big Morongo Regional 2 March 2012

3 Natural History Park on March, In the Imperial Valley, there are numerous records of white-tailed kite around and south of the Salton Sea. Near Blythe, there are white-tailed kite records from the Palo Verde Ecological Reserve and a nearby location (observed on several occasions April 14 through July 20, 2011). White-tailed kite sightings in the Mojave Desert include two from Mojave National Preserve (observed on April 10, 2004, and May 15, 1993) and one from Harper Dry Lake (observed on April 3, 1998). In Inyo County, a white-tailed kite was observed on March 8, 1998, north of Independence. In San Bernardino County, a white-tailed kite was observed near the Cajon Pass at Hidden Lake Swarthout Canyon on July 3, 2006 (ebird 2011). In the San Bernardino Mountains, a white-tailed kite was observed south of Big Bear Lake on May 1, 1994 (ebird 2011). Habitat Requirements The white-tailed kite is commonly associated with certain types of agriculture areas (Grinnell and Miller 1944). It also generally occurs in low-elevation grassland, wetland, oak woodland, low shrub, open woodlands, or savannah habitats. This species also uses fence rows and irrigation ditches (with residual vegetation). Riparian areas adjacent to open space areas are typically used for nesting (County of Riverside 2003), where kites prefer dense, broad-leafed deciduous trees for nesting and night roosting (Brown and Amadon 1968). Within foraging habitat, the specific plant associations seem unimportant; vegetation structure and prey abundance are more important. Rainfall and humidity vary greatly throughout the range, but areas with extensive winter freezes are generally avoided. Nest tree/shrub species range from single isolated trees to trees within relatively large stands and shrubs less than 3 meters (10 feet) tall. Winter habitat is not substantially different than breeding habitat but the proximity to trees is not as important. The white-tailed kite is known to communally roost in the fall and winter, generally in small stands of trees, but roosts have also been observed in open fields on the ground and in orchards (County of Riverside 2003). 3 March 2012

4 Table 1. Habitat Associations for White-Tailed Kite Land Cover Type Grassland, certain agriculture Tree shrub Land Cover Use Habitat Designation Habitat Parameters Foraging Primary Ungrazed grasslands, irrigated pasture, alfalfa, other forage crops Nesting/ roosting Secondary Single isolated trees, trees within relatively large stands, and shrubs Sources: Dunk 1995; Reeves and Smith 2004; Johnson and Horn 2008; Pandolfino et al Foraging Requirements Supporting Information Direct observation surveys Direct observation surveys Small mammals (prey falling within the gram [ ounces] range) comprise over 95% of white-tailed kite prey. However, they occasionally take birds, insects, reptiles, and amphibians (County of Riverside 2003). In California, kites are known to be reliant on California voles (Microtus californicus) as a prey source, and habitat quality is largely dependent on abundance and availability of California voles (Niemela 2007). Lightly grazed or ungrazed fields generally support larger prey populations and appear preferred by white-tailed kites (Johnson and Horn 2008; Pandolfino et al. 2011). Certain types of agriculture are preferred for foraging by white-tailed kites, such as alfalfa, hay, irrigated pasture (Reeves and Smith 2004; Pandolfino et al. 2011); and others are not preferred, such as orchard, vineyards, and most row crops (Erichsen et al 1996; Reeves and Smith 2004; Pandolfino et al. 2011). Wetlands or marshes where California voles tend to be abundant would also be important foraging habitat. Reproduction White-tailed kites build a platform of sticks in the fork of a tree or tall bush. Nests are generally not reused in subsequent breeding seasons, although some reuse has been reported (County of Riverside 2003). 4 March 2012

5 Feb March April May June July Aug Sep Oct Nov Dec BIRDS They lay 3 to 6 eggs (mean of 4.1) that are incubated for 30 to 32 days (Dunk 1995). The young kites fledge at 5 to 6 weeks of age. If prey is abundant, then a second clutch of eggs may be laid. 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 (Erichsen 1995), and total dependency on parents as fledglings is about 1 to 2 months (Dunk 1995). Erichsen et al. (1996) listed several factors they found important in their study of successful white-tailed kite nests: 1) Nests are in rows or patches of trees overlooking low-lying natural vegetation, fallow fields, wet pasture, or alfalfa; 2) nests are less than 1,500 meters (4,921 feet) from fresh water; 3) nests are greater than 100 meters (328 feet) from roads; and 4) nests are within 800 meters (2,625 feet) of natural, fallow, or riparian vegetation. Niemela (2007) found that land uses surrounding kite nests had significantly more agriculture, grassland, riparian, and woodland habitat, and significantly less chaparral habitat than unused sites. Hawbecker (1942) noted that during the breeding season, kites seldom forage farther than a 0.5-mile radius from the nest site. In summary, nest sites are closely associated with foraging habitat that supports dense rodent populations. Table 2. Key Seasonal Periods for the White-Tailed Kite Breeding X X X X X X X X Post-breeding dispersal X X X X Communal night roosting X X X X X X X X Notes: Sources: Dunk 1995; Erichsen Spatial Activity The white-tailed kite is believed to be a primarily non-migratory resident through most of its breeding range (Erichsen et al. 1996). 5 March 2012

6 However, they may be nomadic during periods of low prey abundance. Dispersal occurs during the non-breeding season, leading to a temporary range expansion that includes most of California. Territory size is highly variable because it is regulated ultimately by prey abundance. Home range for non-breeders is difficult to determine since communal roosts may be tens of kilometers away from foraging habitat (Dunk 1995). Communal night roosting occurs frequently within wooded habitat. When females are nesting, male kites may attend communal roosts (Erichsen 1995). Roosting communities may also include newly fledged birds, as well as non-breeding kites (Wright 1978; Waian and Stendell 1970). Waian (1973) observed an increase in roost sizes through fall into winter, reaching a maximum in January and decreasing in number until March; a great deal of variation was seen in roosting density; a eucalyptus tree was used by 48 birds, while 40 kites spread out through 20 lemon trees. Table 3. Movement Distances for the White-Tailed Kite Type Distance/Area Location of Study Citation Territory Size Natal Dispersal Migration Other Ecological Relationships ha ( ac) ha (4 62 ac) ha ( ac) 160 km (99 mi) Unknown San Diego, CA Henry 1983 Eureka, CA Dunk and Cooper 1994 Santa Barbara, Waian 1973 CA San Diego, CA Dixon et al The primary factor known to regulate populations is prey availability (Stendell 1972; Dunk and Cooper 1994). Availability of nesting and roosting sites becomes important in areas where prey are not limiting (Dunk 1995). White-tailed kite abundance and nest success is largely tied to cyclic fluctuations in abundance of its main prey species, the California vole. Therefore, management activity for the white-tailed kite should focus on maintaining habitats suitable for high-density 6 March 2012

7 vole populations. Drought conditions tend to reduce vole populations, which in turn results in lower white-tailed kite abundance. Whitetailed kites nest in trees and shrubs, and conservation and proximity of these features to suitable foraging habitat is important. They also utilize communal night roosts as non-breeders, recent fledges, and juveniles, and proximity of these features to suitable foraging habitat is important. White-tailed kites appear to be sensitive to human disturbance at night roosts (Dunk 1995). Population Status and Trends Global: Stable (Dunk 1995) State: Unknown Within Plan Area: Unknown Once predicted to be headed toward extinction in California due to habitat loss, shooting, and possibly egg collecting (Pickwell 1930), the population of white-tailed kite increased dramatically from the 1940s to early 1980s (Waian and Stendell 1970). Increased agricultural irrigation, agricultural habitat fragmentation, reduced persecution, and the species potential for population growth may have positively influenced numbers (Eisenmann 1971). A brief decline in the California population in the mid-1970s corresponded with a drought and with movements into Oregon (Pruett-Jones et al. 1980). This species also declined in the Central Valley of California between 1990 and 1993 (Erichsen et al. 1996), but such short-term trends may simply reflect changes in prey (vole) abundance. Based on breeding bird survey data, the most significant decline occurred in the Southern California grassland region from 1982 to 1991, with an annual decline of about 40% (Dunk 1995). Threats and Environmental Stressors The primary factor known to regulate white-tailed kite populations is prey availability. Factors influencing population trends directly or indirectly include: 1) conversion of natural or agricultural lands to urban sprawl or commercial properties, 2) clean farming techniques that leave few residual vegetation areas for prey, 3) increased competition for nest sites with other raptors and corvids, 4) drought, 5) increased disturbance at nests, and 6) removal of suitable nesting 7 March 2012

8 habitat (Dunk 1995). Within the Plan Area, the main threats would include reductions in prey abundance with conversion of agriculture to non-agricultural uses, particularly when located in proximity to suitable nesting/roosting habitat. This would also include the removal of tree windrows that could support nest/roost sites. Changing agricultural practices also have the potential to reduce prey availability in the Plan Area, such as the conversion of agriculture that favors prey species (alfalfa, hay, irrigated pasture) to agriculture that does not (row crops, orchard, and vineyard). Within the Plan Area, the reduction of wetlands, a winter forage habitat used by white-tailed kites (Pandolfino et al. 2011), is not expected to be a threat due to other legal protection mechanisms. Conservation and Management Activities No species-specific conservation or management is known within the Plan Area. However, according to Sections 3511 and 4700 of the California Fish and Game Code, which regulate birds and mammals, respectively, a fully protected species may not be taken or possessed without a permit from the Fish and Game Commission, and incidental takes of these species are not authorized. The fully protected status would protect active white-tailed kite nests only. Data Characterization There are data gaps for white-tailed kite occurrences within the Plan Area, illustrated by the lack of recorded nest occurrences within the California Natural Diversity Database. However, there are some scattered records within books (Birds of the Salton Sea), and ebird has compiled numerous records based on periodic reporting from individuals who complete species lists during local birding trips. The main data gap is the current breeding locations of white-tailed kite in the Plan Area. Although there are data gaps in its current breeding distribution and understanding, there is enough information about the foraging, nesting, and roosting requirements for this species that it can be considered for coverage by the Desert Renewable Energy Conservation Plan. 8 March 2012

9 Management and Monitoring Considerations Management for white-tailed kite would be focused on maintaining suitable foraging habitat in proximity to suitable nesting/roosting habitat. Marsh habitat is an important native community for whitetailed kite foraging, and management practices could include maintaining various successional stages of marsh habitat for prey species. Agricultural management practices could also be completed in such a way to benefit foraging opportunities for this species, such as maintaining prey refugia areas and maintaining beneficial crops. Management of agriculture drains and dikes to maintain marsh habitat would also benefit prey species for white-tailed kite. Management of grasslands to maintain ungrazed areas would also benefit prey populations. A small-scale example of successful management of white-tailed kite occurred in Northern California where previously grazed grasslands were removed from grazing. These areas now support large populations of voles and high densities of wintering white-tailed kites, approximately 10 times the raptor density they supported prior to management (Dunk 1995). Conservation of existing trees and shrubs for nesting/roosting and minimization of human disturbance at known nesting/roosting locations would also be important considerations. Goals for monitoring of white-tailed kite might be to first identify high-quality foraging habitat that may be located near suitable nesting/roosting habitat (trees and shrubs) and determine if nesting or communal roosts are present at these locations. The surrounding foraging habitat could then become of higher management priority for maintaining high densities of prey species. There are some inherent difficulties in monitoring a species whose population can fluctuate greatly with rainfall and prey abundance, and because it is nomadic it tends to vacate and establish in areas very quickly. These factors make the choice of the correct unit area for monitoring efforts difficult. Also, because white-tailed kites roost communally at sites that can be tens of kilometers away from foraging sites, home range for non-breeders is difficult to determine (Dunk 1995). 9 March 2012

10 Predicted Species Distribution in Plan Area Literature Cited Species model summary and results will be provided following model development. Brown, L., and D. Amadon Eagles, Hawks and Falcons of the World. 2 Vols. London, United Kingdom: Country Life Books. County of Riverside Birds. Volume 2 The MSHCP Reference Document. Western Riverside County Multiple Species Habitat Conservation Plan. County of Riverside Transportation and Land Management Agency (TLMA). Accessed December 1, Dixon, J.B., R.E. Dixon, and J.E. Dixon Natural History of the White-Tailed Kite in San Diego County, California. Condor 59: Dunk, J.R The Birds of North America Online, edited by A. Poole. Ithaca, New York: Cornell Lab of Ornithology. Accessed December Dunk, J.R., and R.J. Cooper Territory-Size Regulation in Black- Shouldered Kites. Auk 111: ebird ebird: An online database of bird distribution and abundance [web application]. Query for white-tailed kite occurrences in all years between March and July. Version 2. Ithaca, New York: ebird. Accessed: December 1, Eisenmann, E Range Expansion and Population Increase in North and Middle America of the White-Tailed Kite (Elanus leucurus). American Birds 25: Erichsen, A.L The : Nesting Success and Seasonal Habitat Selection in an Agricultural Landscape. Thesis. Davis, California: University of California at Davis. 10 March 2012

11 Erichsen, A.L., S.K. Smallwood, A.M. Commandatore, B.W. Wilson, and M.D. Fry White-Tailed Kite Movements and Nesting Patterns in an Agricultural Landscape. In Raptors in Human Landscapes: Adaptations to Built and Cultivated Environments. (D.M. Bird, D.E. Varland, and J.J. Negro, eds.), pp San Diego, California: Academic Press. Grinnell, J., and A.H. Miller "The Distribution of the Birds of California." Pacific Coast Avifauna Number 27. Berkeley, California: Copper Ornithological Club. Reprinted in Lee Vining, California: Artemisia Press. April Hawbecker, A.C A Life History Study of the White-tailed Kite. Condor 44: Henry, M.E Home Range and Territoriality in Breeding White- Tailed Kites. Thesis. San Diego, California: San Diego State University. Integrated Taxonomic Information System Johnson, M.D., and C.M. Horn Effects of Rotational Grazing on Rodents and Raptors in a Coastal Grassland. Western North American Naturalist 68: Niemela, C.A Landscape Characteristics Surrounding Whitetailed Kite Nest Sites in Southwestern California. A thesis presented to the Faculty of Humboldt State University in partial fulfillment of the requirements for the degree Master of Science. Pandolfino, E.R., M.P. Herzog, S.L. Hooper, and Z. Smith Winter Habitat Associations of Diurnal Raptors in California s Central Valley. Western Birds 42(2): Patten, M.A., G. McCaskie, and P. Unitt. Birds of the Salton Sea. Berkley and Los Angeles, California: University of California Press. Pickwell, G The White-Tailed Kite. Condor 32(5): March 2012

12 Pruett-Jones, S.G. M.A. Pruett-Jones, and R.L. Knight The White-Tailed Kit in North and Middle America: Current Status and Recent Population Changes. Am. Birds 34: Reeves, K.A., and J.R. Smith Survey of Falcons, Kites, Hawks, and Owls in the Lower Mokelumne River Watershed, Sacramento and San Joaquin Counties, California. Accessed December files/pdfs/a-10%20raptor%20report_0.pdf. Small, A California Birds: Their Status and Distribution. Vista, California: Ibis Publishing Co. Stendell, R.C The Occurrence, Food Habits, and Nesting Strategy of White-Tailed Kites in Relation to a Fluctuating Vole Population. Dissertation. Berkeley, California: University of California at Berkeley. Unitt undated. San Diego Natural History Museum PowerPoint presentation to the Independent Science Advisors Workshop for the East San Diego County MSCP. EC_Birds_NHM.pdf. Waian, L.B The Behavioral Ecology of the North American White- Tailed Kite (Elanus leucurus majusculus) of the Santa Barbara Coastal Plain. Dissertation. Santa Barbara, California: University of California at Santa Barbara. Waian, L.B., and R.C. Stendell The White-Tailed Kite in California with Observations of the Santa Barbara Population. California Fish and Game 56: Warner, J.S., and R.L. Rudd "Hunting by the White-Tailed Kite (Elanus leucurus)." Condor 77: Wright, B.A Ecology of the White-Tailed Kite in San Diego County. Thesis. San Diego State University, San Diego, California. 12 March 2012

13 Species Range in California Utah Nevada!( Current Occurrence Point!( Historic and Unknown Occurrence Point Note: Occurrence point size graphically represents the precision level code for the data point but is not scaled geographically. Arizona!( Z:\Projects\CEC\j6668_DRECP\MAPDOC\MAPS\BaselineBioReport\SpeciesProfiles I January 15, Miles P a c i f i c O c e a n Sources: DRECP Species Occurrence Database (2011), CWHR (2008), CEC (2010), USGS (2010), ESRI (2010) Desert Renewable Energy Conservation Plan (DRECP) Baseline Biology Report!(!(!(!(!(!(!( MEXICO FIGURE SP-B18 White-tailed Kite Occurrences in the Plan Area (N=9)