California Partners in Flight Desert Bird Conservation Plan
Verdin (Auriparus flaviceps )
Prepared by: Roy T. Churchwell (email@example.com)
San Francisco Bay Bird Observatory
1290 Hope Street
Alviso, CA 95002
Churchwell, R.T. 2007 Verdin (Auriparus flaviceps). In The Desert Bird Conservation Plan. California Partners In Flight. http://www.prbo.org/calpif/htmldocs/desert.html
action plan summary
Within the Desert Plan’s extent, A. f. acaciarum from southeast California, southern Nevada, southern Utah, Arizona, Baja California Norte to Ensenada, central Sonora. Nominate A. f. flaviceps central Baja and western Sonora (Webster 1999).
Partners in Flight Stewardship Species (Global population in a single biome)
The Verdin is a resident species of the Southwestern desert including the Mojave, Sonora, and Chihuahuan Deserts (Webster 1999). This species range includes southeastern California (Grinnell and Miller 1944, Webster 1999), the southern tip of Nevada (Johnson and Richardson 1952) to the extreme southwestern corner of Utah (Behle et al. 1963, Behle 1976), it then extends through Arizona excluding the northeast corner of the state (Webster 1999, Wise-Gervais 2005), includes the southwest corner of New Mexico, and includes the western half of Texas (Griscom and Crosby 1925) up to, but excluding the Texas Panhandle (Webster 1999) and including the extreme southwestern corner of Oklahoma (Baumgartner and Baumgartner 1992, Webster 1999). In Mexico the range includes most of the Baja Peninsula except the northwest corner, most of the state of Sonora and the northwest corner of Sinaloa, also all but the western edge of Chihuahua, Durango, Zacatecas, the northeastern edge of Jalisco, and the northern edge of Michoacán and México. Then the range extends north to the eastern border of Neuvo León and finally east to the coast including the northern portion of Tamaulipas (Webster and Orr 1954, Webster 1999, Howell and Webb 1995).
The species was once found in coastal San Diego County, the Tijuana Valley, and parts of Baja California where it is now absent (Kading 1905, Garrett and Dunn 1981, Harrap and Quinn 1995). Verdin were also found around Furnace Creek in Death Valley (Grinnell 1931), but have been absent after declining in the early 1970s (Garrett and Dunn 1981 Small 1994). On the eastern edge of its range it is thought to have expanded in Arizona (Lloyd et al. 1998) and also from central Texas up to Oklahoma, although nesting has not been reported in Oklahoma since 1977 (Carnes 2004, Baumgartner and Baumgartner 1992, Carnes 2004). In Mexico it may have recently expanded its range into those areas of Zacatecas, Durango, and Chihuahua where it now occurs (Leopold 1959, Webster 1978, in Webster 1999).
The first type specimen for Verdin was collected by a Russian Naturalist I.G. Vosnesensky around 1841 along the coast near Loreto, Mexico (Grinnell 1931). Now there are seven recognized subspecies, of which only one occurs in California (Auriparus flaviceps acaciarum). The eastern extent of the range of this subspecies has not been agreed upon, but it extends at least to the Colorado River (Hellmayr 1934 and Snow 1967 in Webster 1999) and may occur across Arizona (Phillips 1986 in Webster 1999).
Figure 1. Verdin distribution and density in the U.S., ( http://www.mbr-pwrc.usgs.gov/bbs/htm03/ra2003_blue/ra07460.htm)
Distribution in the West Mojave Planning Area:
Auriparus flaviceps acaciarum is the single subspecies representative of Verdin in the West Mohave Planning Area. Using Christmas Bird Count data, Root (1988) determined that the Mojave Desert has the greatest densities of Verdin at 4.52 individuals/ hour. The species occupies thorn scrub desert habitat of the southeastern portion of the state including the Colorado River Valley (Daggett 1902, Hollister 1908, Stephens 1903, Webster 1999). The species range extends west from the Colorado River including all of Imperial County and the very eastern portion of San Diego County including Anza Borego (Rossem 1911, McCaskie and Banks 1964, Small 1994). The range extends across half of Riverside County to Palm Springs (Grinnell 1904, Miller 1932, Small 1994), and across San Bernardino County (Grinnell 1901, Mailliard and Grinnell 1905, Carter 1937) to the northeast corner of Los Angeles County and the southeast corner of Kern County, but excluding the south- and northwestern corners of San Bernardino county. Populations in Los Angeles and Kern Counties are local; in Los Angeles County at Saddleback Butte State Park and near Lancaster, CA and in Kern County in the area of Rosamond and Ancient Valley near Willow Springs, CA (Small 1994). Finally northern extent of the range is in the southeastern corner of Inyo County and locally along the Amaragosa River (Grinnell 1934, Wauer 1962) and near springs in the Panamint Mountains (Wauer 1964). Their former range included the Tijuana River Valley in San Diego County (Kaeding 1905), and the intermittent population at Furnace Creek, Death Valley National Monument (Grinnell 1934, Wauer 1962). Vagrants have been found in Chula Vista and San Elijo Lagoon San Diego County and Ming Lake near Bakersfield, Kern County, CA (Small 1994).
The Verdin is a small insectivorous passerine of 6 to 8 grams and 9 to 11 cm in length (Webster 1999). Although systematics of the species is in question, the species is currently thought to be the only North American member of the Remizidae family as determined by behavior, calls, and DNA-DNA hybridization (Taylor 1967, Cramp and Perrins 1993, Sheldon and Gill 1996). Due to the bright yellow facial pattern of this species, the adults are not easily confused with other species. Young birds (April to August) lacking this character can easily be confused with other species like the Juniper or Oak Titmice, Bushtit, Lucy’s Warbler, and Bell’s Vireo (Bent 1946, Sibley 2003). Males can sometimes be distinguished from females by a brighter yellow on the face. In the hand, the yellow of the female extends 6-15 mm below the bill and the male 12-23 mm below the bill. Also the female wing length ranges 48-54 mm while the male ranges 50-57 mm (Pyle 1997).
The Verdin is a resident species, and is not thought to be a migrant (Bent 1946). Young birds have been documented to disperse 0.5 to 3 km from their natal territory (Taylor 1967). There is some evidence that birds may disperse in the winter (Taylor 1967, Harrap and Quinn 1995), but that both males and females are territorial in the winter (Harrap and Quinn 1995). These wintering birds often make up the breeding population of that area the next summer (Taylor 1971). The Verdin may join foraging flocks while they feed in the territory, but leave the group as it passes on to other foraging areas (Austin and Smith 1972).
The Verdin is predominately insectivorous (Bent 1946, Taylor 1971) generally feeding in the outer branches of spiny shrubs (Parker 1986) like paloverde (Cercidium spp.), ironwood (Olneya tesota), and Acacia spp. They also feed in riparian habitat (Taylor 1971), and are one of the few species to be found commonly feeding in upland creosote (Larrea tridentate) (Anderson and Anderson 1946). Parker (1986) found that Verdin spent over half of their non-flight time in spiny shrubs that only composed 27% of the vegetative cover in an Arizona wash habitat. In the wash habitat of Arizona Verdin divided their time between feeding in the washes and the adjacent upland flats (Parker 1986). Verdin are known to feed on flowers (Pickens 1929) piercing the base of the tube and drinking the nectar (Webster 1999), visiting saguaro (Carnegiea gigantea) flowers (Taylor 1971), or pulling the flowers off creosote bush and then dropping them (Parker 1986). They also feed on berries and bring them to the nest for their young, and have been observed feeding on palm (Phoenix spp.) dates in the fall (Taylor 1971).
Unlike many species the verdin’s nest is often obviously placed in the outer branches of a spiny shrub including paloverde, acacia, mesquite (Prosopis spp.), cholla cactus (Cylindropuntia spp.), (Bent 1946, Taylor 1971) or ironwood (Jaeger 1949). Other nests are found less frequently in non-thorn bearing shrubs including Tamarisk spp., mistletoe (Phoradendron californicum), almond (Prunus dulcis), elm (Ulmus spp.), Gambel’s oak (Quercus gambelii), lemon, and willow (Salix spp.) to name a few (Taylor 1971). Many descriptions have been made of the Verdin nest (Gilman 1902, Bailey 1923, Hensley 1954, Bent 1946, Taylor 1971, Austin 1976, Webster 1999). The nest is normally spherical or elongated and 18.4 x 13.6 cm. The inside cavity is 4-6 cm in diameter and the entrance hole is 2.5 cm in diameter (Webster 1999). Taylor’s (1971) description is very detailed, describing the three layers of the nest including the twig outside frame including the thorn guarded entrance, the middle layer of small twigs, leaves, spider webbing, and moss, and the nest cup of feathers, fur, or wool. The Verdin constructs both breeding and roosting nests. Two kinds of roosting nests have been found: small lighter nests built in the late summer and larger nests resembling breeding nests in the fall and winter (Taylor 1971). Breeding nests are started by the male and then the female helps complete the structure. While the female is brooding the eggs, she will continue to bring nest material to the nest (Taylor 1971, Webster 1999). Taylor (1971) did not find the nest entrance of nests in his study to be arranged in any direction. Austin (1976) on the other hand found that spring nests were oriented away from the prevailing wind direction while late summer nests were oriented towards the prevailing wind direction. Winter nests in another study were randomly oriented (Buttemer et al. 1987). Verdin nests are very sturdy and persist for many years after they are built giving the illusion that there are more Verdins in the area than there are (Bent 1946). Nests from past years are sometimes used by other nesting birds including Lucy’s Warbler (Swarth 1905), Black-tailed Gnatcatcher (Finch 1982), Bewick’s Wren, and Cactus Wren (Taylor 1971).
The nest contains 3 - 6 but usually four eggs (Baicich and Harrison 1997, Webster 1999). The young are born altricial after an incubation period of 14 - 18 days (Taylor 1971, Baicich and Harrison 1997). The nestlings are first fed by the female, and although originally reported, the young are not fed a regurgitated substance in the beginning (Wheelock 1920, Taylor 1971, Webster 1999). After 5 - 7 days the male helps to feed the young (Webster 1999). The young leave the nest 17 - 21 days after hatching (Baicich and Harrison 1997), but return to the breeding nest to roost for up to 2 weeks (Webster 1999). The male broods the young at night after fledging, as the female will lay a new clutch as soon as 2 days after fledging (Webster 1999). Males and females do not roost together, but both sexes can be found roosting with young (Taylor 1971). A Verdin pair will attempt to complete two successful clutches (Taylor 1971, Webster 1999). There are a few observations of cowbird parasitism of Verdin nests although it is not common (Friedmann 1934, Taylor 1971, Webster 1999), and one published instance of Verdins feeding cowbird young (Austin 1970). The nest entrance may need to be modified in order to make it possible for the cowbird to occupy the nest (Friedmann 1925, Bent 1946). There is one observation of a Verdin laying its egg in a northern mocking bird nest, but the nest was taken by a predator before it could be determined if it would hatch (Carter 1987).
The Verdin is a small bird living in a habitat with extreme seasonal differences in temperature, and this species has been the focus of a great deal of research on how the species copes with these extremes. Goldstein (1974) found the Verdin to be physiologically adapted to living in a cold climate because the species had a higher than expected standard metabolic rate and lower than expected thermal conductance value. By roosting in an insulated nest, the Verdin may save as much as 29-49% in energy when compared to a bird of equal size roosting in the open air (Buttemer et al. 1987, Webster 1989). Another species has been observed using the insulating qualities of the Verdin nest, when as many as 15 black-tailed gnatcatchers were found roosting in a Verdin nest for several nights (Walsberg 1990). Taylor (1978) found that Verdins spent less time moving when temperatures increased to greater than 32ºC. Also, during the warmest parts of the day, it has been found that Verdin use shaded areas as refugia, saving as much as 5 times the evaporative water loss than if they were in the sun (Wolf et al. 1996).
The Verdin is a bird of the desert scrub mostly found in desert riparian areas and desert washes. In California the species is normally associated with paloverde, mesquite, catclaw, creosote bush, smoke tree. They are less commonly found in areas occupied by Joshua tree. They also once occurred in the seep willow and tree tobacco of the Tijuana River Valley (Garrett and Dunn 1981). The species is normally found at low elevations, but has been found up to 915 m in California (Harrap and Quinn 1995).
Although this species is often found near water, it does not need water to survive and has been found as many as 3 miles away from the nearest water supply (Bent 1946).
In creosote desert in Arizona, Tomoff (1974) found Verdins were denser in areas with greater foliage density when compared to areas with lower foliage density. In Tucson where the effect of urbanization on the bird community has been documented, most of the research indicates that Verdin benefit from urbanization to a point due to increased vegetation compared to their native habitat (Emlen 1974, Mills et al. 1989.) In Tucson, Germaine et al. (1998) found Verdin were significantly negatively associated with house density, paved areas, urban open exotic plant areas, distance to vegetation patch, and distance to riparian and were positively associated with upland Sonoran vegetation and undisturbed wash. In Tempe, Verdin were found to be more common in urban areas than in natural habitat (Resenberg et al. 1987)
The Verdin is a common species of the desert washes of the Mojave Desert. Root (1988) found the highest densities of the Verdin in the Mojave Desert. The Verdin is not listed, except as a Partners in Flight Stewardship Species because its global population is found in a single biome (Rich et al. 2004).
The Breeding Bird Survey (BBS) reports that in the Sonoran Desert between 1966 and 2007 the Verdin shows a significant trend of decline (-3.3% annually, P = 0.04). Populations in the Mojave Desert show an even faster rate of decline (-5.4%), but this result was not significant at the α = 0.05 threshold (P = 0.17) – perhaps due to a lower sample size in the Mojave Desert (Sauer et al. 2008). The BBS reports a relative abundance of 3.56 birds/route (Sauer et al. 2005). The Christmas Bird Count reports between 1959 and 1988, that survey-wide the Verdin has a stable population with a relative abundance of 2.09 birds/100 party hours. The survey does not report numbers for California, and although it may not be applicable to California, in Arizona the species shows a significantly increasing trend and a relative abundance of 5.04 birds/100 party hours (Sauer et al. 1996). Webster (1999) reports species density from several studies in California (16-28 individuals/ 40 ha in the Colorado Desert, 20-24 individuals/ 40 ha in the Lower Colorado River Valley, and 17.4 individuals/ 40 ha in Riverside County) for the Verdin Bird of North America account.
The species has a stable population over most of its range in the Mojave Desert, but the decline of the species has been documented in two satellite populations in the Tijuana Valley (Kaeding 1905, Small 1994) and at Furnace Creek in Death Valley (Grinnell 1934, Wauer 1962).
Figure 2. Verdin population trend, 1966-2003. http://www.mbr-pwrc.usgs.gov/bbs/htm03/trn2003/tr07460.htm
The Verdin is one desert species that seems to adjust to minimal habitat disturbance. Patten and Rotenberry (1998) found the Verdin population was stable at their study site after much of the riparian vegetation was removed from a portion of their study area. Also, several authors found that Verdin were successfully established in suburban areas, but that their numbers decline with the amount of development (Rosenberg et al. 1987, Germaine et al. 1998).
Verdin are also found to inhabit riparian areas invaded by salt cedar along the Colorado River (Hunter et al. 1988), but the authors thought the birds may not inhabit the same habitat along the middle Rio Grande because of colder winters in the Rio Grande area. There is the potential for salt-cedar to impact Verdin density in this habitat compared to native habitats, but there was no information found on how salt cedar influences the density of this species.
There is one study documenting the impact of grazing on a riparian bird community along the San Pedro River in Arizona of which Verdin was one of the species (Krueper et al. 2003). In this study, the Verdin population declined with grazing but the trend was not statistically significant. Also, Brook (1999) found Verdin density increased 200% in fenced areas in the Desert Tortoise Research Natural Area that prevented grazing and off-highway vehicle use in the area.
In the Mojave Desert region the Verdin is most dependent on arid riparian wash habitat. These areas are increasingly used for recreational purposes including off-highway vehicle use and firewood gathering. No published information was found on impacts from recreation in desert washes, although PRBO Conservation Science is currently working on these questions.
One final question that is still standing is the possible impact of global warming on the Verdin. Most models indicate the desert Southwest will become warmer as global climate change sets in. For a species like the Verdin that spends the hottest parts of the day in cooler shaded areas, warmer temperatures could have a significant impact on their daily time budget. For example these refuge areas may become less available, or the Verdin may be required to spend even more of their time in these refuge areas leaving less time for other time budget tasks (Wolf 2000).
The Verdin is most dependent on the thorn scrub of the desert riparian and wash habitat of the Mojave Desert. As this habitat becomes more and more popular as a recreation area a need may arise for regulating recreational activity in portions of this desert habitat to protect the Verdin and other species dependent on thorn scrub habitats.
There is evidence that the Verdin can inhabit areas with salt cedar, but further research could elucidate the influence of salt-cedar invasion on Verdin abundance, survival, and fecundity.
There are several satellite Verdin populations in California, including those located in Los Angeles and Kern Counties and the Panamint Mountains. These populations should be monitored to better understand population regulation of Verdin, and determine if the population is increasing, decreasing, or both depending on the location. Indications from Furnace Creek and the Tijuana Valley suggest that Verdin distribution may be shrinking in California.
Lastly, as the impacts of global climate change are felt, the Verdin population along with populations of other desert species should be monitored. Although the final outcome of global climate change is still in question, any change in the desert climate could have the potential to greatly impact survival of desert birds. With the extensive background information on Verdin physiology and the response of this species to heat stress and other environmental factors, the Verdin is a prime candidate for research on impacts of a changing climate.
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