California Partners in Flight Desert Bird Conservation Plan

 

Costa’s Hummingbird (Calypte costae)

 

Photo by Jon Sullivan (http://www.pdphoto.org/PictureDetail.php?mat=pdef&pg=7917)

Prepared by: Susan M. Wethington and Barbara A. Carlson

Hummingbird Monitoring Network
P.O. Box 115
Patagonia, AZ 85624

 

RECOMMENDED CITATION

Wethington, S. M. and B. A. Carlson, 2009 Costa’a Hummingbird (Calypte costae). In The Draft Desert Bird Conservation Plan: a strategy for reversing the decline of desert-associated birds in California. California Partners in Flight. http://www.prbo.org/calpif/htmldocs/desert.html

SHORTCUTS

range map

references

management issues and options

SUBSPECIES STATUS

Subspecies have not been described for Costa’s Hummingbird, which is a monomorphic species with no described geographic variation (Baltosser 1989). Instead, a number of hybrids, including across genera have been described (Baltosser and Scott 1996, Wells et al. 1978, Banks and Johnson 1961, Short and Phillips 1966).

MANAGEMENT STATUS

The Costa’s Hummingbird is identified by Partners In Flight as a species of continental concern due mainly to its limited range distribution (Rich et al. 2004). Of the states in the U.S. where Costa’s occurs, New Mexico is the only one that has listed it as threatened. This is mainly due to its limited and irregular presence in the southern part of the state (New Mexico Department of Game and Fish, http://www.bison-m.org/reports.aspx?rtype=13&status=%27201%27,%27202%27)

DISTRIBUTION

CURRENT BREEDING DISTRIBUTION:

The Costa’s Hummingbird breeding range is primarily in desert scrub associations at lower elevations throughout much of southwestern U.S. and northwestern Mexico.  It commonly breeds in southern California, throughout Baja California, in southern, but primarily southwestern Arizona, and in northwestern Sonora. Other locations with limited breeding in desert scrub include southern Nevada, southwestern Utah, central Arizona, southwestern New Mexico, and northeastern Sonora (Baltosser and Scott 1996, Corman 2005).

Breeding has also been documented in coastal sage scrub and chaparral along the California coast north to at least Santa Barbara County (Garret and Dunn 1981, Lehman 1994) and once at an oak woodland/ grassland site in southeastern Arizona (Wethington and Russell, 2003).

Figure 1: Breeding Bird Survey (BBS) summer distribution map of Costa's Hummingbird in the US. This survey is typically performed in June by volunteers on over 4000 bird counts. The counts are done by vehicle during the morning. (http://137.227.242.23/bbs/htm03/ra2003_red/ra04300.htm).

NONBREEDING DISTRIBUTION:

As desert flower availability declines, many individuals migrate northward into coastal chaparral areas, a period during which very little is known about the Costa's Hummingbird. Some birds possibly breed a second time in the chaparral of the Coast Range, but still remains to be verified. The suggested post-breeding movement pattern of Costa’s to higher elevations during the driest and hottest times in the desert (Baltosser and Scott 1996) is supported by data from Hummingbird Monitoring Network (HMN) monitoring stations in the oak woodlands at elevations between 1300 m and 2100 m in both California and Arizona.

After breeding, most withdraw from the northern part of their breeding range, concentrating in the southern part of their breeding range. Wintering birds are found south into Mexico including locales in Sinaloa, Nayarit, and Jalisco. Some individuals disperse to the north.

HISTORICAL CHANGES IN DISTRIBUTION:

The breeding range has remained relatively stable but many records of vagrancy have occurred since 1970. Many vagrants are reported in the Pacific Northwest, extending into British Columbia and into Alaska (2 records) and as far east as Texas. The first record of Costa’s Hummingbird in Alabama occurred during the winter of 2005/2006 (Fred Bassett, pers. comm.)

ECOLOGY

AVERAGE TERRITORY SIZE:

Territoriality is little studied for Costa’s Hummingbirds. When documented, territories are typically centered on nectar plants. During the breeding season, territories have included 3 to 4 bladderpod bushes (Cody 1968) and 5– 10 chuparosa shrubs, Justicia californica, (Baltosser and Scott 1996). During the non-breeding season, one study documented territories around wooly bluecurls bushes, Trichostema lanatum, where the territory size for adult males averaged 10.4 m2 (SE = 1.9), 3.0 m2 (SE = 0.4) for the juvenile males and females did not maintain territories (Avery and Van Riper 1993). Other nectar plants where territoriality is documented include 25 Cardinal Larkspur plants defended by an adult male (Grant and Grant 1968) and 6500 to 8500 paintbrush flowers, Castelleja spp, within 290 m2 defended by a juvenile male (Hixon and Carpenter 1988). Individuals appear not to defend territories when nectar is superabundant or when plants are dispersed (Baltosser and Scott 1996).

TIME OF OCCURRENCE AND SEASONAL MOVEMENTS:

Their movement patterns are geographically variable and are poorly documented. Costa’s Hummingbird breeds in late winter and spring in the southwestern United States and is thought to migrate to coastal regions in summer and to Mexico in winter (Baltosser and Scott 1996). Costa’s Hummingbirds occur mainly from February to May on their desert breeding grounds in California and Arizona. They start to arrive in late October / early November when nectar plants such as Chuparosa and desert lavender bloom (Baltosser and Scott 1996). In Arizona, individuals arrive at their desert breeding areas in late October with most arriving by late December (Corman 2005). Breeding peaks in March and April and then most have left the desert by late May to destinations unknown (Baltosser and Scott 1996). A few nesting records occur into late June (Corman 2005).  At a site in Palm Springs CA, Costa’s begin to arrive in early November and numbers continue to increase through December. Breeding peaks in late January and continues through mid-May with a second peak in mid-April (BAC). At some low elevation desert HMN monitoring sites in California such as BLM’s Big Morongo Preserve, Costa’s occur throughout the monitoring season (March through October). From mid-May through July, Costa’s occur at HMN monitoring stations in the oak woodlands where many are molting (SMW and BAC).

Along the south California coast in coastal chaparral and sage scrub, the first migrants return in mid-March with the peak of breeding in late May to early June and most have finished by July (Pitelka 1951, Lehman 1994). Migrants arrive in chaparral and coastal sage before most desert breeders have left the desert scrub but numbers continue to increase by late April suggesting that desert breeders move to the chaparral after nesting there is complete (Baltosser and Scott 1996).  

In the southern areas of Nevada, breeding populations occur from March through May. In southwestern New Mexico Costa’s Hummingbirds occur there from mid-March to mid August with most occurring from late April to early May (Baltosser and Scott 1996).

Costa’s Hummingbirds occur throughout Baja all year but seasonal movement patterns are likely. Breeding occurs from February to June with the peak of egg-laying in late March. In southern Sonora, Costa’s Hummingbirds occur from late September through mid March and are considered winter transients. Other records from southwestern Mexico occur in late fall and winter (Baltosser and Scott 1996).

MIGRATION STOPOVER CHARACTERISTICS:

Little information is known. It is likely that stopover locations and durations are dependent upon nectar availability.

FOOD HABITS

FORAGING STRATEGY:

Throughout the year, Costa’s Hummingbirds feed on nectar from flowers, hawk flying insects, and glean other insects from leaves, branches, and tree trunks.

DIET:

Nectar plants are fairly well studied in Arizona and California, but not elsewhere. Chuparosa (Justicia califonica) and Ocotillo (Fouquieria splendens) are the two most important nectar plants species (Latta et al. 1999). Chuparosa has a lengthy flowering period, up to 6 months for some populations, and is the most reliable and productive of midwinter nectar sources (Baltosser and Scott 1996). Ocotillo has a much shorter (3-4 week) but predictable flowering season in March/April (Waser 1979). Other plants include desert lavender (Hyptis emoryi), Lycium spp., fairy duster (Calliandra eriophylla), Agave spp., Penstemon spp.,  Delphinium scaposum,  desert willow (Chilopsis linearis), desert honeysuckle (Anisacanthus thurberi), and others (Baltosser and Scott 1996). In southern California, other plants used include Belaperone California and Mimulus puniceus (BAC). In Mexico, Costa’s visit Salvia elegans and Cestrum thyrsoideum at El Palmito, Sinaloa (Lopez-Segoviano et al. in review) and tree tobacco (Nicotiana glauca) (Baltosser 1989).  In chaparral, coastal sage and oak savanna, preferred nectar flowers are usually Salvia species but also includes Ribes, Trichostema,Diplacus, and Penstemon (Schuchmann 1999).

Arthropod consumption is little studied, but is likely more important for the diet of nestlings than for adults. Typical hummingbird nectar contains few amino acids so arthropods provide the vast majority of the protein requirements for Costa’s and hummingbirds in general. Insects include small flies, gnats and wasps usually obtained by hawking. Also gleans spiders and other arthropods from foliage.

DRINKING:

Visits water sources when available but usually obtains sufficient water from their food.

BREEDING HABITAT

OVERVIEW OF BREEDING HABITAT:

Costa’s Hummingbirds nest primarily in Sonoran and Mojave Desert scrub associations where they prefer dry washes, canyons, and rocky slopes. They occupy much of the lower Sonoran and limited portions of the Upper Sonoran life zones of western North America. In Mojave Desert scrub habitat, nests tend to be near springs or in xeric riparian habitats, thus are less widespread in Mojave plant associations than in Sonoran (Baltosser and Scott 1996). They nest from below sea level (Death Valley) to about 2000 m in some desert mountain ranges (Garrett and Dunn 1981). In Arizona, desert washes are particularly favored (Corman 2005).

Baltosser and Scott (1996) described the following three plant associations where Costa's can be found: 1) dry washes lined with foothill paloverde, blue paloverde, catclaw acacia, ironwood, and smoketree or filled with shrubs such as creosotebush, jojoba, desert lavender and chuparosa; 2) steep rocky slopes with ocotillo and foothill paloverde; 3) gently sloping bajadas covered with saguaro, creosotebush, and cholla cacti. Costa’s Hummingbirds select drier desertscrub even when adjacent to riparian habitat (Brown 1992, Szaro and Jakle 1985).

DOMINANT CANOPY AND SHRUB SPECIES:

Dominant canopy species include foothill paloverde (Cercium microphyllum), blue paloverde (C. floridum), ironwood (Olneya tesota), catclaw acacia (Acacia greggii), desert willow (Chilopsis linearis), and smoke tree (Psorothamnus spinosus). Dominant shrubs include creostotebush (Larrea tridentata), jojoba (Simmondsia chinensis), desert lavender and chuparosa (Baltosser and Scott 1996, Corman 2005). In Baja, canopy species include palo adan (Fouquieria diguetii), small-leaf elephant tree (Bursera micophylla), cadron-barbon (Pachycereus pectenaboriginum), and lomboy (Jatropha cinerea) (Roberts 1989).

NEST SUBSTRATE:

Nests are found in a variety of trees and shrubs including sage, yuccas, Opuntia and other cacti (Bent 1940). During Arizona’s breeding bird surveys, 68% of nests were found in palo verde trees. Nests were also found in ironwood trees, jojoba, catclaw acacia, canyon ragweed, hopbush and goldenweed. Only two nests were found in mesquite (Corman 2005). In California, nests have also been found in graythorn (Condalia globosa), desert willow, laurel sumac (Rhus laurina), large deerbrush (Ceanothus sp), small buckthorn (Rhamnus sp), and a variety of cultivated plants.

NEST SITE:

Nests can be in either dead or alive structures, are frequently placed towards the end of branches in relatively open vegetation, which is subject to much sun and heat (Baicich and Harrison 1997, Corman 2005).

NEST HEIGHT:

Nests are usually within 3 meters of the ground with a range of 0.5 m to 4.8 m (Baltosser and Scott 1996, Corman 2005). For seventeen nests found during Arizona’s breeding bird surveys, the tree height averaged 4.3 m ± 0.9 SD and nests averaged 2.2m ± 0.7 SD off the ground (Corman 2005). In a Mojave Desert study, six nests occurred on trees/shrubs with an average diameter at ground height of 18.3 cm (McCreedy 2007).

It is likely that nests found higher in the canopy, particularly those in the riparian zones are confused with Black-chinned Hummingbird (Archilochus alexandri) nests (Baltosser and Scott 1996).

NEST TYPE:

Small shallow cup made mostly with fine plant fibers and feathers fastened with spider webbing. Plant material can include bark, small leaves, flower bud scales, ball-like flower heads, bits of lichen, dandelion or thistle heads, and other downy material (Baltosser and Scott 1996). Outside diameter averaged 37.5 mm but can be quite variable in size. The nest is often lined with feathers and decorated on the outside with a variety of materials including bits of lichen, bark, small leaves, and other vegetative materials from the area (Woods 1927). Females continue to build and decorate nests after incubation begins.

BREEDING BIOLOGY:

DISPLAYS:

Males display conspicuously, usually on territory during the breeding season. The most frequently observed display as described by Baltosser and Scott (1996) is the Looping Dive- and- Whistle series. Less frequently observed is the Close-Range Flight. Prominent perching and whistling during perching may also be considered displays. The Looping Dive and Whistle display consists of three segments. First the male flies towards the female, makes 1-2 passes above and around her. Then the male climbs steeply and makes a number of aerial loops approximately 25 to 40 m from top to bottom. This display frequently but not always ends in a zigzag flight near the female.

The Close-Range Flight display may be associated with copulation and thus less observed (Miller and Stebbins 1964). The male hovers within 0.5 m of the female; shuttles back and forth within 0.l m for 10-20 seconds, and frequently whistles.
 
For detailed description of these displays, see Baltosser and Scott 1996.

MATING SYSTEM:

Similar to other hummingbird species, females exclusively build nests, incubate, and care for the young. Male display behavior suggests that they attempt to mate with multiple females. There is no evidence of pair bond.

TYPICAL BREEDING DENSITIES:

Resource availability likely influences density of nest placement. Nests have been found within 35 meters of each other while others are 100m or more apart (Baltosser and Scott 1996). In one study area with OHV disturbance, nine nests were found within the 39.1 ha study area (McCreedy 2007).

NUMBER OF BROODS:

Two are possible but the frequency of females attempting two broods is unknown. Females have been observed feeding fledglings while simultaneously incubating. This is direct evidence that multiple broods are attempted. Additionally, the extended time (January through June) of nesting is suggestive of multiple broods (Baltosser 1989).

CLUTCH SIZE:

Two white oval to elliptical eggs averaging 12.4 x 8.2 mm (Bent 1940, Harrison 1979).

INCUBATING SEX:

Female

INCUBATION:

15 – 18 days, on average 16 days (Baltosser and Scott 1996, Corman 2005). The second egg is usually laid two days after the first but incubation begins with the laying of the first egg (Baltosser and Scott 1996).

INCUBATION PERIOD:

15 to 18 days (Baicich and Harrison 1997)

DEVELOPMENT AT HATCHING:

Altricial.

NESTLING PERIOD:

20-23 days (Baicich and Harrison 1997)

PARENTAL CARE:

Exclusively female.

POST-FLEDGING BIOLOGY OF OFFSPRING:

Fledglings frequently perch near the nest and are fed by the female for at least a week (Baltosser and Scott 1996).

POST BREEDING SOCIAL BEHAVIOR:

Three to four weeks after leaving the nests, juvenile males attempt rudimentary displays (Baltosser and Scott 1996). They also wander as exemplified by a juvenile male who was banded in August at a desert location in Arizona, was captured a month later at a oak woodland site approximately 50 miles away and was recaptured at the original capture site 30 hours later (SMW).

Juvenile females may also practice breeding behavior. On May 17, 2005 a gravid juvenile female was captured. 2005 was a particularly good resource year and this record is likely the first evidence that juvenile females are capable of reproducing (BAC).

DELAYED BREEDING:

No information.

NUMBER OF BROODS:

Usually 1, possibly 2 (Baltosser and Scott 1996)

BROOD PARASITISM:

Not observed.

WINTERING GROUNDS NEEDS AND DISTRIBUTION

Costa’s Hummingbirds leave the northern areas of their range for winter and migrate farther south in Mexico to Sinaloa, Nayarit, and Jalisco for winter (Baltosser and Scott 1996). Food resources, especially nectar, appear to define wintering locations and determine duration of occurrence.

LANDSCAPE FACTORS

ELEVATION:

During the breeding season, Costa’s Hummingbirds occur from below sea level to over 1400 m (Baltosser and Scott 1996, Corman 2005).  During non breeding, they have been observed at higher elevations (up to 2400 m) (Corman 2005).

FRAGMENTATION:

Costa’s Hummingbirds are adversely affected by fragmentation. In urban areas in southern California, their density is lower within 500 m of an urban edge and the landscape variables used to evaluate this edge / fragmentation effect are significant predictors of Costa’s abundance (Bolger et al 1997).  Arizona breeding bird atlas data reveal a general avoidance of extensive, irrigated lands (Corman 2005).

DISTURBANCE

FIRE:
Extensive loss of habitat due to increased fire frequency in Sonoran and Mojave Deserts is becoming a critical threat. Introduced drought-resistant grass such as Buffelgrass(Pennisetum ciliare) fuels fires that eliminate native plants that include most nest plants for Costa’s Hummingbirds. The native vegetation in these desert regions are not adapted to fire. Hence, the change in vegetation will irrevocably alter the deserts (Burquez-Montijo et al. 2002), which will likely have an deleterious effect on Costa’s populations.

ADJACENT LAND USE:

See Fragmentation

PESTICIDE:

No information. Since Costa’s Hummingbirds appear to avoid agricultural lands and numbers are reduced in urban landscapes (Corman 2005, Bolger et al. 1997), pesticides are likely not a threat for this species.

PREDATORS:

Predation is typically low on adult hummingbirds and is not perceived to be a major threat to Costa’s Hummingbird population numbers.

CLIMATE:

Less well appreciated is how climate change will likely disrupt the co-occurrence of pollinators with their flowering plants. Models predict phenological shifts in floral resource availability. Hence timing of pollinator movement patterns will need to change if pollinators will arrive at locations when floral nectar is available (Memmott et al. 2007). It is unknown if Costa’s or other hummingbird species have the ability to shift the timing of their movement patterns to match the timing of the new phenology.

COMPETITION WITH OTHER HUMMINGBIRDS:

Costa’s Hummingbirds are usually subordinate to other hummingbird species and may be excluded from areas by these species (Baltosser and Scott 1996). Anna’s Hummingbird, the sister species to Costa’s, is expanding its range into areas occupied by Coasta’s Hummingbirds. However, it is likely that the preferred xeric habitats of Costa’s Hummingbird will limit intrusions by this and other hummingbird species.  

DEMOGRAPHY AND POPULATION TRENDS

DEMOGRAPHICS:

AGE AND SEX RATIOS:

No information.

PRODUCTIVITY MEASUREMENTS:

Reported nest success rates range from 9% to 50%, with predation, abandonment, and weather or accidental destruction as the primary causes of failures (Baltosser and Scott 1996, McCreedy 2007).  The high nest success rate of 50% was reported in an area with Off Highway Vehicle disturbance (McCreedy 2007). There is limited information on individual reproductive success and no information of productivity measures that allow population estimates and trends to be modeled.

SURVIVORSHIP:

Limited information.  From banding studies in southern California (BAC), there are recapture records of individuals living at least 7 years. Further study is needed to determine survival rates.

DISPERSAL:

No information.

POPULATION TREND

Population trend information is limited for Costa’s. In recent summaries, their populations appeared stable (Latta et al. 1999, Baltosser and Scott 1996). Now, the Breeding Bird Survey provides the only trend estimate and Costa’s show a decrease in populations throughout much of its desert breeding habitats (see figure below). This trend information has been classified as inadequate due to low sample sizes, low detection rates, and high variability and the data should be used with caution (Sauer et al 2001, Dunn et al. 2005).

 

Figure 2. Costa's Hummingbird population trend, 1966-2003.  http://www.mbr-pwrc.usgs.gov/bbs/htm03/trn2003/tr04300.htm

MANAGEMENT ISSUES AND OPTIONS

EXOTIC SPECIES INVASION/ENCROACHMENT:

Fire frequency and intensity has increased due to widespread invasion of Sonoran Desert scrub by exotic grasses. This has resulted in the loss of many potential nest and nectar plants for Costa’s Hummingbird across southern Arizona and Sonora (see FIRE, above).

MANAGEMENT:

The greatest threats to Costa’s hummingbirds are desert wildfires, urban sprawl, climate change and possibly competition with Anna’s Hummingbirds (Baltosser and Scott 1996, Bolger et al. 1997, Schuchmann 1999, Memmott et al. 2007).  The accelerating rate of desert scrub habitat loss to the above threats is likely de-stabilizing Costa’s population and minimizing these habitat losses are necessary to manage conservation needs of Costa’s.

Management recommendations made in the Arizona Partners in Flight Conservation plan continue to be applicable to management needs of Costa’s throughout their range. These recommendations include:

1. Encourage maintenance of native vegetation
2. Encourage landscaping with native vegetation
3. Implement full fire suppression in desert scrub habitats that are not fire adapted
4. Reduce fuel loads along roadways (Latta et al. 1999).

Issues addressing climate change are complex and will require new research to understand what management actions will be effective.

ASSOCIATED SPECIES:

Several bird species use the same desert scrub habitat as Costa’s. They include Bendire’s Thrasher, Le Conte’s Thrasher, Harris Hawk, White-winged Dove, Roadrunner, Mourning Dove, Verdin, Cactus Wren, Black-tailed Gnatcatcher, Phainopepla, Gambel's Quail, Gilded Flicker and Gila Woodpecker.

Other species that may use similar habitat components or respond positively to management for Costa’s Hummingbird are: Ladder-backed Woodpecker, Curve-billed Thrasher, Ash-throated Flycatcher, Verdin, Black-tailed Gnatcatcher, Cactus Wren, White-winged Dove, Phainopepla, and Scott’s Oriole (Latta et al. 1999). Additionally, species adversely affected by urban sprawl such as the Sage Sparrow, Rufous-crowned Sparrow, Western Meadowlark, Blackchinned Sparrow and Lark Sparrow (Bolger et al. 2007), could also benefit to management efforts to conserve Costa’s.
 

MONITORING METHODS AND RESEARCH NEEDS:

Long-term monitoring data are vital to deciphering the difference between a true population decline and natural fluctuations in population size. Demographic data that includes productivity and survivorship estimates are essential for estimating these trends. Due to high mobility and low detectibility of hummingbirds in general, specialized monitoring techniques are required to gather these data. More specifically for Costa’s, their early breeding season requires monitoring efforts to start earlier than other breeding birds.

REFERENCES:

Avery, M.L. and Van Riper III, C. 1983. Post-breeding territoriality and foraging behavior in Costa’ Hummingbird (Calypte costae). Southwestern Naturalist 38:374-406.

Baicich, P. J. and Harrison, C.J.O.  1997.  A Guide to the Nests, Eggs, and Nestlings of North American Birds. 2nd ed. Academic Press, San Diego, CA.

Baltosser, W.H. 1989. Costa’s Hummingbird: Its distribution and status. Western Birds 20(2).

Baltosser, W.H., and Scott, P. E. 1996. Costa's Hummingbird (Calypte costae), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/25.

Banks, R.C. and Johnson N.K. 1961. A review of North American hybrid hummingbirds. Condor 63:3-28.

Bent, A. C.  1940.  Life histories of North American cuckoos, goatsuckers, hummingbirds, and their allies. Bulletin of the United States National Museum. 176.

Bolger, D.T., Scott, T.A., and Rotenberry, J.T. 1997. Breeding Bird Abundance in an Urbanizing Landscape in Coastal Southern California. Conservation Biology, 11(2): 406–421

Brown B.T. 1992. Nesting chronology, density and habitat use of Black-chinned Hummingbirds along the Colorado River. Arizona. J. Field Ornithology 63:393-400.

Búrquez-Montijo, A., Miller, M.E., and Martínez-Yrízar, A.  2002.  Mexican grasslands, thornscrub, and the transformation of the Sonoran Desert by exotic bufflegrass.  In Invasive Exotic Species in the Sonoran Region.  B. Tellman ed.  The University of Arizona Press and The Arizona-Sonora Desert Museum.  Tucson, AZ. 

Cody, M.L. 1968. Interspecific territoriality among hummingbird species. Condor 70:270-271.

Corman T.E. 2005. Costa’s Hummingbird. The Arizona Breeding Bird Atlas. Eds

Corman T.E. and Wise-Gervais C. pp 260-261. University of New Mexico Press, Albuquerque, NM.

Dunn, E. H., Altman B. L., Bart J., Beardmore C. J., Berlanga H., Blancher P. J., Butcher G. S., Demarest D.W., Dettmers R., Hunter W. C., Iñigo-Elias E. E., Panjabi A. O., Pashley D. N., Ralph C. J., Rich T. D., Rosenberg K. V., Rustay C. M., Ruth J. M., and Will T. C. 2005. High priority needs for range-wide monitoring of North American landbirds. Partners in Flight Technical Series No. 2. Partners in Flight website: http://www.partnersinflight.org/pubs/ts/02-MonitoringNeeds.pdf

Garrett, K. and Dunn J. 1981. Birds of southern California—status and distribution. Los Angeles Audubon Soc., Los Angeles, CA.

Grant, K. A. and Grant V. 1968. Hummingbirds and their flowers. Columbia University Press, NY.

Hixon, M.A. and Carpenter, F.L. 1988. Distinguishing energy maximizers from time minimizers: a comparative study of two hummingbird species. Am. Zool. 28:913-925.
 
Latta, M.J., Beardmore, C.J.and Corman T.E.. 1999. Arizona Partners in Flight Bird Conservation Plan. Version 1.0. Nongame and Endangered Wildlife Program Technical Report 142. Arizona Game and Fish Department, Phoenix, Arizona.

Lehman, P.E. 1994. The birds of Santa Barbara County. California. University of California Santa Barbara Vertebr. Mus. Santa Barbara

McCreedy, C.  2007.  Potential off-road vehicle impacts on bird populations of Sonoran Desert Xeroriparian habitats of western Arizona.  PRBO Conservation Science, 3820 Cypress Drive, Petaluma, CA, 94954.  PRBO Contribution No. 1611.

Memmott J., Craze P.G., Waser N.M., and Price M.V. 2007.  Global warming and the disruption of plant–pollinator interactions Ecology Letters10: 710–717

Pitelka, F.A. 1951. Breeding seasons of hummingbirds near Santa Barbara, California. Condor 53:198-201.

Roberts, N.C. 1989. Baja California plant field guide. Natural History Publ. Co., La Jolla, CA.

Rich, T.D., Beardmore C.J., Berlanga, H., Blancher, P.J., Bradstreet, M.S.W., Butcher, G.S., Demarest, D., Dunn, E.H., Hunter, W.C., Inigo-Elias, E., Kennedy, J.A., Martell, A., Panjabi, A., Pashley, D.N., Rosenberg, K.V., Rustay, C., Wendt, S., and Will, T. 2004. Partners In Flight North American Landbird Conservation Plan. Cornell Lab of Ornithology, Ithaca, NY.

Sauer, J.R., Hines, J.E., and Fallon, J.  2008.  The North American Breeding Bird Survey, Results and Analysis 1966-2007.  Version 5.15.2008.  USGS Patuxent Wildlife Research Center, Laurel, MD.  http://www.mbr-pwrc.usgs.gov/bbs/

Schuchmann K.L. 1999. Family Trochilidae (Hummingbirds). In Del Hoyo J., Elliot A., Sargatal J.. (Eds). Handbook of the birds of the world. Vol. 5 Barn-owls to Hummingbirds. Birdlife International. Lynx Editions, Barcelona. pp: 468-680.

Short L.L., Jr, and Phillips, A.R. 1966. More hybrid hummingbirds from the United States. Auk 83:253-265.

Szaro, R.C. and Jakle, M.D. 1985.  Avian use of a desert riparian island and its adjacent habitat. Condor 87: 511-519.

Weathers, W.W. 1983. Birds of southern California’s Deep Canyon. University of California Press, Berkely.

Waser, N.M. 1979. Pollinator availability as a determinant of flowering time in ocotillo (Fouquieria splendens) Oecologia (Berl.) 39:107-121.

Wells, S., Bradley R.A., and Baptista L.F. 1978. Hybridization in Calypte hummingbirds. Auk 95:537-549.

Wethington, S.M. and Russell, S.M.. 2003. The seasonal distribution and abundance of hummingbirds in oak woodland and riparian communities in southeastern Arizona. Condor 105:484-495.

Woods, R.S. 1927. The hummingbirds of California. Auk 44:297-318.

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