California Partners in Flight Desert Bird Conservation Plan
Ladder-backed Woodpecker (Picoides scalaris)
Dennis Jongsomjit and Arata, L. 2008. Ladder-backed Woodpecker (Picoides scalaris). In The Draft Desert Bird Conservation Plan: a strategy for reversing the decline of desert-associated birds in California. California Partners in Flight. 
action plan summary
P.s. cactophilus is the subspecies resident in desert areas of se.California, s. Nevada, s.w. Utah, se. Colorado, w. Oklahoma, and w. Texas south (west of 97deg W) to ne. Baja California, Michoacan, Puebla, and Mexico (Lowther, P.E. 2001). Peters (1948) recognized 6 subspecies within P.s. Cactophilus including: P.s. centrophilus (Oberholser, 1911), P.s. giraudi (Stone 1861); also included in synonomy are P.s. bairdi (Malherbe 1861), P.s. mojavensis (van Rossem 1942), and P.s. yumanensis (van Rossem 1942).
Other recognized subspecies of the Ladder-backed Woodpecker throughout N. America are as follows: P.s. eremicus in n. Baja California (Oberholser, 1911), P.s. lucasanus in Baja California south of 32 degrees N (Baird, 1859), P.s. graysoni on Tres Marias Island (Baird, 1874), P.s. sinaloensis in s. Sonora and Sinaloa and s. Mexico (Ridgeway, 1887), P.s. scalaris in ne. Veracruz and Chiapas (Wagler, 1829), P.s. parvus in the Northern Yucatan Peninsula (Cabot, 1845), and P.s. leucoptelurus in Belize (Oberholser, 1911).
Closely related to Nuttall’s Woodpecker (Picoides nuttalli). These two species are almost completely allopatric, but some hybrids have been reported as well as with Hairy Woodpecker (Picoides villosus).
The Ladder-backed Woodpecker is not listed as threatened or endangered at the federal or state level. However, it is on the U.S. Fish and Wildlife Birds of Conservation Concern list (U.S. Fish and Wildlife 2002) for the Edwards Plateau Bird Conservation Region in Texas.
CURRENT BREEDING DISTRIBUTION:
The Ladder-backed Woodpecker occurs as a resident throughout the southeastern part of California in the following counties: Inyo, Kern, Los Angeles, San Bernardino, Riverside, San Diego, and Imperial (Garrett and Dunn 1981, Small 1994).
Its northern limits occur in Inyo Co, north to about Lone Pine, and east through the Coso and Argus mountains. Its range continues to the Tecopa and Kingston mountains in San Bernardino Co, and east to the Colorado River then south along the river to Mexico. Within the Mojave Desert, it occurs in Santa Barbara Co, west into Kern Co to the Walker Pass, then southwest to the Kelso Valley, continuing south to near Palmdale in Los Angeles Co. Its range continues east along the Transverse Ranges to Morongo Valley in San Bernardino Co. In Riverside Co, it occurs in the Colorado desert west through the San Gorgonio Pass, then south through the foothills of the Santa Rosa Mountains continuing into San Diego Co and the Laguna mountains.
Non-migratory year round resident. Some post-breeding dispersal occurs outside of its current normal range mostly during the fall and winter. Such records have occurred north in Death Valley and Panamint Valley in Inyo Co, and further north to Cottonwood Canyon on the slope of the White Mountains. South it has been recorded in the Tijuana River Basin in San Diego Co. In Riverside Co, it has been recorded west of San Gorgonio Pass to San Timoteo Canyon as well as near Valle Vista in the San Jacinto Valley (Garrett and Dunn 1981).
WINTERING GROUND NEEDS AND DISTRIBUTION :
Although the Ladder-backed Woodpecker is non-migratory, food availability during the winter may be limited, requiring differential foraging between the sexes and a switch in foraging substrates (Short 1971, Austin 1976).
Ladder-backed Woodpeckers forage mainly for insects by probing, pecking, gleaning, tapping, and prying various cacti, trees, and shrubs. Also have been seen foraging on the ground. (Austin 1976, Short 1971, Bent 1939).
Ladder-backed Woodpeckers forage on a variety of trees, cacti, and shrubs. Species noted in the literature include chollas and prickly pear (genus Opuntia), mesquite (genus Prosopis), Joshua tree (Yucca brevifolia), agave, cottonwoods (genus Populus), desert ironwood (Olneya tesota), blue paloverde (Cercidium floridum), dwarf willow, and willow (Salix gooddingii). Near chaparral habitat, Ladder-backed Woodpeckers foraged in scrub oaks and live oaks (Grinnell and Miller 1944, Short 1971, Austin 1976).
Differential foraging behavior between male and female Ladder-backed Woodpeckers has been detected in at least two studies. In a study conducted in the Santa Rita Mountains, in Pima County Arizona, males were found to forage primarily in cholla, except during the post breeding season (July-September) when they foraged primarily in mesquite. Females were found to forage primarily in mesquite throughout the year. The sexes also differed in foraging microhabitat, with males foraging lower on thicker branches and trunks than females. While watching one pair in the Mojave desert of Kern County California, Short (1971) noted that the male foraged exclusively in Joshua trees. The female foraged primarily in chollas and small bushes (80%) and secondarily in Joshua trees (20%). This niche segregation may occur, in part, because of greater food demand during the breeding season (April-June) and less food abundance during the winter (October-March) in a habitat with relatively low plant species diversity (Austin 1976).
During winter in Santa Cruz County, Arizona, Ladder-backed Woodpeckers were significantly more abundant (p < 0.05) in riparian woodlands containing sycamores (Platanus wrightii) than in those containing no sycamores. Sycamores, however, were used by Ladder-backed Woodpeckers throughout the year (Stamp 1978, Bock and Bock 1984).
In 14 stomachs, 92% of the contents reported to be animal matter consisting of wood-boring beetle larvae, caterpillars, and ants (Beal 1911). Short (1971) reports stomach contents consisting of beetle larvae, adult beetles, hemipterans, and lepidopterous larvae. Also seen eating fruit (Bent 1939).
MAJOR FOOD ITEMS (BY SEASON):
Short (1971) observed a male and female drinking standing water from a bent and broken Joshua tree limb. Otherwise, no information.
Include bill directing and pointing movements, head swinging, bobbing, and turning, crest raising, wing flicking, wing and tail spreading, and aerial flutter displays (Short 1971).
SOCIAL ORGANIZATION :
TYPICAL BREEDING DENSITIES:
Breeding density information is not widely available in California. In Cercidium woodland (xeric riparian wash) in San Bernardino County, consistently 2 territories / 40 ha from 2004-2008 (Chris McCreedy, pers. comm.). Densities in riparian habitat are much higher than in scrub habitat at sites outside California:
At seven sites in southern Baja California, breeding density varied between habitat type and between mainland and island sites. Scrub habitat density was 4.6 birds/ 100 ha on islands, and 2.5 birds/100 ha on the mainland. Desert riparian woodland density was 13.8 birds/100 ha on islands, and 8.3 birds/100 ha on the mainland (Emlen 1979). The differences between island and mainland sites, however, were not attributable to island/mainland differences in vegetative cover and density or food abundance.
Breeding bird density was relatively higher in riparian woodland northeast of Phoenix along the lower Verde River (Stamp 1978). Density was found to vary between riparian habitat type with 16 pairs/40 ha in cottonwood (Populus fremontii) dominated riparian woodland versus 8 pairs/40 ha in mesquite (Prosopis velutina) dominated riparian woodland. The differences in density may be related to vegetative cover, volume, and foliage height diversity.
In one Arizona study looking at riparian habitat west of Superior, Ladder-backed Woodpeckers were found to have their highest densities in riparian habitats compared to lower densities in desert washes or desert upland (Szaro and Jakle 1985).
Breeding density in a cottonwood and willow dominated riparian forest near Lake Havasu in Yuma County, Arizona was similar to the cottonwood Verde River site noted above, with 36-40 individuals/40 ha estimated over a two year period (Rosenberg et al. 1982).
MATING SYSTEM :
Limited information. Apparently monogamous (Lowther 2001).
DELAYED BREEDING :
Age at first breeding is presumed to be 1 yr (Lowther 2001)
POST-FLEDGING BIOLOGY OF OFFSPRING :
In a five year study conducted in the lower Colorado River valley, Anderson et al. (1982) found evidence for dispersal from the breeding grounds beginning in June and occurring through July. Juveniles are likely pushed out of established territories by dominant individuals/adults before a decline in insect abundance occurs.
NEST TYPE :
Ladder-backed Woodpeckers are cavity nesters. Bancroft (1930) found cavities typically five inches in diameter by fifteen in depth with the entrance holes at the top. He found that no foreign material was brought to the nest so that the eggs lay on chips that fell during excavation. Dennis (1967) found that completed cavities in cross arms of telephone poles in Texas were 6-10 inches in length and the majority of holes are concentrated in the top 2 or 3 feet of the pole.
CLUTCH SIZE :
Limited information. Bent (1939) states “2 to 6 eggs, usually 4 or 5”. One nest contained 4 eggs in the Chemehuevi Wash area of San Bernardino County, CA (PRBO unpubl.).
Both sexes apparently incubate (Bent 1939).
INCUBATION PERIOD :
13 days (Bent 1939)
Little data. In four CA nests monitored from incubation through fledging, young were observed being fed in the nest for 21- 26 days before fledging (PRBO unpubl.). In a fifth nest, young were heard begging in the nest for 17 days. Fledge date was not determined for this nest so this was considered a minimum nestling period (McCreedy pers. comm).
DEVELOPMENT AT HATCHING:
Presumably altricial and nidicolous (Bent 1939).
NUMBER OF BROODS:
Single brooded (Lowther 2001)
WHO TENDS THE YOUNG :
BREEDING HABITAT AND NEST SITE CHARACTERISTICS:
OVERVIEW OF BREEDING HABITAT:
Ladder-backed Woodpeckers occur in the scrub desert habitats of the Mojave and Sonoran deserts and are associated with Joshua tree, cholla, prickly pear, agave, and yucca plants. This species also is associated with blue paloverde, mesquite, willows, and desert ironwood found in desert drainages. In the absence of Nuttall’s Woodpeckers, can be abundant in riparian woodlands dominated by cottonwoods and mesquite.
Nesting information is limited. Ladder-backed Woodpeckers have been found to nest in Joshua tree, desert willow, mesquite, paloverde, desert ironwood, saguaro, oaks, cottonwood, hackberry, yucca, walnut, pine, cardon, and agave as well as telephone and utility poles (Simmons 1925, Grinnell and Swarth 1913, Bancroft 1930, Dennis 1967).
Simmons (1925), besides listing oaks and mesquite, states that the Ladder-backed is partial to cottonwoods and hackberry. In extremely dry and treeless sections of the Southwest the Ladder-backed is found closely associated with yucca and agave. Grinnell and Swarth (1913) state that the birds nest in the dried stalks of these plants in desert regions of southern California. Bancroft (1930) reports that a race of the Ladder-backed in lower California confines its nesting to the saguaro cactus.”
Outside of California:
Outside CA, species include cardon (Pachycereus calvus), desert willow, and mesquite This species requires plants with trunks or branches of sufficient diameter for excavating and nesting (Bancroft 1929, Kozma and Mathews 1997, Shackford and Harden 1980, Reinking and Hendricks 1993).
Bancroft (1929) found that P.s. lucasenus confined itself to nesting in cardón, Pachycereus calvus also known as P. pringlei, in a study done between Santa Rosalía and San Ignacio Lagoon, Baja California, Mexico.
A single Ladder-backed Woodpecker (Picoides scalaris) nest was located in a large desert willow, which was only found in arroyo habitat (Kozma, Mathews 1997) in south-central NM, Chihuahuan Desert.
While studying a small population in the early 1980’s, Shackford and Harden found Ladder-backed Woodpeckers nesting in Mesquite (Prosopis juliflora) in Kingfisher and Canadian Countinties of central Oklahoma. (from Bulletin of the Oklahoma Ornithological Society with Reinking and Hendricks Dec. 1993)
HEIGHT OF NEST:
In the lower Colorado River Valley, nests were found to be located between 6 and 12 m above ground in willow or cottonwood snags. Nests were “much lower” in mesquite and desert washes with the diameter of the limb or trunk being more important than the height (Rosenberg 1991)
In Bent (1939) nest height is described as “3 to 30 (ft), usually from 6 to 14 feet.”
In 14 nests located by PRBO biologists, nest height averaged 3.74 m with a range of 1.3 – 8.2 meters
HEIGHT OF PLANT:
In 14 nests located by PRBO biologists, maximum plant height averaged 7.85 meters with a range of 3.3 – 16 meters (McCreedy, pers. comm.).
Occurs from sea level up to (rarely) 1800 m on the western desert edge of CA where Nuttall’s are absent. Not detected above 1800 m where some Joshua trees persisted in pinyon forest (Short 1971).
Empirical data is limited. May be sensitive to urbanization mainly due to loss of native plants and reduction of vegetation volume. Not detected in urban habitats characterized by exotic vegetation but detected in urban habitat characterized by native vegetation. Also found to be less dense in non-urban exotic habitats (e.g. parks) than in natural desert areas (Mills et al. 1989).
Empirical data is limited, but impacts of disturbance on the occurrence of this bird are probably related to degradation of habitat and loss of plants of suitable size for nesting. Grazing impact probably varies locally and may include loss of vegetative biomass and foliage density used for nesting and foraging due to vegetation cropping and trampling and soil degradation via compaction, increased erosion, and damage to soil crusts. Impacts of OHV use to vegetation may be more severe and likely for similar reasons as those stated above. Other disturbances causing habitat loss and degradation include mining, military training activities, and invasive plants. These types of disturbances affect the timing of recruitment and regeneration of native plants and soils (Lovich and Bainbridge 1999). Disturbance due to fire is another issue that merits further research. In one study, Ladder-backed Woodpeckers were found to increase in relative abundance following a fire disturbance during the winter (Kirkpatrick et al. 2002)
SPECIAL FACTORS :
The presence of Nuttall’s Woodpeckers in otherwise suitable riparian habitat may play a role in limiting the Ladder-backed Woodpecker along the western limit of its range (Short 1971).
SENSITIVITY TO HUMAN-INDUCED DISTURBANCE:
Occurs in suburban areas that contain native plant species (Mills et al. 1989) and nests checked regularly are not abandoned.
Secondary poisoning of adults can occur from ants contaminated with Sodium Monofluoroacetate 1080 (Hegdal et al. 1986). Proximity to soil contaminants, including heavy metals, chemicals, insecticides, polychlorinated biphenyls, and radioactive isotopes has been spatially correlated (within 60m) to lowered nestling survivorship (Fair et al. 2003).
AGE AND SEX RATIOS:
No information on lifetime reproductive success. Of eight nests monitored between 2004-2006, six fledged young, one was predated during incubation, and one had an uncertain outcome (McCreedy, pers. comm.).
Limited data. See “Productivity measures” above.
Data is limited. Ten years of banding data (1992-2001) from 11 MAPS banding stations in the southern central U.S. indicates a survival probability of 0.543 % (0.131 SE) (Michel et al. 2005).
Anderson et al. (1982) found evidence for social population regulation in this species. The Ladder-backed Woodpecker fit into all nine criteria set out by the authors regarding the classification of a socially regulated species. These criteria were related to the timing of population declines, post-breeding dispersal patterns, and breeding season timing and may result from an inconsistent or limiting food supply during the non-breeding.
Breeding Bird Survey data between 1966-2005 are insufficient to determine trends for Ladder-backed Woodpeckers in California (p = 0.8, n = 19 routes), Arizona (p = 0.58, n = 38 routes), or the Western BBS Region (p = 0.87, n = 115 routes). Survey wide, a yearly decline of 1.2% is nearly significant (p = 0.06, n = 230 routes). Significant trends found in the BBS data are a decline of 1.6% in Texas (p = 0.02, n = 129 routes) and a decline of 1.7% in the Central BBS Region (p = 0.02, n = 115 routes) (Sauer et al. 2005) (Figure 2).
Nest site sharing has been observed between Ladder-backed Woodpeckers and other species. In a study by Brush (1983) focusing on secondary cavity-nesters along the lower Colorado River, Arizona a Ladder-backed Woodpecker was found to have reopened an old cavity previously used as an Ash-throated Flycatcher nest site and used it as a roosting site. In the same study Brush found that Ash-throated Flycatchers used old Ladder-backed Woodpecker cavities for their nesting sites. In one case an Ash-throated Flycatcher displaced an incubating Ladder-backed Woodpecker pair. Lucy’s Warblers used smaller, unfinished Ladder-backed Woodpecker excavations for their nest sites. Old nest cavities may also provide nest cavities for Lucy’s Warbler (Unitt 2004).
ACTION PLAN SUMMARY
The Ladder-backed Woodpecker is not listed as threatened or endangered at the federal or state level.
In general, scrub and riparian desert habitat containing a diverse array of native plants for nesting and foraging are necessary. For nesting, plants need to be of sufficient diameter for excavating cavities. Seasonal and sex related differences in foraging substrate needs should also be a consideration in management plans.
Breeding densities of Ladder-backed Woodpecker is much higher in desert riparian forest habitat than in desert scrub habitat. Special attention should be given to protecting these limited riparian areas, which also contain higher breeding densities for several other species.
There is little known on the effects of habitat degradation and habitat loss on this species. These threats may be a significant concern in some parts of its range. A general lack of information of the ecology of the Ladder-backed Woodpecker is also pervasive, making it difficult to effectively manage the habitat needs of this bird.
Establish year-round ecological and demographic monitoring studies to determine habitat needs, establish current densities, and identify population distribution.
Kirkpatrick, C., S. Destefano, R.W. Mannan, J. Lloyd. 2002. Trends in abundance of grassland birds following a spring prescribed burn in southern Arizona. The Southwestern Naturalist. 47:282-292
Michel, N., DeSante, D.F., Kaschube, D.R., and Nott, M.P. 2005. The Monitoring Avian Productivity and Survivorship (MAPS) Program Annual Reports, 1989-2001. NBII/MAPS Avian Demographics Query Interface. .
Sauer, J. R., J. E. Hines, and J. Fallon. 2005. The North American Breeding Bird Survey, Results and Analysis 1966 - 2005. Version 6.2.2006. USGS Patuxent Wildlife Research Center, Laurel, MD.
Simmons, G.F. 1925. Birds of the Austin region. University of Texas Press, Austin.
Small, A. 1994. California birds: their status and distribution. Ibis Publishing Company, Vista, CA.
Szaro, R.C., and M.D. Jakle 1985. Avian use of a desert riparian island and its adjacent scrub habitat. The Condor 87:511-519.
Stamp, N.E. 1978. Breeding birds of riparian woodland in south-central Arizona. Condor 80:64-71.
U.S. Fish and Wildlife Service. 2002. Birds of conservation concern 2002. Division of
Migratory Bird Management, Arlington, Virginia. 99 pp.