Prepared by: Cory R. Davis, 10872 Poblado Road #1523, San Diego, CA 92127 (858) 676-5933, email: quercus92@earthlink.net
SPECIES: Western Tanager (Piranga ludoviciana)
SUBSPECIES STATUS
Hudon (1999) did not recognize any subspecies. However, pairs which breed across most of Canada and south through the Rocky Mountains into southeast Arizona and western Texas, which are typically slightly larger, brighter males and paler females, were distinguished as P.l. zephyrica by Oberholser (1974).
MANAGEMENT STATUS
No special status. Protected under the Migratory Bird Treaty Act.
RANGE IN CALIFORNIA
1. Historical References
The description of breeding range in Grinnell and Miller (1944) is equivalent to description in Small (1994) except where Small noted a local expansion into the San Benito Mountain area of the Diablo Range. Both sources suggest the species can be observed throughout the state, in appropriate habitat, during migration including the offshore islands.
Wintering birds:
Grinnell and Miller recognized a few wintering records from Santa Barbara
and San Diego counties, but Small reports an average of 75 birds annually
winter along the coast from Santa Barbara south through San Diego. These
individuals are most frequently observed around flowering, non-native Eucalyptus
trees (Small 1994). The species typically winters from Mexico to Costa
Rica.
2. Current Breeding Distribution
Small (1994) describes current breeding range as follows:
a. South from Oregon border through Klamath Mountains and outer Northern Coast Ranges to southern Sonoma County and western Solano County, whereECOLOGY
b. They become scarce along the coast until the Santa Lucia Mountains in Monterey County (where they are fairly common).
c. Inland they breed throughout the Warner Mountains and the Cascade-Sierra axis south to the Greenhorn and Piute Mountains of Kern County.
d. In eastern part of state, they breed in mountain ranges from Modoc County south to the Inyo Mountains of Inyo County (where they breed only sparingly).
e. In southern California, they breed in the Santa Ynez Mountains of Santa Barbara County east through the mountains of Ventura and Kern counties and in the Transverse and Peninsular ranges, including the Santa Ana Mountains of Orange County and the higher mountains of San Diego County. Small also notes they are local breeders in Marin, Santa Cruz, and San Luis Obispo counties.
Migration Characteristics
1. General Information
Hudon (1999) considered Western Tanagers as medium-distance complete migrants suggesting that all populations migrate to some extent. In southern part of breeding range, they also move altitudinally before and after migration. Most migration occurs at night and probably at high altitudes (Hudon 1999). Western Tanagers usually migrate alone or in pairs, though they may form groups of up to 30 individuals (Isler and Isler 1987).
2. Time of Occurrence and Seasonal Movements
a. Spring migration period and routes:BREEDING
First migrants appear in southern California in mid-April with most birds moving through by third-week of May, although small numbers continue to migrate through until mid-June. Peak migration in southern and central California occurs about second week of May (Hudon 1999). Western Tanagers migrate throughout California during spring migration including southeastern desert regions.b. Arrival date on breeding grounds:
Earliest birds may arrive on breeding grounds in mid-April and most birds have arrived by early May (Small 1994). Females and first-year males arrive at breeding grounds later on average (Hudon 1999).c. Departure date from breeding grounds:
Western Tanagers may leave their breeding grounds as early as mid-July, but typically not until mid-August (Small 1994).d. Fall migration period and routes:
First birds observed in lowlands (non-breeding areas) in mid-July. Migration peaks in southern California late-August to late September, with fewer birds moving through until early November. In southern California, migration is focused in the coastal areas including the offshore islands.e. Habitat use:
During spring migration in California, Western Tanagers use lowland woodlands and forests throughout the state including desert oases. During fall, fewer birds use oases (Small 1994). Throughout its range, they also use scrub habitats, orchards, parks, and gardens (Hudon 1999).
1. Nest type
Western Tanagers construct a circular, open, flat bowl-like nest with a small cavity for the eggs. It typically consists of small twigs and grasses and lined with soft material such as moss, pine needles, or animal hair (Hudon 1999).
2. Displays
Male establishes and defends a territory from conspecifics by singing and chasing away intruders. Pair bond may form on wintering grounds or during migration. No elaborate courtship displays. Male follows female during nest building and egg-laying periods, suggesting mate-guarding. Wit-like notes are given regularly between male and female when together. Male will often feed female during nest-building and egg-laying stages. Female will flutter her wings toward male prior to being fed. When ready to copulate, female will crouch and flutter her wings, and male will spread his tail and mount female (personal observations, Hudon 1999).
3. Mating System
Western Tanagers appear to maintain a monogamous mating system. However, males often move outside their defended territory (31% of telemetry locations were outside spot-map territory, n = 571 locations, 8 birds) and will move into other male’s territories. This behavior creates the potential for extra-pair copulations (Davis 1999).
4. Average Territory Size
No territory information specific to California. In mixed-conifer forests of west-central Idaho, defended territory (as delineated by spot-mapping) averaged 0.59-1.01 ha and home range (as determined by radio-telemetry) averaged 3.91 ha (n = 8; Davis 1999). In northwest Montana, average home range averaged 2.83 ha and core area of home range averaged 0.81 ha (n = 8;Samuel et al. 1985).
5. Typical Breeding Densities
Breeding densities in Sierra Nevada forests per 40 ha reported as: 13 individuals in open canopy mixed conifer, 7 individuals in closed canopy mixed conifer, 22 individuals in open canopy red fir, and 10 individuals in closed canopy red fir (Beedy 1981). The highest density throughout its entire range as determined by Breeding Bird Survey (BBS) was reported in Sierra Nevada, 21.7 birds/route. In the California foothills the relative abundance was 4.58 birds/route and throughout California the average abundance was 6.57 birds/route.
6. Age of Breeding Birds
Individuals can breed during first full summer, but only do so occasionally (Hudon 1999).
7. Clutch Size
No data from California, however, clutch size is typically 3-5 eggs (Hudon 1999).
8. Incubating Sex
Only females incubate the eggs and brood the young (Hudon 1999).
9. Incubation Period
Incubation lasts approximately 13 days from laying of last egg to hatching of first egg (Hudon 1999). Female leaves nest approximately once every hour to feed, although male feeds her occasionally.
10. Nestling period
Period from hatching of first egg to fledging of last young is approximately 11.3 days (Hudon 1999).
11. Development at Hatching
Young are altricial and downy at hatching. Their limp head, back, and wings are covered in white/gray down and their eyes are closed (Hudon 1999).
12. Number of Broods
Usually only one brood produced, however there was evidence of a second brood being produced after one pair raised a brood to fledging in Idaho (Evans et al. 1998). They will replace broods lost to predation even at a late stage.
13. Who Tends the Young
Both parents feed the young, and female will brood the young up to 3 days before fledging (Hudon 1999).
Post fledging biology of offspring:
Parents continue to feed fledglings for at least two weeks after leaving
nest, and possibly longer. Young are mobile but tend to remain relatively
sedentary. They often stay on the breeding grounds longer than adults (Hudon
1999). Western Tanagers will form loose associations with other species
of birds (Hudon 1999; also see Associated Species, below).
BREEDING HABITAT AND NEST SITE CHARACTERISTICS
1. Overview of breeding habitat
Western Tanagers breed in coniferous forests, mixed-coniferous-deciduous woodlands, riparian woodlands, aspen forests, and oak woodlands. They prefer open, stands with at least some mature trees but will extend into dense forests.
2. Nest Site
a. Substrate:3. Vegetation Surrounding the Nest
No specific data for California, but seems to prefer conifers. Nests noted in Douglas fir, pinon pine, ponderosa pine, white fir (Abies concolor), grand fir (Abies grandis), western hemlock (Tsuga heterophylla), western red cedar (Thuja plicata), lodgepole pine, western larch (Larix occidentalis), spruce, trembling aspen, willow (Salix sp.), red alder (Alnus rubra), and Oregon white oak (Quercus garryana). If placed in conifer, the nest is situated near end of branch among smaller branchlets. When placed in deciduous trees, location is more variable, from close to trunk to end of branches (Hudon 1999).b. Height of nest:
No specific data for California. Mean nest height as measured in: mixed-conifer forest of Idaho equals 13.9 m (range 1.3-32.3 m; n = 85; Evans et al. 1998), central Alberta equals 9.3 m (range: 6.3-12.8 m; n=7; Hudon 1999), pinon-juniper woodland of northeast New Mexico equals 5.4 m (n = 49), Douglas fir forest in northeast New Mexico equals 4.93 m (range 1.4-6.9 m; n = 7), and the range in British Columbia equals 2.4-23 m (n = 43; Hudon 1999). Nest is usually placed in middle to upper canopy (Grinnell and Miller 1944).c. Height of plant:
No specific data for California. Mean height of nest tree as measured in: mixed-conifer forest of Idaho equals 27.7 m (range 11-50 m; n = 85; Evans et al. 1998), pinon-juniper woodland in northeast New Mexico equals 7.4 m (n = 49), and Douglas fir forest in northeast New Mexico equals 15.1 m (range 10.2-20.4; n = 7; Hudon 1999).d. Nest concealment:
No specific data for California. In mixed-conifer forests of Idaho, average nest concealment, based on visibility from 5 m away in each of four cardinal directions, equals 2.07 (n = 28) on scale where 1 equals some indication of presence, 2 equals < 50% of nest visible, and 3 equals > 50% of nest visible (Evans et al. 1999). This measure did not differ significantly between successful nests (n = 14) and failed nests (n = 14). In pinon-juniper woodland of northeast New Mexico, mean overhead nest concealment (percentage of nest not visible from 25 cm directly above nest) equals 46.8%, mean side nest concealment (mean of four measurements of % nest visible from 25 cm to side of nest) equals 54.2% (n = 41).
a. Canopy cover:4. Landscape Factors
No data specific to California. More open stands appear to be preferred, including along edges of stands (Hudon 1999). However, canopy cover, as measured by a densiometer within an 11.3 m plot, was significantly greater in plots centered on a nest (mean = 81.23%; n = 84) than in randomly placed plots (mean = 73.88%; n = 87) in mixed-conifer forests of Idaho (Evans et al. 1998), suggesting they may be selecting for more cover within relatively open stands. The percentage of canopy cover from two sites in Arizona and one in New Mexico was 66.6% (n = 21; Shy 1984).b. Dominant plant species in canopy:
Small (1994) reports they occur in mixed-coniferous forests of Jeffrey pine and fir on drier slopes of higher ranges and common in large pinon pines, aspen, and mountain mahogany. Grinnell and Miller (1944) state that they inhabit open coniferous forest and are less common in dense live oak or pinon woodland. In true fir forests of the Sierra Nevada, Western Tanagers had higher densities in stands dominated by white fir than red fir (Hejl et al. 1988). In other states, Western Tanagers have been associated with stands dominated by: Douglas fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), lodgepole pine (Pinus contorta), pinon pine (Pinus sp.), juniper (Juniperus sp.), spruce (Picea sp.), true fir (Abies sp.), and oaks (Quercus sp.) (Hudon 1999).c. Average shrub cover:
No data specific to California. In northeast New Mexico, the mean number of shrubs within a 5-m-radius circle centered on the nest was 57.6 (n = 49). In mixed-conifer forests of west-central Idaho, vegetation plots in Western Tanager territories had a mean shrub density of 8,688 stems/ha. Mean percent cover from 0.3-1 m was 43.4% and from 1-2 m it was 26.6% (Evans et al. 1998).d. Dominant shrub species:
No data specific to California. In territories of Western Tanagers in mixed-conifer forests of Idaho, shrub diversity averaged 5.23 species/5-m radius circle and huckleberry (Vaccinium sp.) was the dominant species (Evans et al. 1998).e. Average ground cover:
No data specific to California. The percentage of ground cover from two sites in Arizona and one in New Mexico was 38.8% (n = 21; Shy 1984). In territories of Western Tanagers in mixed-conifer forests of Idaho, mean percent ground cover (cover from 0-0.3 m height in 5-m radius circle) was 66.2% (n = 47), which was not significantly different than in unoccupied areas (mean = 62.5%, n = 39). When densities were regressed on habitat variables, the number of territories increased with increased ground cover, which may be the result of tanagers using more open stands (Evans et al. 1998).f. Dominant forb species:
No information.g. Slope:
No data specific to California. In Idaho, there was a significant difference (P = 0.045) toward Western Tanager territories having less of a slope (mean = 9.1 degrees, n = 54) than in unoccupied areas (mean = 11.1 degrees, n = 51). This may be due to the fact that on steeper slopes, canopy closure is actually greater than indicated as measured on the ground (Davis 1999).h. Aspect:
No information.i. Tree DBH:
No data specific to California. In Idaho, the mean dbh of nest trees was 47 cm. There were twice as many large trees (> 38 cm dbh) in nest plots (mean = 4.32, n = 85) than found in random plots (mean = 2.06, n = 87, P < 0.001). No other dbh classes showed significant differences between nest and random plots (Evans et al. 1998).j. Snags:
Western Tanagers used only remaining live trees in burned plots of the Sierra Nevada (Bock and Lynch 1970). In Idaho, the number of snags did not differ significantly between nest plots and random plots (Evans et al. 1998).k. Distance to water:
No data specific to California. In Idaho, only 14.5% of nests were placed within 25 m of water, and the mean distance to water in vegetation plots within territories was 65.6 m.
a. Elevation:DIET
In California, found from < 100 m along coast to 3,000 m in the Sierra Nevada (Small 1994, Hudon 1999). In southern California, they breed primarily in higher mountain ranges.b. Fragmentation and Patch Size:
In Idaho, nest success was not significantly influenced by amount of forest cover, amount of edge, or patch size (within a 1-km radius circle). McGarigal and McComb (1995) observed that Western Tanagers were associated with landscapes more fragmented than the average landscape studied in the Oregon Coast range, but that fragmentation level alone did not explain this species’ abundance. Hansen et al. (1995) observed that Western Tanagers were associated with open-canopy stands with intermediate densities of overstory trees in the western Cascades of Oregon.c. Disturbance (natural or managed):
Most sources suggest that Western Tanagers are not harmed by disturbances and favor stands with openings and edge or ecotone situations including those associated with second growth after logging, lake margins, and rock bluffs. However, in mixed-conifer forests of the Sierra Nevada, densities were significantly reduced after natural fires (Bock and Lynch 1970). Also see Sensitivity to Human-induced Disturbance, below.d. Adjacent land use:
Opening of large forested areas, especially for grazing, could potentially increase the presence of Brown-headed Cowbirds and consequently, brood-parasitism rates. Also see Sensitivity to Human-induced Disturbance, below.
1. Foraging Strategy
Western Tanagers forage mostly in the canopy among larger twigs and branches, but will also forage on the ground. They also fly-catch frequently from the air (Hudon 1999). In the mixed-conifer-oak forest of the central Sierra Nevada, Western Tanagers were considered “medium to high” foragers and preferred foraging at about 5 m, while avoiding 1-3 m. They foraged equally in air (40% of observations) as in foliage (45% of observations) and had a species preference for foraging in white fir (Airola and Barrett 1985).
2. Major Food Items (by season)
During breeding season, major food items are mostly insects: wasps, ants, termites, stinkbugs, cicadas, beetles, grasshoppers, crane flies, dragonflies, caterpillars, scale insects, and sawflies. They will also eat the fruit and buds of some plants: wild cherries (Prunus spp.), elderberries (Sambucus spp.), blackberries (Rubus spp.), and serviceberries (Amelanchier spp.) (Hudon 1999). Stomach contents from specimens taken from various locations in California showed 82% insects and 18% fruit (n = 46; Beal 1907). During the winter they eat both insects and fruit (Hudon 1999).
3. Drinking
Western Tanagers drink infrequently and probably receive enough water from fruit and insects (Hudon 1999). However, Williams and Koenig (1980) noted that migrants in coastal California commonly drank water.
SPECIAL FACTORS (Factors influencing a species occurrence and viability)
1. Brood Parasitism
Brown-headed Cowbirds are known to parasitize Western Tanager nests, and rates of parasitism can be high. No data specific to California. Percentage of nests parasitized ranges from 0% in Idaho (n = 66; Evans et al. 1998) to 71.4% in pinon-juniper woodlands of northeast New Mexico (n = 56, Hudon 1999). They are known to mob cowbirds, but usually after other species have initiated this action. Cowbirds often remove tanager eggs from the nest prior to laying their own. Once the eggs are laid, Western Tanagers generally accept their presence. No parasitized nests were abandoned in New Mexico, even nests with only cowbird eggs, and they will raise cowbirds to fledging (Hudon 1999). Tanager fledging success was 22.4% in parasitized nests and 60.9% for unparasitized nests.
2. Dietary
See DIET, above.
3. Sensitivity to Human-Induced Disturbance
Studies are mixed on the effect of silvicultural practices on Western Tanagers. They may prefer old-growth forests in some areas (British Columbia, Alberta, Montana, and Idaho, see Hudon 1999), but they are not dependent on them. In a Douglas fir forest of northwest California, clear-cutting in blocks of 4-8 ha increased tanager abundance (Hagar 1960). In Montana and Idaho they were significantly more abundant in old growth stands (> 200 years) than in rotation-age (80-120 yr.) stands (Hejl and Woods 1991). However, in northeast Oregon, abundance was not significantly different between old growth and rotation age stands (Mannan and Meslow 1984). In coniferous forest of the Coast Ranges and riparian woodlands of the Cascades of Oregon, peak abundances were found in younger age classes (40-72 yr. and 25-35 yr., Hudon 1999). Finally, in Douglas fir-ponderosa pine forests of Arizona, abundance increased significantly after the removal of most trees forming the canopy (Franzreb and Ohmart 1978).
4. Pesticide Use
No information.
5. Predators
Accipiter hawks, Barred Owls, and domestic cats will prey on adult Western Tanagers (Hudon 1999). Nest predators include: Clark’s Nutcracker, Northern Pygmy-owl, Great-horned Owl, Scrub Jay, Pinyon Jay, Stellar’s Jay, black bear, and rattlesnakes (Hudon 1999). Other nest predators probably include Common Raven, American Crow, and squirrels. They will mob nest predators.
6. Exotic Species Invasion/Encroachment
No information.
7. Weather
In true fir forests of western Sierra Nevada, and at MAPS stations throughout northwest in 1993, recruitment was reduced by severe winter weather (Hudon 1999). In the Chiricahua Mountains of Arizona, a late cold snap caused the starvation and emaciation of Western Tanagers (Ligon 1968).
DEMOGRAPHICS
1. Age and Sex Ratios
No information.
2. Productivity Measures
No data specific to California. Evans et al. (1998) estimated reproductive success, using the Mayfield method, of Western Tanagers in the mixed-conifer forests of Idaho to be 35% (95% C.I. = 24-51%). There was not a significant difference in success between nests in fragmented or contiguous plots. In northeast New Mexico, unparasitized nests fledged an average of 2.44 young/nest. MAPS stations in riparian habitat of Utah estimated fledging success at 1.94 young/adult female (Hudon 1999). Also see Brood Parasitism, above.
3. Survivorship
No data specific to California. A banded male was known to have lived at least 7 years, 11 months. A male in captivity was known to have lived 15 years, 4 months. Annual adult survivorship was estimated to be 68% (95% C.I. = 34-90%, n = 100 birds) in mixed-conifer forests of Idaho (Evans et al. 1998).
ASSOCIATED SPECIES
Species that breed in open forests, especially those which inhabit the upper canopy of deciduous forests, will benefit from Western Tanager management. Airola and Barrettt (1985) grouped the Western Tanager with the Yellow-rumped Warbler and Black-headed Grosbeak in the mixed-conifer-oak forest of the Sierra Nevada because of their use of high foliage and use of a variety of foraging sites and techniques. In burned Jeffrey pine-white fir forests of the Sierra Nevada, they foraged in similar locations as Golden-crowned Kinglets (Regulus satrapa), Mountain Chickadees (Poecile gambeli), and Nashville Warblers (Vermivora ruficapilla; Bock and Lynch 1970). Species that the Western Tanager has been known to show interspecific territoriality include: Red-eyed Vireo (Vireo olivaceus), Yellow Warbler (Dendroica petechia), Eastern Phoebe (Sayornis phoebe), and Black-capped Chickadee (Poecile atricapilla) (Hudon 1999). It also joins mixed-species flocks outside of the breeding season that may include Townsend Warblers (Dendroica townsendi), Purple Finches (Carpodacus purpureus), and Mountain Chickadees (Poecile gambeli) (Hudon 1999).
POPULATION TRENDS
According to U.S. Fish and Wildlife Service’s Breeding Bird Survey (BBS) data (1966-1999), the Western Tanager is increasing in California at a rate of approximately 0.3%/year (P = 0.71, n = 126 routes). Within the Sierra Nevada, they are decreasing at a rate of –0.8%/year (P = 0.5, n = 23 routes). Throughout the entire survey region they are increasing at approximately 0.4%/year (P = 0.34, n = 588 routes) (Sauer et al. 1999).
MANAGEMENT ISSUES - Action plan summary
1. Status
Currently, the Western Tanager does not appear to be declining dramatically in either its abundance or distribution in California. However, few demographic studies have been performed on this species, especially in California. The only population modeling performed on this species using predominantly empirical data, collected in Idaho, resulted in all simulations (n = 100 simulations) crashing to extinction in 55 years or less (Evans et al. 1998).
2. Habitat Needs
Western Tanagers prefer relatively open conifer or mixed coniferous-deciduous forests. Openings or edges created naturally (e.g., lake margins, meadows, burns) or by man-made disturbance (e.g., logging, roads, prescribed fires) are favored in some areas. They may prefer old-growth forests in some regions (British Columbia, Alberta, Montana, and Idaho, see Hudon 1999), but they are not dependent on them. Studies in the southern part of their breeding range (California, Oregon, and Arizona) showed younger stands were used as often as older stands. Perhaps because of the openness of the stands, ground cover is relatively high, although shrub cover may not be particularly important.
3. Concerns
a. Brood parasitism by Brown-headed Cowbirds was high (71.4%) at one study area in northeast New Mexico. However, 37% of parasitized nests still managed to fledge at least one tanager young. Brood parasitism should always be a concern in locations that could potentially harbor large cowbird populations, especially areas with large amounts of grazing.4. Objectivesb. There is a lack of demographic data from California, especially for the southern half of the state. Information about this species in the increasingly fragmented and
developed mountains of southern and central California would be helpful to assess this species’ response to an ever increasing California human population.c. Although Western Tanagers appear not to be discouraged from using edges and artificially thinned stands, managers should be cautious in suggesting that the species will always succeed in these types of situations. Nesting success of some neotropical migrants has been shown to decrease due to increased predation and brood parasitism as the amount of edge increases.
Specific habitat needs differ from species to species, and consequently, forest management should be varied and promote natural diversity. Only one or two management prescriptions should not be applied to large expanses of habitat. The Western Tanager may not require specific management prescriptions if a mosaic of stands of different ages and compositions is provided to support the maximum diversity of birds. However, the following suggestions should be considered:
a. Management of Western Tanagers in California should focus on the species’ breeding habitat, as wintering is limited in the state and may be the result of the introduction of eucalyptus trees.REFERENCESb. As long as forest stands are not exceptionally dense (i.e., > 90% canopy cover), this species should remain within its current distribution.
c. Although highest densities occur at higher elevations within California, lowland forests are important during migration.
d. Management actions should be applied in an adaptive fashion, such that new data can be incorporated into future management decisions.
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Beedy, E.C. 1981. Bird communities and forest structure in the Sierra Nevada of California. Condor 83:97-105.
Bock, C.E. and J.F. Lynch. 1970. Breeding bird populations of burned and unburned conifer forest in the Sierra Nevada. Condor 72:182-189.
Davis, C.R. 1999. Habitat and territory use by selected neotropical migratory birds in mixed-conifer forests of west-central Idaho. M.S. Thesis, Arkansas State University. 91pp.
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Williams, P.L., and W.D. Koenig. 1980. Water dependence of birds in a temperate oak woodland. Auk 97:339-350.