Bullock’s Oriole (Icterus bullockii)
NMPIF level: Species Conservation Concern, Level 2 (SC2)
NMPIF assessment score: 15
NM stewardship responsibility: Low-Moderate
National PIF status: No special status
New Mexico BCRs: 16, 18, 34, 35
Primary breeding habitat(s): Middle-elevation Riparian, Southwest Riparian
Other habitats used: Chihuahuan Desert Shrub, Agricultural, Urban
Summary of Concern
Bullock’s Oriole is a widespread and common species associated with mature riparian habitat. It has shown moderate but statistically significant populations declines in New Mexico and across the western portion of its range, and so bears monitoring.
Associated Species
Yellow-billed Cuckoo (BC1), Mourning Dove, Black-chinned Hummingbird (SC2), Southwestern Willow Flycatcher (SC1), Bell’s Vireo (SC1), Summer Tanager (BC2), Black-headed Grosbeak, Blue Grosbeak, Lesser Goldfinch
Distribution
In the breeding season, Bullock’s Oriole is widely distributed across almost the entire western half of the United States, and portions of southern Canada and northern Mexico. It interbreeds with Baltimore Oriole in the Great Plains region. The species winters along the Pacific slope and southern interior portions of Mexico south to Central America (Rising and Williams 1999).
In New Mexico, Bullock’s Oriole is a fairly common summer resident in lowland areas statewide (Parmeter et al. 2002).
Ecology and Habitat Requirements
Bullock’s Oriole is a characteristic species of riparian woodland areas dominated by cottonwoods, willows or sycamores. In the southwest United States, it is most common in areas with mature cottonwoods, intermixed with willows. It may also use habitat dominated by mature mesquite or salt cedar (Phillips et al. 1964, Rosenberg et al. 1981, Rising and Williams 1999).
This species is present in the state from mid-April to September or later. Suspended nests are placed in isolated trees, often at the edges of woodlands, along watercourses, in shelterbelts, or in urban parks. Typical clutch size is 4-5 (Rising and Williams 1999).
Conservation Status
Species Assessment
|
DISTRIBUTION |
4 |
|
THREATS |
2 |
|
GLOBAL POPULATION SIZE |
3 |
|
LOCAL POPULATION TREND |
4 |
|
IMPORTANCE OF NEW MEXICO TO BREEDING |
2 |
|
COMBINED SCORE |
15 |
Bullock’s Oriole is a Species Conservation Concern, Level 2 species for New Mexico, with a total assessment score of 15. Its highest vulnerability score is a 4, assigned by PIF for its relatively small winter range and by NMPIF for a negative local population trend.
Population Size
Total population for the state is unknown. PIF estimates a species population of 3,800,000, and that in summer, New Mexico holds about 7% of the species population, or about 260,000 birds.
Population Trend
Bullock’s Oriole is widespread and common, but has shown significant long-term declines in the western and southern portions of its range. Since 1966, declines have been sharpest in New Mexico and Oklahoma; however since 1980, BBS data indicate a more stable New Mexico population. BBS data for 1966-2004 are:
|
|
Annual Trend (%) |
P-value |
Number of Routes |
|
New Mexico |
-2.0 |
0.40 |
54 |
|
FWS Region 2 |
-1.2 |
0.20 |
179 |
|
Western States |
-1.0 |
0.02 |
544 |
Threats
Causes of declines in this species are unknown. Bullock’s Oriole nests are frequently parasitized by Brown-headed Cowbirds, and the oriole populations may be negatively affected by human activities that result in cowbird increases. Bullock’s Oriole is largely dependent on riparian habitat, and so is vulnerable to factors such as ground and surface water depletions that may reduce the extent or quality of riparian areas.
Management Issues and Recommendations
No special management efforts are needed for Bullock’s Orioles at this time, apart from overall efforts to maintain the health and integrity of riparian areas. Riparian habitat should be managed to maintain high vegetation density and key structural components such as sycamores and cottonwoods. Studies to assess the impacts of Brown-headed Cowbirds are needed.
Species Conservation Objectives
NMPIF Objectives
Sources of Information
Parmeter, J., B. Neville, and D. Emkalns. 2002. New Mexico Bird Finding Guide. New Mexico Ornithological Society, Albuquerque, NM.
Phillips, A., J. Marshall, and G. Monson. 1964. The birds of Arizona. Univ. of Arizona Press, Tucson, AZ.
Rising, J. D., and P. L. Williams. 1999. Bullock’s Oriole (Icterus bullockii). In The Birds of North America, No. 416 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Rosenberg, K. V., R. D. Ohmart, W. C. Hunter, and B. W. Anderson. 1981. Birds of the Lower Colorado River valley. Univ. of Arizona Press, Tucson, AZ.
