Arizona Bell's Vireo
(Vireo bellii arizonae)
- DESCRIPTION
- DISTRIBUTION
- HABITAT
- CONSERVATION
- MULTIMEDIA
General Description
The Arizona Bell’s vireo (Vireo bellii arizonae) is a small vireo, with a length of 4.5-4.9 in (115-125 mm) and a weight of 0.2-0.4 oz (7-10 g). This vireo has short, rounded wings, which makes the tail look long. The bill is short, straight, and slightly compressed at the base. Male and female Bell’s vireos are the same in plumage color throughout the year. This plumage color varies from generally drab gray to green above, white to yellow below, with an unstreaked breast. The Bell’s vireo has a faint white eye ring. There are two pale wing bars, with the lower bar more prominent. The plumage of juveniles resembles that of adults in worn summer plumage—essentially white and gray, but whiter below with more distinct wing bars.
Legal Status
The subspecies Arizona Bell’s vireo (Vireo bellii arizonae) was proposed for federal listing in 1981 as endangered because of dramatic population declines. The petition failed because significant populations of the subspecies existed in Arizona and New Mexico. California listed the subspecies as endangered in 1988.
Taxonomy
The Arizona Bell’s vireo is a subspecies of vireo within the Vireonidae family. There are 38 species of vireo’s, 12 of which are reported in North America, and 25 subspecies.
Reproduction
The Arizona Bell’s vireo is a summer resident that generally breeds between late March and late September. The Arizona Bell's vireo is a typical breeder of the streamside fringes of willows and mesquite along the lower Colorado River. Nest construction usually lasts 4 to 5 days and is done by the female. The nest is usually placed less than 5 ft (1.5 m) above the ground, with 3.3 ft (1 m) being the average height. A typical vireo nest is a basket not too firmly attached to twigs and made of various fibers such as split large grasses, and mixed with strips of soft inner bark, fine grasses, willow fluff, plant down, spider nests, and considerable cattle hair, all firmly bound together. The lining typically is constructed of the very finest grass tops and a little cattle hair. Three or four eggs usually are laid and both parents share in incubation, which lasts about 14 days. Egg laying typically begins in early April. Nesting occurs through the summer. Both parents participate in the care of the young, feeding them mostly smooth caterpillars. Although normally timid, shy, and retiring, both parents are aggressive defenders of eggs and young. Two broods generally are raised each season. Juveniles undergo a partial post-juvenile molt in July and August.
Diet
The Arizona Bell’s vireo is a summer visiting insectivore on the LCR. It is described as almost entirely insectivorous, and food items predominantly include various bugs, caterpillars, beetles, and grasshoppers. Other summer diet items include adult moths and butterflies and their eggs, ladybird beetles, weevils, leaf beetles, bees and wasps, spiders, snails, and occasionally, wild fruit.
Threats
The near elimination of the Arizona Bell’s vireo as a common breeding resident on the LCR has been attributed to a combination of loss of preferred willow habitats and increased pressure from parasitism by brown-headed cowbirds concurrent with agricultural development. The Arizona Bell’s vireo is a frequent host to brown-headed cowbirds on the LCR. A female cowbird lays an egg in the nest of an absent vireo, usually removing one of the owner’s eggs if any are present, and then leaves, expecting the host to incubate and hatch the egg and raise the nesting. This results in a reduction of nest success for the host bird. Usually the cowbird nestling is much larger than the host’s own nestlings, and the cowbird nestling simply out-competes them. However, early Bell’s vireo nests often escape parasitism if initiated well in advance of the onset of cowbird egg-laying in mid- to late April.
More Information
Additional information on this species, as well as source documentation, can be found in the species accounts located at this link (PDF). The Conceptual Ecological Model (CEM) can be found here (PDF). Technical Reports on this species can be found here.
Updated December 30, 2016
The Arizona Bell’s vireo, until the 1950s, was quite abundant and much more widespread. By the early 1960s, it was reported to be scarce everywhere along the lower Colorado River (LCR), and by 1980, it was estimated that no more than 50 pairs of vireos nested on the both sides of the LCR, south of Davis Dam. Presently, the Bell’s vireo is widespread in the central and southwestern United States and northern Mexico. There currently are several distinct remnant populations of Arizona Bell’s vireos along the LCR. A remnant population of Arizona Bell’s vireo also persists on the Bill Williams River National Wildlife Refuge.
The image below shows the distribution range of the Arizona Bell's vireo.
The Arizona Bell’s vireo inhabits lowland riparian areas, containing willows and mesquite. Arizona Bell’s vireos can also utilize a mixed plant community of honey mesquite and saltcedar. Honey mesquite-saltcedar mixed stands represent the Arizona Bell’s vireos most important habitat outside of the remaining willow habitats of the Bill Williams River National Wildlife Refuge and Needles, California. Honey mesquite offering accessible foraging sites for the Arizona Bell’s vireo along with a well-developed, patchy canopy layer, and saltcedar provides a dense understory.
LCR MSCP Conservation Measures
The Habitat Conservation Plan provides conservation measures specific to each species. Listed below are the species specific conservation measures for the Arizona Bell's vireo. Click on the arrows to expand the table.
| BEVI1—Create 2,983 acres of Arizona Bell's vireo habitat |
Of the 7,260 acres of created cottonwood-willow and honey mesquite, at least 2,983 acres will be designed and created to provide habitat for this species. Patches of created habitat will be designed and managed to support cottonwood-willow types I-IV and honey mesquite type III that provide habitat for this species. The created habitat will be established in patches as large as possible. In addition to the spatial replacement of affected habitat, the quality of created habitat will be substantially greater than affected habitats. Patches of existing cottonwood-willow in the LCR MSCP planning area typically include dense stands of saltcedar that support little vegetative diversity relative to the cottonwood-willow land cover that will be created as habitat. Created habitat will be dominated by native riparian trees (i.e., cottonwood and willow trees), support a tree structure corresponding to structural types I–IV, support a diversity of plant species, and will be created to the greatest extent practicable in patch sizes optimal for supporting the species. The design and management criteria described in the conservation measures for the southwestern willow flycatcher (Section 5.7.2 in the HCP) and yellow-billed cuckoo (Section 5.7.14 in the HCP) will ensure that created cottonwood-willow stands in structural types I-IV will also provide other habitat requirements for this species (e.g., habitat patch size, food requirements). In particular, the management of moist surface soil, slow-moving water, or ponded water conditions and greater diversity of seral stages of cottonwood-willow described in the conservation measures for the southwestern willow flycatcher habitat will also provide these habitat requirements for this species. Created habitat, thus, will approximate the condition of the native habitat of the species that was historically present along the LCR. |
| MRM1—Conduct surveys and research to better identify covered and evaluation species habitat requirements |
Conduct surveys and research, as appropriate, to collect information necessary to better define the species habitat requirements and to design and manage fully functioning created covered and evaluation species habitats. This conservation measure applies to those species for which comparable measures are not subsumed under species-specific conservation measures (Section 5.7 in the HCP). They are not applicable to species for which habitat would not be created under the LCR MSCP Conservation Plan, such as the desert tortoise, relict leopard frog, humpback chub, and threecorner milkvetch. |
| MRM2—Monitor and adaptively manage created covered and evaluation species habitats |
Created species habitats will be managed to maintain their functions as species habitat over the term of the LCR MSCP. Created habitat will be monitored and adaptively managed over time to determine the types and frequency of management activities that may be required to maintain created cottonwood-willow, honey mesquite, marsh, and backwater land cover as habitat for covered species. This conservation measure applies to those species for which comparable measures are not subsumed under species-specific conservation measures (Section 5.7 in the HCP). They are not applicable to species for which habitat would not be created under the LCR MSCP Conservation Plan, such as the desert tortoise, relict leopard frog, humpback chub, and threecorner milkvetch. |
| MRM4—Conduct research to determine and address the effects of brown-headed cowbird nest parasitism on reproduction of covered species |
Research will be undertaken to determine whether brown-headed cowbird nest parasitism is a substantial factor limiting the reproductive success of the southwestern willow flycatcher, vermilion flycatcher, Arizona Bell's vireo, Sonoran yellow warbler, and summer tanager in the LCR MSCP planning area. If so, studies will be implemented to identify effective and practical methods for controlling brown-headed cowbirds. If cowbirds are adversely affecting breeding success and effective control measures are developed, a program will be implemented to monitor the effects of cowbirds on nesting success in LCR MSCP–created habitats to determine the need for cowbird control and to implement cowbird control measures in locations where cowbird control is needed to improve reproductive success. |
| CMM1—Reduce risk of loss of created habitat to wildfire |
Management of LCR MSCP conservation areas will include contributing to and integrating with local, state, and Federal agency fire management plans. Conservation areas will be designed to contain wildfire and facilitate rapid response to suppress fires (e.g., fire management plans will be an element of each conservation area management plan). |
| CMM2—Replace created habitat affected by wildfire |
In the event of created-habitat degradation or loss as a result of wildfire, land management and habitat creation measures to support the reestablishment of native vegetation will be identified and implemented. |
| AMM1—To the extent practicable, avoid and minimize impacts of implementing the LCR MSCP on existing covered species habitats |
To the extent practicable, establishment and management of LCR MSCP–created habitats will avoid removal of existing cottonwood-willow stands, honey mesquite bosques, marsh, and backwaters to avoid and minimize impacts on habitat they provide for covered species. Temporary disturbance of covered species habitats, however, may be associated with habitat creation and subsequent maintenance activities (e.g., controlled burning in marshes and removal of trees to maintain succession objectives). LCR MSCP conservation measures that could result in such temporary disturbances will, to the extent practicable, be designed and implemented to avoid or minimize the potential for disturbance. In addition to implementing AMM3 and AMM4 below, these measures could include conducting preconstruction surveys to determine if covered species are present and, if present, implementing habitat establishment and management activities during periods when the species would be least sensitive to those activities; or redesigning the activities to avoid the need to disturb sensitive habitat use areas; staging construction activities away from sensitive habitat use areas; and implementing BMPs to control erosion when implementing ground disturbing activities. |
| AMM2—Avoid impacts of flow-related covered activities on covered species habitats at Topock Marsh |
Impacts on groundwater levels that support covered species habitat at Topock Marsh will be avoided by maintaining water deliveries for maintenance of water levels and existing conditions. At times, flow-related activities could lower river elevations to levels that could disrupt diversion of water from the river to the marsh. Improvements to intake structures that allow water to continue to be diverted or other measures to maintain the water surface elevation will avoid effects on groundwater elevation. Avoidance of effects could be accomplished with the purchase, installation, and operation of two electric pumps sized to the current inflow at the Topock Marsh diversion inlet. The pumps would most likely need to be operated during summer to make up for the lower flow periods. Implementation of this conservation measure would maintain existing habitat at Topock Marsh for the Yuma clapper rail, southwestern willow flycatcher, Colorado River cotton rat, western least bittern, California black rail, yellow-billed cuckoo, gilded flicker, vermilion flycatcher, Arizona Bell's vireo, and Sonoran yellow warbler. The extent of covered species habitat impacts that will be avoided by maintaining water deliveries to Topock Marsh are presented in Table 4-2 in the HCP. Maintaining water deliveries to Topock Marsh will also maintain razorback sucker and bonytail habitat associated with disconnected backwaters managed for these species. |
| AMM3—To the extent practicable, avoid and minimize disturbance of covered bird species during the breeding season |
To the extent practicable, to avoid and minimize potential impacts on covered bird species, vegetation management activities (e.g., periodic removal of emergent vegetation to maintain canals and drains) associated with implementation of covered activities and the LCR MSCP that could result in disturbance to covered bird species will not be implemented during the breeding season to prevent injury or mortality of eggs and young birds unable to avoid these activities. Table 5-9 in the HCP describes the breeding period for each of the covered species during which, to the extent practicable, vegetation management activities in each species' habitat will be avoided. |
| AMM5—Avoid impacts of operation, maintenance, and replacement of hydroelectric generation and transmission facilities on covered species in the LCR MSCP planning area |
To the extent practicable, before implementing activities associated with OM&R of hydroelectric generation and transmission facilities, measures will be identified and implemented that are necessary to avoid take of covered species where such activities could otherwise result in take. These measures could include conducting surveys to determine if covered species are present and, if so, deferring the implementation of activities to avoid disturbance during the breeding season; redesigning the activities to avoid the need to disturb covered species habitat use areas; staging of equipment outside of covered species habitats; delineating the limits of vegetation control activities to ensure that only the vegetation that needs to be removed to maintain infrastructure is removed; stockpiling and disposing of removed vegetation in a manner that minimizes the risk of fire; and implementing BMPs to control erosion when implementing ground disturbing activities. |
| AMM6—Avoid or minimize impacts on covered species habitats during dredging, bank stabilization activities and other river management activities |
To the extent practicable, before initiating activities involved with river maintenance projects, measures will be identified and implemented that avoid or minimize take of covered species where such activities could otherwise result in take. Such measures could include alternative methods to achieve project goals, timing of activities, pre-activity surveys, and minimizing the area of effect, including offsite direct and indirect effects (e.g., avoiding or minimizing the need to place dredge spoil and discharge lines in covered species habitats; placing dredge spoils in a manner that will not affect covered species habitats). |
Research and Monitoring Activities
LCR MSCP conduct a variety of research and monitoring activities along the LCR encompassing both MSCP and non-MSCP species. For a complete list of all activities, please see the Research and Monitoring Activities web page.
This gallery includes photos of this species. If you require larger photos, please contact our webmaster Michelle Reilly at mreilly@usbr.gov.
