The yellow warbler is a widespread species in North America, breeding as far north as the tundra regions of Canada. The yellow warbler is a medium-sized, foliage-gleaning wood warbler. It is 4.7-5.1 in (12-13 cm) long and weighs 0.3-0.4 oz (9-11 g). Its plumage is more extensively yellow than most other wood warblers, and is unique in having yellow on the inner webs of the tail feathers, except for the middle pair. The yellow warbler has indistinct wing bars. Yellow warbler males exhibit rather distinct geographic variation both within and among three taxonomic groups (aestiva, petechia, and erithachorides). The variation of female and immature yellow warblers is also wide ranging but less well known. The yellow warbler remains common in much of its range as a habitat generalist.
In California, this warbler is listed as a species of special concern.
Originally the Sonoran yellow warbler was named Dendroica petechia sonorana. According to The American Ornithologists’ Union 52nd supplement to their Checklist of North American Birds released July 2011, the yellow warbler is lumped under the Setophaga genera and is now listed as Setophaga petechia sonorana. It is one of three breeding subspecies ascribed to California, brewsteri, morcomi, and sonorana. The Sonoran yellow warbler subspecies, breeds only along the lower Colorado River in California, and from southern Arizona and southwest New Mexico to north-central Mexico and possibly the Colorado River Delta.
The Sonoran yellow warbler breed in the willow and cottonwood habitats that lined the LCR. Yellow warblers begin arriving on their breeding grounds in April. Nest building activity has been observed in mid April, and the egg laying likely begins in late April, with nestlings and fledglings by early May. Nests are typically found in the forks of cottonwoods, willows, or saltcedar from 10 to 20 ft (3-6 m) high. Yellow warblers will attempt several nests throughout the season but typically produce only one brood with a clutch size of 4 eggs. Adults have been observed feeding a fledgling into August.
The yellow warbler is a generalist species that appears to adapt its foraging to variation in local vegetation structure. Yellow warbler may eat ants, bees, wasps, caterpillars, beetles, true bugs, flies, and spiders.
Native riparian vegetation has been severely reduced from its former extent. The halting of annual flooding, increased agricultural, and urban development within historic floodplains, saltcedar invasions, fires, and the loss of much of the remaining riparian vegetation has changed the structure, plant species composition, and function of the lower Colorado River’s riparian system. The resulting major losses of willow-cottonwood riparian on the river were the initial and primary cause of yellow warbler declines. Cowbird parasitism poses a limited to moderate threat to yellow warblers. Predation accounts for the highest reason of nest failures.
Updated November 26, 2012
The Sonoran yellow warbler is a common summer resident confined almost entirely to the lower Sonoran river valleys, including the Colorado River Valley from Ft. Mohave to Yuma, Arizona. It was formerly common along major rivers, like the Rio Grande and lower Colorado Rivers. Since the 1930s, populations in California have declined throughout state along with the loss of breeding habitat, with steeper declines since the 1950s. It was reported that the Sonoran yellow warbler bred “commonly” at the Bill Williams River and Topock Marsh in 1952 but had disappeared from these historic nesting sites after 1955, and was considered extirpated from the valley by 1960. Since the 1960s, the Sonoran yellow warbler has been extirpated as a breeder from Texas north of 29°N, most likely due to the loss of riparian habitat.
The current range of the Sonoran yellow warbler includes the southwestern portion of the United States into northern Mexico. Sonoran yellow warbler populations have fluctuated since their period of high abundance in the early 1900s. Despite population changes and local extirpations, the overall range of the Sonoran yellow warbler today has changed little since 1944. When considering historical cottonwood willow habitat on the LCR prior to the 1900s, Sonoran yellow warbler numbers are likely far below historical population levels.
Click on the map below to see the distribution range of the Sonoran yellow warbler using the interactive GIS map.
In general, yellow warblers are closely associated with moisture-loving deciduous trees throughout much of their extensive North American range. In the arid West, they primarily use cottonwood and willow dominated riparian areas. Yellow warblers use Fremont cottonwood and willow species, with a dense understory of seep willow, mesquite, and tamarisk. Yellow warblers make use of saltcedar and Athel tamarisk as both a nest substrate plant and as nesting habitat along the Colorado River in Grand Canyon and upper Lake Mead, where they have been identified as habitat generalists. Wintering warblers appear most common in planted trees around trailer parks.
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 sonoran yellow warbler. Click on the arrows to expand the table.
|YWAR1—Create 4,050 acres of Sonoran yellow warbler habitat|
Of the 5,940 acres of created cottonwood-willow, at least 4,050 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. The created habitat will be established in patches as large as possible. At a minimum, however, all of the habitat will be created in patches of at least 10 acres, thus, based on the best available information, will meet the minimum habitat patch size requirements of the species. Created riparian forests will support breeding and migration habitats for yellow warblers that migrate along the LCR. In addition, the per-acre quality of created habitat for this species will be substantially greater than that of the affected habitat. Along the LCR, this species formerly nested in cottonwood-willow habitat ranging from gallery forests to early successional stage scrublands. 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 be created to the greatest extent practicable in patch sizes optimal for supporting the species. Created habitat, thus, will approximate the condition of the native habitat of the species that was historically present along the LCR. 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).
|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.
The following list includes different research and monitoring activities for birds. Click on the link for more information.
General Riparian Birds
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