The streaked horned lark (Eremophila alpestris strigata) is a small songbird native to the Pacific Northwest region of North America. It is a subspecies of the horned lark, distinguished by the dark brown streaks on its pale yellow underparts. The streaked horned lark has experienced severe population declines in recent decades due to loss of suitable habitat. Understanding the habitat requirements of this species is key for conservation efforts.
Natural History
The streaked horned lark is a resident subspecies, meaning it does not migrate and occupies the same general region year-round. Its breeding range includes southern British Columbia, western Washington, western Oregon, and northwestern California. The current population is estimated at around 1500 individuals.
This small lark reaches lengths of 15-18 cm and weighs 23-45 grams. Its back is grayish brown with dark streaks, while the underparts are pale yellow with prominent black stripes. Dark brown stripes also occur on the head. The streaked horned lark exhibits sexual dimorphism, meaning males and females have different appearances. Males have a black mask and throat, while females have a pale yellow face and throat.
The diet consists mainly of seeds and insects. Common food sources include grass seeds, beetles, flies, leafhoppers, caterpillars, and spiders. The lark typically forages on the ground in sparsely vegetated habitats, searching for prey items in the soil and dense grasses. Nesting occurs between March and August. The nest consists of a shallow grass-lined cup constructed on the ground and concealed by surrounding vegetation. Clutch size is 2-6 eggs. Multiple broods may be raised per breeding season.
Habitat Requirements
The streaked horned lark occupies a narrow range of open habitats, including native prairies, coastal dunes, fallow agricultural fields, wetland mudflats, sandy beaches, and sparsely-vegetated edges of grassy airports. Several key habitat features are required:
Open Areas with Low-Growing Vegetation
The larks favor habitats dominated by short grasses, low-growing herbs, cryptogamic soil crusts (mosses, lichens, algae), and bare ground. These open spaces provide room for running, landing, and taking off, as well as unobstructed visibility to watch for predators. Vegetation height is ideally under 16 cm. Common associated plant species include fescues, lupines, sedges, fleabanes, and cryptantha. Too much tall, dense vegetation precludes use by larks.
Bare or Sparsely-Vegetated Ground
Bare ground or very sparse vegetation is critical for nesting and foraging. Larks frequently place nests next to or in small patches of bare ground. They also prefer the presence of gravel and disturbed, loose soils which offer improved access to insects and seeds. Hard-packed clayey soils and very thick grasses are avoided. Grassy refuge airports often provide ideal sparse vegetation and are important habitat.
Flat or Gently-Sloping Terrain
The larks favor flat plains or gentle topography with slopes less than 15 degrees. Steep slopes and dense topographic relief are unsuitable. Flat or slightly rolling terrain provides better visibility, ease of movement and flight, and appropriate conditions for nest-building. Coastal prairies, coastal dunes, wetland margins, and other flat regions are prime habitat.
Lack of Trees and Shrubs
The presence of trees and large shrubs is detrimental, as they increase predator perches and decrease visibility for the larks. Tree and shrub encroachment has reduced habitat suitability in some areas. Ideally, cover of trees and shrubs should be less than 10%. Treeless prairies, grassy dunes, agricultural fields, and shorelines offer appropriate openness.
Elevation Under 300 m
Most occupied habitat occurs at elevations below 300 m. Higher elevation sites are typically unsuitable, having deeper snowpack and denser vegetation compared to coastal and lower elevation areas. Exceptions occasionally occur, such as at the Horned Lark Breeding Area in Okanagan Valley at 850 m elevation.
Geographic Distribution
Within the breeding range, specific sites with suitable habitat are patchily distributed from southern Vancouver Island to northwest California. Here are some details on the geographic distribution of core habitat areas:
British Columbia
Only 50-100 larks remain in Canada, mostly near Victoria on southeastern Vancouver Island. They inhabit the Victoria International Airport as well as a few remnant natural habitats including Island View Beach and Royal Roads University lands.
Washington
About 200 larks occur at the Olympia Airport and surrounding prairie lands in Thurston County. Smaller populations frequent the Shelton Airport and prairies, Fort Lewis, and Gray Army Airfield. Scattered sites along the Puget Trough support a few pairs.
Oregon
Roughly 1300 larks remain in Oregon, making it the stronghold. The largest populations breed in the Willamette Valley, including Eugene Airport, Baskett Slough NWR, Ankeny NWR, William L. Finley NWR, and Corvallis Airport. Additional sites span from Astoria to Medford.
California
Only about 50-75 larks occur in California at a few sites: Eureka Municipal Airport, Crescent City Marsh, Lake Earl, and Lanphere Dunes. Habitat loss has extirpated them from central and southern coastal sites.
Habitat Threats
The small streaked horned lark population faces serious threats to its specialized habitat. Ongoing habitat degradation and destruction has caused dramatic declines over the past century. Key threats include:
Urban and Agricultural Development
Filling of wetlands, coastal prairie conversion to farms and cities, and expanding urbanization have destroyed habitat, especially in British Columbia, Washington, and California. For example, the Fraser River delta in British Columbia historically supported thousands of larks, but is now almost entirely developed.
Vegetation Encroachment
Fire suppression and reduction in grazing and mowing has allowed woody vegetation and dense grasses to overtake sites, reducing open areas. Historic prairie habitats have transitioned to unsuitable woodlands and forests.
Exotic Grasses and Shrubs
Introduced grasses like velvetgrass, invasive blackberries, and scotch broom have invaded many areas, crowding out native plants and making habitat unsuitable for larks.
Recreational Disturbance
Off-road vehicles, dogs, and human trampling damage fragile beach, dune, and prairie habitats used by larks. Nests and chicks suffer high mortality.
Weather and Climate Change
Extreme weather like severe winter floods can destroy nests and reduce reproductive success. Climate change may increase these weather impacts while also shifting vegetation communities.
Habitat Management and Conservation
Active habitat management and conservation actions are needed to protect and enhance remaining habitat areas and support streaked horned lark recovery. Some recommended actions include:
Maintain Open Habitat Structure
Conduct burning, grazing, mowing, shrub removal, herbicide application, and other practices as needed to prevent invasion of woody plants and dense exotic grasses. This helps sustain appropriate vegetation height, density, and composition.
Restrict Disturbance
Fence sensitive habitats and install signage to limit recreation impacts from vehicles, dogs, hiking, etc. Control access to beaches and stabilize dunes. Limit construction near nesting areas.
Remove Invasive Species
Manually or chemically remove exotic grasses, blackberries, broom, and other invasives. Replant with native vegetation where possible. Ongoing removal is likely needed to prevent reestablishment.
Protect Habitat from Development
Preserve prairies, coastal habitats, wetlands, and agricultural lands through land trusts, conservation easements, land acquisition, and other protection mechanisms. Manage buffers around existing habitat.
Monitor and Study Populations
Continue research on lark populations, reproduction, survival, movements, and genetics. Survey for new populations. Study habitat use and needs. These provide a basis for management.
Engage Partners and Stakeholders
Work collaboratively with agencies, airports, Native American tribes, land managers, local governments, NGOs, landowners, and others to deliver habitat projects and compatible land uses.
Conclusion
The streaked horned lark needs open prairies, coastal habitats, sparsely-vegetated fields, and similar sites that provide the required habitat features and resources. Habitat loss and degradation remain substantial threats, but targeted management and conservation actions can protect, enhance, and restore suitable habitat areas. Partnerships among land managers and stakeholders will provide the greatest long-term benefit for this rare species. Ongoing habitat conservation and population monitoring are essential for the persistence of the streaked horned lark.