Species Biological Report for the Streaked Horned Lark (Eremophila alpestris strigata) Version 1.0 Female streaked horned lark at Joint Base Lewis-McChord. Photo: Adrian Wolf, Center for Natural Lands Management February 2019 U.S. Fish and Wildlife Service Pacific Region Portland, Oregon Executive Summary The streaked horned lark, a small songbird endemic to the Pacific Northwest, was listed as a threatened species in 2013; critical habitat was designated on the outer coast of Washington, islands in the lower Columbia River and on three units of the U.S. Fish and Wildlife Service’s (Service) Willamette Valley National Wildlife Refuge Complex in Oregon. This Species Biological Report provides an overview of our current understanding of the biology and natural history of the streaked horned lark and assesses its current viability through the framework of resiliency, redundancy, and representation. The streaked horned lark historically occurred on the native prairies, river floodplains, and ocean shores west of the Cascade Range from southern British Columbia, Canada, south through the Puget lowlands and outer coast of Washington, along the lower Columbia River, throughout the Willamette Valley, on the Oregon coast, and into the Umpqua and Rogue Valleys of southwestern Oregon. Its range has contracted, and it is now found only at scattered sites in the south Puget lowlands, the outer coast of Washington, the lower Columbia River, and the Willamette Valley in Oregon. The streaked horned lark has been extirpated from British Columbia, the Oregon coast, and the Rogue and Umpqua Valleys of Oregon. Streaked horned larks are birds of wide open spaces. Habitat used by larks is generally flat with substantial areas of bare ground and sparse low-stature vegetation. Streaked horned larks historically selected habitat in relatively flat, open areas maintained by natural processes of flooding, fire, and sediment transport dynamics. The interruption of these natural processes due to flood control dams, fire, suppression, and reduction of sediment transport by dams has resulted in a steep decline in the extent of suitable habitat for the lark. The current threats to the streaked horned lark include loss of habitat and natural disturbance processes; incompatible habitat management; the adverse effects of military training, aircraft operation, and agricultural activities; small population issues and potential inbreeding depression; predation pressure on small populations; male-skewed sex ratio at some sites; avian pox in the south Puget lowlands; and possible poisoning caused by rodenticides used in agricultural fields. Conservation measures to benefit the lark have also been implemented at a number of sites throughout the lark’s range. The most recent rangewide population estimate for streaked horned larks is likely fewer than 1,600 individuals. We divide the lark’s current range into three regions: the south Puget lowlands, the Washington coast and Columbia River, and the Willamette Valley. Our assessment of the current threats and conservation actions in each of these region shows that the streaked horned lark has numerous local populations that are distributed across the south Puget lowlands, the Washington coast and Columbia River, and the Willamette Valley. However, most local populations are small, and some are declining and at risk of disappearing. In recovery planning, the Service uses the conservation principles of resiliency, redundancy, and representation to inform our approach to assessing viable populations of threatened and endangered species. Viability is gauged by the ability to withstand disturbances of varying magnitude and duration (resiliency), the ability to withstand catastrophic population and species- ii level events (redundancy), and the ability to adapt to changing environmental conditions (representation). The viability of a species is also dependent on the influence of new or continued stressors now and in the future that act to reduce the species’ redundancy, representation, and resiliency. After assessing the current status of the streaked horned lark, threats, and conservation measures, we conclude that the species current viability is characterized by low to moderate levels of resiliency, redundancy, and representation. A note on terminology: The term population is generally accepted to mean a group of potentially interbreeding individuals within a defined area. Although streaked horned larks spread out across their current range in the breeding season, most of the members of the subspecies congregate in the winter, either in the Willamette Valley or on the islands in the lower Columbia River. It is possible then, that all streaked horned larks across the range have the potential to interact with each other. Given this fact, we will use the term “population” in three specific contexts in this document: • When discussing all individuals in the subspecies across the current range, we will use the term “rangewide population.” • When referring to the larks that breed in any of the distinct regions within its range, we will refer to the “regional population.” • Within each region, there are numerous breeding sites or areas of habitat to which individuals return each year during the breeding season. We will refer to these breeding site aggregations as “local populations.” iii Contents Introduction ................................................................................................................................................... 1 Species Information ...................................................................................................................................... 2 Legal Status ............................................................................................................................................... 2 Description and Taxonomy ....................................................................................................................... 2 Life History ............................................................................................................................................... 3 Habitat Characteristics .............................................................................................................................. 5 Historical and Current Population Status and Trends ............................................................................... 6 Historical Status .................................................................................................................................... 6 Current Status ........................................................................................................................................ 9 Regional and Rangewide Population Trends ...................................................................................... 14 Influences on Viability ................................................................................................................................ 15 Habitat-related Threats ............................................................................................................................ 15 Loss of Natural Ecological Disturbance Processes ............................................................................. 15 Successional Changes in Grassland Habitats and Encroachment of Woody Vegetation .................... 16 Spread of Invasive Beach Grasses ...................................................................................................... 17 Loss of Habitat to Agricultural, Industrial and Urban Development .................................................. 17 Incompatible Management Activities at Occupied Sites .................................................................... 18 Transient Agricultural Habitat ............................................................................................................ 21 Small Population Issues .......................................................................................................................... 22 Small Rangewide Population .............................................................................................................. 22 Low Genetic Diversity, Small and Isolated Populations, and Low Reproductive Success ................ 23 Male-skewed Sex Ratio ...................................................................................................................... 24 Disease .................................................................................................................................................... 24 Predation ................................................................................................................................................. 25 Stochastic Weather Events ...................................................................................................................... 26 Aircraft Strikes at Military and Civilian Airports ................................................................................... 26 Recreation ............................................................................................................................................... 27 Pesticide Poisoning ................................................................................................................................. 27 Climate Change ....................................................................................................................................... 28 Summary ................................................................................................................................................