Streaked Horned Lark Occupancy and Abundance Protocols

The streaked horned lark (Eremophila alpestris strigata) is listed as threatened under the Federal Endangered Species Act (USFWS 2013) and as endangered by the State of Washington, yet no standardized range-wide survey protocol or monitoring strategy exists. Assessing population distribution, abundance and trends is critical for making informed management decisions and to understand relationships between animal populations and environmental conditions. Such information is used to describe changes in the size of rare or declining populations, identify mechanisms for population changes, assess changes in ecological conditions, and evaluate the effectiveness of conservation actions (e.g., progress towards recovery).

To gain a better understanding of lark distribution and abundance, we advocate a hierarchical approach (see Olson and Pearson 2014). This hierarchical approach consists of three components:

  1. A probability of occurrence map that determines the sampling frame where one should look for and count larks. This map would preferably be range-wide (or regional) in scale and portray the species probability of occurrence based on habitat suitability and current distribution. This is a landscape-scale assessment. The extent of the map may be defined by political, geographical, and/or biological boundaries.
  2. A statistically-based sampling plan (or set of plans) to monitor population trends within occupied sites (a temporal assessment that may be conducted at the site or landscape scale). Trends may be based on abundance or occurrence as appropriate.
  3. Survey protocols for determining site occupancy status within suitable habitat – site scale assessment. Once the best places to look for the species have been identified, these protocols help determine how to search in a manner that is likely to detect the species if it is present.


The first step in this process is to develop a landscape-scale map that would quantitatively or qualitatively express the probability of lark occurrence within the defined map extent based on factors determined to affect occupancy. This map would then be used to concentrate survey, management, conservation, and other efforts in areas where occurrence probability is moderate to high, while also enabling such efforts to be reduced or eliminated in areas of low probability of occurrence. This results in a much more efficient and for a statistically based sampling approach. The second step is to develop species-specific survey protocols to determine site occupancy status using methods that take into account the uncertainty associated with detecting the presence of animals. The final step is to develop a strategy for assessing species abundance and trends within occupied sites.

We organize this document as follows:

  1. Recommendations on developing a probability of occurrence map and, in the absence of such a map, a potential interim sampling framework approach. These recommendations allow us to move forward with surveys even though the occurrence map has not been built.
  2. Lark breeding phenology and detectability information needed to develop occupancy and survey protocols.
  3. Sampling strategy for assessing breeding season lark abundance and trend at sites with public access and recommendations for potential road–side surveys for sites without public access.
  4. Field protocols for assessing a site’s occupancy status by breeding larks.