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Published: January 2008
Pages: 25
The 2006 Streaked Horned Lark surveys included in this report were funded by Washington Department of Transportation and by The Nature Conservancy (See Appendix I for a summary of the sites surveyed during the 2006 field season). The research conducted in previous seasons and in Canada was funded largely by other sources (See Acknowledgments). The purpose of this report is to present our estimates of Streaked Horned Lark survival, fecundity and population growth rate and examine patterns of site fidelity. Table 1 and Figure 1 are copied in whole or in part from our manuscript that compares demographic values between the Streaked and Pallid Horned Larks and was submitted to the journal Ecology for review.
Abstract
Abstract
Estimates of population growth rate (lambda, λ = 0.61±0.10 SD) indicate that the streaked horned lark (Eremophila alpestris strigata) population is declining rapidly (40% per year). This estimate includes only vital rates from populations in the Puget lowlands, lower Columbia River and the Washington coast and does not include rates from populations in the Willamette Valley of Oregon. Estimates of immigration are not built into our estimates of lambda and as a result, the decline in absolute population size could be less than 40% per year if the population is being rescued by immigration. This rapid population decline is apparently the result of both low fecundity and low survival. The low fecundity (0.91 female fledglings/female/year) was the result of low egg hatchability, fledging success, high clutch depredation, and long intervals between initial nests that failed and re-nests. Adult survival (0.51±0.06, n =58) was also quite low, while juvenile survival (0.16±0.04, n = 88) was relatively high. We compared survival, fecundity and population growth rate between E. a. strigata and another subspecies of horned lark, the pallid horned lark (E. a. articola), located in a relatively healthy ecosystem near Smithers, B.C. Canada. Although the breeding season was more than twice as long for E. a. strigata in Washington, E. a. articola in British Columbia produced 35% more fledglings per egg laid and the net result was higher annual fecundity for E. a. articola. Adult survival was 18% higher and juvenile survival was 13% higher (without dispersal â€" see below) for E. a. articola. This contemporaneous comparison using nearly identical methods between closely related subspecies lends further support to our estimate of a declining streaked horned lark population throughout a large proportion of its geographic range. Adult survival had the greatest influence on population growth rate for E. a. strigata suggesting that conservation actions that improve adult survival are likely to have the greatest benefit to E. a. strigata. Adult E. a. strigata exhibited extremely high site fidelity (no breeding dispersal observed among regions). We observed examples of E. a. strigata natal dispersal with juveniles moving from the Puget lowlands to the Washington coast and lower Columbia River to breed. Because we did not observe examples of natal or breeding dispersal into the Puget lowlands and because this population is apparently declining and continuing to experience threats, there appears to be a high probability that E. a strigata populations will be extirpated in this region in the near future unless this trend is reversed.
Suggested citation
Pearson, S.F., A.F. Camfield, and K. Martin. 2008. Streaked Horned Lark (Eremophila alpestris strigata) fecundity, survival, population growth and site fidelity: Research progress report. Washington Department of Fish and Wildlife, Wildlife Science Division, Olympia, WA.