Annual Survival and Breeding Dispersal of a Migratory Passerine, the Scissor-tailed Flycatcher

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Journal of Field Ornithology

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Knowledge of survival rates is critical for advancing our understanding of the dynamics ofpopulations and here we report apparent annual survival and breeding dispersal of Scissor-tailed Flycatchers (Tyrannus forficatus) breeding at two sites in southwest Oklahoma (Ft. Sill and Wichita Mountain WildlifeRefuge [WMWR]). Our Cormack-Jolly-Seber estimate of apparent adult survival for the period from 2008 to2105 was relatively low (0.514) compared to estimates for 36 other migratory and socially monogamouspasserines breeding in North America, and was independent of sex (males: N = 151; females: N = 119),breeding status (territory holder or floater), body mass, site, year, and precipitation during the year prior tobreeding. Although apparent survival did not differ between sites, dispersal (N = 66 individuals) was morecommon and breeding dispersal distance (BDD) was greater for Scissor-tailed Flycatchers at Ft. Sill whereanthropogenic disturbance was more frequent. BDD also increased with body mass at Ft. Sill (but not atWMWR) and, after accounting for it, BDD at Ft. Sill tended to be greater for birds that failed to breedsuccessfully in the past year. Older birds and males had the longest BDDs at WMWR, and males exhibited asimilar tendency at Ft. Sill. We contend that our estimate of apparent survival is low, not because ofinherently low survivorship, but, instead, as a consequence of frequent permanent emigration from ourpopulation. We also suggest that the greater BDD of older birds (WMWR) and males (both sites) reflects ahistory of selection for dispersal in response to frequent habitat disturbance. Frequent habitat disturbance, inaddition to the opportunity to prospect for territories both before and after breeding, probably enable theearliest spring arrivals (typically older birds and males) to often relocate between years.


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