Annual survival and breeding dispersal of a migratory passerine, the Scissor-tailed Flycatcher

Abstract

Knowledge of survival rates is critical for advancing our understanding of the dynamics of populations 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 Wildlife Refuge [WMWR]). Our Cormack-Jolly-Seber estimate of apparent adult survival for the period from 2008 to 2105 was relatively low (0.514) compared to estimates for 36 other migratory and socially monogamous passerines 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 to breeding. Although apparent survival did not differ between sites, dispersal (N = 66 individuals) was more common and breeding dispersal distance (BDD) was greater for Scissor-tailed Flycatchers at Ft. Sill where anthropogenic disturbance was more frequent. BDD also increased with body mass at Ft. Sill (but not at WMWR) and, after accounting for it, BDD at Ft. Sill tended to be greater for birds that failed to breed successfully in the past year. Older birds and males had the longest BDDs at WMWR, and males exhibited a similar tendency at Ft. Sill. We contend that our estimate of apparent survival is low, not because of inherently low survivorship, but, instead, as a consequence of frequent permanent emigration from our population. We also suggest that the greater BDD of older birds (WMWR) and males (both sites) reflects a history of selection for dispersal in response to frequent habitat disturbance. Frequent habitat disturbance, in addition to the opportunity to prospect for territories both before and after breeding, probably enable the earliest spring arrivals (typically older birds and males) to often relocate between years. RESUMEN.Supervivencia anual y dispersi on reproductiva de un paseriforme migratorio, Tyrannus forficatusEl conocimiento de las tasas de supervivencia es fundamental para entender la din amica de poblacional y aqu ı reportamos la supervivencia anual aparente y la dispersi on reproductiva de Tyrannus forficatus en dos sitios en el suroeste de Oklahoma (Ft. Sill y Wichita Mountain Wildlife Refuge [WMWR]). Nuestra estimador de Cormack-Jolly-Seber de la supervivencia adulta aparente durante el per ıodo de 2008 a 2105 fue relativamente bajo (0.514) en comparaci on con las estimaciones de otros 36 paseriformes migratorios y socialmente mon ogamos que se reproducen en Am erica del Norte y fue independiente del sexo (hombres: N = 151; mujeres: N = 119), estado reproductivo (titular del territorio o flotante), masa corporal, sitio, año y precipitaci on durante el año anterior a la reproducci on. Aunque no encontramos diferencias en la supervivencia aparente entre los sitios, la dispersi on (N = 66 individuos) fue m as com un y la distancia de dispersi on reproductiva (BDD) fue mayor para los individuos en Ft. Sill donde la perturbaci on antropog enica es m as frecuente. BDD tambi en aum...

Natal dispersal does not entail survival costs but is linked to breeding dispersal in a migratory shorebird, the southern dunlinCalidris alpina schinzii

“…This can be particularly problematic when comparing survival of immigrants and philopatric individuals because delayed natal philopatry can bias the survival of immigrants whose natal sites are not monitored. More generally, this also implies that survival estimates can be biased in populations that receive immigrants (Chernetsov et al 2009, Becker et al 2018), and that survival estimated from individuals born within the study area should be less prone to biases due to permanent emigration (Pakanen et al 2015b).…”

Characterizing patterns of introgressive hybridization between two species ofTyrannusfollowing concurrent range expansion

“…These alleles could either be beneficial, making individuals better adapted to new environments and enabling further expansion (Arnold 1997, Barton 2001, Grant et al 2004, or detrimental, leading to reduced fitness of individuals at the periphery and a contraction of recent expansion (Rhymer & Simberloff 1996, Arnold 1997, Muhlfeld et al 2009). Beyond local effects, introgression has the potential to be widespread in these species because of low natal and breeding philopatry in both species (Gamble & Bergin 2012, Regosin 2013, Becker et al 2018. Ephemeral hybridization events could lead to the spread of introgressed alleles as hybrids disperse into other portions of the species' ranges to breed in subsequent years.…”

Emigration and survival correlate with different precipitation metrics throughout a grassland songbird's annual cycle

“…Therefore, true survival and site fidelity in mobile species are often combined into a single metric, apparent survival (Sandercock 2006). While apparent survival is assumed to be equivalent to (or at least, a good surrogate for) true survival by many authors, growing evidence suggests that in grassland birds, apparent survival estimates may largely be shaped by dispersal (Gilroy et al 2012, Schaub and Royle 2014, Taylor et al 2015, Becker et al 2018). Thus, adopting modeling approaches that attempt to distinguish survival from emigration are required to elucidate the environmental factors that shape life‐history traits and behaviors within and among species.…”