Inferring the timing of long‐distance dispersal between Rail metapopulations using genetic and isotopic assignments

Abstract

The stochastic and infrequent nature of long-distance dispersal often makes it difficult to detect. We quantified the frequency, distance, and timing of long-distance dispersal in a nonmigratory, secretive wetland bird, the California Black Rail (Laterallus jamaicensis coturniculus), between an inland and a coastal metapopulation separated by greater than 100 km. Using 15 microsatellites in conjunction with stable carbon, nitrogen, and sulfur isotopes, we classified Rails as residents of their capture population, recent migrants that dispersed to their capture population less than one year before capture, established migrants that dispersed to their capture population more than one year before capture, and seasonal migrants that dispersed away from their capture population to forage, but returned the next season. Most Rails (195 of 204, or 95.6%) were classified as residents, but we detected two established migrants that had moved >100 km more than a year before capture. Seven Rails appeared to be seasonal migrants, but comparisons of feather isotope values with isotope values from wetland soils indicated that the isotope values in the feathers of these Rails likely resulted from natural environmental variation (e.g., source element effects) rather than long-distance dispersal of individuals. Thus, these seven Rails were most likely misassigned by isotopic population assignments due to small-scale variation in the isoscape. Using genetic data in conjunction with isotopic data allowed us to not only infer the timing of long-distance dispersal events, but to successfully track long-distance movements of nonmigratory Rails between metapopulations even when environmental variation of isotopes occurred across small spatial scales.

Validating dispersal distances inferred from autoregressive occupancy models with genetic parentage assignments

“…Colonization probabilities for wetlands decreased strongly as isolation increased (Figure ), and we detected mostly short‐distance dispersal (Figure ), indicating that spatially clustered patches acting as “stepping stones” may be important to facilitate movements. Black rails are, however, capable of long‐distance dispersal, moving up to 28 km within our metapopulation and more than 100 km between metapopulations, although such movements are rare (Hall & Beissinger, ). Because many of the wetlands that rails inhabit in the foothills frequently become unsuitable, maintaining connectivity will be important for conserving rails as they track patch suitability.…”

“…Colonization probabilities for wetlands decreased strongly as isolation increased (Figure 1), and we detected mostly short-distance dispersal (Figure 2), indicating that spatially clustered patches acting as "stepping stones" may be important to facilitate movements. Black rails are, however, capable of long-distance dispersal, moving up to 28 km within our metapopulation and more than 100 km between metapopulations, although such movements are rare (Hall & Beissinger, 2017). Because many of the wetlands that rails inhabit in the foothills frequently become unsuitable, maintaining connectivity will be important for conserving rails F I G U R E 1 Model-averaged annual colonization probabilities as a function of buffer radius measure (BRM; panels in column (1)) and incidence function measure (IFM; panels in column (2)) connectivity values (scaled to the mean) for a metapopulation of California black rails (Laterallus jamaicensis coturniculus) from 212 wetlands in the Sierra Foothills, CA.…”

“…Data available from the Dryad Digital Repository: https://doi. org/10.5061/dryad.27mk2 (Hall & Beissinger, 2016) and https://doi. org/10.5061/dryad.3bb81dv (Hall, Van Schmidt, & Beissinger, 2018…”

Noose Carpets: A Novel Method to Capture Rails

“…Walk‐in traps have also been used in concert with audio lures to capture rails (Kearns et al 1998, McKernan et al 2016, Harrity and Conway 2017). The use of nocturnal spotlighting (from a boat, an all‐terrain vehicle [ATV], or on foot) to capture rails by hand or with a dip net is common where conditions permit, such as tidal marshes along the United States Atlantic Coast (Hon et al 1977, Perkins et al 2010, Mills et al 2011), moist rice fields in Texas, USA (Perkins et al 2010), short‐statured riverine tidal marshes in California, USA (Tsao et al 2009, Girard et al 2010, Hall and Beissinger 2017), and coastal pine‐savannas in Mississippi, USA (Soehren et al 2018). Woosh nets and mist nets have been used with varying degrees of success.…”

“…For example, king rails ( Rallus elegans ) have been captured with woosh nets in Ohio, USA (Shirkey et al 2017, Kane et al 2019). Zembal and Massey (1983) herded radiomarked light‐footed Ridgway's rails ( R. obsoletus levipes ) into strategically placed mist nets, Rush et al (2010) flushed clapper rails ( R. crepitans ) from nests into mist nets, and Hall and Beissinger (2017) caught California black rails ( Laterallus jamaicensis coturniculus ) in mist nets. Specialized mist nets have also been used effectively with audio lures to capture clapper rails along the northern coast of the Gulf of Mexico (J. Feura, Mississippi State University, Coastal Research Extension Center, personal communication) and California black rails in the western United States (Girard et al 2010).…”