Concentration of a widespread breeding population in a few critically important nonbreeding areas: Migratory connectivity in the Prothonotary Warbler

Abstract

One of the greatest challenges to informed conservation of migratory animals is elucidating spatiotemporal variation in distributions. Without such information, it is impossible to understand full-annual-cycle ecology and effectively implement conservation actions that address where and when populations are most limited. We deployed and recovered light-level geolocators (n = 34) at 6 breeding sites in North America across the breeding range of a declining long-distance migratory bird, the Prothonotary Warbler (Protonotaria citrea). We sought to determine migratory routes, stopover location and duration, and the location of overwintering grounds. We found that the species exhibits a large-scale, east‒west split in migratory routes and weak migratory connectivity across its range. Specifically, almost all individuals, regardless of breeding origin, overlapped in their estimated wintering location in northern Colombia, in an area 20% the size of the breeding range. Additionally, most of the individuals across all breeding locations concentrated in well-defined stopover locations in Central America while en route to Colombia. Although error inherent in light-level geolocation cannot be fully ruled out, surprisingly much of the estimated wintering area included inland areas even though the Prothonotary Warbler is considered a specialist on coastal mangroves in winter. Based on these results, conservation efforts directed at very specific nonbreeding geographical areas will potentially have benefits across most of the breeding population. Our findings highlight the importance of using modern technologies to validate assumptions about little-studied portions of a species’ annual cycle, and the need to distribute sampling across its range.

Habitat‐dependent occupancy and movement in a migrant songbird highlights the importance of mangroves and forested lagoons in Panama and Colombia

“…Contemporary declines have occurred despite much of the preferred bottomland forest breeding habitat being cleared prior to 1966 (Dickson, Thompson, Conner, & Franzreb, 1995). Because of threats due to habitat loss, continuing population declines, and relatively low population size for such a widespread species, the prothonotary warbler is considered a Bird of Conservation Concern in the United States (USFWS, 2008 (Tonra et al, 2019). Because of threats due to habitat loss, continuing population declines, and relatively low population size for such a widespread species, the prothonotary warbler is considered a Bird of Conservation Concern in the United States (USFWS, 2008 (Tonra et al, 2019).…”

“…The prothonotary warbler population has declined by about 1% per year over large portions of the breeding range since the 1960s (Sauer et al, 2015) with declines reaching 5.5% per year in some years (Ziolkowski, Pardieck, & Sauer, 2010). Contemporary declines have occurred despite much of the preferred bottomland forest breeding habitat being cleared prior to 1966 (Dickson, Thompson, Conner, & Franzreb, 1995 (Tonra et al, 2019). This previously unknown area of importance is further inland than the coastal mangrove forests thought to be the primary overwintering habitat for prothonotary warblers.…”

“…Point count surveys were carried out across all sites in Panama and Colombia during the overwintering season (November 2016 to February 2017, Figure 2). We conducted surveys after the prolonged fall migration and prior to spring migration (Tonra et al, 2019). Each site had 4 to 37-point locations, and many points (62%) were surveyed twice, once at the beginning of the dry season (November/ early December) and again in the middle of the dry season (late January/early February).…”

“…The importance of this region in supporting individuals from across the species' breeding range is supported by migratory connectivity research using stable isotopes (Reese et al, in review), population genetics (DeSaix et al, 2019), and geolocators (Tonra et al, 2019).…”

“…Overall, while some research has emphasized the value of disturbed habitats to overwintering migrants (e.g., shade coffee farms;Johnson & Sherry, 2001), our findings add to a body of literature demonstrating that in many species mature forests are of greater conservation value, based on bird numbers (e.g., Bayly, Rosenberg, Gomez, & Hobson, 2019;Cespedes & Bayly, 2018) and the amount of resources available (e.g.,Smith & Robertson, 2008).A recent study byRuiz-Gutierrez et al (2016) using banding data from a network of stations throughout Mexico, Central and South America showed that it was common for prothonotary warblers to be transient rather than resident between November and March. It is possible that a prolonged southerly fall migration period, which has been documented with geolocator data(Tonra et al, 2019), could explain transient birds in more northerly latitudes. It is possible that a prolonged southerly fall migration period, which has been documented with geolocator data(Tonra et al, 2019), could explain transient birds in more northerly latitudes.…”