Connecting breeding and wintering grounds of Neotropical migrant songbirds using stable hydrogen isotopes: a call for an isotopic atlas of migratory connectivity

Abstract

There is an overdue and urgent need to establish patterns of migratory connectivity linking breeding grounds, stopover sites, and wintering grounds of migratory birds. Such information allows more effective application of conservation efforts by applying focused actions along movement trajectories at the population level. Stable isotope methods, especially those using stable hydrogen isotope abundance in feathers (δ2Hf) combined with Bayesian assignment techniques incorporating prior information such as relative abundance of breeding birds, now provide a fast and reliable means of establishing migratory connectivity, especially for Neotropical migrants that breed in North America and molt prior to fall migration. Here we demonstrate how opportunistic sampling of feathers of 30 species of wintering birds in Cuba, Venezuela, Guatemala, Puerto Rico, and Mexico, regions that have typically been poorly sampled for estimating migratory connectivity, can be assigned to breeding areas in North America through both advanced spatial assignment to probability surfaces and through simpler map lookup approaches. Incorporating relative abundance information from the North American Breeding Bird Survey in our Bayesian assignment models generally resulted in a reduction in potential assignment areas on breeding grounds. However, additional tools to constrain longitude such as DNA markers or other isotopes would be desirable for establishing breeding or molt origins of species with broad longitudinal distributions. The isotope approach could act as a rapid means of establishing basic patterns of migratory connectivity across numerous species and populations. We propose a large‐scale coordinated sampling effort on the wintering grounds to establish an isotopic atlas of migratory connectivity for North American Neotropical migrants and suggest that isotopic variance be considered as a valuable metric to quantify migratory connectivity. This initiative could then act as a strategic template to guide further efforts involving stable isotopes, light‐sensitive geolocators, and other technologies.

Prolonged stopover and consequences of migratory strategy on local-scale movements within a regional songbird staging area

“…The d 2 H values ranged from À178% to À76% for blackpolls and from À112% to À57% for vireos, with lower d 2 H values indicating a more northern/western breeding area and, thus, a greater distance traveled to the capture site. Based on established feather isoscapes (Bowen et al 2005, Hobson et al 2014, these d 2 H values indicate likely breeding origins ranging from the eastern Maritime provinces for both species to as far away as northwestern Canada and possibly Alaska for blackpolls, and as far west as central Quebec, western Ontario, and southeastern Manitoba for vireos. We were unable to calculate movement rate, distance of sustained migratory flights, or flight distance per stop for 6 blackpolls and 4 vireos not re-detected beyond the capture site.…”

“…We used the stable hydrogen isotope ratio of feathers (d 2 H) as a coarse proxy of the breeding latitude (Wassenaar and Hobson 2001). Although the precision in breeding latitude is coarse (Hobson et al 2014), this method provides an index of the relative distance that migrants traveled before arriving at our capture site. Feathers were cleaned, weighed, and analyzed for d 2 H at the Cornell University Stable Isotope Laboratory, Ithaca, New York, USA.…”

Shorebird hunting in Barbados: Using stable isotopes to link the harvest at a migratory stopover site with sources of production

“…Alternatively, captive birds subjected to simulated latitudes using carefully selected or ''spiked'' food and drinking water could potentially be used for such calibrations (Hobson et al 1999a(Hobson et al , 1999b. Meanwhile, using the Lesser Scaup calibration algorithm appeared to fit the data reasonably well and our choice of variance from the calibration algorithm was of a similar magnitude to that seen previously (Hobson et al 2014).…”

“…Band return data are of limited value because capture and marking of a sufficient sample of birds is daunting and, to date, have produced low returns (Hobson 2003, Dunn et al 2010; but see Lanctot et al 2009). Exogenous markers such as satellite telemetry transmitters and archival tags such as geolocators suffer from similar issues: it is challenging to equip a representative sample of the population and/or to recapture a sufficient number of individuals due to potentially low return rates (Hobson et al 2014, Weiser et al 2016, particularly at stopover sites where individuals may stay for only a few days or hours.…”

“…For instance, in North America, the average abundance of deuterium in amount-weighted precipitation (d 2 H p ) follows well-described, continentwide patterns (Bowen et al 2005). Local deuterium is incorporated into food webs, allowing the creation of continent-wide, tissue-dependent ''isoscapes'' that can be used to assign individuals to approximate regions of origin (Wunder et al 2005, Hobson et al 2014. The application of stable isotopes to determining the origins of migratory animals can target the segment of the population exposed to harvest and has been used effectively to describe the origins of many migratory species, including shorebirds (Atkinson et al 2005, Catry et al 2012, Franks et al 2012).…”