Toward a Deuterium Feather Isoscape for Sub-Saharan Africa: Progress, Challenges and the Path Ahead

Abstract

A key challenge to the application of continent-wide feather isoscapes for geographic assignment of migrant birds is the lack of ground-truthed samples. This is especially true for long-distance Palearctic-Afrotropical migrants. We used spatially-explicit information on the δ 2H composition of archived feathers from Green-backed/Grey-backed Camaroptera, to create a feather δ 2H isoscape for sub-Saharan Africa. We sampled from 34 out of 41 sub-Saharan countries, totaling 205 sampling localities. Feather samples were obtained from museum collections (n = 224, from 1950 to 2014) for δ 2H assay. Region, altitude, annual rainfall and seasonal patterns in precipitation were revealed as relevant explanatory variables for spatial patterns in feather δ 2H. Predicted feather δ 2H values ranged from -4.0 ‰ to -63.3 ‰, with higher values observed in the Great Rift Valley and South Africa, and lower values in central Africa. Our feather isoscape differed from that modelled previously using a precipitation δ 2H isoscape and an assumed feather-to-precipitation calibration, but the relatively low model goodness fit (F10,213 = 5.98, p<0.001, R2 = 0.18) suggests that other, non-controlled variables might be driving observed geographic patterns in feather δ 2H values. Additional ground-truthing studies are therefore recommended to improve the accuracy of the African feather δ 2H isoscape.

Stable isotope analyses as a forensic tool to monitor illegally traded African grey parrots

“…However, the known wild African grey parrot feathers reflected differing d 2 H values relative to their capture sites and aligned with the suggested weak east to west gradient in d 2 H precipitation values across central Africa (Hobson, 2005;Bairlein, Norris & Nagel, 2012;Reichlin, Hobson & Wilgenburg, 2013;Guti errez-Exp osito, Ram ırez & Af an, 2015). However, the known wild African grey parrot feathers reflected differing d 2 H values relative to their capture sites and aligned with the suggested weak east to west gradient in d 2 H precipitation values across central Africa (Hobson, 2005;Bairlein, Norris & Nagel, 2012;Reichlin, Hobson & Wilgenburg, 2013;Guti errez-Exp osito, Ram ırez & Af an, 2015).…”

“…Feathers from wild origins were collected from a wide range throughout the natural distribution of African grey parrots and allowed for a comparison to be made between known wild and captive d 2 H signatures. However, the known wild African grey parrot feathers reflected differing d 2 H values relative to their capture sites and aligned with the suggested weak east to west gradient in d 2 H precipitation values across central Africa (Hobson, 2005;Bairlein, Norris & Nagel, 2012;Reichlin, Hobson & Wilgenburg, 2013;Guti errez-Exp osito, Ram ırez & Af an, 2015). Museum samples from known wild origins which fall outside of the natural distribution is possibly a result of a reduced distribution of this species in recent years (BirdLife International, 2017a, b), compared to the time of initial sample collection (1908)(1909)(1910)(1911)(1912)(1913)(1914)(1915)(1916)(1917).…”

“…Museum samples from known wild origins which fall outside of the natural distribution is possibly a result of a reduced distribution of this species in recent years (BirdLife International, 2017a, b), compared to the time of initial sample collection (1908)(1909)(1910)(1911)(1912)(1913)(1914)(1915)(1916)(1917). Ultimately incorporating multiisotope analyses could define the origins of African grey parrots, and other species more accurately (Hobson et al, 2012b;Hobson et al, 2013), as the isotope patterns across Africa are complex and influenced by multiple factors Guti errez-Exp osito et al, 2015). Despite the African d 2 H gradient being less uniform and the increased isotope variability in wild birds, there are several additional factors which potentially allow for the origins of illegally traded African grey parrots to be determined.…”

“…d 2 H values differ with distance from the coast (Hobson, Michener & Lajtha, 2007) and d 13 C and d 2 H with increased aridity (Rubenstein & Hobson, 2004;Neto, Newton & Gosler, 2006;Hobson, Møller & Wilgenburg, 2013) and anthropogenic change (Hobson, 2007;Hobson et al, 2013), resulting in possible isotope differences between the African grey parrots from the more forested and mesic central Africa and from the xeric and agriculturally transformed western and eastern regions (Mayaux, 2004; Hobson et al, 2013). Ultimately incorporating multiisotope analyses could define the origins of African grey parrots, and other species more accurately (Hobson et al, 2012b;Hobson et al, 2013), as the isotope patterns across Africa are complex and influenced by multiple factors Guti errez-Exp osito et al, 2015). The variability in d 13 C and d 2 H isotope values in the unknown and captive feathers was greater than the wild samples, and likely a result of differences in diet.…”

Matching geographical assignment by stable isotopes with African non-breeding sites of barn swallows Hirundo rustica tracked by geolocation

“…Recently, there are endeavours to amend δ 2 H isoscape(s) by e.g. the application of feather samples with spatially explicit information [64]. However, beside the use of archival samples, systematic sampling and isotopic measurements of feathers of known origin and across several years are still fundamental for the delineation of a sound feather δ 2 H isoscape for Africa.…”