Morphological differences and migration patterns of greater and lesser snow geese in New York State

Abstract

Lesser (Chen caerulescens caerulescens, LSGO) and greater snow goose (Chen caerulescens atlantica, GSGO) populations have increased substantially in the past 50 years. The light goose conservation order established in 1998 (Canada) and 1999 (U.S.) aimed to increase snow goose harvest and stabilize populations because breeding ground abundance was thought to negatively impact arctic ecosystems. In the Atlantic flyway, where LSGO and GSGO are both available for harvest, techniques to differentiate sub‐species in the field using morphology may be helpful for harvest management because mid‐continent LSGO are ~16 times more abundant than GSGO (n < 1,000,000). We investigated percentages and spatial distribution of LSGO and GSGO in the spring harvest in NY as this information could be useful for snow goose population and harvest management decisions. We developed a discriminant function analysis (DFA) using heads from snow geese harvested during spring 2016 to 2018 and were able to differentiate between LSGO and GSGO with 95.5% accuracy. Based on the DFA results, we estimated that spring harvest in New York state was 80% GSGO and 20% LSGO. Using band recoveries from autumn and spring harvests, we also identified that GSGO harvest occurred farther west during spring than autumn and in the 2010s than prior two decades. Our results indicate that GSGO comprise most snow goose harvest in New York state and provide evidence for a shift in spring migration patterns of GSGO since the 1990s.

Discrimination among similarly colored goose species in federal harvest surveys

“…Although we did not find statistical support in our top selected ML tree for the differentiation of lesser and greater snow geese, we did find some non‐significant differentiation in clade B from a cluster of samples harvested in the Atlantic Flyway (Figure 1). Our inability to discriminate lesser and greater snow geese in the Atlantic Flyway using central tail feather length contrasted with Sliwinski et al (2023), who classified lesser and greater snow geese with 95.5% accuracy using head measurements. However, their classification accuracy was based on an initial classification of samples to subspecies from head and culmen length measurements described in Humphries et al (2009), not genetic classification.…”

“…Ross's and snow geese diverged more recently (around 2.1 million years ago) than cackling and Canada geese (Ottenburghs et al 2016), and Ross's and snow geese likely nested together in Arctic refugia during past glaciation events (Ploeger 1968). Compared to dark geese, the biology of light geese favors greater degrees of genetic interchange: sympatric nesting in large colonies (Kerbes et al 1983), mate pairing in winter when geese from various breeding areas intermix (Ganter et al 2005), frequent hybridization and production of fertile offspring (Trauger et al 1971, Weckstein et al 2002, Ottenburghs et al 2017), and large‐scale distributional shifts and inter‐mixing among populations during recent decades (Johnson and Troy 1987, Cooke et al 1988, Jónsson et al 2020, Alisauskas et al 2022, Sliwinski et al 2023). Additionally, both species groups exhibit asymmetric sex‐mediated gene flow and size‐based sexual selection, which can complicate the understanding of evolutionary histories.…”