Occurrence of hybrid geese in Sweden—a conservation problem?

Abstract

This report provides basic data about hybrid geese and mixed pairs in Sweden; combinations of species, numbers, trends and origins, which can serve as a framework for future studies. Data published in national, regional and local magazines and reports as well as unpublished observations through August 2007 have been analysed. Sightings in this report were based on the observers’ suggestion of parent species. No less than 17 species were involved in the hybrid geese sighted in Sweden. Some of the combinations of species involved the red-listed species Lesser White-fronted Goose, the nominate race of Taiga Bean Goose and Red-breasted Goose. The first combinations of species appeared in Sweden already 1918–1930s, but since the last half a century, the number of hybrid geese in Sweden shows a positive trend. Several explanations to this increasing trend is proposed but not further analysed. Among all the several theories proposed for hybridisation in geese, field data from Swedish goose haunts support at least two; the ”Best-Option-Hypothesis” and ”Interspecific mate choice following false imprinting”.

Images of Barnacle Goose Branta leucopsis hybrids – a photo documentation of some crosses with different Anser species

“…The hybrids presented in this study are all relatively rare. To the best of my knowledge, these are the first pictures of a Barnacle Goose x domestic Swan Goose hybrid and according to a recent study on goose hybrids it should be the first observation in Sweden (Kampe-Persson & Lerner 2007). The bird carried a greyish-green ring NL-H20 02 8705 (underlined 02 standing in vertical position) belonging to a breeder associated with the NHDB-ringenbureau in Holland.…”

“…Hybridisation between goose species is common but reporting is hampered by a number of factors (Kampe-Persson & Lerner 2007). Correct classification of parentage is for obvious reasons a key factor.…”

Use of foster parents in species conservation may cause conflicting objectives: hybridization between Lesser White-fronted Goose Anser erythropus and Barnacle Goose Branta leucopsis

“…Besides the birds released within the Swedish conservation program, an early mixed breeding pair in Sweden was reported already in 1985. According to Kyrk (1987) and Kampe-Persson & Lerner (2007) this pair consisted of an escaped Lesser White-fronted Goose male (from a park) breeding with a female Barnacle Goose in a feral population of the latter species close to Stockholm, thus having no connection to hybrids jumped from zero in 2003/2004 to ten in 2004/2005 (including two older hybrids not reported earlier but probably from the breeding in 2002). Our data suggest that mixed pairs were successfully breeding annually from 2004 to 2013 (Figure 1).…”

“…As a response, the Swedish conservation program decided at an early stage to remove Lesser White-fronted Goose males in mixed pairs, and their offspring, whenever possible. Kampe-Persson & Lerner (2007) provide a general overview of goose hybrids recorded in Sweden, including LWfG × BG hybrids. So far, no attempt has been made to investigate numbers and dispersal of LWfG × BG hybrids in detail, nor to evaluate whether the culling of mixed pair males and their hybrid offspring were successful to reduce putative conservation problems.…”

“…Scattered reports in the more interior parts of Germany (Figure 4), where Barnacle Geese were rare in the past decades, may originate from captive populations. Both Lesser White-fronted Goose and Barnacle Goose are known to hybridize with other species in the wild and in captivity (McCarthy 2006, Kampe-Persson & Lerner 2007, Ottenburghs et al 2016b. Hence, observations of hybrids are not necessarily linked to the Swedish conservation program for Lesser White-fronted Goose but may originate from captive or naturalized populations.…”