First pairing in Snow GeeseAnser caerulescens: at what age and at what time of year does it occur?

Abstract

In migratory birds, the place and time of pair formation are important parameters for population structure and dynamics. Geese are not only migratory but also exhibit long‐term monogamy, and therefore the first pairing event in a bird's lifetime is of particular importance. Through behavioural observations of young, known‐age, marked birds conducted on the wintering grounds during three winter seasons we investigated two aspects of the timing of first pair formation in the Wrangel Island population of Snow Geese Anser caerulescens: (1) the age at which birds first form pair bonds, and (2) the seasonal pattern of first pair formation. Wrangel Island Snow Geese paired considerably later in life than Snow Geese from a low‐Arctic population: almost none of the birds formed pairs in their second winter, and many were still in sibling groups for at least part of that season. The proportion of birds in pairs continued to increase until at least 5 years of age. Most pairing took place during the observation periods, and in general the proportion of birds in pair bonds increased gradually throughout the winter season. The amount of pairing during spring migration or summer varied annually and among cohorts, indicating that even very young birds may be able to form pair bonds quickly if conditions on the breeding grounds are unusually favourable. Pairing later and remaining in family groups longer may be a response to breeding conditions in this high‐Arctic colony. Here, productivity is typically low due to harsh weather and predation, whereas Snow Geese breeding in the low Arctic are less restricted and form pairs and start to breed when younger. The fact that most, but not all, pairing takes place on the wintering grounds helps explain why a previous study found a certain amount of gene flow between the two Wrangel Island subpopulations with separate wintering grounds.

Intercontinental Gene Flow among Western Arctic Populations of Lesser Snow Geese

“…Our data on spatial genetic structuring imply that female Lesser Snow Geese have more fidelity to winter than to breeding areas, as suggested previously (Ryder and Alisauskas 1995, Robertson and Cooke 1999, Ganter et al 2005. The subpopulations of Lesser Snow Geese (SWI and NWI) that breed on Wrangel Island differed significantly in mtDNA haplotype frequency (Tables 1, 3), while birds that winter in the same area (SWI and BI) were not genetically differentiated.…”

“…Colonially nesting Lesser Snow Geese pair mainly on the winter grounds or during spring migration (Cooke et al 1975, Ganter et al 2005, and fidelity to winter areas is greater than to breeding areas (Cooke et al 1975, Cooke and Sulzbach 1978, Cooke and Abraham 1980, Ganter and Cooke 1998, Williams et al 2008. Pairing while the NWI and SWI subpopulations are geographically segregated (i.e., during winter and early spring) may limit gene flow.…”

“…Significant spatial genetic structure among breeding populations may result from natal philopatry of females (Chesser 1991a, b), even though populations share migratory pathways and wintering areas (Ely andScribner 1994, Scribner et al 2003). Alternatively, fidelity to wintering grounds, followed by pair formation on or near these areas, may be critical in defining regional patterns of spatial genetic structure of goose populations (Prevett 1972, Cooke 1987, Cooke et al 1988, Ryder and Alisauskas 1995, Robertson and Cooke 1999, Ganter et al 2005.…”

Movement and persistence by Ross’s Geese (Chen rossii) in Canada’s arctic

“…Regardless, there appears to be considerable overlap in distribution outside the arctic, at a time when pair formation by Ross's Geese is most likely to occur, as it does in closely related and largely sympatric Lesser Snow Geese (see Prevett and MacInnes 1980;Ganter et al 2004). It appears that subpopulations of light geese are extensively interconnected by broadly overlapping migration networks, which likely enhances gene flow.…”

“…This is probably linked to the constant and high transfer of individuals among demes (Drake and Alisauskas 2004;Ganter et al 2004) further complicated by hybridization between species (Trauger et al 1971). Such high rates of dispersal between regions do not necessarily preclude finer-scale spatial structuring, as has been detected in Greater Snow Geese (C. caerulescens atlantica; Lecomte et al 2009).…”