Migration routes and key stopovers of Anser fabalis fabalis (Anseriformes): critical protection gaps

Abstract

The population of Anser fabalis fabalis wintering in Europe have shown decline in recent decades. At the same time, the population dynamic of most migratory birds largely depends on the quality of migratory stopover sites, which are necessary to replenish internal reserves. The migration ecology of Anser fabalis fabalis wintering in Europe has not been sufficiently studied. Only in general terms we know about the timing of migration, while the places of key stopovers in Russia are not described. There is no information about conservation status of key sites and the intensity and duration of their use by Anser fabalis fabalis individuals. Without this knowledge, it is impossible to organise effective protection of any migrating population. We have analysed the dynamics and phenology of migrations, as well as the conservation status of stopover and pre-migration sites of Anser fabalis fabalis nesting in the forest zone of Western and Central Siberia and wintering in Northern Germany and Poland, based on data from GPS/GSM transmitters. We used data from 45 completed spring migrations from 25 tagged birds and 36 completed autumn migrations from 20 birds over the period 2019–2023. The migration start from wintering sites occurs in late February, on average 20 February ± 10.9 days. Arrival of the birds in the breeding areas occurs in late April, on average 01 May ± 9.4 days. Over 2019–2023, we found a trend for a shift in the dates of spring migration start (Mann-Kendall test: τ = -0.22, p < 0.05) and finish (Mann-Kendall test: τ = -0.35, p < 0.05) to earlier dates. Based on data from individual bird’s migration routes, 1031 migration stopovers with a total duration of 3529.7 days were allocated. Of these, 616 (59.8%) stopovers were located in Russia, where the birds spent 1831 (51.9%) days. Key stopovers are located in the Baltic Region, the Sviyaga-Vyatka interfluve and the centre of the River Volga Region. The start of the autumn migration occurs between 27 September and 25 October, on average 18 October ± 7.9 days. The arrival at wintering sites occurs between 15 October and 11 December, on average 8 November ± 13.4 days. Over 2019–2023, there was a trend of an increasingly later arrival on wintering sites (Mann-Kendall test: τ = 0.45, p < 0.05). The start of the autumn migration occurred also later (Mann-Kendall test: τ = 0.44, p < 0.05). Pairs with broods are characterised by a longer autumn migration (Mann-Whitney test: U = 67.0, Z = 2.58, p < 0.001), and they spend significantly more time on the pre-migration sites (Mann-Whitney test: U = 71.5, Z = 2.29, p < 0.01) and autumn stopovers (Mann-Whitney test: U = 67.5, Z = 2.56, p < 0.01). The migration speed of pairs without broods was higher than of pairs with broods (Mann-Whitney test: U = 69.0, Z = -2.5, p < 0.01). Only 15.3% of stopovers are covered by the existing network of Protected Areas, where the Anser fabalis fabalis individuals spend only 19.2% of the total time. The results of this study can be used to develop an effective strategy for the Anser fabalis fabalis conservation during the period of migrations. We propose a hunting ban and/or the creation of Protected Areas within the main key stopover sites in Russia.