Springtime migratory restlessness and departure orientation of Great Knots (Calidris tenuirostris) in the south compared to the north Yellow Sea

Abstract

Background:The motivation of birds to proceed with migration is associated with both endogenous and exogenous factors. According to their migratory situation and to the characteristics of stopover sites, birds might exhibit migratory motivation differently among sites. Although migratory motivation of migrating birds has been well studied in many species, the investigation of the same species in different migratory situations and at different stopover sites is still limited. We predicted that birds at different stopover sites could differ in migratory disposition, including expression of migratory restlessness and responses to environmental cues. Methods:Here we compared migration motivation and orientation of Great Knots (Calidris tenuirostris) at two stopover sites, Chongming Dongtan in the south Yellow Sea, which is a temporary rest site, and Yalujiang Estuary Wetland in the north Yellow Sea, which is a critical refuelling site, during northward migration. Modified Emlen funnels, with thermal paper inside to record scratches of the birds, were used to detect activity (intensity and direction) of birds. Environmental conditions, including wind direction and speed, cloud cover, tide condition, times of the day (before and after sunset) were recorded during experiments. Generalized linear models were used to detect the effects of endogenous and exogenous factors on the migratory motivation of the birds. Results:In the south Yellow Sea, the migratory activity intensity of Great Knots was positively related to wind assistance. In the north Yellow Sea, where birds exhibited higher intensity of migratory activity than in the south, the intensity increased and the motivation to initiate migration grew stronger as the season advanced. The Great Knots exhibited wind-related orientation behaviour in the funnels at both sites. Conclusions:The results suggest that the intensity of migratory motivation differed between the two sites. Departure decisions of Great Knots appear to be affected mainly by external factors at the temporary rest site in the south Yellow Sea but possibly by endogenous factors at the final pre-breeding refuelling site in the north Yellow Sea.

Persistent use of a shorebird staging site in the Yellow Sea despite severe declines in food resources implies a lack of alternatives

“…The coastal wetland of the Yalu Jiang estuary (39°40’–39°58’N, 123°34’–124°07’E, hereafter Yalu Jiang) (Figure 1) is a critical staging site in the northern Yellow Sea, especially for Bar-tailed Godwits Limosa lapponica of the subspecies menzbieri and baueri and Great Knots Calidris tenuirostris (Barter 2002, Riegen et al 2014, Choi et al 2015, Hua et al 2017). More than 250,000 shorebirds, including 100,000 Bar-tailed Godwits and 55,000 Great Knots (Barter 2002), use the coastal wetland for replenishing fuel during northward migration (Ma et al 2013, Riegen et al 2014), with 17 species meeting the 1% Ramsar criterion for wetlands of international importance (Bai et al 2015).…”

Migration departure strategies of shorebirds at a final pre-breeding stopover site

“…For example, departure from a final stopover site before arriving at the breeding ground will directly determine the arrival date at the breeding grounds and time window for breeding is relatively narrow, especially for birds breeding at high latitudes. In consequence, endogenous schedules might prevail over exogenous factors in this stage of the migration and birds might show less flexibility in date selection than those departing from non-breeding or other stopover sites (Warnock 2010;Hua et al 2017;Shamoun-Baranes et al 2017). Departure decisions from final stopover sites have been little studied (Greenberg and Marra 2005).…”

More than just refuelling: lengthy stopover and selection of departure weather by sandpipers prior to transoceanic and transcontinental flights

“…Thus, most migration routes consist of multiple stopover sites where migrants prepare for successive stages of their journeys. Different migration strategies occur among species, among populations traversing different routes, between age classes and sexes, at different sites in a sequential journey, and even among individuals within these groups (McKinnon et al 2014, Deppe et al 2015, Hua et al 2017, Vansteelant et al 2017.…”