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

Abstract

SummaryMany shorebird populations are in decline along the East Asian-Australasian Flyway. The rapid loss of coastal wetlands in the Yellow Sea, which provide critical stop-over sites during migration, is believed to be the cause of the alarming trends. The Yalu Jiang coastal wetland, a protected area in the north Yellow Sea, supports the largest known migratory staging populations of Bar-tailed Godwits Limosa lapponica (menzbieri and baueri subspecies) and Great Knots Calidris tenuirostris. Monitoring of the macrozoobenthos food for these shorebirds from 2011 to 2016 showed declines of over 99% in the densities of the bivalve Potamocorbula laevis, the major food here for both Bar-tailed Godwits and Great Knots. The loss of the bivalve might be caused by any combination of, but not limited to: (1) change in hydrological conditions and sediment composition due to nearby port construction, (2) run-off of agrochemicals from the extensive shoreline sea cucumber farms, and (3) parasitic infection. Surprisingly, the numbers of birds using the Yalu Jiang coastal wetland remained stable during the study period, except for the subspecies of Bar-tailed Godwit L. l. menzbieri, which exhibited a 91% decline in peak numbers. The lack of an overall decline in the number of bird days in Great Knots and in the peak numbers of L. l. baueri, also given the published simultaneous decreases in their annual survival, implies a lack of alternative habitats that birds could relocate to. This study highlights that food declines at staging sites could be an overlooked but important factor causing population declines of shorebirds along the Flyway. Maintaining the quality of protected staging sites is as important in shorebird conservation as is the safeguarding of staging sites from land claim. Meanwhile, it calls for immediate action to restore the food base for these beleaguered migrant shorebirds at Yalu Jiang coastal wetland.

Phenological mismatch in Arctic‐breeding shorebirds: Impact of snowmelt and unpredictable weather conditions on food availability and chick growth

“…Although recent studies suggest shorebirds have some capacity to advance laying dates (Gill et al, 2014;Grabowski et al, 2013;Liebezeit et al, 2014;Saalfeld & Lanctot, 2017), advancement rates are likely limited by low plasticity in the start and progression of migration, which is controlled by a combination of endogenous and photoperiod cues (Karagicheva et al, 2016;Piersma et al, 2008). However, migration rates are limited by flight speeds, food availability at migration stop-over sites, and weather conditions encountered during migration (La Sorte & Fink, 2017;Zhang et al, 2018). However, migration rates are limited by flight speeds, food availability at migration stop-over sites, and weather conditions encountered during migration (La Sorte & Fink, 2017;Zhang et al, 2018).…”

Migration timing influences the responses of birds to food shortage at their refuelling site

“…This is supported by the observation of Great Knots departing from YLE by mid-May with their body mass being doubled during stopover . Although the peak numbers of Great Knots in late April were similar in the two years at YLE, the count in May 2015 was lower than in 2012 (Zhang et al 2018). Because the time window for breeding at high latitudes is narrow, arriving too early at the breeding site can mean experiencing cold weather and food shortage (Klaassen 2003).…”

“…1). The food of Great Knots at YLE has dramatically declined since 2013, with available food in 2015 (average 97 bivalves per m 2 ) being less than one-fifth of that in 2012 (average 697 bivalves per m 2 ) (Zhang et al 2018). It is highly dependent on small bivalves for its food at the refuelling site, where the birds double their body mass before departing for their breeding grounds , Choi et al 2017.…”

“…The Great Knot is an endemic shorebird in the East Asian-Australasian Flyway. This caused an 85% reduction in daily food intake rate and thus it is unlikely for birds to store sufficient fuel at departure for a successful migration to the breeding grounds (Zhang et al 2018(Zhang et al , 2019. The arrival period of the Great Knots at YLE lasts for 1 month, and most birds depart from YLE within about 1 week and thus there is great variation in LOS among individuals, with the early arrivals staying for nearly 2 months, whereas late arrivals stay for only 1 month .…”

Keeping safe and fed: large heterospecific shorebird flocks to decrease intraspecific competition

“…Nowadays, the intense use of coasts for recreational activities is one prominent ecological factor that negatively affects shorebirds that perceive humans as predators Niles 2012, Cestari 2015). Therefore, with the advance of urbanization and human population on beaches -and as long as resources are still available in some coastal areas -it is expected that some gregarious shorebird species may be more frequently found in flocks because this strategy may increase collective caution against human disturbances (Mori et al 2001, Cestari 2009, Zhang et al 2018.…”