Alternative habitat: the importance of the Nanpu Saltpans for migratory waterbirds in the Chinese Yellow Sea

Abstract

SummaryThe natural coastal wetlands of the East Asian-Australasian Flyway (EAAF) are disappearing at alarming rates, leading to rapid declines of many populations of waterbirds in the most species-rich flyway in the world. The identification and assessment of possible alternative habitats that may buffer the loss of natural wetlands should, therefore, be a priority for the conservation of migratory waterbirds using this flyway. Coastal saltpans are functional wetlands that support large numbers of waterbirds worldwide. The Nanpu Saltpans in the northern Bohai Bay of the Yellow Sea in China are one of the largest (290 km2) saltpan complexes in the world. In this paper, we document the value of the Nanpu Saltpans for supporting waterbirds. The surveys, carried out from 2013 to 2016, included waterbird counts in the saltpans (93 km2) at high and low tide and on the adjacent natural tidal flats (57 km2) at low tide. Of the 89 waterbird species recorded, 27 had maximum counts exceeding the 1% threshold value of estimated flyway populations. The maximum counts of waterbirds in northward migration and southward migration in the Nanpu Saltpans were 96,000 and 93,500, respectively, including both foraging and roosting birds; these figures do not account for turnover, so the total number of birds using the site is likely to be higher. The maximum counts on the adjacent tidal flats at low tide amounted to 73,000 and 20,000 waterbirds during northward and southward migration, respectively, and most of them were foraging birds. In the boreal winter, few birds fed in the saltpans, but several thousand fed on the tidal flats. Waterbirds used the inland ponds (2.0–18.0 km from the intertidal area) mainly for feeding both during low tide and high tide and used the nearshore ponds (0.3–4.3 km from the intertidal area) mainly for high-tide roosting. Some species, such as Black-tailed Godwit Limosa limosa, Marsh Sandpiper Tringa stagnatilis, Pied Avocet Recurvirostra avosetta, and Black-winged Stilt Himantopus himantopus, occurred mainly in the saltpans; other species preferred tidal flats, such as Red Knot Calidris canutus, Great Knot Calidris tenuirostris, Bar-tailed Godwit Limosa lapponica, Eurasian Curlew Numenius arquata, Relict Gull Larus relictus, and Grey Plover Pluvialis squatarola. This study clearly demonstrates the joint ecological function of the Nanpu Saltpan complex and adjacent tidal flats as a key staging area for waterbirds in the EAAF, and as such both urgently warrant protected status.

Multiple habitat use by declining migratory birds necessitates joined‐up conservation

“…Policy developments in China suggest that loss of intertidal flats from land claim for development will slow. Several intertidal areas have been proposed as tentative sites for World Heritage listing, and a recent announcement from the Chinese government detailed that business‐related land claim is to cease and decisions on future land claim activities made only by the central government (Lei, ; Melville, ; Stokstad, ). Preventing further loss of intertidal flats will hopefully slow the rapid decline of many shorebird species, yet beneficial effects may be undermined unless adjacent supratidal habitats are also managed for shorebird conservation.…”

“…Despite the focus on intertidal habitat conservation, at a relatively small scale on nonbreeding grounds (including staging and stopover sites), shorebirds regularly switch between intertidal habitat, generally used for foraging at lower tides, and supratidal habitat, often used for high tide roosting-an important period of sleep, rest, and digestion (Choi et al, 2014;Rogers, 2003). In the Yellow Sea and elsewhere in the EAAF, supratidal habitats are also used by some shorebirds for foraging (e.g., Masero et al, 2000;Green, Sripanomyom, Giam, & Wilcove, 2015;Lei et al, 2018). The same coastal development that has contributed to intertidal flats loss in the Yellow Sea has also caused most natural supratidal wetlands to be replaced by artificial "working wetlands" including aquaculture, agriculture, and salt production (Cai, van Vliet, Verburg, & Pu, 2017;Xu, Gao, & Ning, 2016), and shorebirds are known to utilize such artificial habitats as they do natural supratidal wetlands (Basso, Fonseca, Drever, & Navedo, 2017;Masero & Pérez-Hurtado, 2001).…”

Predictors of Gull-billed tern (Gelochelidon nilotica) nest survival in artificial coastal saltpans, Bohai Bay, China

“…These losses pose serious threats to waterbird populations dependent on these wetlands for staging, non-breeding, or breeding habitat (Warnock et al, 2002;Kirwan & Megonigal, 2013;Ma et al, 2014). Concurrently, artificial wetlands are rapidly expanding, caused by commercial enterprises such as salt production, and are creating a combined landscape mosaic of both anthropogenic and natural origins that can provide alternative or supplemental breeding and foraging habitats for waterbird species (Houston et al, 2012;Bluso-Demers et al, 2016;Rocha et al, 2017;Lei et al, 2018;Barnagaud et al, 2019).…”

“…Distinct from natural wetlands, waterbirds breeding in saltpans are confronted with different challenges (i.e., instantaneous water level adjustment, disturbance due to commercial activities of salt collection, little vegetation and soil substrates easily flooded by heavy rainfall). Salt concentrations found in saltpans, often exceed 300 mg/L, and can only be tolerated by a handful of salt-adapted species, such as Pied avocet (Recurvirostra avosetta), Black-winged stilt (Himantopus himantopus), Black-tailed godwit (Limosa limosa) and Marsh sandpiper (Tringa stagnatilis) (Walmsley, 1999;Lei et al, 2018). Few studies have examined the breeding success of waterbirds in these artificial wetlands (Martin, 1987;Tavares et al, 2008;Que et al, 2015;Rocha et al, 2016).…”

“…Urban areas such as the city of Tianjin have a long-established salt production industry, with the area of commercial saltpans in the region increasing from 60.0 km 2 in 1979 to approximately 457.8 km 2 in 1988 at the expense of natural wetland habitat (Wang, Xu & Zhu, 2015). While saltpans and other artificial wetlands are known to provide foraging habitat for a number of migratory waterbird species (e.g., Li et al, 2013;Lei et al, 2018), little is known about whether these artificial habitats are able to provide alternative breeding habitat for birds within this landscape mosaic (Yasué, Patterson & Dearden, 2007;Chokri & Selmi, 2011;Que et al, 2015).…”