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

Abstract

Background Coastal saltpans are a common supratidal human-modified wetland habitat found within many coastal landscape mosaics. Commercial salt production and aquaculture practices often result in the creation of exposed coastal substrates that could provide suitable breeding habitat for waterbird populations; however, few studies have quantified waterbird breeding success in these artificial wetlands. Methods Here we examine the nesting behavior of the Gull-billed tern (Gelochelidon nilotica) breeding in the Nanpu coastal saltpans of Bohai Bay, Yellow Sea, China over three consecutive nesting seasons (2017–2019) by using nest survival model in Program MARK. Results The results revealed that nest survival of Gull-billed terns in coastal saltpans (0.697) was higher than previously published estimates from other regions, with an estimated daily survival rate (DSR) of 0.982 ± 0.001 (±95% CI). High nest survival was mainly attributed to low levels of human disturbances and low predation rates, while exposure to strong winds, flooding and silting were the main factors causing nest failure. Model-averaged estimates revealed that eggs laid in nests located on ‘habitat islands’ with feather or clam shell substrates were most likely to hatch. Initiation date, nest age, clutch size and quadratic effects of nearest-neighbor distance, nearest distance to road and nearest distance to water were all significant predictors of nest success, but the nest survival declined overall from 2017 to 2019 due to the degradation and loss of breeding habitat anthropogenically caused by rising water levels. Discussion Coastal saltpans represent an alternative breeding habitat for the Gull-billed tern populations in Bohai Bay, but conservation management should prioritize flood prevention to improve the extent and quality of breeding habitat, concurrent with efforts to create further ‘habitat islands’ with suitable nesting substrate.

Artificial Wetlands as Breeding Habitats for Shorebirds: A Case Study on Pied Avocets in China’s Largest Saltpan Complex

“…Flooding and abandonment were the main causes of nest failure. In comparison with other waterbirds breeding in the Nanpu saltpans, this nest survival was much higher than that of Kentish plover (Que et al, 2015) but lower than that in gull-billed tern (Wu et al, 2020), both of which were also estimated in the Nanpu saltpans but at different sites. These differences may be due to the different human disturbance levels occurring within the Nanpu saltpans.…”

“…Research on Kentish plover (Charadrius lexandrinus) breeding in saltpans located in the EAAF showed that its nest survival was among the lowest reported for this species, and human disturbance was the main cause of nest failure (Que et al, 2015). Surprisingly, gull-billed tern (Gelochelidon nilotica) breeding in these saltpans had higher nest survival than previously published estimates from other regions (Wu et al, 2020). The relative strength of the factors shaping breeding success for ground-nesting waterbirds will vary according to the geographical position of saltpans on the flyways.…”

“…The study sites for Kentish plovers were located in dikes formed from crystallization and shrimp ponds with high levels of anthropogenic disturbance (e.g., egg collection, irrigation, and trampling by pedestrians or vehicles) (Que et al, 2015), while the study sites for gullbilled terns were mainly isolated islets or abandoned ponds with low human disturbance (Wu et al, 2020). Both avocet and gull-billed tern nest survival were strongly and negatively affected by rainfall and anthropogenic activities (water pumping activity for salt production), which led to flooding events (Wu et al, 2020). Our models showed that the DSR was negatively correlated with precipitation and decreased as the breeding season progressed.…”

“…Most predators, such as gulls (Nogueira et al, 1996), corvids (Goutner, 1985), foxes (Cadbury and Olney, 1978;Goutner, 1985;Hötker and Segebade, 2000), and Rattus spp. (Cuervo, 2004;Wu et al, 2020), hunt in both natural and artificial habitats, although certain predators, such as stray dogs (Chokri and Selmi, 2011) or poachers (egg collectors) (Que et al, 2015), are more likely to hunt in artificial habitats. However, the rate of nest predation in Nanpu saltpans was comparatively low for avocets.…”

“…Anthropogenic wetlands such as coastal saltpans could provide alternative coastal habitats for waterbirds in the EAAF (Murray et al, 2014;Lei et al, 2018;Jackson et al, 2020). The importance of coastal saltpans for waterbirds as feeding and roosting habitats in the EAAF and other flyways is increasingly recognized (Takekawa et al, 2001;Sripanomyom et al, 2011;Green et al, 2015;Lei et al, 2018;Jackson et al, 2020); however, data on the role of coastal saltpans as breeding habitats for waterbirds in this flyway are very limited and contradictory (Que et al, 2015;Wu et al, 2020). Research on Kentish plover (Charadrius lexandrinus) breeding in saltpans located in the EAAF showed that its nest survival was among the lowest reported for this species, and human disturbance was the main cause of nest failure (Que et al, 2015).…”