Physiological, Morphological and Behavioural Responses of Self-Feeding Precocial Chicks Copying with Contrasting Levels of Water Salinity during Development

Abstract

Combined physiological and behavioural responses to salt loads during development have rarely been studied in air-breathing vertebrates able to inhabit hypersaline habitats, but they may be of particular importance in understanding, for example, the differences among species in patterns of habitat use or ontogenetic diet switches. Here, we compared the physiological and behavioural responses of self-feeding precocial chicks developed in contrasting levels of water salinity. The model species was the Black-winged Stilt (Himantopus himantopus) a precocial shorebird that breeds in a range of habitats from freshwater to hypersaline wetlands. Specifically, we compared resting metabolic rate (RMR), heat shock proteins (Hsp70), plasma ions, hematocrit, body mass, body size, growth rate and head-shaking behaviour of captive-reared Black-winged Stilt fledglings developed under fresh (0 ‰), saline (20 ‰), and hypersaline (60 ‰) water. Contrary to expectations, none of the physiological and morphological variables measured differed significantly among treatments. Likewise, the RMR of wild and captive-reared fledglings was similar. Surprisingly, the saltgland mass of wild fledglings from freshwater and those from hypersaline habitats was also similar. However, head-shaking, a behavioural response associated to minimize salt intake and to expel the secretions of salt glands, differed according to salinity source: head-shaking rate increased with increasing salinity. The results of this study support the key role of behavioural osmoregulation in avoiding salt stress during development.

Climate and human water use diminish wetland networks supporting continental waterbird migration

“…In saline lakes particularly, waterbirds are reliant on adjacent freshwater wetlands to balance physiological demands of saltwater environments (i.e. osmoregulation), especially during brood rearing when chicks are freshwater dependent (Rocha et al, ; Wollheim & Lovvorn, ). Loss of peripheral wetlands was greater (−53%) than those in upper watersheds (−47%) and likely a result of compounding upstream water diversions.…”

The drying of Lake Urmia and its consequences for waterbird assemblages

“…Freshwater wetlands adjacent to saline lakes are essential to waterbirds since these balance the physiological demands of saltwater environments (i.e. osmoregulation) (Rocha et al 2016). Therefore, protecting these wetlands around Lake Urmia is important to conserve migratory birds during drought periods because the adaptive capacity of migratory waterbirds to mitigate changing resource distributions has been proved by Rakhimberdiev et al (2018).…”

Wetland salinity induces sex-dependent carry-over effects on the individual performance of a long-distance migrant

“…Many waterbirds, as well as some passerines, can cope successfully with a diet that imposes high osmotic loads 51 , 52 . For instance, the ability of some waterbirds to inhabit saline wetlands has been attributed to a suite of behavioural, anatomical, and physiological adaptations to either eliminate excess salt or to reduce the intake of saline water by selecting diets with high ‘free water’ contents to compensate for their limited physiological capabilities 6 .…”