A lack of suitable roosts increases the threat of intertidal foraging habitat loss to migratory shorebirds

The loss of intertidal foraging habitats at stopover sites is the primary
cause of population declines in many migratory shorebirds. However, the
absence of high-tide roosts can exacerbate this impact by increasing the
energy consumed for alarm flights and longer commutes between foraging and
roosting sites, which has been poorly quantified during time-constrained
spring stopovers. We monitored alarm flights at roosts using camera traps
and tracked the commutes between roosting and foraging sites of great
knots (Calidris tenuirostris) and bar-tailed godwits (Limosa lapponica) at
Yalu Jiang Estuary, a critical stopover site for shorebirds in the North
Yellow Sea. We analysed the energy costs of alarm flights by human
disturbances and commuting using flight energetic models. Camera trap
monitoring revealed that 20 of 67 (29.9%) roosting records at aquaculture
ponds recorded human disturbance that resulted in alarm flights. Birds
travelled 2.8 times farther than the optimal commuting distance when
nearby high-tide roosts were available. Flight energetic models estimated
that alarm flights and extended commuting resulted in an additional energy
expenditure of 355.9–902.3 kJ, equivalent to 3–4 days of foraging effort
based on food intake rates. Synthesis and applications. Foraging sites and
nearby high-tide roosts are integral habitat components for shorebirds to
acquire energetic surpluses, especially at migration staging areas. While
protecting intertidal flats to provide foraging habitats for shorebirds,
human activities should be minimised and disturbance should be avoided at
aquaculture sites during the high tide periods of spring tides to provide
safe roosts for shorebirds. Artificial roost structures (floating roosts,
roost islands, etc.,) could also be an effective solution for providing
additional roosting habitats for shorebirds.