Record numbers of grasshopper-eating waders (Oriental Pratincole, Oriental Plover, Little Curlew) on coastal west-Kimberley grasslands of NW Australia in mid February 2010
103 – 108
1 August 10
Theunis Piersma, Chris Hassell
Global Flyway Network, c/o Department of Marine Ecology, Royal Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands.
Following a record count of close to 3 million Oriental Pratincoles Glareola maldivarum on Eighty Mile Beach, NW Australia, in Feb 2004, we report similarly large numbers of grasshopper-eating specialists representing three wader families (Glareolidae, Charadriidae and Scolopacidae) on grassland areas in the same region. In the late morning of 11 Feb 2010, as the midday heat had driven the grassland birds to the relative coolness of the Indian Ocean beaches, we counted 514,900 Oriental Pratincoles and 144,300 Oriental Plovers Charadrius veredus along 75 km of Eighty Mile Beach (165 km southwest of the town of Broome). Two days later similar numbers of Oriental Plovers were present along 45 km of the same beach, where we also counted 241,400 Oriental Pratincoles and over 14,200 Little Curlews Numenius minutus, the latter being absent during our previous count. Then, at Roebuck Plains cattle station (32 km east of Broome) during the late afternoons of 13, 14 and 17 Feb 2010, we recorded at least 60,000 Oriental Pratincoles moving around in flocks of up to 25,000. Huge numbers of small, 2–4 cm long, grasshoppers must have attracted the wader masses to these grasslands. Variation in seasonal rainfall is probably the main factor leading to these large aggregations of grassland waders. Relatively limited amounts of rain may result in a burgeoning grasshopper population, but persistent heavy rain may reduce the availability of food leading the birds to seek drier conditions elsewhere. In Feb 2010, these factors probably operated together and led to the aggregations of grasshoppers and waders we witnessed. The number of Oriental Plovers we counted doubles the population estimate for the region. Recent increases in the numbers of grassland waders recorded in NW Australia can probably be attributed to limited observer effort during the austral summer.