Wrybills disappearing from Great Barrier Island


The small consolation is that it's not our rats that are responsible!!  by John Ogden

 

Wrybills are tiny waders, and one of very few bird species with a sideways-curved bill. They are found only in New Zealand, where they breed on the braided rivers of the eastern South Island, and migrate to North Island estuaries to feed in the winter. The species is a highly specialized and unusual member of the plover family; its sideways bill allowing it to poke under river pebbles for hidden insects, worms and crustaceans. Wrybills are truly an iconic New Zealand bird, but sadly, like much of our biodiversity, they are heading towards extinction.

 

The NZ wrybill (anarhynchus frontalis) or ngutuparore, a male in breeding plumage showing the distinctive curved bill.  Photo: stevex2.wordpress.com
 


Every year a few wrybills visit Great Barrier, stopping for a few months to feed on invertebrates in the mud at Whangapoua estuary. At high tide they generally hang out with New Zealand and banded dotterels on the Okiwi spit, where I have been counting them since 1999.

 

Figure 1 (see p.12) says it all: in the decade from 2000 to 2010 wrybill numbers on Okiwi Spit have declined to zero or single birds only. The exceptional count of twenty wrybills in 2000 doesn’t effect the validity of these results (the correlation remains highly significant even if it is removed). Moreover, if the slope of the line is extrapolated backwards, a figure of 17 wrybills is ‘predicted’ for 1980, and 15 were actually counted in March that year (Ogle 1981).

 

Wrybills are classified as ‘Nationally Vulnerable’ by the Department of Conservation (Robertson et al. 2012; Dowding, 2013) and showed a population decline from 1985–1999 (Atlas of New Zealand Birds 2007). The predicted future decline is between 10 and 50%. Counts by the Ornithological Society of New Zealand from 2006–2009 demonstrate continued losses (Riegen 2010).


The Okiwi birds might represent ‘overspill’ from the declining winter flock in the Gulf of Thames, but it appears that this more northerly site will soon be lost.


The main cause of the decline in wrybills is clear: destruction of their breeding habitat on the braided river beds of the South Island(Rebergen 2011). As more water is taken from the rivers for irrigation and dairy farming, the river-beds are invaded by weed plants such as broom, gorse and lupins. The nesting areas of grey pebble banks and flats are reduced, and as river levels fall, predators such as feral cats, stoats, weasels and rats gain easier access. The key to wrybill’s survival lies in maintaining enough natural predator-managed and weed-free river habitat in Canterbury and Otago. This illustrates, in a Great Barrier context, the threats facing so many migratory birds, which nest in one place but spend their winters in far distant locations.

The wrybill’s curved beak in plan view – a unique curve of 15–22 degrees to the right.

 

Environmental News Issue 34 2015