The Wrybill Anarhynchus frontalis: a brief review of status, threats and work in progress ADRIAN C. RIEGEN '1 & JOHN E. DOWDING 2 •231 ForestHill Road, Waiatarua, Auckland 8, NewZealand, e-maih riegen @xtra.co. nz; 2p.o. BOX36-274, Merivale, Christchurch 8030, New Zealand, e-maih [email protected]. nz Riegen,A.C. & Dowding, J.E. 2003. The Wrybill Anarhynchusfrontalis:a brief review of status,threats and work in progress.Wader Study Group Bull. 100: 20-24. The Wrybill is a threatenedplover endemic to New Zealandand unique in havinga bill curvedto the right.It is specializedfor breedingon bareshingle in thebraided riverbeds of Canterburyand Otago in the SouthIsland. After breeding,almost the entirepopulation migrates north and wintersin the harboursaround Auckland. The speciesis classifiedas Vulnerable. Based on countsof winteringflocks, the population currently appears to number4,500-5,000 individuals.However, countingproblems mean that trendsare difficult to determine. The mainthreats to theWrybill arebelieved to be predationon thebreeding grounds, degradation of breeding habitat,and floodingof nests.In a recentstudy in the MackenzieBasin, predation by introducedmammals (mainly stoats,cats and possibly ferrets) had a substantialimpact on Wrybill survivaland productivity. Prey- switchingby predatorsfollowing the introductionof rabbithaemorrhagic disease in 1997 probablyincreased predationrates on breedingwaders. A recentstudy of stoatsin the TasmanRiver showedthat 11% of stoat densexamined contained Wrybill remains.Breeding habitat is beinglost in somerivers and degraded in oth- ers,mainly by waterabstraction and flow manipulation,invasion of weeds,and human recreational use. Flood- ing causessome loss of nestsbut is alsobeneficial, keeping nesting areas weed-free. The breedingrange of the speciesappears to be contractingand fragmenting, with the bulk of the popula- tion now breedingin three large catchments. Researchis currentlybeing undertaken on longevity,survival to breedingage, and natal dispersal. Further data on theseaspects are requiredto assistin modelingtrends in the population.Nearly all of the recent demographicdata have beencollected in the MackenzieBasin, where the populationis almostcertainly in decline.There is reasonto believethat the datamay not be typical,and demographic data are requiredfrom otherparts of the breedingrange. INTRODUCTION "scything"motion (Turbott 1970). Largely because of its unu- sual bill, the Wrybill is currentlyplaced in the monotypic The Wrybill Anarhynchusfrontalisis a smallgrey andwhite genusAnarhynchus (Turbott 1990). However, otherfeatures ploverunique in the bird world, beingthe only specieswith of the skull are typical of Charadrius (Burton 1972), and a laterally curvedbill. In breedingplumage, it showsslight Holdaway et al. (2001) have suggestedthat the Wrybill sexualdimorphism--males have a narrowblack frontalbar shouldbe placedin that genus. between the forehead and crown which the females lack After breeding,most of the population migratesto the (Marchant & Higgins 1993). large harbours of the Auckland region in North Island Wrybills are endemicto New Zealand,where they breed (Sibson1963), in particularthe ManukauHarbour and Firth only on braidedriver systemseast of the SouthernAlps be- of Thames,which togetherappear to supportabout 85% of tween 43 and 45øS (Marchant & Higgins 1993, Fig. 1). the population(Davies 1997, Sagaret al. 1999, Fig. 1). Indi- Braidedrivers are rare globally, but are characteristic of South vidual adultstend to be faithful to a winteringsite, but there Island, New Zealand. They developedduring glacial melt are no apparentlinks betweenbreeding and wintering areas when vastwater-flow carriedgravels into the valleys.They (Hay 1984) About 90% of birds leave the North Island har- consistof numerouslinked channelsspread across gravel- bours in August and migrate south. Some non-breeding filled floodplains,often several km wide. Wrybills appearto adults and first-year birds migrate south later (October- be well adaptedto breedingon thegreywacke shingle of these November)and a few (mostlyfirst-year birds) remain in the riverbeds;eggs and chicks are highly cryptic,and incubating northernharbours for the entire breedingseason (Marchant adultsare secretiveand well-camouflaged. The bill, the distal & Higgins 1993). third of which curvesto the right by 12-26ø (Hay 1984), is The breedingbiology of the specieswas studiedin detail usedon the riverbedsto probeunder stones for insects,par- by Hay (1984), andfurther information on breedingecology ticulafiy mayfly Deleatidiumspp. larvae (Pierce 1979). On was provided by Hughey (1985a). Wrybills normally first the mudflatsof northernharbours it is effectivelyused in a breed at two years,but breedingin the first year has been * Correspondingauthor • Bufietin100April2003 20 Riegen & Dowding: Wrybill Anarhynchus frontalis 21 recorded(Dowding et al. 1999). They nearly alwaysbreed NEW ZEALAND as monogamouspairs in well-spacedterritories (Hay 1984), and the laying seasonextends from late Augustto Decem- ber. Replacementclutches are laid after loss and double- brooding occursregularly - the number of pairs double- • .•Auckland broodingvaried from 11 to 32% during three consecutive seasonson the upperRakaia River (Hay 1984). Birds begin leavingthe breeding grounds from late December,and nearly all have left by early February. Since 1979, the New Zealand Wader Study Group (NZWSG) has metal-bandedmore than 5,000 Wrybills on the winteringgrounds, studying longevity, recruitment and movements,particularly within the Aucklandregion. Since 1987, a colour-bandingstudy has been in progress,primar- ily in theTasman and Tekapo Rivers of theMackenzie Basin, central South Island. In thispaper, we briefly review currentknowledge of the SOUTHISL7 speciesand the threatsit faces,report on somerecent find- ings andresearch in progress,and identify areasof research TasmanR._ /'• • AshleyR, that would assistwith conservationof the Wrybill. McKenzie ' •RaikaiaR. Waitaki R. STATUS AND POPULATION Status •' Keysites mentioned intext The Wrybill (see Fig. 2) is classified as "Vulnerable" by BirdLife International (2000), and is consideredthreatened Fig. 1. Locationmap showingthe main Wrybill breedingsites on by habitatloss, invasive species, native speciesand human the rivers of South Island, New Zealand, and the main wintering disturbance.In New Zealand,the Departmentof Conserva- sites around Auckland on North Island. tion hasrecently ranked the speciesas "NationallyVulner- able";the two rankingsare equivalent(Molloy et al. 2001). Population size whena countof 4,143 birdsrepresented an apparentdecline of 19% in sevenyears (Riegen & Dowding 2001). Because Duringbreeding, the populationis widely andthinly spread this was of considerableconcern, a further count was under- on SouthIsland riverbeds. Many areasare difficult of access, takenin May 2002. This includedflocks that together tradi- andthe speciesis highly crypticin thishabitat. An accurate tionallyheld about95% of the populationand resulted in a censusunder these conditions is virtuallyimpossible. Popu- total of 4,650 andestimated population of about4,900. lation size hastherefore been estimated by countingwinter- Someof thevariation apparent in thesecounts may be due ing flocks in the North Island harbours. to annualdifferences in productivity,but sightingsof colour- There are few quantitativedata from before 1940; counts bandedbirds in the Aucklandflocks also suggest that there from the 1950ssuggested a populationof about5,000 birds may be considerablymore local movementbetween roost (Sibson1963). Countsof Wrybills (and otherwaders) have sites in winter than previously thought (J.E. Dowding, been undertaken in the Manukau Harbour and Firth of unpubl.data). Auckland' s locationon a narrowisthmus, with Thameseach winter since the early 1960s(Veitch & Habraken harbourson both sides,may also createproblems - high 1999).Combined totals for the two harboursaveraged 3,770 water differs by aboutthree hourson the two coastsand at duringthe 29 years,1962-1990. On thebasis that 85% of the least two flocks are known to commute between the har- populationis foundon theseharbours (Sagar et al. 1999),the bours,feeding on the falling tide on both (Dowding2001). nationalpopulation averaged about 4,500 over thoseyears. The Ornithological Society of New Zealand (OSNZ) also Population trends conducted national wader counts between 1983 and 1994. Theseshowed a winteringpopulation ranging from a mini- Becauseof the difficulty in obtainingaccurate estimates of mum of 2,807 in 1987 to a maximum of 4,418 in 1988. Based populationsize from the winter counts,it is clearly alsodif- on thesecounts the populationwas estimatedat 3880 (Sagar ficult to detect overall trends.Veitch & Habraken (1999) et al. 1999). notedthat the Wrybill may be declining,but high variabil- Becausethese estimates varied considerably,a national ity in the countsthey analysedfor Manukau/Firthof Thames Wrybill censuswas undertaken in May 1994 (Riegen1994). (a minimum of 2,120 in 1963 and a maximum of 7,807 in Winter Wrybill flocksare normally very denseand counting 1969) obscuredany clear trend. canbe difficult.Flocks containing >300 birdswere therefore Neverthelessthese counts (and the nationalWrybill cen- photographedand countedfrom the photos. The census suses)do suggesta changein winter-siteallegiance in recent appearedto have had goodcoverage and resultedin a total years,with numbersfalling in the Firth of Thamesand ris- count of 5,111 birds,