MasonRiver–December2018

TheMasonisafoothills-fedriverthatrunsinanorthtosouthdirectionintotheWaiauimmediatelyupstreamoftheWaiautownship–seeattachedmaps.About6.5kmupstreamfromthisconfluencetheLotteryRiverrunsintotheMason,theformerriverissignificantlylargerthantheMason.

BelowtheLotteryconfluence,theMasonwouldappeartoprovidegoodnestingandfeedinghabitatfor braided river birds. This river wouldn’t be subject to the large floods in the Waiau that aresourced from rainfall at themain divide. The bed is often 100m ormore inwidth (photo 1) andcurrently there are fewweeds. On the date of the visit inmost places therewere 1 – 3 activelyflowingbraids.

Above theLottery confluence, theMasonnarrows significantly, isoften flankedbycliffs, inplacestreetopsalmostmeetover it,and itseemstoconsistmainlyofonechannel (photo2). Inplaces ithas gravel bars to about 30m wide. This isn’t classic braided river bird habitat. For the 1.5kmupstreamfromtheconfluence(toInlandRoad),theLotteryisalsoquitenarrowandsinglechannel,butfurtherupstreamitseemstobecomemorebraided–butwithweed-coveredbermsandislands(2015and2016GoogleEarthimages).

InthelowermostfewkilometresoftheMasonthereareseveralgraveloperations,currentlymainlyjust crushing and screening. There seems to be little vehicle access to the riverbed and few 4wdtrackswereseen–althougharecentfloodmighthaveobliteratedsome.Thisdoesn’tappeartobeanareawithamajorhumandisturbanceproblem.

I visited theareaonbehalfofBRaidon5/12/18after informationobtained fromECan thatHenryPinckney,averyenvironmentallyaware farmeratTheGatesproperty,hadseen riverbirdsonhisfarm.Plansforhisfarmincluderegenerationofnativebushandplantingofnewbushandpredatortrappingalongtheriverandindeedofhisentirefarm.Henrysaysheknowsof4otherlandownersalongtheMasontotheLotteryconfluencewhoalsowouldbeinterestedinriversidetrapping.

BirdObservations

Henrytookmealongtherivertoabout2kmupstreamfromTheGates.Inthisareain2017hesawuptoabout40black-billedgullsandanuncertainnumbernestedhere.Thisyearatthestartofthebreeding season therewere around 20 black-fronted terns in the area – but hewasn’t aware ofthemnesting.Piedstilts,piedoystercatchersandparadiseducksalsonestinthearea.Wesawapairofoystercatchersandaparadiseduck.

BestuseoftheremainingavailabletimewastotraversetheMasonfromit’smouthasfarupstreamaspossible,whichendedupbeingjustshortoftheInlandRoadbridgeovertheLottery–adistanceofabout7.5km.

Birdlifealongtheriverwasdisappointing.Inthelower1.3km9piedstilt,2piedoystercatcherand1black-backed gull were seen. The behaviour of one of the stilts suggested breeding in the area.Furtherupstreamonlytwopairsofparadiseducks,withducklings,wereseen.

ThelowerpartoftheMasonwouldappeartobegoodnestinghabitatforbandeddotterel,andtheotherbraided riverbirds. Factors causing thepaucityof thesebirds could include recent flooding,latenessinthebreedingseason,predation,orapreferenceforthelargerareasofthenearbyWaiau.TheMasonhas similaritieswith theKowai -which is a tributaryof theWaimakariri. InNovember2018therewasahighdensityofbreedingbandeddotterelintheKowaijustaboveit’smouthwheretheywereprotectedfromlargefloodsinthemainriver.

Henry informed me that there is a cat problem around Waiau township, and there are largenumbersofblack-backedgullsalongtheWaiau.

Conclusions

• The lower part of theMasonwould appear to be good feeding and breeding habitat forbraided river birds. However, other than pied stilt, few were seen. The total absence ofbandeddotterelwassurprising.Predationcouldbeafactorwithcatsandblack-backedgullsperhapsmostlikely.Itwouldbeinterestingtorevisitthisareaearlierinthebreedingseasonnextyeartoseeifthesituationisthesame.

• Above the confluencewith the Lottery, conditions in both rivers do not represent classicbraided riverhabitat.However, some speciesdooccurandevenbreedhere–withblack-billedgullsnestingontheMasoninTheGatespropertyin2017andternsseenherein2018.Anyeffortsoflocalfarmerstotraptherivermarginsshouldbeencouraged.

G.Davey,10/12/18

Photo1.LowerMason,fromInlandRoadbridge

Photo2.MasonRiverinTheGatesproperty