The prob­lem with Canada geese

Kapi-Mana News - - OPINION - By ROBIN CHESTER­FIELD

For much of the year, the Canada geese prob­lems are not ob­vi­ous around Pau­ata­hanui.

Be­cause the birds’ pre­ferred food – short pas­ture grasses and her­ba­ceous wet­land plants – is read­ily avail­able, the geese feed in small groups over a wide area and their im­pact on the en­vi­ron­ment is not great.

But at other times, geese will de­scend in groups of up to 30 on the tidal basins that are the feed­ing spots for na­tive wad­ing birds, strip­ping the fring­ing salt-marsh plants and foul­ing the wa­ter.

Other na­tive birds, in­clud­ing spoon­bills, herons and king­fish­ers, are un­able to feed at prime lo­ca­tions when Canada geese are roost­ing in large num­bers (up to 40 birds) on the banks at the mouth of the Pau­ata­hanui stream and from Horokiri Stream to Ra­tion Creek.

The prob­lem gets worse at the start of the breed­ing sea­sons, when pairs are seek­ing safe nest­ing sites.

A good nest­ing site needs quick, easy ac­cess to a re­li­able water­way and a plen­ti­ful food source nearby for par­ent birds.

Such sites are es­sen­tial un­til the goslings fledge, and then through­out the sum­mer un­til the moult is over and the adult birds can fly again.

Suit­able breed­ing and moult­ing sites are of­ten lim­ited, so sev­eral pairs of geese will nest around the same site.

The geese will de­fend their nest sites ag­gres­sively, to the ex­tent the gan­der will hold an in­trud­ing duck un­der wa­ter un­til it drowns.

An av­er­age nest will con­tain be­tween six and nine eggs.

So, as hap­pened in the Pau­ata­hanui Re­serve when the geese first nested there, we had seven adult birds (one a non-breeder) and 26 goslings roost­ing along about 15 me­tres of grassed track, feed­ing there and in the ad­ja­cent pond.

Canada geese are large birds that eat and poo a lot, so it doesn’t take many in such a small area for a month or more to do dam­age.

Pub­lic ac­cess tracks are fouled to the point where they be­come un­us­able. But more im­por­tant is the in­tru­sion into and foul­ing of habi­tat used by na­tive species, such as herons, shov­el­ers, and es­pe­cially pied stilts.

For the past few years, a tidal basin in the re­serve has been the pre­ferred nest­ing site for up to six Canada geese breed­ing pairs.

How­ever, the tidal basin is also the nest­ing site and main feed­ing ground for the na­tive pied stilt.

By us­ing the shell is­lands, where the stilts nor­mally nest, as look­out posts, and by foul­ing and mud­dy­ing the stilt feed­ing ground, the Canada geese en­dan­ger an im­por­tant south­ern North Is­land pied stilt breed­ing colony.

And by feed­ing ravenously on the fringe of the tidal area, the geese are se­ri­ously dam­ag­ing the her­ba­ceous salt-marsh plants.

The con­cen­tra­tion of th­ese geese into small niche ar­eas for ex­tended pe­ri­ods causes the prob­lem and cre­ates the need to con­trol their num­bers.

We had hoped that pop­u­la­tion con­trol of geese in the re­serve could be achieved by find­ing the nests and pre­vent­ing the eggs from hatch­ing, but this has not been ef­fec­tive.

In 2013 there were no goslings hatched in the re­serve, but late in the breed­ing sea­son, three pairs of geese that had raised clutches far­ther afield brought their goslings into the re­serve, so our ef­forts at con­trol­ling num­bers were largely in­ef­fec­tive.

In North Amer­ica, where Canada geese are in­creas­ingly en­ter­ing the ur­ban en­vi­ron­ment, ex­pe­ri­ence in­di­cates that in­ter­fer­ing with breed­ing by ad­dling eggs is not enough to off­set the ef­fect of the 20 to 30-year life ex­pectancy of the geese.

From be­ing rare visi­tors of one or two birds in the 1980s, the lo­cal flock is now more than 70 birds and grow­ing rapidly.

Canada geese are in­creas­ing through­out New Zealand and are caus­ing so much dam­age to crop­land and the habi­tat of na­tive birds and plants, that the species is now on the pest bird list.

It is ob­vi­ous that to pro­tect the habi­tat of na­tive birds and plant species, con­trol of Canada geese must be tack­led on a broader ba­sis than just ad­dling eggs.

Men­ace: A Canada goose with goslings.

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