With the exception
of a few birds on the east coast in the Gisborne area and the very odd
bird on the west coast, the Bay of Plenty is as far south as the northern
sub-species of the N.Z. dotterel, is found. It is estimated
that there are about 1,350 of this subspecies and rather less than 100
of the southern c. obscurus aquilonius subspecies which is found on Stewart
Island and which is a slightly larger bird. In the eastern Bay of
Plenty the birds nest on the dunes at several estuaries in the Opotiki
area, namely those of the Waiotahi, Waioeka and Waiaua rivers where they
have been extensively studied over recent years by Mr A Glaser of the Department
of Conservation. They also nest at Ohiwa harbour further west and at Whangaparaoa
near Cape Runaway.
Trapping of potential
predators has been carried out by D.O.C over recent years in the Waiotahi,
Waioeka and Waiaua areas - the principal predators caught being hedgehogs,
stoats, and weasels. The population of black- backed gulls, Larus dominicanus,
is reduced when they become dangerous to eggs or chicks. I have noticed
that quite often three chicks are hatched but are quickly reduced to two-the
parents being unable to protect the third. Over recent years the
population of spur-winged plover, Vanellus miles, has greatly increased
and they are often to be found in large numbers in the dotterel nesting
areas. Although there are records of these birds molesting chicks
their principal detrimental effect is interference with the chicks' access
to food.
As a result of Mr Glaser's
work it has been shown that a dotterel having lost its nest through predation
or any other cause will frequently nest again, if necessary, two or three
times.
Through banding it has
been proven that fledglings disperse quite widely, a bird hatched and banded
at the Waiaua estuary was seen at Pollen Island in the Waitemata Harbour
area.
After nesting the local
dotterels flock at Ohiwa Harbour, starting to assemble usually in late
February. In recent years this flock, at its height, has amounted to around
70 birds. It usually starts to disperse in May. For some reason
they seem to populate the furthest of the three estuaries ( Waiaua) first.
The birds are very territorial and much squabbling takes place when a bird
encroaches on someone else's patch.
It is suspected this year
that there may be a female/female pairing at the Waiotahi Estuary.
It is know that there is only two pairs at this location but there are
three nests containing eggs.It is possible that one nest has been abandoned
and the pair re nested but this is not thought to be the case. Advantage
has been taken of female/female pairings in places where the birds are
particularly scarce by robbing nests which will be replaced by fertile
hens and giving the eggs to the unmated bird to incubate.
Six years ago a stoat
den with kits was found at Waiaua and on analysis the remains of 11 dotterels
were identified; since the stoat probably hunted over night and the
male bird is known to incubate at night a disproportionate number of pairs
would have been broken. However it seems that there must be a “pool”
of birds somewhere possibly local fledglings because in the season following
the number of birds breeding at Waiaua was back to the usual 6 or 7 pairs.
One advantage that the
dotterel nesting areas in this region have over many of those further north
is that they are not plagued by holiday makers to any great extent;
in some places unless chicks are fledged by Christmas little hope is held
out for their survival as a result of human interference.
