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Rat incursions
have intensified over this dry summer
but Glenfern is repelling invaders
by effort and ingenuity.
The pourous end of the
fence at Arthur's Bay.
Photo: David Speir
History: Two aerial bait drops were
carried out on Kotuku Peninsula on June 24th and August 6th 2009. A
track network on a 50m x 50m grid of tracking tunnels had been installed
the year between the finishing of the pest exclusion fence and the
aerial drops. The grid had been delineated into 16 Pathways – each being
6-8 hours work for a person to place or retrieve index cards in the
tracking tunnels. The monitoring process allows us to find and respond
to incursions.
Monitoring for rodents commenced monthly in September with peanut butter
being placed on ink cards in every one of a thousand tunnels by 8 people
over a two day period. Two days later the cards were retrieved to
establish the presence of rodents. The buffer zones around each end of
the fence were being monitored once in between each monitoring run. Over
the first two months only one rat print showed up under a house in
Arthur’s Bay (Orama). In October Paul Keeling arrived to ascertain the
presence of cats and rabbits and trap for same. Over three weeks on the
peninsula he caught one cat and established that there were no rabbits
or cats remaining inside the fence.
In November there were incursions around
the end of the fence in Arthur’s Bay and across the harbour in Port
FitzRoy. In December there were several prints in Arthurs Bay, along the
shore line in Port FitzRoy and one rat came ashore in the Kotuku Scenic
Reserve and left prints in 5 tunnels across the peninsula. It took five
days responding to these prints with traps and bait. In January a rat
came ashore at Wingers on the Karaka Bay side and around the end of the
fence in Port FitzRoy.
Because of the number of rats that were
being caught and detected outside of the fence and along the shorelines
on both sides of the peninsula the buffer zones were extended all the
way to the Garden Bays on each side. Bait was also placed in the old
bait station network along the shoreline around the peninsula. Bait on
cradles in tunnels were alternated with traps throughout the buffer
zones.
In February multiple incursions were
detected along the shorelines of Karaka Bay, Port FitzRoy and Kotuku
Reserve. As a result the buffer zone monitoring was stepped up to every
3-4 days. By responding with a trap in the tunnel the same or following
day as the prints were found, the rat was generally caught as it seemed
to frequent the tunnel that it had found safe. This then became the
normal practice and it was decided to decrease the gap between
monitoring runs to three weeks. Most of the cards that were still viable
were left out or replaced after monitoring this time to provide an idea
of what took place during the intervening period.
In March two monitoring runs were
conducted. The buffer zones were increased again by extending them
inland from the foreshore into the adjacent hinterland to detect those
rats missing the shoreline defences. Up until the 5th March there had
been 12 rats caught on the Port FitzRoy side and 4 on the Orama side
inside the fence. However there were 19 caught outside the fence on the
Orama side and 6 on the Pt FitzRoy side.
 On the first day of monitoring while the
cards were being placed 8 rat prints were picked up in the extended
buffer zone in Port FitzRoy, another in Kotuku Bay and one in Karaka Bay
that had to be dealt with. On the second day of monitoring a rat was
caught in Kotuku Bay, Karaka Bay and one in the Port FitzRoy buffer
zone. On the third day of monitoring further prints were detected in the
Port FitzRoy and Orama extended buffer zones.
By the 13th, using the instant response
method 9 rats were caught in traps where prints were found in Port
FitzRoy and Kotuku and another 4 plus a mouse inside and 5 outside at
Orama. By the 16th 4 more caught inside at Port FitzRoy and 2 outside
with 3 plus a mouse inside and 13 outside at Orama.
Distinctively ratty prints.
The second monitoring run in March showed
a similar level of incursions to the earlier one two weeks before. These
were dealt with in the same manner as well as the buffer zones being
attended to every 2-3 days. This indicated a drop-off in the incidence
of incursions in the buffer zones, particularly on the Orama side.
For the April round all the viable cards
were left or replaced in the tunnels at the end of the last round and
traps were left set in the areas where prints were found.
The team took traps with them this time to
place in tunnels where prints were found. These traps are baited with
peanut butter and macadamia nuts. When the cards are brought back to
base the results are displayed on a large map of the peninsula with
coloured pins representing dead rats (red), prints with traps (green),
prints without traps (white), traps sprung (black) and bait on cradles
(blue). This proved a good way to get an overall feel and plan the
response.
In the May round all the cards were
replaced as the ink on the cards was not lasting long enough. When the
monitoring started 24 rats were found dead in traps placed in the
response phase of the April round. Over the next two days another 14
rats were caught from fresh prints and the next 10 days of response
monitoring caught a further 12 rats.
Mice prints were detected for the first
time this round near the edges of the paddocks, one trapped above the
Wingers and one print on the driveway near the Glenfern front gate.
A lot is being learned about rat dynamics
in the Great Barrier context where there are no possums, hedgehogs or
mustelids.
• When rats trip traps without being
caught they become trap shy, so these traps are replaced with cradles,
bait and cards.
• A single rat is often responsible for
more than one set of prints although traps are placed in all tunnels
with prints.
• With the long dry summer the rats that
come ashore gravitate up the streams and damp gullies into the middle of
the peninsula.
• The shorelines on both sides of the
peninsula and Kotuku Bay have the main concentration of prints and rat
kills. The next highest concentration occurs on the ridge above the
dwellings at Wingers and Arthurs Bay.
• Rats often dwell in barren terrain where
there is no ready food supply.
My grateful thanks to the Biodiversity
Funds, World Wildlife Fund, Auckland City Heritage Fund, Lotteries,
Covertex and the ARC for their assistance with the fence, eradication
and monitoring. Also the volunteers who keep coming back and show such
commitment to this project. |
