Activity board
Three breeding seasons ago, Ark in the Park translocated hihi in their second year at the Ark produced a minimum of 26 chicks, yet now no hihi have been heard for over a year. Did the hihi adults and chicks disperse or were they predated?
If dispersal occurred to unsafe areas, Ark members could never combat this, but what if it were predation within the Ark area? Predator levels have been shown to be very low in the Ark, allowing existing native bird species to increase and the introduced robins to make substantial gains.
Hihi are obviously more readily predated by the introduced mammalian predators, evidenced by the fact that they died out in mainland forests in the 1880s. The hihi habit of roosting and nesting in tree hollows made them very vulnerable, particularly to rats as they could climb trees and seek prey using their sense of smell.
Adrien Martineau, a Master of Science student from France, spent 9 months at the Ark in 2010 plotting all the bait stations with GPS and analysing data accumulated up to 6 years from the bait uptake cards the volunteers record when renewing bait at the bait stations.
Lots of bait taken indicates the previous presence of rats; no or minimal bait uptake can indicate no rats since the previous baiting.
The complex computer analysis showed that within the Ark were certain hot spots of activity where rat numbers would drop only to rise again later in the year in a repeated pattern.
From this came the idea that there might be embedded populations of rats that never were eliminated because not all members had access to bait.
Lizzie McDonald, in her final year at Auckland University of Technology, studied this by measuring the actual spacings of the bait stations in some of these hot spots, confirming that because of the hilly topography, the nominal 100m spacing of lines was often much more than had been assumed.
This meant that the distance could have been greater than that of the typical home territory of forest-dwelling rats. Arrays of monitoring tunnels between these divergent lines indicated indeed that rats dispersed from the hot spots further and further away until presumably they came to bait stations when the numbers would go down again.
With this information, Ark can try to place additional bait stations in hot spots to ensure that more rats, perhaps all, will have access to bait allowing the core parts of the Ark to have a minimal rat presence.
Meanwhile, Ark members realise that spread into the Ark at the perimeter will always occur. But how far can the predator control effect extend beyond a perimeter? To answer that, Eru Nathan will be analysing lines of monitoring tunnels, which will start within the Ark and extend beyond the perimeter, as part of his MSc.
Rats obviously fascinate Ark members as another of the students from Belgium will look at the actual monitoring tunnels used. The original rodent monitoring done throughout New Zealand used white plastic tunnels, as Ark have used also from 2003.
Because we had insufficient of these in 2010 for the new forest blocks that the kokako led us into, Ark deployed the currently more commonly used black cardboard tunnels. An observation from sites where one of each was placed in proximity seemed to show a preference for one type [or was that an avoidance of the other?].
A preference [or avoidance] needs to be tested, as rodent monitoring is a vital part of gauging how successful Ark control is and will allow them to consider what other translocations might be considered in the future.
Rats again feature in Ami Maxwell’s summer studentship where a study of rats in the canopy is being done. Ami went through the Ark climbing course and with the other trained climbers is placing monitoring tunnels in a series of trees.
Both canopy tunnels and ground-based tunnels at each tree will have the same peanut butter lure that is traditionally used for rodent monitoring.
Although only small numbers of trees can be studied because of the practical difficulties in climbing, this type of comparison has rarely been reported elsewhere and may give interesting clues to wildlife managers anywhere who have to contend with introduced rodents.
For the opportunity to see the Ark in the Park area in the Waitakere ranges, and to go on the Walking Waitakere Wednesday Walks series, please email me on: kaylindley@xtra.co.nz.