Tuesday, August 11, 2009

The Problem with mice

This came through an email list I monitor, from Elton Smith, Conservation Manager of Orokonui Eco-Sanctuary.

The Problem with Mice

There is no best practice or standard operating procedure to eradicate or control mice

DoC does not intend to write a best practice. There is simply not enough data available

There is no way to predict the success or failure of mice eradications at an early stage – mice are almost impossible to detect at low levels.

38% of mouse eradications fail (5% Norway Rat).

50% of Brodifacoum operations fail in eradicating mice

50% of aerial operations fail to eradicate mice

The preferred habitat of mice is rank grass although in the absence of rats mice can be found in high densities in a wide range of habitats. Densities can reach 160 mice per hectare.

The mean home range of mice can be as little as 8-10m between April and July

A 50m grid is deemed to be too coarse (by some) to accurately detect mice at low levels. The recommended spacing is 10m. Who on earth has the resources to monitor at this rate?

Recent research has show that mice can cover large distances in very low numbers (500m +) and appear to be very trackable in tunnels

Live mice have been seen carried by kaka, morepork, weka and kingfisher.

Monday, August 10, 2009

Species Specific Science on 1080

I am trying to learn as much as I can about the 1080 debate. My subjective view from personal experience of travel in the bush is that 1080, while doubtlessly not the ideal solution, has at least helped our biodiversity hold out against the wave of invaders. I am actively challenging the assumptions I have though by trying to approach this issue with an open mind.

An interesting resource is the Lincoln University database that looks at 1080 at a species specific level through the food web.

Secretary Island Project

I spoke with Megan Willans the other day, she is DOC's programme manager Biodiversity in Te Anau. Megan leads the project that is trying to establish the first population of rock wren in a mostly predator free environment on Secretary island in Fiordland.

Megan reports that there have now being two transfers of birds to Secretary Island from the Murchison mountain totaling 24 birds. Birds have been seen in pairs and carrying nest materials, and hopefully this summer breeding will be confirmed.

Megan has shared her translocation proposal with me and I will upload this information over time in readable chunks! Firstly, the "need"....

An initial transfer of nine birds to Secretary Island took place in March/April 2008. A survey in November located two pairs near the release sites. One of these females was seen carrying nest lining material. Further surveys will take place over the breeding period to ascertain if breeding has occurred.

To develop a genetically viable/robust population a further 20-40 rock wren are proposed to be transferred to Secretary Island over the coming 2-3 years.
As outlined in the initial translocation proposal set below are further details of the need for the establishment of a rock wren population on Secretary Island.

Rock wren inhabit alpine ranges dissected with bush clad valleys and farmland. Their weak flight means that populations are also physically isolated from each other and discrete populations are susceptible to local extinction.
The rock wren is listed as ‘nationally vulnerable’ according to the New Zealand Threat Classification System (Hitchmough, 2005). Relatively little is known about the abundance and distribution of rock wren throughout their range. This lack of information reflects the isolation and relative inaccessibility of the birds’ preferred habitat.

An analysis of database and anecdotal records (Michelsen and Gaze, 2006), as well as some resurveying of past study sites (Willans 2007), have recently taken place to gain more rigorous information on recent trends in rock wren populations. This information has given reason to attempt translocating rock wren to a predator free environment a second time.
Consistent anecdotal accounts of decline throughout the range of rock wren suggest that there is decline occurring in some areas possibly due to predation (Michelsen-Heath and Gaze, 2006). The ground-feeding and hole-nesting habits of rock wren is likely to be a contributing factor in making them vulnerable to introduced mammalian predators.

An intensive population survey of rock wren, undertaken in the Murchison Mountains took place over the summer of 2006/07. Whilst the Murchison Mountains population appears healthy, comparisons made with data collected during the summer of 1984/85 (Michelsen-Heath, 1989) showed a 44% decline in rock wren density over the last twenty years (Willans, 2007). Evidence of predation by stoats and mice on rock wren nests was observed during both studies. Predation of adult or fledged juvenile rock wren was not observed during either study; however this may take place especially to recently fledged juveniles.

The results from this research are likely to reflect their status in other areas on the mainland. It has been concluded that the priority to secure a population of rock wren in a predator free environment remains. Secretary Island provides suitable habitat free of mice, and stoats presently in very low numbers are likely to be eradicated in time.

It is believed that this translocation is appropriate as it will contribute to the Rock Wren Recovery Statement goal (Gaze, 2004) “to ensure that rock wren are established in an environment where a population can be expected to survive in the absence of management”, by securing a self sustaining population on an island near to predator free, creating an additional insurance population for a species which is in decline on the mainland.

One consideration deemed important when choosing the release sight included the present natural range of rock wren. Secretary Island is adjacent to, and contains similar habitat to, the alpine ranges in Doubtful Sound where rock wren still inhabit.

It is planned to reintroduce threatened species to Secretary Island to restore the former biotic community (Wickes, in prep). This restoration programme includes a proposal to introduce rock wren. The extinct relative, bush wren, were likely to be present historically on Secretary Island. It is also possible that rock wren did exist on the island. Reintroducing the taxon to Secretary Island may restore some of the ecological processes lost with their extinction.
Secretary Island is Fiordland’s second largest (8140 hectares), and highest island rising to 1196 metres above sea level. It supports a diverse range of plant communities and habitats, ranging from lowland beech-podocarp forest through to sub-alpine scrub, tussock tops and herb fields. It has been estimated that about 150 hectares may contain suitable rock wren habitat, which would provide a large area to establish a viable population of rock wren.

Secretary Island is not entirely pest free yet. Two pests inhabit the island; deer (Cervus elaphus) and stoats (Mustela erminea). The island is now subject to an intensive pest control programme to eradicate and prevent re-establishment of stoats (Golding et al., 2005) and deer (Crouchley et al., 2007) to provide a sanctuary for threatened species.
Evidence of stoat predation on rock wren chicks and eggs in nests has been documented on a number of occasions in the Murchison Mountains (Michelsen-Heath, 1989 and Willans 2006, 2007). It is expected that on Secretary Island stoats will either stay at very low density (with a trap check and re-bait every six months), or they will be eradicated and therefore will pose minimal risk to translocated rock wren.

Deer pose less threat to rock wren, however they are known to eat many of the same plants rock wren feed on and nest in/under e.g. tussocks, small leafed coprosma’s and other divaricating plants. In the same way deer also impact on the insect community and insects are the key food source in the rock wren diet. Eradicating or maintaining a very low deer density will benefit rock wren on the island.

Secretary Island is isolated from the mainland which has meant other pest species such as rodents (Rattus sp. and Mus musculus) and possums (Trichosurus vulpecula) have not invaded by swimming to the island. Evidence of mouse predation on rock wren nests in the Murchison Mountains has also been documented on a number of occasions (Michelsen-Heath 1989 and Willans 2006, 2007).