Background

This measure relates to indicator 1.4.2 – Security of threatened and at risk taxa.

The lesser short-tailed bat belongs to a family found only in Aotearoa New Zealand. The northern subspecies is classified as ‘Nationally Vulnerable’, the central subspecies as ‘Declining’ and the southern subspecies as ‘Recovering’ under the New Zealand Threat Classification System. These bats are threatened by predation, forest clearance and land development, and potentially (because they eat insects and fruit on the forest floor) by toxins used to manage predators in their habitat. DOC monitors short-tailed bats to measure their survival in relation to predator management.

Short-tailed bats have high survival with predator management.

What did we measure?

DOC has monitored the annual survival of southern lesser short-tailed bats in the Eglinton Valley, Fiordland since 2006 and central lesser short-tailed bats in Pureora Forest, King Country since 2012 (Figure 1). These sites have different forest types, patterns of predator abundance, and histories of predator management.1

DOC staff catch adult short-tailed bats in mist nets and attach transmitters so females can be tracked to maternity roosts. Short-tailed bats use several maternity roosts in a season. A harp trap set outside the roosts is used to capture and mark a sample of the colony, approximately 200 bats a year, using passive integrated transponders (PIT). Antennae are placed around the maternity roost entrances to detect marked bats as they come and go. Annual survival is estimated from the number of marked individuals that are re-detected in following years. Population models for other bat species show average adult female survival rates above 0.79 p.a. result in population growth (Pryde et al., 2005).

What did we find?

  • Survival of southern lesser short-tailed bats has been high in the Eglinton Valley since monitoring began, except for 2007 when beech tree masting caused a rat irruption that was not adequately suppressed by predator control over a small area. In subsequent mast events, adult female survival rates were above 0.79 for four of five events (Figure 2).
  • Survival of central lesser short-tailed bats in Pureora Forest was also high, with adult female survival rate over 0.79 in all years (Figure 3).
  • Diphacinone and pindone were found in guano (bat poo) from Pureora Forest when toxins were used for nine or three months. No toxins have been found in guano since 2017, but pindone residue was found in a dead bat in 2018 and another in early 2019. There is no sign pindone was the cause of death, and the risk of toxin exposure has to be balanced with how effectively the treatment reduces rat numbers and allows bat populations to recover.
  • High survival rates for adult females in Pureora Forest since 2017 suggest that five weeks of pindone, with periodic aerial 1080, may be an effective combination for management of this population.

Figures

Figure 1: Locations of two monitored populations of lesser short-tailed bats.The Eglinton Valley is mostly beech forest, and predator numbers are driven by periodic pulses of abundant food from beech mast seeding. Pureora is a diverse podocarp and hardwood forest and predator numbers are consistently high.

Figure 2: Survival of adult and juvenile female southern lesser short-tailed bats in the Eglinton Valley calculated using RMark. Bars indicate the beech mast and management response in the preceding season. Values are means ± 95% confidence intervals.

Figure 3: Survival of adult and juvenile female central lesser short-tailed bats in Pureora Forest calculated using RMark. Bars indicate the management method used each year. Values are means ± 95% confidence intervals.

Data quality

This measure complies with the data quality guidelines used in New Zealand’s Environmental Reporting series.

The survival estimates are highly accurate and reliable because capture histories have been collected for many individual bats over a long period and recapture rates are high. Methods have been published in peer reviewed journals and use standard analyses for this type of data. However, because it reports on only two populations, this factsheet is partially related to the national indicator.

Survival for the 2021 / 22 season cannot be verified until 2023.

Glossary of terms

95% confidence interval is the range of values that have a 95% likelihood of containing the true value.

Mast seeding is the synchronous production of large quantities of seeds within a population of plants at irregular intervals. This occurs in a number of New Zealand forest tree and tussock grass species.

RMark is an interface to the software package MARK developed by Laake (2013). MARK was developed by Gary C. White to derive parameter estimates from animals that are marked and then re-encountered at a later time.

Survival is the proportion of a population that remains alive over time. It is a fundamental demographic parameter and, together with estimates of reproduction and dispersal, shows whether a population is increasing, decreasing or stable. Due to natural mortality, even a healthy population will not have 100% survival, but this will be balanced by recruitment.

Additional resources

Edmonds, P., H., O’Donnell, C.F., 2017. Survival of PIT-tagged lesser short-tailed bats (Mystacina tuberculata) through a pest control operation using an aerial application of the toxin 1080. New Zealand Journal of Ecology 41, 186–192.

Laake, J.L., 2013. RMark: An R interface for analysis of capture-recapture data with MARK (AFSC Processed Rep. No. 2013-01). Alaska Fisheries Science Centre, NOAA, US Department of Commerce., Seattle, WA.

McGlone, M.S., McNutt, K., Richardson, S.J., Bellingham, P.J., Wright, E.F., 2020. Biodiversity monitoring, ecological integrity, and the design of the New Zealand biodiversity assessment framework. New Zealand Journal of Ecology 44, 3411.

O’Donnell, E., C. F.J., Hoare, J.M.2., 2011. Survival of pit-tagged lesser short-tailed bats (Mystacina tuberculata) through a pest control operation using the toxin pindone in bait stations. New Zealand Journal of Ecology 35, 30–43.

Pryde, M.A., O’Donnell, C.F., Barker, R.J., 2005. Factors influencing survival and long-term population viability of New Zealand long-tailed bats (Chalinolobus tuberculatus): implications for conservation. Biological Conservation 126, 175–185.

Walker, S., Kemp, J.R., Elliott, G.P., Mosen, C.C., Innes, J.G., 2019. Spatial patterns and drivers of invasive rodent dynamics in New Zealand forests. Biological Invasions 21, 1627–1642.

  1. In the Eglinton Valley, a combination of racumin and diphacinone was used in bait stations over a small area (900 ha) in 2007. Pindone in bait stations was applied in 2010 and 2012, with aerial 1080 operations over larger areas (up to 26,000 ha) in 2015, 2017, 2019, and 2020. Since 2018, rat populations have not been supressed as effectively as by earlier aerial operations, and bait stations were also used for two months in spring. In Pureora Forest, diphacinone cereal pellets were used in 2013 over three months. Since then, pindone pellets have been used; at first for nine months per year, then dropping to two months and, since 2017, only for five weeks in spring, just before the bat breeding season. There was also an aerial 1080 operation in Pureora Forest in 2016.↩