Background
This measure relates to indicator 1.5.2 Species occupancy of natural range.
The conservation status of New Zealand bats / pekapeka was reviewed in 2022.
Long-tailed bats are Nationally Critical. Predators are a major threat, although management has helped in some places. Outside conservation areas, forest clearance and development can reduce and disturb their habitat.
The three sub-species of short-tailed bats are Nationally Vulnerable (northern), Nationally Increasing (southern) and Declining (central). They are less widespread than long-tailed bats, but are also threatened by predators and habitat degradation.
DOC uses automatic recording devices to improve knowledge of bat distributions.
What did we measure?
DOC uses a National Biodiversity Monitoring Programme to assess state and trends for biodiversity at nearly 1,400 sites evenly spaced across on public conservation land (PCL). Approximately 280 randomly-selected sites are measured each field season (September–May) so that every site is measured on a 5-year rotation.
Traditionally, bat monitoring staff have had to work at night, and monitoring was rarely done in remote areas. As an alternative, DOC has been using automatic recording devices (ARDs) to detect bats at all sites in this programme. Staff place one ARD at each site and set it to record any bat echolocation calls (which are higher pitch than most humans can hear) made over one night, from 8pm to 6am. The digital recordings are processed and checked by artificial intelligence and DOC staff.
Here we show presence/absence results from bat ARDs over twelve years of monitoring. DOC uses this data to update our knowledge of bat distribution.
What did we find?
Long-tailed bats were recorded at 14.1% of sites where ARD have been set (Table 2). This includes a new record in the Longwood Range in Southland.
Short-tailed bats were recorded at 2.4% of sites. Most records are in the range of the central sub-species (Figure 1) and include new records from Raukumara on the East Coast and from Remutaka Forest near Wairarapa, where bats were believed extinct.
Naive occupancy results indicate that bats are more common in woody habitats (forest and shrublands), but were also detected in open habitats. Both species were less commonly recorded at sites in national parks (Table 1) than at sites in other types of conservation land.
We are not yet able to show a trend in bat records from this data (Figure 2).
Figure 1: Sites on public conservation land (PCL) where bats were detected with automatic recording devices (ARD) set for one night. Use the drop-down list to see records of short- or long-tailed bats; white circles represent all sites with ARDs set. Exact locations have been randomly shifted by a small distance.
Figure 2: Number of sites with bats recorded using automated recording devices set out for one night at sites on public conservation land (PCL) over the last twelve seasons.
| Land status | Vegetation type | Long-tailed record | Short-tailed record | ARD set out |
|---|---|---|---|---|
| National park | Non-woody | 10 (9.3%) | 0 (0%) | 107 |
| National park | Woody | 34 (10.3%) | 3 (0.9%) | 330 |
| Other PCL | Non-woody | 11 (3.9%) | 0 (0%) | 279 |
| Other PCL | Woody | 138 (21%) | 30 (4.6%) | 657 |
| Record type | 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | 2020 | 2021 | 2022 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Long-tailed | 5 | 5 | 8 | 10 | 3 | 30 | 27 | 19 | 33 | 32 | 38 | 29 |
| Short-tailed | 2 | 1 | 3 | 0 | 1 | 7 | 5 | 6 | 3 | 5 | 7 | 4 |
| ARD set out | 46 | 79 | 245 | 263 | 264 | 249 | 255 | 272 | 253 | 261 | 256 | 251 |
Data quality
This is a partial measure of medium accuracy and complies with the data quality guidelines in New Zealand’s Environmental Reporting Series.
Indices of bat abundance are not reported because of changes in the detection sensitivities of different ARD models used from year to year.
Figure 2 shows trends in records of positively identified bat species. Conclusions from these should be made with caution:
Each year represents a different random selection of sites, not a repeated measurement of the same site. It takes five years to measure the complete set of sites.
Standard use of ARDs to survey bats takes up to six fine nights at one location. To efficiently measure a large network of sites, this programme uses a single device set for one night. The chance that bats are present in the area, but not recorded depends on factors such as the weather and how close bats pass to the ARD. Without more nights, or more ARDS, to account for those factors, these records cannot prove bats are absent. Similarly, records in new locations must be checked with intensive surveys before they are confirmed as new bat populations.
Long-tailed bats fly a long way, with distances between their roosts and foraging grounds of 10 to 25 km or more. This means the same bats could be detected at more than one site and – because they live in colonies with a collective foraging range of 150km² – it is possible that the same colonies are detected at several different sites.
Glossary of terms
Automatic recording device (ARD) is a device that records audio/visual information and does not require the presence of an operator.
Echolocation is a method bats and some other animals use to locate objects, like prey or obstacles, by sending out sound waves to be reflected back off the objects. The strength, timing and direction of the reflected sound shows each objects’ position.
Processing is the conversion of recorded information (audio/visual) into data that can be analysed (a spreadsheet of identified species). Processing can be automated (performed by a computer algorithm) or manual (performed by a person).
Naive occupancy is the proportion of sites where a species has been recorded. For example, a naive occupancy of 0.8 means that the species was recorded at 80% of sites. This does not account for sites at which a species was present but not detected.
Modelled occupancy is the estimated proportion of sites where a species is present, using repeated surveys to calculate a probability of presence at sites where the species was not detected. This method has not been used on the bat records reported here because only one device is set out for one night, and sites are re-visited at 5 year intervals.