Background
This measure relates to indicator 1.3.2 – Invasive species dominance.
Ungulates are browsing mammals including goats, deer, thar and chamois. They were introduced to Aotearoa New Zealand and wild ungulates are now widespread across public conservation land (PCL), where they affect indigenous plants’ growth and survival.
DOC monitors the national distribution and abundance of ungulates to help understand their impact and guide management. In 2023, DOC used this data to help identify priorities for its work under Te Ara ki Mua, a framework for adaptive management of wild animals. This baseline information can also be compared against future trends and/or management results.
Ungulates occur at 83% of sites on public conservation land, an increase from 63% in 2013.
What did we measure?
DOC uses a national monitoring programme to assess state and trends of terrestrial biodiversity at nearly 1,400 sites evenly spaced across public conservation land. Approximately 270 of these sites are measured each field season (September – May), so that every site is measured on a five-year rotation (Table 1).
At each site, DOC staff monitor vegetation, birds and signs of non-native mammals. Ungulate faecal pellet counts are counted on four transects. From these data, we calculate site occupancy (whether pellets are present or absent) and abundance (indicated by pellet counts per transect).
We report the effects of time, habitat (woody or non-woody vegetation) and park type (national park or other PCL) on ungulate occupancy (shown by presence/absence of faecal pellets) and abundance (shown by faecal pellet index or FPI). Data are modelled with a Bayesian zero-inflated negative binomial model which takes into account underlying differences between sites. Since 2017, most sites have been re-measured (Table 2), allowing better estimation of change over time.
What did we find?
- Over all habitat and park types, ungulates occupied 82.6% (95% credible interval (CI) = 80.2–84.9%) of PCL in 2022/23 – this has significantly increased over time (Figure 1).
- 14% of sites where no ungulate pellets were found in the first measurement had pellets found in the second measurement, while 6% of sites had pellets found in the first measurement but none found in the second (Table 2).
- The average FPI for ungulates was 87.5 pellets (95% CI = 77–100.1 pellets) in occupied areas and 75.2 pellets (95% CI = 66.5–85.3 pellets) across all PCL, and has also increased over time.
- Occupancy and abundance were generally lower in national parks (Figures 1 and 2). Figure 3 shows abundance in different parks.
- Occupancy and abundance vary across PCL (Figure 4).
Figures
Figure 1: Ungulate occupancy on public conservation land (PCL) over the last eleven seasons. Click on the key to show model estimates for different vegetation (woody, non-woody) and land (national park, other PCL) types. Hover over an individual point to show the value and 95% credible interval.
Figure 2: Model estimates of ungulate faecal pellet indices (FPI) on public conservation land (PCL) over the last eleven seasons. The upper panel shows FPI trends in ungulate-occupied sites, the lower shows trends over all PCL. Click on the key to see different vegetation (woody, non-woody) and land (national park, other PCL) types. Hover over an individual point to see the value and 95% credible interval.
Figure 3: Average observed ungulate faecal pellet indices (FPI) for the most recent measurements at sites in different park. Enter a park name in the box or hover over a point to see details. Several outliers are not visible but can be seen using the tools on the top right of the figure. Values are means ± 1 standard error.
Figure 4: Observed ungulate faecal pellet indices (FPI) for the most recent measurement at each site on public conservation land (PCL). Click on a site to see all its measurements since 2011. The ‘present/absent’ layer outlines in black those sites that had ungulates present, and ‘park level’ shows aggregated park averages. True site locations have been randomly jittered.
Tables
| Vegetation class | Land status | 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | 2020 | 2021 | 2022 | Total plots |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Non-woody | National parks | 0 | 21 | 18 | 25 | 23 | 16 | 26 | 16 | 22 | 23 | 15 | 25 | 108 |
| Non-woody | Other PCL | 0 | 42 | 56 | 48 | 56 | 51 | 55 | 58 | 50 | 55 | 50 | 57 | 280 |
| Woody | National parks | 35 | 8 | 60 | 72 | 71 | 62 | 64 | 60 | 64 | 69 | 65 | 60 | 329 |
| Woody | Other PCL | 33 | 23 | 152 | 123 | 115 | 130 | 128 | 142 | 122 | 114 | 128 | 117 | 659 |
| Annual total | 68 | 94 | 286 | 268 | 265 | 259 | 273 | 276 | 258 | 261 | 258 | 259 | 1,376 |
| State at first measure 2011-2018 | Observed | Not observed |
|---|---|---|
| Observed | 820 (64%) | 82 (6%) |
| Not observed | 185 (14%) | 203 (16%) |
Data quality
This measure is classified as a partial measure of high accuracy and complies with the data quality guidelines used in New Zealand’s Environmental Reporting Series. Results are reliable because data has been collected at a national scale, for over 10 years. It was analysed using standard methods for this type of animal abundance index.
Faecal pellet indices are often used to monitor ungulate abundance and have been shown to be correlated to known population size (Forsyth et al., 2007) and other count methods (Forsyth et al., 2014).
Glossary of terms
95% credible interval (CI) indicates that the true mean lies inside the interval with 95% probability given the posterior probability distribution.
Faecal pellet index (FPI) method involves counting the number of faecal pellets in 30 plots along four 150-m-long transect lines. In this network, there are four lines at each site. The total number of pellets counted in all the plots on a line is an index of relative abundance.
Occupancy indicates whether or not a site is being used by a species. A model is used to estimate the proportion of sites the species occupies, adjusted for the probability of detection.
Ungulate is the collective term for a group of herbivorous mammals that walk on the tips of their hoofed toes (e.g. deer, goats, tahr and chamois). Faecal pellets from these mammals cannot be easily told apart and so are aggregated into the group ‘ungulates’. Pigs are also ungulates but are not counted because their dung is easily identified.