Background
This measure relates to indicator 1.3.2 – Invasive species dominance.
Ungulates are introduced browsing mammals including goats, deer, thar and chamois. Wild ungulates are widespread across Aotearoa New Zealand’s public conservation land (PCL) and can significantly affect indigenous plant growth and survival. DOC measures the national distribution and abundance of ungulates to help understand their impact and guide management. The data also provide baseline information to compare against future trends and/or management results.
Ungulates occur at 82% of sites on public conservation land, an increase from 63% in 2013.
What did we measure?
DOC uses a national monitoring programme to assess the status and trends of biodiversity at approximately 1,400 sites evenly spaced across PCL. Approximately 280 of these sites are measured each field season (September - May), so that every site is measured once on a five-year rotation (Table 1). DOC staff count ungulate faecal pellets on transects at each site, and also measure vegetation, birds and signs of other introduced mammals.
Data are modelled using a Bayesian zero-inflated negative binomial model to show the effects of time, habitat type (woody or non-woody vegetation) and park status (national park or other PCL) on ungulate occupancy (shown by presence/absence of faecal pellets) and abundance (shown by faecal pellet index or FPI), taking into account underlying differences between sites. Most sites have been re-measured from 2017 (Table 2), allowing better estimation of change over time.
What did we find?
- Over all habitat and conservation land types, ungulates occupied 82.7% (95% credible interval (CI) = 80.4–85.1%) of PCL in 2021/22 - this has significantly increased over time (Figure 1).
- 15% of plots where no ungulate pellets were found in the first measurement had pellets found in the second measurement, while 6% of plots had pellets found in the first measurement but none found in the second (Table 2).
- The average FPI for ungulates was 81 pellets (95% CI = 71–93.3 pellets) in occupied areas and 68.6 pellets (95% CI = 60.5–78 pellets) across all PCL, and this has also increased over time.
- Occupancy and abundance were generally lower in national parks (Figures 1 and 2). The FPI in different parks can be explored in Figure 3.
- Occupancy and abundance vary across PCL (Figure 4).
Figures
Figure 1: Ungulate occupancy on public conservation land (PCL) over the last ten 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 ten 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 | Total plots |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Non-woody | National parks | 0 | 21 | 18 | 25 | 23 | 16 | 26 | 16 | 22 | 23 | 15 | 108 |
| Non-woody | Other PCL | 0 | 42 | 56 | 48 | 56 | 52 | 55 | 58 | 50 | 55 | 51 | 280 |
| Woody | National parks | 35 | 8 | 60 | 72 | 71 | 62 | 64 | 60 | 64 | 69 | 65 | 329 |
| Woody | Other PCL | 33 | 23 | 152 | 123 | 115 | 129 | 128 | 142 | 122 | 114 | 127 | 658 |
| Annual total | 68 | 94 | 286 | 268 | 265 | 259 | 273 | 276 | 258 | 261 | 258 | 1,375 |
| State at first measure 2011-2017 | Observed | Not observed |
|---|---|---|
| Observed | 640 (62%) | 64 (6%) |
| Not observed | 159 (15%) | 169 (16%) |
Data quality
This measure is classified as a partial measure of high accuracy and complies with the data quality guidelines used in the Environmental Reporting Series. Results are reliable because data has been collected at a national scale, for 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 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 20 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 differentiated and so are aggregated into the group ‘ungulates’. Pigs are also ungulates but are excluded because their faeces are easily differentiated.
Additional resources
Dorazio, R.M., Royle, A.J., 2005. Estimating size and composition of biological communities by modeling the occurrence of species. Journal of the American Statistical Association 100, 389–398.
Forsyth, D., MacKenzie, D., Wright, E., 2014. Monitoring ungulates in steep non-forest habitat: A comparison of faecal pellet and helicopter counts. New Zealand Journal of Zoology 41, 248–262.
Forsyth, D.M., Barker, R.J., Morriss, G., Scroggie, M.P., 2007. Modeling the relationship between fecal pellet indices and deer density. The Journal of Wildlife Management 71, 964–970.
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.
Moloney, P.D., Forsyth, D.M., Ramsey, D.S., Perry, M., McKay, M., Gormley, A.M., Kappers, B., Wright, E.F., 2021. Occupancy and relative abundances of introduced ungulates on New Zealand’s public conservation land 2012-2018. New Zealand Journal of Ecology 45.