Abundance and distribution of ungulates

Background

This measure relates to indicator 1.3.2 – Invasive species dominance.

Ungulates like goats, deer and chamois are widespread across Aotearoa New Zealand’s public conservation land (PCL) and can significantly affect indigenous plant growth and survival. DOC measures national distribution and abundance of ungulates to help understand their impact and direct management. The data also provide baseline information to compare against future trends and/or management results.

Ungulates occur at 82% of sites on PCL, 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. A random sample of 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 shows the sample size in each season. Ungulate faecal pellets are counted at each site, as well as measurements of vegetation, birds and other introduced mammals.

Data are modelled using a Bayesian zero-inflated negative binomial model to examine the effects of vegetation type (woody or non-woody), park status (national park or other PCL) and year on ungulate occupancy (shown by presence of faecal pellets in plots on transects) and abundance (shown by faecal pellet index or FPI), taking into account intrinsic differences between sites. Sites started to be re-measured from 2017 (Table 2), allowing better estimation of change over time.

What did we find?

Overall habitat and conservation land types, ungulates occupied 82.5% (95% credible interval (CI) = 80–85%) of PCL in 2020/21 and has significantly increased over time (Figure 1).
The average FPI for ungulates was 87 pellets (95% CI = 76.3–99.7 pellets) in occupied areas and 75.7 pellets (95% CI = 66.4–86.6 pellets) across all PCL.
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 nine 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: Ungulate faecal pellet indices (FPI) on public conservation land (PCL) over the last nine seasons. The upper panel shows FPI trends in ungulate-occupied sites, the lower shows trends over all PCL. Click on the key to see model estimates for 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

Table 1: Number of sites measured each season for different vegetation (woody, non-woody) and land (national park, other public conservation land) types.
Vegetation class	Conservation land status	2011	2012	2013	2014	2015	2016	2017	2018	2019	2020	Total plots
non-woody	national parks	0	21	24	24	22	17	25	22	22	22	112
non-woody	other PCL	0	43	58	45	56	59	59	59	45	56	286
woody	national parks	35	8	54	73	72	60	65	54	64	70	323
woody	other PCL	33	22	150	126	115	120	123	141	126	113	644
Annual total		68	94	286	268	265	256	272	276	257	261	1,365

Table 2: Number of sites that have been re-measured since 2011, grouped by the interval between measurements and whether ungulate pellets were observed in each measure.
		Repeat measure
Interval	First measure	Observed	Not observed
2011-2015	Observed	42	5
2011-2015	Not observed	9	9
2012-2015	Observed	39	7
2012-2015	Not observed	23	24
2013-2018	Observed	143	16
2013-2018	Not observed	57	52
2014-2019	Observed	166	14
2014-2019	Not observed	37	34
2015-2020	Observed	71	6
2015-2020	Not observed	11	13

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 framework.

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. Previous research has shown the index to be related to actual deer abundance (Forsyth et al., 2007).

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 broad range 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.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.

Lee, W., McGlone, M., Wright, E., 2005. Biodiversity inventory and monitoring: A review of national and international systems and a proposed framework for future biodiversity monitoring by the Department of Conservation, Landcare Research contract report LC0405/122 for the Department of Conservation, Wellington (unpublished). Landcare Research.

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.