Abundance and distribution of ungulates

This measure relates to indicator 1.3.2 – Invasive species dominance.

Background

Ungulates such as goats, deer and chamois are widespread across New Zealand’s public conservation land (PCL) and can have significant impacts on the recruitment and survival of palatable plant species. DOC is measuring their national distribution and abundance to help understand this impact and direct management efforts. These data also provide baseline information against which future trends and/or management results can be compared.

Ungulates are present across 82% of PCL, an increase from 63% in 2013.

What did we measure?

DOC has developed a national monitoring programme to assess the status and trends of biodiversity in approximately 1,400 sites that are spaced evenly across PCL. A random sample of approximately 280 of these sites are measured each year, so that every site is measured once on a five-year rotation. Table 1 shows the sample size in each year. Ungulate faecal pellets are counted at each site, and data are collected about vegetation, birds and signs of other introduced mammals.

Sites started to be re-measured in 2017 (Table 2), allowing improved estimation of changes in ungulate occupancy (presence/absence of pellets in plots on transects) and abundance (faecal pellet index or FPI). The data are modelled using a Bayesian zero-inflated negative binomial model to examine the effects of vegetation class (woody or non-woody), park status (national park or other PCL), year at site, site and transect on the occupancy and abundance of ungulates.

What did we find?

Ungulates occupied 82% (95% credible interval (CI) = 79.3–84.6%) of PCL in 2019/20, a significant increase since 2012/13 (Figure 1).
The average FPI for ungulates was 74.4 pellets (95% CI = 64.2–86 pellets) in occupied areas and 63.6 pellets (95% CI = 54.9–73.4 pellets) across all PCL (Figure 2).
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 (see Figure 4 - Map).

Figure 1: Ungulate occupancy on public conservation land (PCL) over the last eight seasons. Click on the key to show predicted values for different vegetation class (woody, non-woody) and land status (national park, non-national park) combinations. Hover over an individual point to show the value and 95% credible interval.

Figure 2: Ungulate faecal pellet indicies (FPI) on public conservation land (PCL) over the last eight seasons. ‘Occupied FPI’ represents FPI trends in ungulate-occupied areas, whereas ‘PCL FPI’ represents trends in FPI across all PCL. Click on the key to see predicted values for different vegetation class (woody, non-woody) and land status (national park, non-national park) combinations. Hover over an individual point to show the value and 95% credible interval.

Choose an area

Figure 3: Average observed ungulate faecal pellet indices (FPIs) for the most recent measurements at sites in each park. Enter a location in the box at the top (it will turn red) or hover over a point to see the 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.

Table 1: Number of sites measured each season for vegetation class (woody, non-woody) and land status (national park, non-national park) combinations.
Vegetation class	Conservation land status	2011	2012	2013	2014	2015	2016	2017	2018	2019	Total plots
non-woody	national park	0	21	24	24	22	17	25	22	22	112
non-woody	non-national park	0	43	58	45	56	59	59	59	45	283
woody	national park	35	8	54	73	72	60	65	54	64	323
woody	non-national park	33	22	150	126	115	120	123	141	126	643
Annual total		68	94	286	268	265	256	272	276	257	1,361

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

Figure 4: Observed ungulate faecal pellet indices (FPIs) for the most recent measurement at each site on public conservation land (PCL). Click on an individual site to see all measurements since 2011. Choose the ‘present/absent’ layer to outline in black those sites that had ungulates present, and choose ‘park level’ to switch to aggregated park averages. True site locations have been randomly jittered.

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 estimate ofrelative abundance is the total number of pellets summed over the plots on each line. Previous research has shown FPI to be linearly and positively related to the known abundance of deer Forsyth et al. (2007).

Occupancy indicates whether or not a site is being used by a species. A model is used to estmate the proportion of sites at which the species occurs, adjusted for the probability of detection.

Ungulate is the collective term for a broad range of animals that walk on the tips of their (generally hoofed) toes (e.g. deer, goats, chamois and tahr). Faecal pellets from these hoofed mammals cannot be easily differentiated and so have been 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.