Abundance and distribution of hares & rabbits

Background

This measure relates to indicator 1.3.2 – Invasive species dominance.

Rabbits and hares are scattered across Aotearoa New Zealand public conservation land (PCL), but may have significant local impacts on the recruitment and growth of indigenous plants in some habitats. In particular, their browsing can affect the survival of some threatened plants. National changes in rabbit and hare abundance or distribution may help direct DOC’s management. The data also provide a baseline to compare with future trends and/or management results.

Rabbits and hares are most common in non-woody vegetation.

What did we measure?

DOC has developed a national monitoring programme to assess status and trends of biodiversity by repeated measurement of approximately 1,400 sites evenly spaced across PCL (Figure 4. Approximately 280 randomly selected sites are measured each field season (September - May) so that every site is measured on a 5-year rotation (Table 1).

Rabbit and hare faecal pellets are counted separately. DOC staff also record vegetation, birds and signs of other introduced mammals. Pellet count data are modelled with a Bayesian zero-inflated negative binomial model to show the effects of vegetation type (woody or non-woody), park status (National park or other PCL) and year on the animals’ occupancy (presence/absence of pellets) and relative abundance (shown by faecal pellet index or FPI), taking into account underlying differences between sites.

Sites were re-measured from 2017 (Table 2), allowing better estimation of change over time.

What did we find?

  • Overall habitat and conservation land types, occupancy was 25.4% (95% credible interval (CI) = 23.7–27.2%) and rabbit occupancy was 4.4% (95% CI = 3.1–5.9%) in 2020/2021. There is no change in either species’ occupancy over time (Figure 1).

  • The occupancy of both hares and rabbits was higher in non-woody vegetation

  • The occupancy of both hares and rabbits was lower in national parks.

  • Overall habitat and conservation land types, hare abundance was 9.2 pellets (95% CI = 7.2–11.9 pellets) in occupied areas and 3.4 pellets (95% CI = 2.8–4.1 pellets) across all PCL, while rabbit abundance was 6.6 pellets (95% CI = 2.8–15.5 pellets) in occupied areas and 0.5 pellets (95% CI = 0.3–1.1 pellets) across all PCL in 2020/2021.

  • The abundance of both species has remained stable over time (Figure 2).

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National park / woodyNational park / non-woodyOther PCL / woodyOther PCL / non-woodySeasonHare occupancyRabbit occupancy

Figure 1: Rabbit and hare occupancy on public conservation land (PCL) over the last nine seasons. Click on the key to show predicted values 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.

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National park / non-woody National park / woody Other PCL / non-woody Other PCL / woody Occupied FPIAll sites FPIHareRabbit

Figure 2: Faecal pellet indices (FPI) showing relative abundance of rabbits and hares on public conservation land (PCL) over the last nine seasons. The upper panel shows FPI trends in areas occupied by the animal, 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 show the value and 95% credible interval

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Observed hare FPIObserved rabbit FPIPark

Figure 3: Average observed rabbit and hare faecal pellet indices (FPIs) for the most recent measurements at plots in each park since 2011. Enter a location in the box at the top 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.

+−
Site occupancy
Both present
Hares only
None
Rabbits only
Leaflet | Powered by Esri | Tiles © Esri — Esri, DeLorme, NAVTEQ

Figure 4: Observed rabbit and hare 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 each species present. Site locations have been randomly jittered.

Table 1: Number of sites measured each year for different vegetation class (woody, non-woody) and land status (national park, other PCL) combinations.
Vegetation class Conservation land status 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Total plots
non-woody national park 0 21 24 24 22 17 25 22 22 22 112
non-woody non-national park 0 43 58 45 56 59 59 59 45 56 286
woody national park 35 8 54 73 72 60 65 54 64 70 323
woody non-national park 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 pellets were observed.
Repeat measure
Hare
Rabbit
Interval First measure Observed Not detected Observed Not detected
2011-2015 Observed 0 0 0 0
Not detected 3 62 0 65
2012-2015 Observed 39 4 10 2
Not detected 4 46 4 77
2013-2018 Observed 54 6 1 12
Not detected 6 202 9 246
2014-2019 Observed 51 6 3 12
Not detected 6 188 8 228
2015-2020 Observed 11 3 0 2
Not detected 5 82 1 98

Data quality

This measure is classified as a partial measure and complies with the data quality guidelines used in the Environmental Reporting framework.

Faecal pellet counts are often used to monitor leporid abundance and have been shown to be correlated with other measures. A previous study showed the method used here (to count the standing crop of pellets, rather than clearing each plot and revisiting to count new pellets deposited in a known period of time) should not unduly bias results.

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 circular (0.18m radius) plots along four 150-m-long transect lines. In this network, there are four lines at each site. The estimate of relative abundance is the total number of pellets summed over the plots on each line.

Leporid is the collective term for animals in the family Leporidae, including rabbits and hares.

Occupancy indicates whether a site is being used by a species. A model is used to estimate the proportion of sites the species uses, adjusted for the probability of detection.

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.

Fernandez-de-Simon, J., Dı́az-Ruiz, F., Cirilli, F., Tortosa, F.S., Villafuerte, R., Delibes-Mateos, M., Ferreras, P., 2011. Towards a standardized index of European rabbit abundance in Iberian Mediterranean habitats. European Journal of Wildlife Research 57, 1091–1100.

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 (unpublished) for the Department of Conservation, Wellington.

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.

Parkes, J.P., 2001. Methods to monitor the density and impact of hares (Lepus europaeus) in grasslands in New Zealand. Department of Conservation.

Perry, M.E., Robertson, A.W., 2012. Cleared and uncleared pellet plots as indices of brown hare density. New Zealand Journal of Ecology 157–163.