available evidence Justin Irvine Evidence based decision making - - PowerPoint PPT Presentation

Using sound science and best available evidence

Justin Irvine

Evidence based decision making

• Approaches to monitoring for decision making
• Research findings: making use of these.
• Tools

Deer management plans: what do you need to put these into practice?

Sustainable deer management means ensuring that the resource base can support the deer density.

• i.e. that the deer are in good condition because the

habitats they depend on are in good condition. The harvest (stags, venison) from the population is therefore linked to the habitats

• Local knowledge is invaluable
• But decisions need to be transparent:
• Qu. “What information is used to decide and act on the

numbers to be culled, or the target densities? “

Adaptive Management

• We don’t know exactly how the system

(habitat, deer numbers) will respond to management actions – other factors beyond

• ur control.
• Therefore we need to learn from our actions

to see if they are achieving what we want or expect.

Wetter winter by 2050 = increased mortality? Wetter summers by 2050 = increased fecundity UK Climate Projections UKCP18 http://ukclimateprojections.metoffice.gov.uk/

Changes in sheep stocks across the Highlands and Islands (1969–2014).

• 4. Overall Trends – Sheep versus deer

6 8 10 12 14 16 18 20 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8

Sheep density (Nat Log)

Parish deer density (km2) Redrawn from Clutton-Brock and Albon (1989)

Replacement of sheep by deer? (NW Highlands)

So planning takes place under uncertainty.

Typical deer management plan aims to: …..maintain the habitats, forage and shelter required to sustain a healthy, resilient and productive deer herd,

• …..capable of supporting an ongoing stag cull
• …..in keeping with the main natural heritage
• bjectives (public interest)

Deer management based on habitat:

Habitat condition Deer density culling guides managed by Stag off- take Density dependence

Adaptive Management: Building knowledge

Objectives Options/ methods Action Monitor evidence

Stag numbers, habitat condition Cull, fence, Number (or %) to cull.

• grazing impact,
• deer numbers
• calf:hind

Deer density, stag population size, habitat condition

Monitoring to better support management decisions:

What type of data do you need?

• 1. Habitat condition, grazing impact.
• 2. Counts: Deer density & calf:hind ratio
• 3. Cull numbers,

• 1. Habitat condition
• Assessment of grazing and trampling impacts by larger

herbivores: not just deer

Recording impacts over time

Work involved – random selection, marking of plots, training of staff, recording baseline measurement

• Recording of baseline height data from

heath/grass mosaic plot

Recording impacts over time

For example: dwarf-shrub heath

MAIN INDICATORS Grazing and Trampling Impact Dwarf-shrub heath Heavy Moderate Light % of heather Calluna vulgaris or blaeberry Vaccinium myrtillus shoots browsed >66% 33-66% <33% Browsing of cross-leaved heath Erica tetralix, cowberry Vaccinium vitis-idaea, bearberry Arctostaphylos uva-ursi or crowberry Empetrum nigrum Extensive Local None Grazing-induced growth forms; drumstick, topiary, or carpet Widespread Local Scarce Stem and branch breakage of heather Conspicuous Inconspic. Inconspic. Red deer/sheep scars Frequent

• V. local

Scarce % flowering and fruit of heather or blaeberry (summer browsing) Sparse Patchy Abundant Herbivore dung, sheep and/or deer V conspic. Moderate Low After Macdonald et al (1998)

• Approx. 50 km2
• 88 plots (2-3 per km2)

Resource input:

• 6-8 plots per day

(stalker – 1-2 weeks)

Impacts over time

Tools to help?

• In the pipeline
• SWARD (Supporting Wide Area Range

management for Deer)

• 2. Deer density:

Counting deer

• Counts do not give absolute numbers
• Need to be repeatable to identify trends (up
• r down) – (one-off counts can be misleading)
• Use counts as density estimates: more useful

for linking to habitat condition

• Recruitment rate (calf:hind ratio) influences

population growth

Population dynamics

Population size Calf recruitment Natural mortality Numbers culled

Stable when recruitment=mortality+cull Increasing when recruitment > (mortality+cull) decreasing when recruitment < (mortality+cull)

External factors (climate & sheep)

Example (using SNH pop model available

• n web)

Starting with 500 stags and 500 hinds

• Calf:hind ratio 30% = 150 calves (75 male)
• 17% cull

Population after 4 years will have declined to about 370 hinds and 370 stags. Same regime with calf:hind ratio 40% = 180 calves (90 male) Population after 4 years = 437 hinds, 437 stags Importance of using actual estimates of recruitment

Density dependence: Results from Rum North Block

As hind density increases,

• Calving dates get later and overwinter mortality of calves

increases but more so in males.

• Fecundity declines
• Birth weight declines
• Sex ratio becomes more female biased
• Stag antlers decline
• Stag emigration increases

per km2 1972 Present day Density 6.5 12.8 Stag density 8.2 2.7

• 3. Cull

The percentage of the estimated population culled varied markedly across the red deer range

• 10% to 30%

Historically, a 1/6th (17%) cull was advocated to maintain a stable population

• based on a calf:hind ratio of around 33 per 100

hinds.

• However, across Scotland the calf-hind ratio has

been around 40% (recent small decline since populations have been relatively high is consistent with density dependence)

SWARD: deer population modelling allows variable recruitment and mortality rates

Count and cull: What cull is needed to reach target density?

Plan for deer counts: once every 5 years - translate into density:

• Use population model to estimate change in

numbers under different cull levels to achieve required density

• Confirm with count 5 years later (and modify cull

if necessary) Recruitment counts = Calf:hind ratio

• To ensure that the right estimate of fecundity is

used in the model = big influence on outcome

Cull data can reveal population performance: Example from Norway

• As density increases, size of animals and

reproductive rate declines.

• Kvinnherad municipality, Hordaland County,

West Coast Norway

• Density estimate has increased from around

4.3 in 1991 to about 11.4 in 2012 (526km2)

• [Cf North West Sutherland = 5 deer per km
• ver 1700km2 ]

Deer culled km-2 Prop hinds calving Deer culled km-2 Year

Slaughter weight (kg) Slaughter weight (kg) Stag yearlings & calves Hinds yearlings & calves

Deer management based on habitat:

Habitat condition Deer density culling guides managed by Stag off- take Density dependence

Tools

• Best Practice Guidance on habitat monitoring
• Tools on SNH website for population modelling

SWARD (under test):

• Manages your data for habitat condition, count

and cull data

• Produces maps of habitat condition
• Guidance on culling to achieve density or stag

numbers DeerMAP: illustrates deer distribution and density as a result of changes such as culling and fencing

Discussion sessions

• What are the barriers to putting this into

practice? i.e. You have a plan: what is stopping you providing the evidence to demonstrate that it is being implemented?

Justin.irvine@hutton.ac.uk