When hunting has significant impact on wildlife

Population effects of harvesting grouse

How difficult can it be?

Actually, quite a lot!

Can A harvest reduce the growth poorly formulated of small game populations?

question!

When will harvest reduce the population growth below its YES!levels? normal

500 500 400 400 300 300 200 200 100 100 0 0

-0.4 -0.4

-0.2 -0.2

0.0 0.0

0.2

Without harvest With harvest

0.4

Looking for effects 1. Increased production of young 2. Decreased predation § Additive – Compensatory

3. Population change § Reference population § Before after

In the following: - Ruffed grouse in Wisconsin 1985-1995 - Willow grouse in Sweden, 1992-1995 - Willow grouse in Norway, 1996-1999 - Willow grouse on state land in Sweden, 1996-2011

Possible grouse dynamics

12000 12000 10000 10000 8000 8000 6000 6000 4000 4000

Annual cycle • Autumn • Winter • Summer

2000 2000 00

8

NO compensation through increased production

6

§ Large annual variation § Iceland an exception

Willow grouse Sweden 1996-2011 Hunted/Closed Areas

2

4

§ For any grouse species

0

Breeding success

§ No reports on density dependence

0

5

10 Adult Density

15

From Errington to Erlinge & Marcström § Doomed surplus have to die § Predators as garbage cans § “If we fail to take a human harvest – nature will do it for us” § Predators can regulate their prey § Predator control increase prey abundance § But if predators can reduce numbers of prey … § What about hunters and predators together?

Additive mortality using radio-marked grouse § Additive in hunting season § Weak, if any, compensation after hunting season Smith, A. and Willebrand, T. 1999. Mortality causes and survival rates of hunted and unhunted willow grouse. - J Wildlife Manage 63: 722–730.

Is hunting mortality additive or compensatory to natural mortality? Effects of experimental harvest on the survival and cause-specific mortality of willow ptarmigan Brett K. Sandercock1,2*, Erlend B. Nilsen2, Henrik Brøseth2 and Hans C. Pedersen2 J.Anim.Ecol. 2011.

Small, R. J. et al. 1991. Predation and Hunting Mortality of Ruffed Grouse in Central Wisconsin. - The Journal of Wildlife Management 55: 512–520.

Harvest and Population trends Sum of compensation § Ruffed Grouse 91% harvest § No change in population development § Immigration necessary

Pedersen, H. C. et al. 2004. Weak compensation of harvest despite strong density-dependent growth in willow ptarmigan. - Proc. Biol.

Sci. 271: 381–385.

Small, R. J. et al. 1991. Predation and Hunting Mortality of Ruffed Grouse in Central Wisconsin. - The Journal of Wildlife Management 55: 512–520.

Swedish long-term investigation 1996 – 2011

0.8

15 10 0

5

Antal

15

2005

2010

2000

2005

År

2010

År

0.0

0.1

0.1

0.2

15 10 5

0.2

0.3

0.3

Harvest2000

Rate

0.4 2005 År

0.4 2010

0.5

0

0.0

0

0

5

Antal

Antal

5

10

0.4

15

10

0.6

Frequency

2000

0.2

Apparant Survival

0

5

20

1.0

Antal

10

1.2

25

15

Harvest rates.

All years, all areas

0.6 2000

2004

2008 År

2012

Dispersal+ Migration Females

Scale and connectivity

1. High annual natural mortality 2. Large recruitment required 3. From where?

Summarize so far … § Additive mortality during harvest season using radio-marked grouse. § Seasonal migration & dispersal change local population size § Recruitment is a LARGE scale process § Dispersal 1. emigration 2. patch-movement 3. immigration

§ Landscape quality – Breeding density

Changes in population Changes in harvest?

2

3

4

5

6

2 ●

3

4

5

6

●

●

●

●

6

●

7

1

●

●

● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ●● ●● ● ● ● ●● ●● ● ●●

●●

● ●

●

●

●

●

● ● ●● ● ● ●

●

●

●

● ● ● ●●

●

●

●● ● ●● ● ● ● ●● ●

●●

●

● ●

●

5 ● ● ●

● ● ● ● ● ● ● ●● ● ●● ● ● ● ● ● ●

●

● ● ●

●

●

●

● ●

6

●

●

●

●

● ● ●

●

●

●

● ●

4

§ Bag statistics is needed § Including effort, numbers § Caution – bag as a proxy for population abundance § Other index or count is needed! bag § Two different questions: ●

●●

● ● ●

● ● ● ●●

3

effort

●

● ●

2

● ●

●

1

● ●

●

●

●

●

●

●●

● ● ●●

●●

●

● ●

● ●

●

● ●

● ● ●

●● ● ● ●● ● ●● ● ● ● ● ● ● ●● ●

● ●

● ●

●

● ● ● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ● ● ● ● ●

● ●

●

● ● ●● ● ●

●

● ● ● ● ● ●● ● ● ● ● ● ● ●● ● ● ● ●●● ● ●

●

● ● ●

●

●

● ●

6 5

●

● ●

● ●

2

3

4

●●

●

1

2

3

4

5

●

●

● ● ● ● ●

●

6

7

●●

● ● ● ●

●

● ●

●

●

●

● ●

●

● ●

● ● ● ● ● ● ●

●

● ● ●

● ● ● ● ● ● ●● ●●● ● ● ● ● ● ●● ●● ● ● ● ●● ● ● ● ● ● ● ● ●

5 10

20

30

●●

● ● ● ●

● ●

●

●

●●

● ● ● ●● ● ● ● ● ● ●● ● ● ● ●

● ● ● ● ●●● ●

●

●●

●● ● ● ● ● ● ● ● ● ● ● ●●● ● ● ● ● ● ● ● ● ● ● ● ● ● ●

●

●

●

● ●

● ●

● ●

●

● ● ● ● ● ● ●

●

●

● ● ●

●●

●

●

●

●

● ● ●●

●●

● ●

● ● ●

●

● ●

●

●

●

●

●●

●

●

●

●

●

●●● ● ●● ● ● ●● ●● ● ●● ●● ●● ● ● ● ● ●

●

●

●

●

●

●

● ● ●

●

§ The role of hunting in a population decline § The role of hunting in keeping a declined population at low abundance density ●

●

●

●

●

●● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ● ● ●● ●● ●● ● ● ● ●● ●

●

30

4 3 2 1

●

●●

chick

● ●

20

5

●

5 10

●

State land – Sweden

Avoid reaching 30% harvest over a to large area

Closed hunting on state land.

One of three counties, 2009 1.5

Västerbotten

1.5

Jämtland

0.5 −0.5 −1.5

−1.5

−0.5

0.5

●

2008

2009

1.5

Norrbotten

−1.5

−0.5

0.5

●

2008

2009

2008

2009

Large scale forces are present 3.5 3

3

2.5 2.5 2 2

Relative change in density

1.5 1.5 1

0.5

1

00.5

-0.5 0 -1 -0.5

-1.5

Breeding success

-1

-2 -1.5 -2

North Sweden North Norway North Finland Distance North Sweden Rodent index north Sw North Norway North Finland Distance North Finland Triangles

In the end … § Hunters often care about their wildlife § Can contribute to observations & data § Managers organize & educate § Researchers analyze § Annual feedback § Mutual trust