Alan Fielding & Paul Haworth

Transcription

1 Alan Fielding & Paul Haworth

2 Outline Loss of sub-adult habitat (displacement) Population-level effects of mortality (collision) Non-breeding birds Breeding birds Loss of golden eagle ranges (displacement) Methods also applicable to other species

3 Loss of sub-adult habitat Generally do not breed until 5+ Young birds disperse and become nomadic Avoid occupied ranges Avoid certain habitats, e.g. Conifer plantations, lochs, suburban areas Remaining habitat is sub-adult habitat

4 Loss of sub-adult habitat May affect sub-adult survival. Leads to a population decline as new vacant ranges remain unfilled. Thus, wind farms, even away from occupied ranges, may impact on the Scottish population. Loss of sub-adult habitat, in regions with little persecution, could increase threat to national population by encouraging emigration to regions with significant persecution.

5 Loss of sub-adult habitat Fielding et al (2006) described a method to assess the amount of sub-adult habitat. Upland regions >6 km from occupied golden eagle nests, excluding conifer forests and lochs. 20,475 km 2 of sub-adult habitat, in Scotland. In 2006, 378 km 2 was overlapped by 232 of the 527 potential wind farm schemes (1.85%). Not a significant problem at that scale.

6 Example: Skye

7 Fielding et al (2006) conclusion Nationally, wind farm developments did not give grounds for serious concern Extent of non-breeding eagle habitat lost to wind farms, by displacement, was minimal About 2% if all schemes were installed, Evidence that birds would not be displaced from regions free from persecution But, particular care in planning wind farm schemes and in assessing cumulative impacts is needed in some regions(nhzs).

8 Where are we now (Sept 2009)? (Worst case -all wind farm categories)

9 Where are we now (Sept 2009)? Sub-adult habitat lost (km 2 )

10 Population-level effects of wind farm mortality Population modelling approach needed Requires vital rates for Annual survivorship rates (non-breeding and breeding birds) Annual reproductive rates Estimates of mortality (collisions) Population geographical boundaries (NHZ?)

11 Population-level effects Non-wind farm example: removal of red kites from Wales for Irish re-introduction Removals (~mortality) modelled by reducing reproductive output. 462 young fledged by 325 successful pairs. Mean young per pair = 1.42 (462/325). Remove 50 newly fledged birds 462 reduces to 412 and Mean young per pair = 1.27 (412/325).

12 Welsh Red Kite population trajectories with and without removals. k = for both (over 50 years), short term decline to (2.8% annual increase). Not considered biologically significant.

13 Population-level effects: Arithmetic Approach NHZ with 74 pairs has mean fledging rate of 0.45 per year (FR = 0.45) = 33.3 birds (74 x 0.45) per year or 833 over 25 years. Assuming Whitfield et al s (2006) lower limit for favourable conservation status of 0.40 applies to pre-adult survival (PAS), Expect 13.3 of 33.3 to survive to age four.

14 Population-level effects: Arithmetic Approach Over 25 years 500 of 833 fledged birds will die from natural causes, leaving 333 survivors. If range turnover is 4.5% 167 adults (74 x 2 x x 25) are expected to die over 25 years. Leaves an healthy excess of 166 young adults to enter the floating population ( ) Additional mortality estimated by reducing the number of birds surviving to become adults. But, not a simple calculation

15 Population-level effects: Arithmetic Approach Population-level effect of the death of a subadult bird depends on its age. Assume FR = 0.40 and PAS = 0.40 and 31 pairs PAS of 0.4 implies an annual sub-adult survival rate of Assume that wind farms kill one sub-adult (less than 4 years old) each year. What are the predicted losses of adult birds?

16 Population-level effects: Arithmetic Approach No wind farm Age class of bird killed by the wind farm Yr1 Yr2 Yr 3 Yr 4 Age Fledged to to to to Additional Loss Effect of additional mortality is the same for each transition between age classes But, effect on number of adults is magnified as birds get older because there are fewer, subsequent, natural deaths

17 Population-level effects: Matrix Models Adapt approach used by Whitfield et al (2004). Estimated vital statistics for persecuted and unpersecuted populations to compare population trajectories. Adapt the model by adding in additional wind farm mortality. Whitfield et al (2006a and b) have tables of population scenarios for each NHZ. Similar tables now exist for Hen Harrier (Fielding et al, 2009).

18 The need for data Robust population models need robust vital statistics. Rates may vary between years and between regions. Two examples: Productivity map Productivity over time What happens when published vital statistics predict a decline in the absence of additional mortality but the species isn t declining?

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20 The need for data

21 Range Loss What happens if eagles are displaced from some of their range? What are the population level effects of range abandonment? Answer to both is it depends... No simple answer

22 Quantifying Range Loss Eagles use different parts of their ranges disproportionately. Species rarely use habitat evenly need to quantify to estimate loss Assess loss by: Empirical observation data (best practice) PAT model (McLeod et al 2002) But, impacts depend on local context evidence from an analysis of impacts of afforestation (Whitfield et al, 2001, 2007).

23 PAT Model with Empirical Data

24 Range Loss: Population-level Effects Depends on range productivity. Effects can be counter-intuitive. Two extreme examples 10 pairs, 7 unproductive and 3 pairs fledging 1 young each per year FR = 3/10 = 0.3 per year (below this golden eagle populations are not viable) Scenario 1: 3 unproductive ranges abandoned Scenario 2: 3 productive ranges abandoned

25 Range Loss: Population-level Effects Scenario 1: 3 unproductive ranges abandoned Now 7 pairs and FR increasesto 0.43 (3/7) Population in a more favourable status Also, less new recruits needed each year Scenario 2: productive ranges abandoned Now 7 pairs but FR is now 0 Population in a less favourable condition Population now a significant sink

26 What are the thresholds? Recently asked to complete cumulative impact assessment for 1 Peregrine death over 300 years (1 between 1709 and 2009!). Obviously nonsense, but also clear that 1 death every 2 years needs an assessment. So, where is the biologically significant threshold? To quote SNH (2009) we need a biologically sound approach Obviously species-dependent.

27 What are the thresholds? Similar to Type I and II errors in a significance test. What are relative costs of these errors? One biological, one financial When setting thresholds need to take account of: Socio-economic factors Wider biodiversity issues (e.g. climate change, land management) Conservation status of a species, what are its trends, is it already committed to extinction?

28 But where are the impacts? > 500 turbines installed, very little mortality reported Burger Hill -3 pairs of red-throated divers within 200 m of turbines. birds have continued to use LowriesWater over the last 25 years, in that time there has never been a bird collision ( Hen harriers breeding close to turbines (250 m at Cruach Mhor and 500 m at Ben Aketil) 11 young have successfully fledged at Cruach Mhor ( Golden plover 4 years, mean distance from >20 nests to turbines < 200 m (supposed displacement distance of Pearce-Higgins et al(2009)).

29 Pearce-Higgins et al (2009) From Table 1 17 turbines, 932 ha, 60m hubs 42 turbines, 648 ha, 70m hubs Cumulative impacts must be informed by real evidence and not ES estimates or indirect evidence - this must be a continuous iterative process. Where are the monitoring data?

30 References Whitfield, D. P., McLeod, D. R. A., Fielding, A. H., Haworth, P.F. and Broad, R. A The effects of forestry on golden eagles Aquila chrysaetos on the island of Mull, western Scotland. Journal of Applied Ecology, 38: McLeod, D. R. A., Fielding, A. H., Haworth, P. F., Whitfield, D.P., McGrady, M. J., Predicting home range use by golden eagles Aquila chrysaetos in western Scotland. Journal of Avian Science, 2: Whitfield, D. P., Fielding, A. H., McLeod, D.R.A. and Haworth, P. F Modelling the effects of persecution on the population dynamics of golden eagles in Scotland. Biological Conservation,119: Whitfield, D. P., Fielding, A. H., McLeod, D. R. A., Haworth, P.F. and Watson, J A conservation framework for the golden eagle in Scotland: refining condition targets and assessment of constraint influences. Biological Conservation, 130(4): Fielding, A.H., Whitfield, D. P. and McLeod, D. R. A., Spatial association as an indicator of the potential for future interactions between wind energy developments and golden eagles Aquila chrysaetos in Scotland. Biological Conservation, 131(3): Whitfield, D. P., Fielding, A. H., Gregory, M. J. P., Gordon, A.G., McLeod, D. R. A., Haworth, P. F., Complex effects of habitat loss on golden eagles. Ibis 149: Fielding, A. H., Haworth, P. F., Whitfield, D.P. and McLeod, D.R Raptor Species Conservation Frameworks: Hen Harrier Framework Final Project.Report to Scottish Natural Heritage.

31 Thank you