Publication - Research and analysis
Effects of displacement from marine renewable developments on seabirds breeding at the Isle of May
The project has produced a model which estimates the consequences of displacement and barrier effects on the time/energy budget of breeding seabirds.
8. Appendix 1
List of simulation and cost model parameters detailing assumptions and references.
| Parameter Group | Parameter Name | Parameter Value | References | Comments |
|---|---|---|---|---|
| Input layers | Resolution of model | 1km 2 | - | - |
| Prey density | Raster of number of individuals per location | - | Distribution simulated to represent prey | |
| Distance | Distance from Isle of May to every other cell | - | ||
| Bathymetry | Depth at every location | British Geological Survey under licence: http://www.bgs.ac.uk/products/offshore.html | ||
| Rules for selecting foraging location | Prey density >1 prey individual Dive depth > 0 Distance < 50km | Stephens & Krebs 1986; Daunt et al 2011a,b,c Thaxter et al 2009, 2010. Wanless et al 1990, 2000, 2005 | foraging theory; empirical data from Isle of May | |
| Model details | Prey interference competition model a i = Q*P -m a is the intake rate of an individual |
Q = 0.4; m = 0.6: P = number of guillemots at the location |
Hasswell & Varley 1969; Ens & Goss-Custard 1984; Dolman et al. 1995, Goss-Custard et al. 1995. |
m increased to 0.9 in clustered prey scenario |
| Behaviour | Flight direction | Range of directions from empirical data | Daunt et al 2011 a,b Thaxter et al 2009,2010. |
|
| Flight vs foraging direction | Equivalent values | Daunt et al. 2011 a,b | ||
| Flock size | Empirical data from 1 birds to 50 birds | Daunt et al 2011 c | Data sampled when direction data is chosen Assume that prey are disturbed due to high density of birds close to the colony | |
| Prey density decay | decay rate = 0.001 | Lewis et al 2001 | ||
| Wind farm presence | Displacement rate | 100% | - | Only for birds that choose to forage where the wind farm is located |
| Displacement distance (within 5km) | Birds remain within 5km | - | Assume that birds would aim to locate a suitable foraging location close to the wind farm to minimise added costs | |
| Cost Model | Cost model details | - | Daunt & Wanless 2008, Wanless 1997 | |
| Number of trips per day (chick rearing) | 2.02 | Enstripp et al 2006 | ||
| Distance travelled | From simulation results | Based on guillemots flying out and returning on the same bearing | ||
| Flight Cost | Flight speed | 19.1 ms -1 | Pennycuick 1997 | |
| Division of labour between mates | - | Daunt & Wanless 2008 | ||
| Foraging Cost | Assimilation efficiency | 0.78 | Hilton et al 2000b | |
| Cost of flight | 7361.72 kJ day -1 | Pennycuick 87,89 | ||
| Cost of resting on sea surface | 810.28 kJ day -1 | Croll & McLaren 1993 | ||
| Cost of staying at the colony | 1168.91 kJ day -1 | Hilton et al 2000a | ||
| Cost of warming food | 51.92 kJ | Gremillet et al 2003 | ||
| Energy requirements of chick | 221.71 kJ day -1 | Harris & Wanless 1985 | ||
| Prey density | 6.1kJ g -1 | Harris et al 2008 | ||
| Time spent resting at sea and at colony | Empirical data | Wanless et al 2005 | ||
| Time spent foraging, dependent on prey availability | Max prey intake rate of 5g min -1 Intake rate does not increase until more than 200 individuals per km 2 |
Enstipp et al 2007 | Expert knowledge; assumption that intake rate and therefore foraging is dependent on the availability of prey | |
| Diving efficiency ( DE) |
DE = 0.36-(0.0021*dive depth (m)) |
Daunt & Wanless 2008 | ||
| Diving depth distribution | 50% benthic; 50% water column from normal dist (mean 11.71, sd 8.07m) |
Daunt et al 2006; Daunt & Wanless 2008 |
||
| Negative energy budget | > 12 hours foraging | - | Assumption that this is one foraging trip, if more than 12 hours then returns to the colony to relieve mate | |
| Wind Farm Costs | Birds need to fly around the wind farm (barrier ) both on outward and return journey sampled from a normal distribution | Cost sampled from a normal distribution (mean =20km, sd= 5km) | - | Value based on size of wind farm (Approx. 40km perimeter, 14km length, 9km wide) |
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