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)


Back to top