Modelling population-level impacts of wind farm collision risk on Welsh Red Kites

Hereward, H.; Macgregor, C.; Gabb, O.; Connell, A.; Thomas, R.; Cross, A.; Taylor, R. (2024). Modelling population-level impacts of wind farm collision risk on Welsh Red Kites (Report No. BTO Research Report 766). Report for British Trust for Ornithology (BTO).

TY - RPRT
TI - Modelling population-level impacts of wind farm collision risk on Welsh Red Kites
AU - Hereward, H
AU - Macgregor, C
AU - Gabb, O
AU - Connell, A
AU - Thomas, R
AU - Cross, A
AU - Taylor, R
AB - The Welsh Red Kite population is currently in ongoing recovery after a historic decline driven by persecution, and a consequent population bottleneck during the first half of the 20th Century. Trends from the BTO/JNCC/ RSPB Breeding Bird Survey (BBS; Heywood et al. 2023) show that the population has grown rapidly over the past few decades. Nonetheless, the Red Kite remains a conservation concern, in particular around two Special Protection Areas (SPAs) designated for the species’ conservation: the Berwyn SPA and the Elenydd–Mallaen SPA. Wind turbines represent a known threat to Red Kite populations, causing additional mortality through collisions. A large number of wind farm sites are currently at various stages of development (ranging from aspirational schemes to proposals under assessment) in Wales, especially in Mid Wales where Red Kites are at their highest density and where the Elenydd-Mallaen SPA is situated. In this context, RenewableUK Cymru contracted BTO and BSG Ecology to undertake Population Viability Analysis (PVA) to model the potential impacts of current and proposed (including early concept) wind farm developments on the Welsh population of Red Kites.Modelling used spatially-explicit Red Kite population estimates produced by combining data from (i) Bird Atlas 2007—11 (Balmer et al. 2013), (ii) the BBS, and (iii) the Avian Population Estimates Panel (Woodward et al. 2020). PVAs were run using lower and upper bounds and intermediate values for published, calculated and estimated demographic parameters. All possible combinations of demographic parameter levels were modelled, and a rejection sampling procedure applied to retain a final ‘baseline’ model set whose range of population trajectories reflected the observed population trend of Red Kite in Wales. Scenarios of wind turbine collision mortality were applied to describe the impact of each developer’s proposed sites in turn, as well as their combined impact, with outcomes assessed at the national (Wales) scale, at the scale of Natural Resources Wales’ regional ‘Area Statements’, and on the population of each of the two focal SPAs. Model outcomes were assigned to five categories according to whether they predicted population decline, population stability, or three different levels of population growth. From the initial set of 37,500 candidate models, rejection sampling retained 19,775 models that reflected the observed recent population growth. Under the baseline scenario (which includes all existing wind turbines but no further future developments), all models predicted population stability or increase at all spatial scales. Across virtually all combinations of impact scenarios and outcome scales, impacts are projected to be relatively small, even under the scenario where all developers’ plans were modelled in combination. Under this scenario, the probability of the Welsh population of Red Kite stabilising is 28% (compared to 17% under the baseline scenario). There is also a small but non-zero probability of each SPA population declining under this scenario (Elenydd-Mallaen SPA: 4%; Berwyn SPA: 0.4%; compared to 0% in both SPAs under the baseline scenario). However, for every impact scenario, population decline is predicted to be less likely than continued growth, at all outcome scales; an average of 12% of the national Red Kite population could be killed per year in collisions with new wind turbines before our models would suggest population decline as being more probable than not (all else being equal). In general, modelled impacts were larger for spatially-smaller outcome scales with relatively high-density Red Kite populations (especially the two SPA populations). Thus, impacts were larger for the high-density Elenydd-Mallaen SPA population than for the Berwyn SPA population where the current density of Red Kites is lower.Whilst impacts upon population trends may appear relatively small, these may propagate into substantial differences in population size given enough elapsed time. For example, the median population size estimate for the Elenydd-Mallaen SPA in the year 2050 is approximately half as large under the scenario where all developers’ plans were modelled in combination than under the baseline scenario, even though both estimates are greater than the most recent (2022) population estimate and therefore represent population growth.These results may provide reassurance that currently proposed levels of wind farm development are unlikely to prevent the continued growth of the Welsh Red Kite population, even in the most extreme scenario where all sites currently in development go ahead. However, they highlight that greater caution is justified for developments in proximity to the two SPAs designated for Red Kite, in order to minimise risk to the higherdensity populations of these areas.
DA - 2024/03//
PY - 2024
SP - 26
SN - BTO Research Report 766
UR - https://www.bto.org/our-work/science/publications/reports/bto-research-reports/00766-population-impacts-windfarms-red-kites-wales
LA - English
KW - Wind Energy
KW - Collision
KW - Birds
KW - Raptors
ER -

Export Citation to RIS

Abstract

The Welsh Red Kite population is currently in ongoing recovery after a historic decline driven by persecution, and a consequent population bottleneck during the first half of the 20th Century. Trends from the BTO/JNCC/ RSPB Breeding Bird Survey (BBS; Heywood et al. 2023) show that the population has grown rapidly over the past few decades. Nonetheless, the Red Kite remains a conservation concern, in particular around two Special Protection Areas (SPAs) designated for the species’ conservation: the Berwyn SPA and the Elenydd–Mallaen SPA. Wind turbines represent a known threat to Red Kite populations, causing additional mortality through collisions. A large number of wind farm sites are currently at various stages of development (ranging from aspirational schemes to proposals under assessment) in Wales, especially in Mid Wales where Red Kites are at their highest density and where the Elenydd-Mallaen SPA is situated. In this context, RenewableUK Cymru contracted BTO and BSG Ecology to undertake Population Viability Analysis (PVA) to model the potential impacts of current and proposed (including early concept) wind farm developments on the Welsh population of Red Kites.

Modelling used spatially-explicit Red Kite population estimates produced by combining data from (i) Bird Atlas 2007—11 (Balmer et al. 2013), (ii) the BBS, and (iii) the Avian Population Estimates Panel (Woodward et al. 2020). PVAs were run using lower and upper bounds and intermediate values for published, calculated and estimated demographic parameters. All possible combinations of demographic parameter levels were modelled, and a rejection sampling procedure applied to retain a final ‘baseline’ model set whose range of population trajectories reflected the observed population trend of Red Kite in Wales. Scenarios of wind turbine collision mortality were applied to describe the impact of each developer’s proposed sites in turn, as well as their combined impact, with outcomes assessed at the national (Wales) scale, at the scale of Natural Resources Wales’ regional ‘Area Statements’, and on the population of each of the two focal SPAs. Model outcomes were assigned to five categories according to whether they predicted population decline, population stability, or three different levels of population growth. From the initial set of 37,500 candidate models, rejection sampling retained 19,775 models that reflected the observed recent population growth. Under the baseline scenario (which includes all existing wind turbines but no further future developments), all models predicted population stability or increase at all spatial scales. Across virtually all combinations of impact scenarios and outcome scales, impacts are projected to be relatively small, even under the scenario where all developers’ plans were modelled in combination. Under this scenario, the probability of the Welsh population of Red Kite stabilising is 28% (compared to 17% under the baseline scenario). There is also a small but non-zero probability of each SPA population declining under this scenario (Elenydd-Mallaen SPA: 4%; Berwyn SPA: 0.4%; compared to 0% in both SPAs under the baseline scenario). However, for every impact scenario, population decline is predicted to be less likely than continued growth, at all outcome scales; an average of 12% of the national Red Kite population could be killed per year in collisions with new wind turbines before our models would suggest population decline as being more probable than not (all else being equal). In general, modelled impacts were larger for spatially-smaller outcome scales with relatively high-density Red Kite populations (especially the two SPA populations). Thus, impacts were larger for the high-density Elenydd-Mallaen SPA population than for the Berwyn SPA population where the current density of Red Kites is lower.

Whilst impacts upon population trends may appear relatively small, these may propagate into substantial differences in population size given enough elapsed time. For example, the median population size estimate for the Elenydd-Mallaen SPA in the year 2050 is approximately half as large under the scenario where all developers’ plans were modelled in combination than under the baseline scenario, even though both estimates are greater than the most recent (2022) population estimate and therefore represent population growth.

These results may provide reassurance that currently proposed levels of wind farm development are unlikely to prevent the continued growth of the Welsh Red Kite population, even in the most extreme scenario where all sites currently in development go ahead. However, they highlight that greater caution is justified for developments in proximity to the two SPAs designated for Red Kite, in order to minimise risk to the higherdensity populations of these areas.