## Abstract

The consequences of bird mortality caused by collisions with wind turbines are increasingly receiving attention. So-called acceptable mortality limits of populations, that is, those that assume that 1%-5% of additional mortality and the potential biological removal (PBR), provide seemingly clear-cut methods for establishing the reduction in population viability.

We examine how the application of these commonly used mortality limits could affect populations of the Common Starling, Black-tailed Godwit, Marsh Harrier, Eurasian Spoonbill, White Stork, Common Tern, and White-tailed Eagle using stochastic density-independent and density-dependent Leslie matrix models.

Results show that population viability can be very sensitive to proportionally small increases in mortality. Rather than having a negligible effect, we found that a 1% additional mortality in postfledging cohorts of our studied populations resulted in a 2%?24% decrease in the population level after 10 years. Allowing a 5% mortality increase to existing mortality resulted in a 9%-77% reduction in the populations after 10 years.

When the PBR method is used in the density-dependent simulations, the proportional change in the resulting growth rate and carrying capacity was species-independent and largely determined by the recovery factor (Fr). When Fr = 1, a value typically used for robust populations, additional mortality resulted in a 50%-55% reduction in the equilibrium density and the resulting growth rate. When Fr = 0.1, used for threatened populations, the reduction in the equilibrium density and growth rate was about 5%.

Synthesis and applications. Our results show that by allowing a mortality increase from wind farm collisions according to both criteria, the population impacts of these collisions can still be severe. We propose a simple new method as an alternative that was able to estimate mortality impacts of age-structured stochastic density-dependent matrix models.

We examine how the application of these commonly used mortality limits could affect populations of the Common Starling, Black-tailed Godwit, Marsh Harrier, Eurasian Spoonbill, White Stork, Common Tern, and White-tailed Eagle using stochastic density-independent and density-dependent Leslie matrix models.

Results show that population viability can be very sensitive to proportionally small increases in mortality. Rather than having a negligible effect, we found that a 1% additional mortality in postfledging cohorts of our studied populations resulted in a 2%?24% decrease in the population level after 10 years. Allowing a 5% mortality increase to existing mortality resulted in a 9%-77% reduction in the populations after 10 years.

When the PBR method is used in the density-dependent simulations, the proportional change in the resulting growth rate and carrying capacity was species-independent and largely determined by the recovery factor (Fr). When Fr = 1, a value typically used for robust populations, additional mortality resulted in a 50%-55% reduction in the equilibrium density and the resulting growth rate. When Fr = 0.1, used for threatened populations, the reduction in the equilibrium density and growth rate was about 5%.

Synthesis and applications. Our results show that by allowing a mortality increase from wind farm collisions according to both criteria, the population impacts of these collisions can still be severe. We propose a simple new method as an alternative that was able to estimate mortality impacts of age-structured stochastic density-dependent matrix models.

Original language | English |
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Pages (from-to) | 6274-6287 |

Number of pages | 14 |

Journal | Ecology and Evolution |

Volume | 10 |

Issue number | 13 |

DOIs | |

Publication status | Published - 2020 |

## Keywords

- bird mortality
- collisions
- Ornis 1% mortality criterion
- population viability
- potential biological removal
- threshold assessment methods
- wind farm
- national
- Plan_S-Compliant_TA