Breeding Density and Collision Mortality of Loggerhead Shrike (Lanius ludovicianus) in the Altamont Pass Wind Resource Area

K Shawn Smallwood,Noriko L Smallwood

doi:10.3390/d13110540

Abstract

Loggerhead shrike (Lanius ludovicianus) has declined across most or all of its geographic range. The species’ raptorial behavior requires maintenance of large territories, which means populations of breeding shrikes require large areas of habitat and are therefore sensitive to habitat loss and habitat fragmentation. We estimated breeding densities of loggerhead shrikes in the Altamont Pass Wind Resource Area (APWRA), California, where annual shrike mortality caused by wind turbine collisions was high until just before our study began in 2016. Based on surveys across an annual average 50 randomized sampling plots in 2016–2019, we estimated an average 129 breeding pairs/year across the 167.6-km2 APWRA. Relative to the size of the study area, density in the APWRA was relatively high compared to densities reported from other study sites across North America. It was higher than predicted by application of the Partners in Flight estimator, which was based on Breeding Bird Surveys along roads. We also found that loggerhead shrikes in the APWRA were limited by the availability of nest substrate and by California ground squirrels (Otospermophilus beecheyi) and their burrow complexes, which have keystone effects on vegetation and wildlife in the APWRA. To most effectively conserve loggerhead shrikes in the APWRA, wind turbine mortality should be minimized, ground squirrels conserved instead of eradicated as pests, and appropriate trees and shrubs cultivated where they are needed.

Highlights

The habitat of loggerhead shrike (Lanius ludovicianus) in grassland, sagebrush, and savannah environments has rapidly diminished as these environments have been converted to intensive anthropogenic uses [1,2,3]
Land stewardship varies by ownership, in the intensity of control efforts directed towards California ground squirrels (Otospermophilus beecheyi), Diversity 2021, 13, 540 which are a keystone species of the Altamont Pass Wind Resource Area (APWRA) for their roles as prey of large predators, excavators of burrows used by many other animal species, and modifiers of vegetation through consumption and seed dispersal (Figures 2 and 3)
The Altamont Pass Wind Resource Area supports substantial numbers of breeding loggerhead shrikes in California, but until recently might have served as an ecological sink for shrikes due to wind turbine collision mortality

Summary

Introduction

The habitat of loggerhead shrike (Lanius ludovicianus) in grassland, sagebrush, and savannah environments has rapidly diminished as these environments have been converted to intensive anthropogenic uses [1,2,3]. Due to habitat loss and habitat fragmentation, regional abundances of loggerhead shrike have declined in California, including a significant decline in Breeding Bird Survey data from 1968 through 2004 [4]. Since 2004, the spread of West Nile Virus (WNV) across North America 1999–2005, and into California by 2005, might have contributed to the decline [5]. These declines prompted designations of special status to the species. The U.S Fish and Wildlife Service listed loggerhead shrike as a bird species of conservation concern in Bird Conservation Region 32, which encompasses coastal California. The California Department of Fish and Wildlife listed loggerhead shrike as a California species of special concern, priority level 2

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Discussion

Conclusion