Abstract
Context
The concept of landscape heterogeneity is central to species conservation; yet understanding the processes by which heterogeneity affects species can be challenging in practice. Complex and sometimes difficult-to-measure responses of species may reflect the outcome of life-history trade-offs shaped by different landscape properties.
Objectives
We tested the hypothesis that a mosaic of forest stand types affected hunting and breeding success for California spotted owls (Strix occidentailis occidentalis).
Methods
We integrated high-temporal-resolution GPS tags, video monitoring of nest sites, long-term assessments of reproductive status, and high-resolution remotely sensed vegetation data in a mixed-ownership landscape in the Sierra Nevada, California to test our hypothesis.
Results
Spotted owls made shorter nocturnal movements in homogenous territories with large areas of medium-aged forest apparently because this forest type allowed direct movement paths to foraging sites. However, spotted owls delivered prey at a higher rate to nest sites when they had more forest edge in their territory, which presumably provided greater access to large-bodied woodrat (Neotoma spp.) prey. Further, spotted owl reproductive output was relatively high in heterogenous territories containing a mix of mature and open forest.
Conclusions
The benefits heterogenous forests provide to hunting success appeared to outweigh costs associated with additional commuting distance to foraging sites and provided potential fitness benefits to spotted owls. We suggest that the effects of landscape heterogeneity can vary not only among, but also within, species and can reflect the outcome of trade-offs among different life history activities. Understanding the effects of landscape properties on biological communities will benefit from additional empirical and mechanistic studies of individual species.
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Data availability
Data and R code is available from CJZ on request.
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Acknowledgements
We thank the many technicians who assisted in collecting the data for this project. We also thank the Museum of Vertebrate Zoology, University of California-Berkeley, California and Burke Museum of Natural History and Culture, University of Washington for allowing us access to their specimen collections. Lastly, we thank Jim Baldwin for help with statistical methods and data visualization.
Funding
Funding was provided by the US Forest Service Region 5, Pacific Southwest Research Station, and Sierra Pacific Industries.
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MZP, SCS, BPD, KNR, and JJK conceived the study; CJZ, RJG, BPD, and KNR led data collection, with contributions from KGK, WJB and SAW; CJZ, GMJ, HAK, JJK, and MZP designed the analysis; CJZ, GMJ, HAK, and MZP analysed the data; CJZ, GMJ, HAK and MZP wrote the manuscript. All authors provided critical feedback and gave final approval for publication.
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Zulla, C.J., Jones, G.M., Kramer, H.A. et al. Forest heterogeneity outweighs movement costs by enhancing hunting success and reproductive output in California spotted owls. Landsc Ecol 38, 2655–2673 (2023). https://doi.org/10.1007/s10980-023-01737-4
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DOI: https://doi.org/10.1007/s10980-023-01737-4