Population monitoring is a fundamental component of wildlife management, and is necessary to track site- and regional-level status and recovery of species of conservation concern. The wood turtle (Glyptemys insculpta) is a species of conservation concern for federal and state agencies because of population declines across the species’ range. We developed and tested a survey and analysis design to assist agencies in the Upper Midwest, USA, with establishment of long-term monitoring programs for wood turtle populations. In spring of 2016, we conducted 8 replicate population surveys at 8 candidate long-term monitoring sites in northeastern Minnesota, USA. Using field survey data and simulation models, we assessed the influence of distance from river surveyed, number of survey replications, and number of sites on abundance estimates; we also delineated important survey covariates and compared demographic estimates based on distance from river surveyed. We estimated site-level abundances and compared survey designs using a multinomial N-mixture model that included a removal sampling observation process. Mean abundance estimates were similar when surveying 2 transects (i.e., the river-land interface to ∼25 m inland) or 4 transects (i.e., the river-land interface to ∼55 m inland), but decreasing the survey distance from river reduced the precision of estimates. Mean abundance estimates were similar with ≥6 replications. Air temperature was an important predictor of survey-specific detection probability, with maximum detectability at 19−23°C. Sex ratio and mean carapace length did not differ based on whether we surveyed 2 or 4 transects, and percentage of individuals by size class was nearly identical between the sampling designs. Simulations indicated that 75% of mean abundance estimates were within ±8% of true abundance when ≥15 sites were surveyed. The wood turtle survey and analysis design we developed and tested was effective for estimating abundance of wood turtle populations in northeastern Minnesota, and we encourage its use as a template for wood turtle monitoring programs in the Upper Midwest.
Bibliographical noteFunding Information:
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. We thank A. F. Badje, M. D. Nelson, R. R. Buech, M. Schrage, D. Ryan, J. Hines, C. N. Lapin, M. A. Hamady, Y-M. Lee, and C. D. Hall for discussions and suggestions related to survey design. We thank K. Huston, C. Reno, A. Holleran, K. Goebel, J. Flory, M. Swingen, and N. Ose for assistance with population surveys. We thank M. T. Jones and 2 anonymous reviewers for providing suggestions that improved the quality of this manuscript. This study was funded by the Minnesota Department of Natural Resources through a Competitive State Wildlife Grant (#F14AP00028), with additional financial support provided to M. Cochrane through a University of Minnesota Integrated Biosciences Graduate Program summer fellowship.
© The Wildlife Society, 2017
Copyright 2017 Elsevier B.V., All rights reserved.
- Glyptemys insculpta
- N-mixture model
- removal sampling
- visual encounter survey