Logistic regression models—or “sightability models”—fit to detection/non-detection data from marked individuals are often used to adjust for visibility bias in later detection-only surveys, with population abundance estimated using a modified Horvitz-Thompson (mHT) estimator. More recently, a model-based alternative for analyzing combined detection/non-detection and detection-only data was developed. This approach seemed promising, since it resulted in similar estimates as the mHT when applied to data from moose (Alces alces) surveys in Minnesota. More importantly, it provided a framework for developing flexible models for analyzing multiyear detection-only survey data in combination with detection/ non-detection data. During initial attempts to extend the model-based approach to multiple years of detection-only data, we found that estimates of detection probabilities and population abundance were sensitive to the amount of detection-only data included in the combined (detection/non-detection and detection-only) analysis. Subsequently, we developed a robust hierarchical modeling approach where sightability model parameters are informed only by the detection/non-detection data, and we used this approach to fit a fixed-effects model (FE model) with year-specific parameters and a temporally-smoothed model (TS model) that shares information across years via random effects and a temporal spline. The abundance estimates from the TS model were more precise, with decreased interannual variability relative to the FE model and mHT abundance estimates, illustrating the potential benefits from model-based approaches that allow information to be shared across years.
Bibliographical noteFunding Information:
This project was funded in part by the Minnesota Department of Natural Resources (Game & Fish Fund) and federal Wildlife Restoration (Pittman-Robertson) Program (https:// wsfrprograms.fws.gov/subpages/grantprograms/ wr/wr.htm) to Althea A. ArchMiller. The Minnesota Department of Natural Resources provided funding and field support for the sightability trials and operational surveys. JF received partial support from the Minnesota Agricultural Experimental Station. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. This project was funded in part by the Minnesota Department of Natural Resources (Game & Fish Fund) and federal Wildlife Restoration (Pittman-Robertson) Program. The Minnesota Department of Natural Resources provided funding and field support for the sightability trials and operational surveys. JF received partial support from the Minnesota Agricultural Experimental Station. We would like to thank J. Giudice for sharing data and insight.