Program and Agenda

Abstract

UNDERSTANDING THE SOURCES OF BIASES IN POPULATION SIZE ESTIMATES BASED ON ROADSIDE SURVEYS IN CANADA

Bird point-counts from the North American Breeding Bird Survey (BBS) have been used to estimate population sizes of landbird species by Partners in Flight (PIF). Their estimates relied on three key assumptions: (A1) roadside surveys sample habitats in proportion to their availability; (A2) roadside counts are similar to off-road counts; and (A3) their adjustments for timing and detection ranges accounted for imperfect detection. We used a combination of roadside and off-road surveys from the Boreal Avian Modelling Project (BAM) and BBS to test these assumptions. We used model-based techniques with covariates for local habitat conditions and regional factors to relax A1. We estimated an effect size for roadside surveys as such, thus further relaxing A2. We used a combination of removal and distance sampling to adjust for unequal sampling effort and other factors affecting availability and detectability (testing A3). We found that our Canadian (2 species) and Alberta specific (77 species) population estimates were on average 6 (range 0.2 to 20.0) times higher than corresponding PIF estimates. We attributed the inter-specific variation to consequences of the 3 assumptions. Effects related to A1 and A2 varied greatly among species but without significant bias as between methods. The effects of A3 were less variable and consistently positive. Our findings indicate that habitat-sampling and roadside biases can affect ranking of species based on population sizes estimated from roadside surveys, while effects of detectability markedly bias population estimates for most species.

Authors

Solymos, P., University of Alberta, Canada, solymos@ualberta.ca

Bayne, E. M., University of Alberta, Canada, bayne@ualberta.ca

Mahon, C. L., Environment Canada, Canada, lisa.mahon@ec.gc.ca

Hache, S., Environment Canada, Canada, Samuel.Hache@ec.gc.ca

Fontaine, P., University of Alberta, Canada, trish.fontaine@ualberta.ca

Cumming, S. G., Universite Laval, Canada, stevec.boreal@gmail.com

Stralberg, D., University of Alberta, Canada, stralber@ualberta.ca

Schmiegelow, F., University of Alberta, Canada, fschmieg@ualberta.ca

Song, S., Environment Canada, Canada, samantha.song@ec.gc.ca

Details

Oral presentation

Session #:S13
Date: 9/26/2014
Time: 14:45
Location: Emerald Mountain - Bible Point

Presentation is given by student: No