Estimating annual harvest of American Woodcock (Scolopax minor) in the United States during 1964-2016: data, model code, and supplemental estimates

Abstract

Harvest of American woodcock (Scolopax minor) in the United States has been estimated using two different hunter surveys: 1) the Duck Stamp Survey (DSS, 1964-2001), which estimated harvest by hunters who also hunted ducks or geese and purchased a Federal Migratory Bird Hunting (“Duck”) Stamp, but failed to survey hunters who did not purchase Duck Stamps (which were not required for hunting woodcock); and 2) the Harvest Information Program (HIP, 1999-2019), which was initiated in 1999 and designed to survey nearly all hunters who targeted woodcock. The two surveys overlapped during only 3 years (1999-2001), and in most states, the HIP survey estimated much higher woodcock harvest based on its more complete sampling frame of woodcock hunters. We developed Bayesian hierarchical models to use combined data streams to estimate total harvest during 1964-2016 (Arnold 2019) or 1964-2013 (Saunders et al. 2019) in the Eastern and Central Management Units by estimating unobserved harvest by hunters who never or only occasionally hunted waterfowl. Both approaches used annual Duck Stamp sales as a covariate to assess annual participation by hunters who occasionally hunted waterfowl, and also used the 3 overlap years (1999-2001) to estimate harvest by hunters who never hunted waterfowl. However, our approaches differed in how we assessed participation by occasional waterfowl hunters: 1) as residuals from splines fit to long-term duck stamp sales (Arnold 2019), which posited a smooth change in total waterfowl hunters through time, with residuals reflecting short-term participation or non-participation in waterfowl hunting, or 2) relative to maximum annual duck stamp sales (Saunders et al. 2019), which posited a constant number of potential waterfowl hunters in each state (max stamp sales), but with annual changes in relative participation in waterfowl hunting corresponding to yearly stamp sales. Our estimates were remarkably similar for combined harvest in the Central Management Unit, but diverged substantially for the Eastern Management Unit. We have no way of assessing which set of assumptions is closer to the truth, and present both models here in hopes that future researchers will continue to refine our methods to produce even more robust estimates of historical woodcock harvest.