Spatial and temporal variation in harvest probabilities for American black duck

Abstract

Assessing spatial variation in waterfowl harvest probabilities from banding data is challenging because reporting and recovery probabilities have distinct spatial patterns that covary temporally with harvesting regulations, hunter effort, and reporting methods. We analyzed direct band recovery data from American black ducks banded on the Canadian breeding grounds from 1970 through 2010. Data were registered to a 1-degree grid and analyzed using hierarchical logistic regression models with spatially correlated errors to estimate the annual probabilities of band recovery and the proportion of individuals recovered in Canada. Probability of harvest was estimated from these values, in combination with independent estimates of reporting probabilities in Canada and the USA. Model covariates included estimates of hunting effort and factors for harvest regulation and band reporting methods. Both the band recovery processes and the proportion of individuals recovered in Canada had significant spatial structure. Recovery probabilities were highest in southern Ontario, along the Saint Lawrence River in Quebec, and in Nova Scotia. Black ducks breeding in Nova Scotia and southern Quebec were harvested predominantly in Canada. Recovery probabilities for juveniles were correlated with hunter effort, while the adult recoveries were weakly correlated with the implementation of stricter harvest regulations in the early 1980s. Mean harvest probability decreased in the northern portion of the survey area but remained stable or even increased in the south. Harvest probabilities for juveniles in 2010 exceeded 20% in southern Quebec and the Atlantic provinces. Our results demonstrate fine-scale variation in harvest probabilities for black duck on the Canadian breeding ground. In particular, harvest probabilities should be closely monitored along the Saint Lawrence River system and in the Atlantic provinces to avoid overexploitation.

Increases in the Number of American Black Ducks Wintering in Nova Scotia, 1970–2015

“…As climate warming continues, waterfowl at middle latitudes are likely to continue to further delay migration and eventually may not even migrate at all (Notaro et al 2016), leading to further increases in northern areas. These results highlight that distribution and trends of black ducks vary across their range, and provide further support to efforts to understand and manage black ducks at smaller spatial scales (Roy et al 2015;Robinson et al 2016). …”

“…However, several lines of evidence do not support this contention. First, harvest pressure on black ducks banded in the preseason in Nova Scotia is relatively high and most of those birds are harvested in Canada (Roy et al 2015), limiting the opportunity for local population growth in Nova Scotia. Second, birds wintering in Nova Scotia (southeastern Canada) represent birds from a variety of regions, with most coming from northeastern Canadian breeding grounds (Robinson et al 2016).…”

Continental‐scale dynamics of avian influenza in U.S. waterfowl are driven by demography, migration, and temperature

“…Edges in the network were defined as the number of mallards moving between two nodes at a four-week (monthly) time resolution averaged across 5 yr. For example, the edge weights assigned for the first four-weeks in 2007 were calculated by (1) compiling recovery records for those weeks in 2003, 2004, 2005, 2006, and 2007; (2) quantifying the number of records describing movement along edges in each year; and (3) assigning edge weights as the average number across years. We use this edge definition to align the BBL and AIV surveillance data sets because recovery distributions did not differ significantly across years (Mielke and Berry 2007) and averaging across years minimizes noise due to unobservable bird movements or variation in hunting effort (Roy et al 2015). Extended network methods and a justification of these spatial and temporal decisions are provided in Appendix S2.…”

Evaluation of a two‐season banding program to estimate and model migratory bird survival

“…The difference in adult and juvenile recovery probabilities is probably due to differential vulnerability to harvest (Roy et al. 2015). It is generally accepted that juvenile ducks have higher recovery probabilities than adult ducks because they are naïve to hunting pressure and more vulnerable to harvest (Anderson 1975, Boyd and Hyslop 1985, Krementz et al.…”