Fall Survival of American Woodcock on Cape May, NJ

Science Center Objects

The American woodcock is a popular game bird in much of eastern North America. The woodcock population declined between 1968- 2000 at an annual rate of 2.3% in the Eastern region and 1.6% in the Central region. Estimated annual survival of woodcock banded in the Eastern region was estimated to be 0.354 for the period 1967-74. Estimates for the migration period, a period when substantial mortality could occur are unknown.

The Challenge: Research goals of this project are to: determine survival rates of American woodcock (Scolopax minor) during fall migration on Cape May, NJ.  I will determine age and sex-specific timing of migration and passage of woodcock through Cape May, NJ. The ultimate goal is to provide information to be included in specific management models for declining migratory bird populations.  I will use radio telemetry to track and monitor woodcock on Cape May and record when birds leave or die.

The Science: Cape May, New Jersey is an important stopover area for American woodcock (Scolopax minor, hereafter woodcock) during fall migration along the Atlantic Coast of the United States.  Previous research has indicated that many woodcock stop in Cape May prior to crossing the Delaware Bay; however, little is known about their survival while there.  Due to the importance of this stopover location, we wanted to better understand woodcock survival in Cape May during fall migration as well as estimate turnover rates for woodcock migrating through Cape May.  During late fall to early winter of, 2010-2013., we captured and marked a total of 267 woodcock with VHF transmitters and radio-tracked them weekly from November through early January each year.  Of the 267 marked birds, our radio-tracking efforts indicated that 114 migrated from Cape May, 87 remained in Cape May, 63 died, and 3 were censored.  We used a multi-state model within Program MARK to estimate survival and emigration probabilities for our marked woodcock.  Our best-supported model indicated that survival rate varied by year but was constant by week within each year.  Weekly survival rate estimates ranged from 0.894 (95% CI = 0.834 – 0.934) in 2010 to 0.962 (95% CI = 0.928 – 0.981) in 2011, which equates to a 9-week period survival rate ranging from 0.365 to 0.706, respectively. 

The Future: Our study provides some of the first information about woodcock survival rates at mid-latitude stopover sites, but we were unable to assess the relation(s) between survival rates and covariates likely to influence survival rates.  Information on the influence of body condition, habitat selection, and environmental conditions (e.g., accumulated thermal units and precipitation) on survival at these stopover sites is needed.  Incorporating the results from the Allen et al. (2017) resource selection function (RSF) model as an individual’s habitat suitability index may provide insight into the quality of habitat an individual is using.  That is, if individuals using areas with greater RSF values have higher survival rates, then landscapes could be managed to increase RSF values in areas where they are currently low.  For example, Allen et al. (2017) found that potential roost fields in close proximity to migratory stopover diurnal covers, in particular deciduous wetland forest, was an important factor in a woodcock’s decision to select a particular diurnal cover.  It would be prudent, however, to evaluate the effects of habitat selection on vital rates prior to prescribing a particular management action.