Atlantic coast joint venture waterfowl implementation plan
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Appendix B Stepping Continental NAWMP Population Objectives in Joint Venture Habitat Goals As part of its responsibility in implementing the goals stated by NAWMP, joint ventures are developing habitat goals that are biologically linked to the breeding population goals. Ultimately, these goals are to be expressed as an amount of habitat that needs to be protected, enhanced or restored in the ACJV area in order to contribute to achieving NAWMP waterfowl population objectives at the regional and continental scales. At this time there is no consensus on how migratory or wintering waterfowl populations and habitat relate to the breeding objectives of NAWMP. The NAWMP National Science Support Team (NSST) has therefore recommended an interim method that uses a combination of MWS and harvest data to proportionally allocate the continental objectives between the various joint ventures. An evaluation of these methods indicates that this allocation works reasonably well for most duck species (exceptions include: Mottled Duck, whistling-ducks, Blue-winged Teal and Wood Ducks) but not for geese in general (M. Koneff, pers. comm.). Implicit in such an endeavor is the assumption that local or regional actions are hierarchical in nature and can be aggregated to, in this case, a larger spatial scale. Although intuitive, there is no clear consensus on the functional form of such a relationship. In the absence of a clear analytical solution to the problem, the NSST reviewed alternative approaches and reached consensus in November 2003. As the official technical advisory committee of NAWMP, the NSST recommendations are being followed by non-breeding joint ventures in North America. The method being recommended by the NSST is a three-step approach that allows non-breeding joint ventures to “step-down” the continental population goals into regional goals that can be used for planning habitat delivery programs. The NSST recommends that these numbers not be used as a performance metric per se, but only for baseline planning purposes. As such the first step of the process is to determine the proportion of the continental population goals a joint venture might be responsible for over-wintering. The second step is to explicitly state the assumptions being made as to the regional requirements of waterfowl, resource availability and assess trends of the resource. Lastly, joint ventures need to evaluate the validity of the assumptions made in the second step. The NSST recommendations only concern the first of this process: determination of the proportional allocation of continental objectives to the regional scale. The NSST is advocating the use of MWS and county level, species specific harvest data as a reasonable first approximation of the wintering distribution of waterfowl. It was noted that use of this approach incorporates all the potential biases that have been identified regarding the MWS data (Heusmann, Eggemann and other citations here). Although there are local data sets that might overcome some of these limitations, there is no other data set that covers the entire joint venture that could be used as a surrogate. Likewise, the county level-harvest data contain their own biases but lack of an alternate surrogate argues in favor of their use. As a first approximation of objectively determining how many acres the ACJV needs to protect, restore or enhance, we used the NSST approach to calculate what the Waterfowl Technical Committee has termed a Wintering Habitat Capability Index (WHCI). MWS data for all four flyways from 1955 - 2001 were obtained from the U.S. Fish and Wildlife Service, Division of Migratory Bird Management. These data were used to determine the proportion of the total wintering population index counted within each state of the ACJV between 1990 and 2001. These years were used to account for observed shifts in resource availability and use and changes in the MWS population index since the mid-1970s (Tables B.1 and B.2). The mean proportion for each state was then multiplied by the NAWMP population goal for each duck species. The resulting value is the WHCI for a given state and species combination (Table B.3). To reiterate, the WHCI values do not represent actual population numbers, they are only intended to be numbers that can be converted into habitat goals at a time when we have the necessary information. An alternative to the use of MWS data is to use just the county-level harvest data. Although this might reduce the bias thought to exist in the MWS data, the county-level harvest data is not without its own biases and assumptions. However, it is possible to use the county-level harvest data to estimate a proportional allocation of the continental population goal to every county within the ACJV. Harvest data from December through February were used to reduce the effect of migration on the proportion of total harvest estimated for each county. The state-level WHCI index is derived by then summing county-level objectives within a state (Table B.3). Unfortunately, there are numerous technical issues with both of the approaches explored as part of these analyses. In addition to the obvious biases associated with using the MWS and harvest survey data in ways they were never designed to be used we have identified the following issues that need to be resolved before we can quantitatively determine habitat objectives for the ACJV.
Table B.1. Mean (1970 -1979) Mid-winter Survey counts for selected species in the Atlantic Coast Joint Venture. Mean totals are averages of yearly totals for the entire U.S. portion of the Atlantic Flyway. Species abbreviations are 4-letter ABA codes.
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