Criteria for Inclusion on the
WatchList of Birds of Conservation Concern |
Criteria for inclusion on the WatchList are those used by Partners in Flight in its species assessment process. On a continental basis, each species is given six scores, each reflecting some aspect of potential vulnerability. Scores range from 1, meaning that the bird is probably benefiting from the factor under consideration, to 5, meaning that the factor creates extremely high vulnerability for the bird. Four of these six scores are added together, as explained below, to come up with a total vulnerability score. That sum, therefore, can range from a low of 4 to a high of 20.
Two of the six scores measure vulnerability based on range size. The assumption behind use of these scores is that a species with a small range is potentially at greater risk of population decline or extinction due to site-specific or stochastic events (an oil spill, hurricane, etc.) than one with a larger range. One of these scores reflects vulnerability based on the size of the bird's breeding range, and the other is for the smallest area the species occupies during its non-breeding season. The non-breeding distribution score can reflect risks related to the sum areas of concentration during migration, or, more commonly, the size of the wintering range. In order that the sum vulnerability score not be overly weighted by distribution, and because values for breeding distribution and non-breeding distribution are highly correlated with each other, only the larger of these two scores is used.
Similarly, there are two scores based on perceived threats, one for threats during the breeding season and the other for threats in the non-breeding season. This is the most subjective of these scores, reflecting the sense that experts have as to what they expect population trend to be for the species in the future based on factors such as the trend in availability of suitable habitat. As examples, birds that thrive in suburban sprawl get very low threat scores while those dependent on pristine native grasslands get high threat scores. Again, because of correlation between these two scores and an interest in not placing excessive emphasis on threats, only the higher of these two scores is used in summing for a total vulnerability score.
The other two scores are based on population, one on population size and the other on population trend. The assumption behind the use of population size is that a species that is composed of a very small number of individuals is potentially more subject to extinction than one consisting of a much larger number of individuals (but remember the Passenger Pigeon - even huge populations can crash to zero under the worst of circumstances). Population trend is used because a bird whose population has been declining in past years is often more of a conservation priority than one that has been increasing. It must be cautioned that population trend should not be overly weighted. A very rare bird with a small population size and distribution such as the Kirtland's Warbler has actually been increasing in population size, yet it remains a very high conservation priority. On the other hand, an abundant and widespread bird such as the Eastern Meadowlark has been undergoing substantial population declines, and while we must be cognizant of its problems and status, it is certainly not a high conservation priority where it occurs.
Among the landbirds analyzed by Partners in Flight, the lowest summed scores go to species such as the Black Vulture, Mourning Dove, American Robin, and Northern Cardinal. All are abundant, occupy large ranges, benefit from human changes to landscapes, and are stable or increasing in population size. At the other end of the spectrum, summing at 20, are birds such as the Lesser Prairie-Chicken, Florida Scrub-Jay, Black-capped Vireo, and Golden-cheeked Warbler. Somewhere between these extremes lies a threshold, above which a species is of sufficient conservation concern to warrant inclusion on the Green List.
Applying these criteria to all birds
Partners in Flight has created a Watch List that only includes landbirds. American Bird Conservancy and the National Audubon Society wanted to create a list that included all of the birds of the continental United States and Canada that are of conservation concern. In order to create the WatchList, ABC and Audubon used PIF-assigned scores, and then assigned PIF criteria to shorebirds, waterbirds, and waterfowl. As much as possible, assessment scores assigned by initiatives involved with those birds (the shorebird, waterbird, and waterfowl initiatives) were closely followed, reflecting the expertise of the individuals working most closely with those birds. However, adjustments were sometimes necessary because scores were not calibrated among initiatives. For example, assignation of a score of 3 for population trend by the waterbird initiative did not mean the same thing as a 3 assigned to a landbird. This lack of calibration has plagued all previous efforts to come up with a single, unified list. Previous lists were mixing apples and oranges, being based on scoring systems that are superficially similar, but in which individual scores, and thus summed scores, have been assigned on the basis of widely varying criteria. ABC and Audubon staff took the data and assumptions upon which scores were assigned by the various initiatives, and ran them through an evaluation process identical to that used by PIF. By these means, we created a complete list of the birds of the continental United States and Canada, each with scores for the above six factors consistently assigned, with total vulnerability scores that had consistent meaning through the entire list. This had never before been successfully done.
Threshold for inclusion
As mentioned previously, determining the placement of a bird on or off the WatchList is based on the assessment of four factors: population size, range size, threats, and population trend (Panjabi et al. 2005). Each of these factors is scored on a scale of 1 to 5, where 1 means low conservation risk and 5 means high conservation risk. For range size and threats, separate scores are calculated for breeding and nonbreeding seasons; to create a combined national score, the highest of the respective breeding and nonbreeding scores is used. Thus, the combined score is a sum of four scores and ranges from 4 to 20.
To be on the WatchList, a species needs a combined score of 14 (or 13 if the population trend score is 5). To be on the list of species of Highest National Concern (Red WatchList), a species needs a combined score of 16, plus a score of 8 or more for threats plus trend and a score of 8 or more for range size plus population size. To be on the Rare list (Yellow WatchList, in part), a species needs a combined score of 14, a score of 8 or more for range size plus population size, and a score of 7 or less for threats plus trend. To be on the Declining list (Yellow WatchList, in part), a species needs a combined score of 14, a score of 7 or more for threats plus trend, and a score of 7 or less for range size plus population size.
Population size estimates come from a variety of sources: waterfowl (North American Waterfowl Management Plan Committee 2004); waterbirds (Delaney and Scott 2006); shorebirds (Morrison et al. 2006); seabirds (Kushlan et al. 2002); landbirds (Rosenberg and Blancher 2005); and occasionally other sources that were felt more reliable for specific species than the above general references. For consistency, score thresholds for all four factors use Partners in Flight thresholds (Panjabi et al. 2005).
Range size estimates are all calculated from the NatureServe maps (Ridgely et al. 2005).
Threats were evaluated by the various North American bird conservation initiatives (Brown et al. 2001, Kushlan et al. 2002, Rich et al. 2004) then calibrated to the PIF definitions (Panjabi et al. 2005) for consistency.
Population trends were derived from the Breeding Bird Survey (Sauer et al. 2005), the Audubon Christmas Bird Count, or a combination of the two, if reliability scores for the surveys were high enough (Butcher and Niven 2007). For species that aren't well covered by the BBS or CBC, trend information is available from the same sources with population size information: waterfowl (North American Waterfowl Management Plan Committee 2004); waterbirds (Delaney and Scott 2006); shorebirds (Morrison et al. 2006); seabirds (Kushlan et al. 2002); landbirds (Rich et al. 2004); BirdLife data zone ( http://www.birdlife.org/datazone/species/index.html ); and occasionally other sources that were felt more reliable for specific species than the above general references.
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