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Posted by Bill Pranty on 20:02:08 08/29/06
In Reply to: Re: Nutmeg Mannikin posted by Roxanne
Hi Roxanne,
Criteria for determining the establishment of a species depends on the authority. Posted below are the criteria of the American Birding Association Checklist Committee, for which I am chair. These criteria wi be published in the forthcoming 7th edition of the ABA Checklist, and may be edited somewhat from what is provided here.
Best regards,
Bill Pranty
Bayonet Point, Florida
RECOMMENDED REVISED ABA CHECKLIST COMMITTEE CRITERIA FOR JUDGING THE STATUS OF EXOTIC BIRDS IN THE ABA AREA
As we use the term, an exotic bird is one that does not occur naturally within the ABA Area but has been imported by humans. Some exotics have been deliberately released for aesthetic, hunting, or other purposes, whereas other exotics have escaped from captivity. Populations of some exotics primarily waterfowl and gamebirds are feral, derived from domesticated stock, while populations of most other exotics are naturalized, derived from wild-caught individuals. Virtually all of the exotics found within the ABA Area escaped or were released locally, but in at least one case (Eurasian Collared-Dove in Florida via the Bahamas), a species naturally colonized the ABA Area from elsewhere.
The ABA Checklist Committee (CLC) has revised its criteria for determining when an exotic bird is considered to be established and therefore can be added to the Checklist. The need for additional and more responsive criteria became obvious when four exotics (i.e., the Black Francolin, Ringed Turtle-Dove. Crested Myna, and Blue-gray Tanager) that had been added to earlier Checklists were later removed because their populations disappeared. Numerous studies of exotic species albeit mostly short-term studies of unmarked individuals have now been conducted in the ABA Area, and our knowledge of exotics is vastly improved compared to previous decades. Additionally, the widespread use by birders of digital cameras or camcorders, coupled with the publication of several new field guides, have increased our confidence in the identification of several exotics, most notably psittacids. Finally, the persistence in California and Florida of several non-countable exotics for 30 or 40 years has prompted many birders to wonder why such species have not already been added to the Checklist.
Thus, in 2004, the CLC convened a sub-committee to prepare revised criteria for determining the establishment of exotic birds within the ABA Area. Members of the subcommittee were Kimball Garrett of California, Christopher Haney of Virginia, Mark Lockwood of Texas, and Bill Pranty of Florida. Members of the subcommittee presented their recommendations to the ABA CLC, and these recommendations were ratified with some modifications in April 2006. The revised ABA CLC criteria are based on a combination of previous criteria of the CLC, criteria long in place by the California Bird Records Committee, criteria recently revised by the Florida Ornithological Society Records Committee (FOSRC), and comments by CLC members. The CLC emphasizes that among all the states and Canadian provinces, only two local bird records committees those in California and Florida have in place any formal guidelines to guide decisions regarding exotic species. Needless to say, the methods used by local committees to add exotics to their lists vary considerably, highlighting the need for standardized criteria across North America. We hope that local bird records committees will adopt our criteria, as such action would result in a more uniform method for adding exotics to official bird lists throughout the ABA Area. Our criteria will also be shared with the AOU s Committee.
The original criteria published in the first ABA Checklist accepted exotics that were ... breeding in the wild for at least ten years and [were] increasing in abundance or maintaining a stable population without direct help from man. (These criteria have been diluted in popular usage to the simpler present ten years and surviving. )
Exotic birds may establish populations in one or more parts of the ABA Area and then may spread to other regions (e.g., European Starling and House Sparrow released into New York City and subsequently colonized most of North America), may occur in several areas from numerous independent introductions (e.g., Monk Parakeet in the eastern U.S.), or may persist locally with little or no range expansion for a duration ranging from short (e.g., Blue-gray Tanager in Florida) to long (e.g., Red-whiskered Bulbul in Florida). Exotic species respond differently to release into the ABA Area as a result of variation in their physiological, ecological, and behavioral characteristics and/or requirements, which will be largely unknown or speculative at the time of first establishment.
The ABA Checklist Committee considers an exotic bird to be established in the ABA Area when the following eight criteria are met:
1) The species is recorded in the form of a published photograph or a specimen archived in an ornithological collection. This criterion ensures that species identification can be confirmed.
2) There is a more-or-less-contiguous population of interacting or potentially interacting individuals, rather than a scattering of isolated individuals or pairs. Most exotics present within the ABA Area are limited to metropolitan areas. For persistence, it is vital that exotic birds in these areas are not isolated from each other but rather occur in sufficient proximity to allow interaction and therefore gene flow. Some exotics are found in the ABA Area as a single interacting population, while others occur in several populations that are isolated from each other.
3) The population is not currently and is not likely to be the subject of a control program where complete eradication may be a management goal that is likely to succeed. Some exotics (e.g., Mute Swan) present a clear danger to native species or habitats, or to agriculture or commerce, and in some areas, a listing as established may create a conflict between some birders and land management personnel.
4) The population is large enough to survive a routine amount of mortality and nesting failure. We cannot provide a numerical threshold for determining when an exotic species is established. The reason for this should be obvious no single number would be adequate for populations as varied as large, long-lived parrots with low reproductive potential and small, short-lived finches with high reproductive potential. Demographic characteristics such as habitat preferences, lifespan, reproductive output, dispersal frequencies and distances, and genetic viability will need to be considered separately for each species. Members of the CLC will critically review each species based on the documentation provided and will make a judgment based on the best available evidence. Much attention will be given to factors such as population size, distribution, and, particularly, evidence of successful breeding. However, we recognize that some number of individuals is preferable as a baseline to judge when a species may be established. The FOSRC prefers that populations ideally contain at least several hundred individuals, and the CLC agrees that in almost all cases, populations numbering only dozens of individuals may be too small to be considered established. Additionally, information should be provided to indicate that there is little or no evidence that ongoing releases play a substantial role in population maintenance. For gamebirds whose numbers may be artificially supplemented from time to time, evidence should be provided that these releases are not necessary to maintain population size or persistence.
5) Sufficient offspring are being produced to maintain or increase the population. Such criteria will vary from species to species, according to factors affecting the population, both natural (competition from other species; effects of hurricanes) and artificial (recapture for the pet trade; culling by hunters). Certainly, a species whose numbers are increasing and whose range is expanding is a better candidate for establishment over a species whose numbers and range are stable. Species with declining numbers and/or contracting range should have a much greater evidentiary threshold to meet before being considered established.
6) The population has been present for at least 15 years. Previous CLC criteria used a 10-year persistence threshold. As we have seen with several exotics, 10 years is an insufficient period to judge the likelihood that an exotic will persist. Accordingly, we have increased the persistence criteria to 15 years. The ABA CLC readily acknowledges that 15 years may also be insufficient in some cases to determine establishment; populations of many exotics follow a boom and bust cycle over several decades (Pranty 2001, 2002). With long-lived species (e.g., Amazona parrots) or when gamebird populations are regularly subsidized, one could argue that persistence should be for 30 or more years for genuine trends in the population to become obvious. Our point here is that like numerical criteria, no simple formula of the number of years for persistence can apply to all species. Flexible persistence criteria ( at least 15 years ) and lack of numerical criteria will allow Committee members to exercise their own judgment in potentially uncertain or controversial cases, but only in the context of strong biological evidence and with the intention that the final judgment be a conservative one.
7) The population is not directly dependent on human support. Although somewhat subjective, this criterion is meant to exclude from consideration those exotics that rely on direct human support for their ongoing survival and/or persistence (reliance on bird feeders; periodic releases of additional individuals). For instance, the Monk Parakeet population in Illinois is virtually wholly dependent on bird seed provided by humans during winter months (Hyman and Pruett-Jones 1995), and this population would not be considered by the CLC to be established.
8) A publication, ideally in a peer-reviewed journal or book, describes, how, when, and where the above seven criteria have been met. A publication will streamline the voting process by members of the CLC and local committees by clearly presenting evidence of establishment. In the absence of a publication, the CLC may still vote on a motion to add an exotic to the ABA Checklist if such evidence has been gathered by a Committee member or some other interested individual. In the latter two instances, a detailed analysis of the issue must be published in a suitable scientific source if the species has been determined to be established.
The ABA Checklist Committee has not attempted to determine the distributional status of exotic birds that it has deemed established. In the past, we have accepted the determination of local bird records committees. However, based on the varied and usually undefined criteria of local committees, the ABA CLC may soon attempt to determine the established distributions of the 17 exotics currently on the ABA Checklist, as well as each exotic added to subsequent Checklists.
Established exotics that become extirpated will be removed from the main list and will be placed in an appendix. Whether birders can continue to count these species on their lists will be determined by the ABA Rules Standards, and Ethics Committee, not by the ABA Checklist Committee. For species whose populations seem to be approaching extirpation but remain extant (e.g., the Budgerigar in Florida), we recommend waiting until the population is actually extirpated before voting on a motion to remove the species from the main list.
The CLC has chosen to grandfather in the 17 exotics currently on the ABA Checklist. These species are the Mute Swan, Chukar, Himalayan Snowcock, Gray Partridge, Ring-necked Pheasant, Rock Pigeon, Eurasian Collared-Dove, Spotted Dove, Budgerigar, Monk Parakeet, Green Parakeet, White-winged Parakeet, Red-crowned Parrot, Red-whiskered Bulbul, Spot-breasted Oriole, House Sparrow, and Eurasian Tree Sparrow.
The Crested Myna recently was moved to an appendix of extirpated exotics, the Yellow-chevroned Parakeet was recently removed from the Checklist because its placement on the Checklist in 2002 was based on an error, and the European Starling is considered a native vagrant. If a CLC member or another individual believes that one or more of these grandfathered species should be removed from the Checklist, then data should be gathered and published so that the Committee can vote on a motion for removal. The CLC readily acknowledges that some exotics already on the Checklist do not meet one or more of the above criteria, and that these species perhaps would not be considered established if the new criteria were applied to them.
In addition to the 17 exotics currently on the ABA Checklist, literally dozens of other species have been observed within the ABA Area; over 100 exotic birds have been documented in Florida (Pranty 2004). At some future point, the ABA CLC intends to compile a list of all exotic birds that have been recorded within the ABA Area.
Literature Cited
Hyman, J., and S. Pruett-Jones. 1995. Natural history of the Monk Parakeet in Hyde Park, Chicago. Wilson Bulletin 107: 510 517.
Pranty, B. 2001. The Budgerigar in Florida: Rise and fall of an exotic psittacid. North American Birds 55: 389 397.
Pranty, B 2002. The use of Christmas Bird Count data to monitor populations of exotic birds. The 102nd Christmas Bird Count, 2001 2002. American Birds 24 28.
Pranty, B. 2004. Florida s exotic avifauna, a preliminary checklist. Birding 36: 362 372.
(c) American Birding Association 2006
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