I will just add to Bill's assessment that, try as we might, the Christmas Bird Count "protocol" (= count everything you can count) is a very crude instrument for monitoring bird populations and it is probably not worth worrying too much about fine tuning most of the counts. That said, avoiding obvious double-counting is standard procedure on most CBCs, and Bill is correct that we have always strived to determine the most accurate totals for waterfowl, gulls, etc, as well as large soaring birds such as eagles and vultures (even the flocks of crows coming in to roost).
Beyond that, I have participated in many different CBCs around the country (and in the tropics) and have been compiler of at least 6 CBCs, and I can say that there is tremendous variation in strategies used to get numbers of species and counts of individual species. Most CBCs do put more of an emphasis on species totals, focusing on covering representative habitats, finding rare birds, and not going much beyond "representative" counts of common birds. Other CBCs employ more of a "blitz" strategy to go after national high counts for targeted species. Some counts (like ours) make liberal use of owl tapes and other lures; other CBCs discourage these – in my experience this variable alone probably accounts for more variation in counts of common birds than any other aspect of effort or coverage. The beauty of the CBC though is that there are so many of them that have been running for so many years. The real scientific value is in identification of broad patterns across large geographic areas over long time periods. For example, as Kevin kept pointing out during the compilation, when the Ithaca CBC had large numbers of woodpeckers in recent years, so did every other count in NY and across the Northeast. Similarly big years for finches are easily detected, the declines in species such as kestrels and pheasants, increases in wintering Turkey Vultures and many other species, cycles in Wild Turkey numbers, etc. are all very apparent in the CBC data, even if each individual CBC count is very "fuzzy." So, while it is tempting to want to fine-tune our local counting to track very local populations, the CBC is probably not the best tool for that. But it's all fun! KEN Ken Rosenberg Conservation Science Program Cornell Lab of Ornithology 607-254-2412 607-342-4594 (cell) [email protected]<mailto:[email protected]> On Jan 4, 2013, at 2:48 PM, Bill Evans wrote: Jody, The concept of avoiding double counting is implied in the nature of the CBC, and there is a spectrum in the level of attentiveness in avoiding double counting for different species, different locations, and by different birding parties. The key idea amidst all the variables, as you note, is maintaining the utility of the data for long-term interpretation of changes, and this involves consistency of monitoring (even if it is rough around the edges). Of course there is no realistic means for preventing double-counting of chickadees in a neighborhood with multiple feeders, but every year there is a concerted effort not to double count waterfowl at Stewart Park -- the highest tallies are typically taken instead of adding each observer’s sightings, or as I recall, one person is designated to count geese, gulls etc. on the lake. Swans have only been documented on (I believe) 6 Ithaca CBCs in the past 100+ years, all in the last two decades. Whatever count total is used, this year is our record high count. I don’t recall any years like this one when we had multiple flocks in passage, so the previous count totals were likely highly accurate and not subject to being double-counted. However, the evidence suggests that a section-added count of ~400 is a 100% overestimate. Using the section-added total would likely be a gross deviation from the status quo with regard to the accuracy of past swan counts on our CBC. Like the coordinated effort at Stewart Park to prevent multiple waterfowl counts, the swan tally could be corrected with a bit of coordination in observations this year and foresight in future years (i.e., noting flock size, location, trajectory, and time). So, while I generally agree with the importance of maintaining the status quo in counting procedures, I don’t agree with projecting the status quo of a section-added count (i.e., for chickadees) on swans. Asher, section counts would not be denied their birds. As one can see from the map, section counts in fact help ascertain the accuracy of the migration tally. Bill E The evidence suggests some flocks were double and even triple counted, but as Ken pointed out there are still some things that don’t add up. 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