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Interpreting the CBC circle history report
The report generated by the
circle history request page is not
perfect, but the author hopes it is useful in most cases.
Format of the report
- The state(s), circle name, and coordinates are shown at the top.
If the circle has multiple coordinates, only the name and coordinates
of the first are shown.
- The body of the report is a table, with each column representing
one year that the circle has been run. If there are too many years
to fit on one line, each row is folded to fit on multiple lines.
- The first row enumerates the ``CBC numbers'' in which the circle
has been counted. The first CBC was in 1900, so add 1899 to this
number to get the year of the Christmas around which the count
period was centered. For example, CBC number 87 was run in
December 1986 and January 1987.
- The second row shows the total party-hours effort for each year.
A value of ``-0.1'' means that the effort was unknown.
- Each successive row shows the counts for one kind of bird in
each year. Most rows are for standard species, but there are
- If the reported form was not narrowed down to species, it
is lumped into the smallest appropriate taxon. For example,
birds reported as ``duck sp.'' are reported under Family
Anatidae. Taxonomy is based on the AOU Check-List,
- Color morphs (e.g., Blue Goose), well-marked races
(e.g., American Green-winged Teal), and some other distinctions
below species level (e.g., ``small Canada Goose'')
appear on their own line.
In the older counts, racial identifications were much more
common. If you see a strange name such as Treganza's Heron,
refer to the
six-letter bird code system page and look at the ``tree file''
to find names for all the various races. For example,
if you do a text search for the string ``Treganza,'' you will
find that Treganza's Heron is a race of Great Blue Heron.
- For reports of hybrids or species pairs (such as Downy/Hairy
Woodpecker), the name may be split over two lines, and the
second line will start with ``x'' to indicate a hybrid, or ``/''
for a species pair.
- Any of these may appear in one cell of the report:
- The number of birds seen.
- A hyphen ``-'' if no birds of that kind were seen that year.
- A plus ``+'' if seen during count week but not count day.
- The abbreviation ``unk'' if the number was not given.
- If a question mark ``?'' appears,
that means the record appeared with a code implying that
the regional editor was not completely convinced of the
identification. If you feel that a record has been
unfairly stigmatized, please submit any additional evidence
to your regional compiler for reconsideration. In the near
future we hope to set up a review procedure.
- The last two columns of each row display the mean and standard
deviation of the counts in that row.
Beware: if counters
have used different names over the years, these statistics may be
meaningless. For example, if the species has been split, older
records may be lumped into a higher taxon, while newer years appear
under the split name. This can make it look like the species
suddenly appeared in the circle at the year of the split, because
pre-split records will appear on a different line.
One annoying feature is that recent splits can
make records from before the split impossible to extract.
For example, two former species of towhees (Brown and
Rufous-sided) have been split recently, but the program that
generates this report does not make any assumptions about which
records pertain to which side of the split. Therefore, if you
are interested in monitoring trends in towhee populations, you
will be frustrated because all older records for both forms are
lumped together in the line for genus Pipilo. There is no
easy general solution for this problem. If you really need the
numbers in such cases, please write me; they can be extracted
with some work.
Next: Christmas Bird Count Database corrections
See also: The Christmas Bird Count database project
Previous: Christmas Bird Count: Circle history report request
John W. Shipman,
Last updated: 1999/02/07 22:26:59