Bird Abundance
How many birds are there?
We can look at the number of birds of a particular species that have
been reported by various bird-monitoring projects, either across the
species' range, or for a particular locality.
Abundance may be presented as maps, tables, or graphs.
We'll use Steller's Jay for our example.
A simple index of abundance is available from the eBird yearly report for a state or region.
This table shows the average number of Steller's Jays reported per
checklist, throughout 2002, in California, Oregon, and Washington.
Note that the abundance values take into account observers who submitted a checklist, but did not see any Steller's Jays.
Steller's Jays were seen throughout the year in this region, in roughly similar abundance each month.
Another measure of abundance is the frequency with which a species is reported.
One example is the proportion of checklists from a specific location
reporting that species, or the percentage of feeders in a state or
region. This is a measure of how likely it is we'll see a species at a
given time or place. See the location section of How to Explore Data.
A third measure of abundance is the mean group size, which
tells us how many individuals of a species we are likely to see, when
we see that species. This measure also indicates which species are
typically seen in flocks and which are more likely to be seen singly or
in pairs.
The two maps of Steller's Jay show the mean group size reported by
participants of Project FeederWatch and Great Backyard Bird Count,
respectively.
The Project FeederWatch species map shows the average over the five-month Feederwatch season (Nov-April)...
...whereas the Great Backyard Bird Count data are collected during an intensive four-day count in February.
Both the "snapshot" of Great Backyard Bird Count and the full winter
season represented by Project FeederWatch indicate a similar overall
distribution of Steller's Jays and similar areas of highest group size.