It can be very difficult to count large or even small flocks of birds, especially when they keep moving around. To estimate the number of birds in a flock, use the "blocking" method. First count the birds in an imaginary block of typical density. Keep the block small, to include only 10 to 25 birds. Then visually superimpose the block onto the entire flock and estimate how many times it fits. Finally, multiply this number by the number of birds in the original block. To get the best estimate, repeat this procedure at various times throughout the day and average your results.

Mixed-species flocks

When large, mixed-species flocks appear in your yard, keeping track of the kinds and numbers of birds can be difficult. First, estimate the total flock size using the method above. For example, estimate a flock at 80 birds. Now, take several “samples” of those 80 birds, such as small groups that are easily visible under the feeder, and estimate the proportion of each species in each group. For example, a group of 10 birds might include 5 Dark-eyed Juncos, 4 American Tree Sparrows, and 1 White-throated Sparrow. If that group seems representative of the entire flock, apply your calculated proportion to the total of 80 birds, and estimate the total flock at 40 juncos (50% of flock), 32 Tree Sparrows (40% of flock), and 8 White-throated Sparrows (10% of flock).

Males and females observed at separate times

Some species are “sexually dimorphic,” that is, the male and female look different. An example is the Northern Cardinal. Some days, the male and female both may visit your feeder, but they never appear at the same time. Obviously you have two different cardinals in your yard. Still, you may count them as two individuals only if you see them together at the same time. Why? Because for FeederWatch data to be scientifically valid, participants must follow the exact same counting procedure for all species.

Can’t identify species

If you cannot identify a bird, write down “Mystery Bird” and the number counted. Sketch or photograph the bird and pay attention to its field marks. Then consult a bird identification guide and try to determine the species. If you are still unsure, remember that local birders can be an excellent resource for helping you identify an unfamiliar bird at your feeder. Try contacting a local bird club, Audubon chapter, or nature center. When you later confirm your identification, replace “Mystery Bird” with its correct name. Learn more about how to identify birds.

Rosy finches

Research has shown that these birds are actually several different species. On the paper data forms, all rosy finches are lumped together. If the species is known, enter your report in the write-in box instead of in the "Rosy-Finch (all species)" line. Online participants may add individual species to their checklist using the "Add a Species" function.

Black-capped and Carolina chickadees

These species are difficult to tell apart. Even knowing their songs and calls won’t help every time because they can learn each other’s vocalizations. If you live near the area where the ranges of these species overlap (see map at right), please record your chickadees as “Carolina/Black-capped Chickadee Mix.”

Tag-along birds

When a mixed-species flock in your Count Site is joined by a nonfeeder bird such as a creeper, kinglet, or warbler, you may count the “tag-along bird” even if it doesn’t actually visit your feeder. (The bird was indirectly attracted to your feeder site.)