Numbers of birds in flocks

Manomet Center for Conservation Sciences

• Most field biologists think they are good at estimating numbers of birds in flocks, but

• In fact, it is the rare person who estimates bird numbers with good precision

• Periodic practice improves estimating abilities

People differ in estimating tendencies

• Many tend to underestimate numbers

• Many tend to overestimate numbers

• Rare individuals tend to be accurate

Estimating accuracy will tend to vary with:

The size of the flock (most people tend to underestimate numbers in large flocks)

The size of the birds (most people tend to underestimate numbers when birds are small and to overestimate when birds are large)The color of birds (a tendency to overestimate when birds are light-colored versus dark-colored)

Estimate the number of dots

How many birds?

The size of the flock

837

15

most people tend to underestimate numbers in large flocks

How manyLarge ?Small ?

The size of the birds

40 eachMost people over-estimate numbers of large birds

The color of birds

How many light and dark?

54 eacha tendency to overestimate when birds are light-colored versus dark-colored

An estimating strategy• Guess the flock size

• Is there more than one species ?

• Are birds fairly evenly dispersed ?

An estimating strategy If guess was

• 20 - 100, count 10 birds and then estimate by blocks of 10 for remaining

• < 20, count the birds

• 100 - 500, count 25 or 50, then ‘block count’the rest of the flock by 50’s

• >500, count (estimate if flying) 100 and then ‘block count’ the rest by 100’s

An estimating strategy

• Finally, estimate the percentage of each species in the flock

Beware of estimates forflocks where birds areunevenly dispersed

1. Guess the flock size2. Is there more than one species ?

3. Are the birds fairly evenly dispersed ?

The guessed number should exceed 100So, mentally block off 25 birds

By blocks, extrapolate flock size

How many black? How many blue? 9690

1. Guess the number

Now, using the known ‘blocks’, estimate (you have 20 seconds)

OK, What was your estimate?

How about 3400 ?

These exercises were to provide tips

Each person will have different tendencies -- the goal is to learn your own … practice to learn them.

Part 2 provides practice exercises

You also can practice by counting 1/3 cup of beans or a teaspoon of rice. Grab beans (or rice), throw in a box top,estimate, then ‘count’ using cups-full (or teaspoons full).

The endThe end