Counting herons without disturbing them

Counting herons gives you a sense of how many birds use a stretch of water, and whether that number changes from one visit to the next. The method is simple: pick a fixed point, count the same area each time, and keep the count short enough to finish before the birds move on.

Steps

1. Fix your counting point at the vantage point you chose, and stay there for the whole count.
2. Divide the water into sections using landmarks such as a post, a bend or a clump of reeds. Count one section at a time, moving in the same direction each visit.
3. Count the standing birds first. Use a tally in groups of five, drawing a line through each group, so the total is quick to check.
4. Count birds that arrive or leave separately, and write down the direction and the time.
5. Stop the count if a bird lifts or the whole group moves. Note the total so far and the reason, then start again on another visit.

What can go wrong

The usual problems are counting the same bird twice as it moves between sections, and missing birds hidden in reeds or behind a bank. A bird that walks behind a clump may return to the count later. Set a simple rule: count each bird once, when you first see it in a section, and do not count it again when it moves into the next section.

Counts also go wrong when you rush to finish. Hurry and you will miss a bird or count one twice, so take your time and accept that a count is an estimate.

How to tell it went right

A good count can be repeated. If you return to the same point, at a similar time and in similar light, the numbers should fall in much the same range. Large swings usually point to a counting error rather than a real change in the birds.