I hope I'm mostly preaching to the choir when I say that counting birds whenever possible (vs. just ticking species) is important for many reasons. The folks at team eBird have summarized the importance of doing so and some basics to try when counting flocks in their excellent post, "Bird Counting 101". For those facing more advanced counting situations they followed up with "Bird Counting 201". Here I'd like to show one of my favorite ways to count big flocks of birds using digital photographs.
Bird photography is very useful beyond aesthetic reasons. For example, when documenting a rare bird or for use in identifying challenging species a few photos can be invaluable. I have also found that flock shots (however janky) are great for counting bird numbers from the leisure of my laptop. I know I'm not the first birder who has thought of this (indeed, one main way to census flocks of waterfowl etc. is to study aerial photos), but I'd like to share a few tips I've found to be helpful.
First, a great use for a zoom lens is to pull back to fit the flock into the frame. Sometimes a modest point & shoot camera or smart phone may be even better than a telephoto if you are close to a big flock. If you still can't fit the flock in, try to estimate how much of the flock you are getting in the image to use as your basis for multiplying your estimation later. When I'm looking at an image on my computer, I like to use the paintbrush feature in Photoshop Elements (about any image processing software will have similar features), with the pixel radius set to about the body size of each bird. This lets me count individuals by dabbing them each with a spot of virtual paint, eliminating re-counts. I also like to change the color in sets of birds according to the general size of the flock (like every 10, 25, or 100 birds.) This gives me a nice visual of each block of birds and helps me pick up where I left off if I lose count. Not only does this give a really accurate count of the flock but I think it helps me improve my visualization of blocks of birds in the field if I can't get a shot to count later. Here are a few examples of this technique that I've used to get a good count of birds in a flock.
The winter of 2007/2008 produced an amazing irruption of Bohemian Waxwings in Colorado. Here is what I estimated to be about 1/3 of a flock in my Longmont neighborhood on 29 December 2007. How many birds do you think are in this frame?
I arrived at 698 individual birds, each dabbed with a spot of color (in separately colored blocks of 100.) Click on the image to see the color dabs in higher resolution.) Since I thought I was able to fit about 1/3 of the birds in the frame, I estimated the flock to be ~2100 birds.
Here's an example from last fall. On 5 October 2012 an amazing overflight of Sandhill Cranes swept the overcast skies of Boulder. Skein after skein of vocalizing birds traversed the city in the afternoon hours, and amidst my errands I swung into a Safeway parking lot to take a wide-angle shot of one wave.
To count the birds I tweaked up the brightness and contrast and then dabbed the birds in colored groups of 100, arriving at 378 birds. By comparing this group to the multiple other skeins I saw flying by that afternoon I estimated my observation total at 2400 Sandhill Cranes. Adding photos like this along with field notes to eBird checklists is a great way to make your friendly neighborhood eBird reviewer happy!!
Like much of the United States, Colorado is in the midst of an historic redpoll irruption this winter. On 24 November, 2012, I caught up to a large flock that had been reported frequenting Baseline Reservoir in Boulder. When the flock picked up and whirled around I grabbed a shot with every bird in the frame. Care to estimate the count before scrolling down??
In this frame I came up with 60 birds, here dabbed in color blocks of 10. On a personal note, at the time I saw it, this flock was about triple the size of all of my prior cumulative redpolls in the state (a number that has since skyrocketed from several more large flocks I've encountered this winter.)
You don't even need a telephoto rig to try this technique- here's another Bohemian Waxwing flock (from Niwot, Colorado 22 Feb 2013) digibinned with my iPhone through the beta bins that I keep in my car. I propped the binocular on my window (partially rolled up to achieve a good height) and clicked a few shots for a private census.
This time spotting by 20s I came up with 160 birds in the cottonwood tree.
OK, ready for your homework? See what you come up with on this one... ◔_◔