These walkers are a hoot since they are actively singing, dancing and cruising the island looking for Mr. or Ms. Right. Once two walkers fall in love, the bond they form is lifelong, broken only by death or disappearance of the partner. Such monogamous couples are the nesters. These no-nonsense adults find one another quickly each year, mate, then begin the serious business of incubating their egg and raising their chick. You can see the counting problem.
Walkers move around, sometimes alone and sometimes in groups of five or more.
With nesters, sometimes only one parent is at the nest, and sometimes both are present. Making sure you're counting each bird only once is tough. The U.S. Fish and Wildlife Service solution is to count nests, double the number, then estimate the number of walkers and chicks. LAST year the nest count was about 388,000. My own guess for this year, which includes the chicks that will hatch this month, is more than 1 million individuals.