Birds in better condition than last year but still face an ecological roulette

by Larry Niles (Part 3 of 3)

With the stopover period winding down, we can say the red knot and other shorebird species left the bay in better condition than the disastrous condition of last year. So what does it mean?

First, the last four years have been a sort of ecological roulette for the birds. Horseshoe crab numbers remained at only 1/3 the potential population possible on Delaware Bay leaving birds at the mercy of good conditions to get enough eggs. Last year, water temperatures stayed low during the mid-May depressing the spawn and the density of eggs. Although the average was 8000-eggs/square meter, there were less than 2000 eggs/ meters square in the month of May.

This year, the weather and water temperature added to a good spawn in May and the birds appeared to have left in good condition. Unfortunately, it’s only chance. If bad weather or cool temperatures return, they will face another bad year. We need more crabs to smooth out the rough years. The bay can support three times the current number.

An increase in the number of horseshoe crabs would transform the bay. In 1990 and 1991, we had three times the number of crabs we have now. But we had 10 times the density of eggs because of multiple breedings by females and more eggs reaching the surface as one crab digs up another’s eggs. Additionally, it lasted for two months, unlike this year’s eggs, which lasted only a few weeks.

Dr. Larry Niles has led efforts to protect red knots and horseshoe crabs for over 30 years. Read the paper that describes the work of a team of scientists measuring egg densities in 1991 before the overharvest of crabs here.