Duck surveys
By DON MORROW
Although ducks migrate through St. Marks National Wildlife Refuge from August through early June, I survey duck populations on the interior pools and ponds at the refuge from late October through mid-March. Outside of my monitoring period, it’s mostly just Blue-winged Teal, most of which winter in South America and have a longer migratory period than other duck species.
With most birds, a change in day length is the main trigger that gives them the urge for going. This causes hormonal and behavioral changes that lead to migration. Some bird species respond by preparing for, and leaving, on their migratory journey. These are sometimes called calendar migrants, because their migration timing is closely tied to calendar dates. They are long distance, usually intercontinental migrants, like Pectoral Sandpipers and Scarlet Tanagers.
However, for other species migration timing is strongly influenced by weather. They are shorter distance, primarily intra-continental migrants and are called weather migrants. Ducks are classic weather migrants. Fall migration for ducks can be delayed in warmer years when they take advantage of good weather to put off their Southbound migration. Spring migration is tied to competition for favorable nesting territories and ducks usually leave on time in the Spring, but may leave early.
Because weather affects migration timing, duck numbers at the refuge can be volatile. Numbers show that a moderately warm Fall delayed migration into the refuge, but that winter numbers jumped up to normal levels in December. Duck numbers stayed high through mid-February, a time at which they have usually dropped by fifty percent or more. The mid-March duck survey logged only 188 ducks, an 87% drop in the last month down to a seasonally appropriate level. Their delay in leaving was unusual. It coincided with extreme winter weather across most of the country, which may have been a contributing factor.
Twenty-six waterfowl species were recorded at the refuge this winter and there were just over 2,000 ducks at the high point in mid-December. Snow Geese stayed late into the winter and we had a single Canada Goose sighting. Canada Geese once wintered on the refuge in the thousands. A warming climate has led them to winter further north, but we often get strays.
All three species of scoters; Black, Surf and White-winged, were seen in the nearshore waters near the lighthouse, as was a female Long-tailed Duck. Thirty-five Canvasback and 104 Ruddy Duck were on Lighthouse Pond in January, high numbers for both of these species. American Black Ducks were on the refuge, continuing an unbroken winter record at the refuge. St. Marks NWR is the only spot in Florida where black ducks regularly winter. This year was a good duck year.
Each duck season at St. Marks is both an echo of all previous years and a unique experience in itself. Winter is turning into spring and ducks have gotten the urge for going. Come down to the refuge to see the last of them before they’re gone for the year.
Don Morrow can be reached at donaldcmorrow@gmail.com.
