Prime Hook NWR
Description: Prime Hook National Wildlife Refuge is located southeast of Milford, DE. Although its property runs along the Delaware Bay shoreline, the refuge does not include the beach shoreline of the bay. The refuge consists of 9,700 acres, approximately 7,400 of which is freshwater marsh, tidal marsh and open water. Other habitats include 1,000 acres of timber and brush and 1,300 acres of grasslands and croplands. Water levels on more than 4,200 acres of marsh are raised or lowered at different times of year by a system of low dikes and water control structures. The refuge is split into four management areas: Unit 1, the northernmost, is a saltwater marsh located between Slaughter Beach Road and Fowler Beach Road. Unit 2 is a 1,500-acre freshwater impoundment between Fowler Beach Road and Prime Hook Road. Unit 3 is a 2,500-acre freshwater impoundment between Prime Hook Road and Route 16. Unit 4 is a 200-acre brackish impoundment located to the south of Route 16.
Refuge biologist, Annie Larsen, has anecdotal reports of shorebirds making extensive use of the Unit I salt marsh during high tide, especially in large snow goose eat-out areas in spring and fall migration. However, limited access to the unit has precluded the gathering of systematic data. Shorebird use at other units has been documented by volunteers who survey the refuge once a week throughout the year. The peak spring migration for shorebirds occurs in May and dominant species are Dunlin, Short-billed Dowitcher and Semipalmated Plover. Fall migration runs from beginning of July to about the end of November and dominant species are Dunlin, Semipalmated Plover and Semipalmated Sandpiper.
International Shorebird Survey (ISS) provides records for the following impoundments within Prime Hook NWR. Broadkill: BBPL (34), DUNL (150), RUTU (90), SAND (180), SEPL (136) and SESA (55).
Route 16 Marsh: BBPL (15), DUNL (165), GRYE (30), LEYE (21), LESA (1,200), RUTU (20), SAND (12), SBDO (94), SEPL (350), SESA (808) and WRSA (12).
Survey Method: Ground surveys at the impoundments within a 2-hour period centered on high tide. Lighting conditions can be difficult at impoundments when one is facing towards the south, especially in Unit 4. To minimize this, surveys should be conducted in late afternoon or on cloudy days whenever possible.
Large potions of each unit in Prime Hook are not readily visible from vantage points on the ground; boat or airboat surveys may be needed to access these areas. Aerial surveys of the impoundments at various stages of water level management may be needed to determine if ground surveys are sufficient for Prime Hook.
Selection Bias: This bias is a potential problem if portions of impoundments receiving significant shorebird use cannot be surveyed from the ground. Pilot studies will be needed to determine the extent of this problem using some combination of air and/or boat surveys in tandem with ground surveys.
Measurement Error: This may vary among species viewed at large distances within the impoundments. Also, vegetation growth following draw downs could reduce the visibility of shorebirds in some impoundments.
Measurement Bias: Any shift from specific to generic identifications (such as “peeps”) could result in significant bias. The same is also true of changes in detection rates resulting from the change or growth of vegetation.
Pilot Studies: Aerial surveys are the only way to get information on shorebird use in the Unit I salt marsh. Annie Larsen is working with Karen Bennett (DNREC) to see what the refuge can do in the near future to obtain this information.
Local Contacts: Annie Larsen, Refuge Biologist, Prime Hook NWR