Crepuscular Ducks Low light movement of waterfowl in inland water bodies of North Carolina Brian Bockhahn 2015

Hypothesis questions Do waterfowl roost on inland lakes at night during migration, and to what extent? Do waterfowl move around inland water bodies during low light periods? What light levels are optimum for movement? Which species move around and do they show light level preferences? Implications on bird counts and surveys.

Where? Christmas Bird Count (CBC) sites Falls Lake Jordan Lake Kerr Lake Roanoke Rapids Lake Lake Phelps Swift Creek

Where? CBC sites

Falls Lake - COE North of Raleigh, east of Durham 12,000 acres Depth 20-30’ 26 miles long 175 miles shoreline Widest point 1 mile Flood control, water supply, wildlife habitat, and recreation Elevation 251 msl

Jordan Lake - COE Southwest of Raleigh 37,000 acres Depth up to 30’ 18 miles long 200 miles of shoreline Widest point 1.7 miles Flood control, water supply, wildlife habitat, and recreation Elevation 216 msl

Kerr Lake - COE Border of NC and VA north of Henderson 50,000 acres Depth up to 130’ 34 miles long 850 miles of shoreline Widest point 2 miles Flood control, water supply, wildlife habitat, recreation and hydroelectric power Elevation 296 msl

Roanoke Rapids Lake - Dominion 4,600 acres Depth up to 62’ 8 miles long 47 miles of shoreline Widest point 1.25 miles Flood control, water supply, wildlife habitat, recreation and hydroelectric power Eleation 132 msl

Lake Phelps – second largest natural lake Crewsell, Washington county NC 16,600 acres Depth up to 9’, average 4.5’ 6 miles wide 20 miles of shoreline Natural lake, pocosin Elevation 132 msl

Swift Creek Northeast of Rocky Mount Flows into Tar River 12 miles long slough Natural river, beaver swamps, some green impoundments for waterfowl Elevation 75 msl

How? Sky Quality Meter Measures sky brightness Magnitudes per square arcsecond Site to site, day to day 80 degree cone, with direction of angle important

SQM compare to actual TOD SQM Reading 508 Sunset – 7 SQM 541 Dusk 13 SQM Time of Day - PM

SQM 6

SQM 7

SQM 8

SQM 9

SQM 10

SQM 11

SQM 12

SQM 13

SQM 14

SQM 15

SQM 16

SQM 17

SQM 18

Data collected Date Location Temp Cloud % Weather Base reading Both dawn and dusk Flat reading Each sighting Time of day SQM reading Quantity Species Direction of flight

Identification techniques Flight profile Flight styles Flock patterns Call notes, flight sounds

Data – species detected Canada Goose Wood Duck*** Gadwall** American Wigeon American Black Duck*** Mallard*** Blue-winged Teal Northern Shoveler Northern Pintail Green-winged Teal Double-crested Cormorant Canvasback Scaup sp Bufflehead Hooded Merganser*** Red-breasted Merganser Ruddy Duck American Woodcock Display

Crepuscular Ducks Data Sheet Date: 1/3/12 Time: PM   Location: Kerr Lake Dam Temp: 36 Clouds: 80% Weather: cold, light south winds TIME SQM QTY SPECIES DIRECTION OF FLIGHT  450 5.0 FLAT READING  455 6.2 5 HOODED MERGANSER SW OVER DAM  506 6.4 3  SW OVER DAM  5  2  515 7.6 2  516 7.8  3  518  8.1 525   9.5  527  9.9  6  529  10.5  8  531  10.7  12  MALLARD  HOODED MERGANSER  29 AMERICAN BLACK DUCK  14  24  AMERICAN BLACK DUCK  533  11.2  NORTHERN SHOVELER  GADWALL

Light levels SQM chart Total Waterfowl Dusk 13 SQM Sunset – 7 SQM SQM Reading

Species to SQM significant correlations

Peak Flights by SQM SQM Reading

Implications Bird Surveys – Pre-dawn and Post-dusk are important times to be in the field to survey for waterfowl. Migration pathways/flight lanes can be discovered or explored and should be monitored. Dams, rivers, lake coves and widest water body points. Surveying at peak times will increase accuracy of population estimates.

Conclusions Waterfowl regularly roost/stopover for night on inland water bodies. Waterfowl do move around and low light levels with peaks in the 11-14 SQM range. just before to after dusk before to just after dawn. 10 species of dabblers and 7 species of divers were detected and some do have light level preferences. Optimize time for best survey/inventory results.

Further considerations Daily monitoring to assess change throughout the season. Different numbers each night? Do they migrate to feed and then return to roost again or just stop over for a night? How does wind and weather influence low light flights? Freezing conditions play a role? Does flock size play any role in light preference? Collect yearly data. Is there any preference to dawn vs. dusk?