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Techniques for Studying Nest Success of Ducks in Upland Habitats in the Prairie Pothole Region

Procedures for Nest Searches

Using the Cable-Chain Drag

The cable-chain drag (Higgins et al. 1969, 1977) was developed by biologists to locate duck nests in grassland habitat. Some investigators use a single 61-m (9.5-mm-diameter) chain instead of the cable-chain drag. The relative flushing efficiency of the two drags has not been tested. Most investigators believe the cable-chain drag is more efficient in dense, herbaceous cover, and some consider it useful as a standard method when comparing nest densities. Others prefer the chain drag because it is easier to maintain, covers a larger area per sweep, and is less likely to tangle or to hang up on obstacles than the cable-chain drag. Drags pulled by vehicles are most effective in grassland, cropland, and short brush such as Symphoricarpos sp. Areas of tall brush and trees or wetlands must be searched by walking or wading. Hand-pulled rope drags with cans or sections of chain attached can be used when access with vehicles is not feasible (e.g., where crops are growing). Trained dogs are often used to help find nests.

Two drivers and a spotter are used to locate nests with the cable-chain drag (Fig. 1). The need for a spotter is essential when searching tall dense cover. Preferably, the crew leader (also the recorder) should drive the vehicle on the left, accompanied by the spotter.

JPEG -- Picture of cable-chain drag.

Some studies require repeated searches of the same field during a nesting season. Best results are obtained when the subsequent searches are conducted by the same persons in the same positions as on previous searches. This enables better recall of nest locations if the marker was lost or when the nest location was not recorded accurately.

Before starting a nest search, the investigator should map the permanent features of each field. The direction of travel should be determined after scouting the shape and topography of the cover block and locating such obstacles as boundary fences, wetlands, and tree plantings (Fig. 2). Usually, the search should begin parallel to the longest straight field edge.

GIF -- Diagram of search pattern for cable-chain drag.

To start a search, the drag is stretched between the vehicles and all twists and entanglements are removed. While dragging, it is essential that each driver maintain proper alignment and distance relative to the other vehicle. Improper alignment (Fig. 3) occurs when one vehicle gets too far ahead or too close to the other. The distance between vehicles can be adjusted by slowing down or stopping to allow the other driver to resume the proper interval. Both drivers should watch along the drag as much as possible and still maintain a straight course in the field. The ability to do both simultaneously diminishes greatly as vehicle speed increases. Search speeds should be held between 3 and 10 km/h.

GIF -- Examples of proper and improper intervals.

When the dragging units approach the end of the field, the inside or pivot driver should slow down until the other driver enters the turn, causing the cable chain to go slack. Then the pivot driver makes a U-turn and waits in the back track until the other vehicle has attained the proper interval and alignment (Fig. 2).

Both drivers and the spotter must be constantly alert for twists or entanglements in the cable-chain drag. Twists most commonly occur during turns at the end of a field, or after the drag has flipped over a rock, tall shrub, or other obstacle. Twists can usually be corrected by untangling the chains; it is not usually necessary to remove the cable from the vehicles. Wire, dead brush, or other debris caught in the drag should be removed immediately to avoid damaging eggs.

The drivers are responsible for species identification when the hen flushes. Major distinguishing features are the size of the hen and the arrangement and contrast of dark and light colors of the plumage, especially on the wings and tail. The waterfowl identification guides Ducks at a Distance (Hines 1978} and Waterfowl Identification in the Central Flyway (Central Flyway Waterfowl Council 1974), provide illustrations showing these key characteristics. If in-flight identification of the hen is not made, the species can usually be determined at the nest from the size and color of eggs, down, or breast feathers (see Appendix A).

Locating Nests

The spotter's main job is to constantly watch the drag for flushing birds. When a bird flushes, the spotter must mentally mark the site and keep his eyes on it while guiding one of the designated drivers to the flushing location. To do this requires strict discipline; the spotter must avoid the tendency to follow the flight of the bird. Marking the flushing location is aided by noting nearby plants, rocks, or other landmarks. If both vehicles immediately stop when a bird flushes, the nest will usually be close to the drag. Drivers must avoid sudden stops that distract the spotter. If a driver has marked a flushed bird, he should remain in the vehicle and assist the spotter in guiding the other driver to the site. The spotter and one driver should not leave their vehicles until the nest is found.

Only one person should visit the nest unless more persons are required for habitat measurements. The recorder should avoid excessive disturbance of the vegetation that might attract predators. Care should be taken to avoid stepping on well-concealed nests. It is wise to not take a step until the ground is carefully inspected.

Nests can usually be found by following vocal and hand-signal directions from the spotter. Hens without nests might be flushed while they are selecting nest sites or digging scrapes. If a nest cannot be found after a reasonable effort, the approximate flushing site should be marked with a flag so that the area can be searched again on foot on another day. This procedure reduces the amount of trampled vegetation around nests. If the bird does not flush during the second visit, the marker should be removed and no further effort made to find the nest.

Marking Nest Locations

After recording the necessary nest data, the recorder covers the eggs with down and other nest material to conceal them from avian predators. To determine if investigator disturbance has caused nest abandonment, some workers place a small object, such as a strip of yarn, over the covered nest in such a way that its disarrangement by a returning hen can be detected on a subsequent visit.

Slender willow stakes flagged with short strips of cloth or fluorescent tape are recommended for marking nest sites so they can be relocated. Stakes should be long enough to stand above anticipated vegetative growth. Wire survey flags can be used in short cover.

Stakes should be firmly anchored at least 15 cm into the soil, at a standard distance (4 m is recommended) and direction from the nest. Nest identification numbers should be recorded with waterproof ink on the stake or flag. Care should be taken to write the same number on the nest marker as on the nest record form.

The exact location of all nests should be plotted on a map or aerial photo. Landmarks such as rock piles, wetlands, brush clumps, fences, and other landscape features should be used for referencing nest locations. Compass directions and measured distances from nests to natural features are useful in pastures because cattle are attracted by conspicuous nest markers and often dislodge flagged stakes. To aid in relocating nests, number and map the drag strips.

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