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The Institute's biologists have searched for ways to efficiently and accurately answer critical questions about the mallard life cycle.

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Anatomy of the Research Project

In Tune With Ducks

Small radio transmitters are surgically implanted in hens to allow researchers to follow the birds' every movement. These transmitters, unlike some earlier models, have no effect on the ducks as they go about their lives. Before the hen is released, a series of measurements are taken to see if body condition and nesting success are correlated to one another. By using handheld and truck-mounted radio receiving antennas, biologists are able to follow the movement of the birds on a daily basis to gather critical information about nesting cover, clutch size, predation rates, hatch dates, and brood fate. Each transmitter is expensive, costing $200.

Attaching Radio Transmitters

Following capture, each bird is fitted with a USFWS/CWS leg band and weighed. In addition, females are surgically implanted with a radio transmitter. Each transmitter emits a unique radio frequency to allow identification of each individual bird. The transmitter is placed inside the body cavity on the side opposite the ovary (birds only have one ovary). Surgeries are performed by highly trained staff in modified truck campers. Truck campers are used to allow the surgeons to go to the bird instead of having to bring the bird to the surgeon, thereby, minimizing the handling time for each bird. Following surgery, each bird is held for 1 hour to ensure she has fully recovered from the anesthesia before being returned to her pond.

Radio Telemetry

Once a female is marked with a radio transmitter, she is located twice daily using a highly directional truck-mounted receiving system and triangulation. When a bird is located in the same place for 3 consecutive days, she is approached on foot using a hand-held antenna to determine if she is in nesting cover. If she is in nesting cover, very precise triangulation is done with the hand-held antenna. In the afternoon, when the bird is no longer on her nest, the researcher returns to find the nest, and collect habitat information. Radio-marked birds allow Assessment staff to determine nest-site habitat selection, hatching rates, the number of nests a bird attempts in a season and, for those birds that successfully hatch a nest, subsequent duckling survival.

Predator Indices

Because predation is so important in determining the population dynamics of ducks, it is important to estimate abundances and distributions of predator species on Assessment sites. Avian and mammalian predators are indexed in several ways at each site: (1) early in Spring (before the trees have leaves) all active hawk and owl nests are located and mapped; (2) all predator sightings are recorded to derive an index to the numbers of predators seen/staff hour on the study area; and (3) all likely areas (e.g., road edges, muddy wetland edges, recently tilled fields) within areas searched for duck nests are examined for tracks of mammalian predators.

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