Mist netting is a specialized, non-lethal method used by researchers to capture wild birds and bats for scientific study. The technique involves deploying a fine, nearly invisible mesh net, which resembles a sheet of mist when properly set up in the field. This passive capture technique is a standard tool in ornithology and chiropterology worldwide, providing scientists with opportunities to gather direct data on flying animal populations.
Anatomy of a Mist Net
A mist net is constructed from thin, high-quality material, typically black nylon or polyester thread, suspended between two vertical poles. The netting material is extremely fine, often having a low denier (thread thickness) to be nearly undetectable by birds or bats in flight.
The main body of the net consists of horizontal panels, or shelves, created by thicker support lines called trammels. Nets commonly feature three to five shelves, which form loose, baggy pockets of netting material. When a bird or bat flies into the net, the impact causes it to fall into one of these deep pockets, where it becomes gently entangled and held securely until the researcher arrives. The size of the mesh varies significantly; small passerine birds typically require mesh sizes between 16 and 38 millimeters, while larger species or bats may necessitate different dimensions.
Essential Applications in Research
Mist netting is a widely accepted technique used to monitor the health and dynamics of avian and bat populations across diverse habitats. This method allows researchers to collect biological data that cannot be obtained through remote observation alone.
A primary application is population monitoring, where repeated captures help scientists estimate local abundance, density, and demographic trends over time. Mist netting is also fundamental to tracking migration patterns through banding and tagging programs. After capture, a uniquely numbered, lightweight metal band or tag is applied to the animal, acting as a permanent identifier. Recaptures yield information on survival rates, longevity, dispersal, and routes taken during seasonal movements.
The method also allows for the collection of biological samples, such as feather or blood samples, for genetic analysis, assessing body condition, or screening for parasites and diseases.
Safe Deployment and Extraction Protocol
The operational mechanics of mist netting are centered on minimizing stress and preventing injury to the captured animals. Proper site selection requires nets to be placed away from open sky or water where the fine mesh might become visible. Nets must also be avoided during adverse weather, such as heavy rain, strong winds, or temperature extremes, as these conditions increase the risk of hypothermia, hyperthermia, or muscle strain.
Once deployed, the net must be continuously monitored by trained personnel, with mandatory check frequencies ranging from every 15 to 30 minutes, depending on the weather and capture rate. This regular checking ensures that no animal remains entangled for an extended period.
Extraction requires specific, species-appropriate techniques, often involving the use of a specialized “bander’s grip” to secure the animal gently while the net strands are systematically untangled. The extraction process should be rapid, ideally taking no longer than five minutes per animal. If an animal is severely entangled, a small strand of the net is cut to facilitate a quick, safe release.
Following removal, the animal is placed in a breathable cloth bag and kept in a shaded area while processing, which includes banding, measurement, and sampling. The entire process, from extraction to release, is often limited to a 10-minute window to reduce the overall period of stress and confinement.
Regulatory Oversight and Animal Welfare
The use of mist nets is strictly controlled by regulatory oversight to ensure compliance with animal welfare standards and conservation laws. Researchers must obtain special permits, such as the United States Geological Survey (USGS) Federal Bird Banding Permit, or equivalent permits from federal and state wildlife agencies, before operating mist nets. These permits are necessary because many captured species, particularly migratory birds, are protected by law.
Permit requirements mandate that all personnel involved receive extensive training in capture, handling, and extraction techniques. This training is designed to minimize the risk of injury, with studies showing an average mortality rate of less than one percent.
Ethical protocol requires researchers to be aware of a species’ susceptibility to stress. They must be prepared to close nets immediately if conditions become unfavorable or if the number of captured animals exceeds the team’s ability to process them quickly.