Mist nets are used by ornithologists and bat biologists to capture wild birds and bats for banding or other research projects. Mist nets are typically made of nylon mesh suspended between two poles, resembling an oversized volleyball net. When properly deployed, the nets are virtually invisible. The grid size of the mesh netting varies according to the size of the species targeted for capture. Net dimensions are approximately 1–2 m high by 6–15 m long. A dho-gaza is a type of mist net used for larger birds, such as raptors. The use of mist nets usually require specific permits specified by country specific wildlife protection legislations. Mist net handling requires training and skill to avoid injury to the captured birds or bats. A 2011 research survey found them to have a low rate of injury while providing high scientific value.
Mist netting is a popular and important tool for monitoring species diversity, relative abundance, population size, and demography. Although setting up mist nets is time consuming and requires certification, there are certain advantages to visual and aural monitoring techniques, such as sampling species that may be poorly detected in other ways. It also allows easy standardization, hands-on examination, and reduces misidentification of species. Because they allow scientists to examine species up close, mist nets are often used in mark-recapture studies over extended periods of time to detect trends in population indices (Dunn and Ralph 2004).
Specific uses of mist nets are:
- Mark-recapture for population sampling
- Humane capture and relocation of small birds or bats
- Tagging and tracking
- Testing health of bird or bat species and for ectoparasite studies
Because there is still debate as to whether or not these techniques provide precise data measurements, it is suggested that mist netting is used as a supplement to aural and visual methods of observation. One of the main disadvantages of mist nets is that the numbers captured may only represent a small proportion of the true population size (Dunn and Ralph 2004). Mist netting is a unique method in that it provides demographic estimates throughout all seasons, and offers valuable guides to relative abundance of certain species or birds and/or bats (Dunn and Ralph 2004).
Mist-nets can be important tools for collecting data to reveal critical ecological conditions in a variety of situations. This summarized study, "Effects of forest fragmentation on Amazonian understory bird communities" by Richard O. Bierregaard and Thomas E. Lovejoy, used mist-nets to analyze the effects of forest fragmentation on understory bird communities in terra firme forest of Central Amazon.
Data from intensive mist-netting mark-recapture programs on understory birds from isolated forest reserves were compared to pre-isolation data from the same reserves to investigate changes related to isolation from continuous forest (Bierregard and Lovejoy 1989). Birds surveyed were from a variety of ecological guilds, including nectivores, insectivores, frugivores, obligatory army ant followers, forest edge specialists and flocking species. The periodic sampling by mist-netting capture program provided the quantitative basis for this project. Reserves of varied sizes (1 and 10 hectare) within the Biological Dynamics of Forest Fragments project site were sampled with transects of tethered mist-nets once every three or four weeks. Capture rates from isolated reserves were compared to pre-isolation rates to measure changes in population size and/or avian activity due to isolation (Bierregard and Lovejoy 1989). Data was analyzed in the following ways: capture rates per net hour as a function off time since isolation, percent recapture as a function of time since isolation, abundance distribution of species against the species rank by abundance, percent individuals banded according to species and feeding strategy, and finally, capture rates per net hour in isolated reserves against capture rates per net hour in continuous forests. A summary of the results and discussion as stated by Bierregaard and Lovejoy is as follows:
- “...changes in the understory avian community in isolated patches. Following isolation, capture rates increase significantly as birds fleeing the felled forest entered new forest fragments. Movement to and from the reserve is limited as witnessed by an increase in recapture percentages following isolation. Species of birds that are obligate army ant followers disappeared at the time the surrounding habitat was removed from 1 and 10 ha areas. The complex mixed-species of insectivorous flocks typical of Amazonian forests deteriorated within 2 years of isolation of 1 and 10 ha forest fragments. Several species of mid-story insectivores changed their foraging behavior after isolation of small forest reserves.”
All of this data was collected using mist-nets, and gave way to these different dimensions of information about the understory bird community at this site. Data such as this can be extrapolated to gain understanding of ecological effects of factors impacting ecosystems, such human activities or environmental changes. This is just one example of the use of mist-nets as a tool for ecological and biological sciences, as well as possible ecosystem management implications mist-net data offers.
There are several disadvantages to using mist nets. Mist nets are very time consuming. They have to be set up properly without mistakes. An animal caught in a mist net can become entangled, so the net must be checked often and the animal removed promptly. Disentangling an animal from a mist net can be difficult and must be done carefully by trained personnel. If an animal is heavily tangled a few strands the mist net may need to be cut to avoid injuring the animal which damages the net as well. Also, mist nets will not capture birds in direct proportion to their presence in the area (Remsen and Good 1996) and can miss a species completely if it is active in a different strata of vegetation, such as high in the canopy. They however can provide an index to population size.
People using mist nets must be careful and well trained since there is a possibility that the birds caught in the net can become harmed in the process. One study found the average rate of injury for birds in mist nets is lower than any other method of studying vertebrates, between 0 and 0.59% while the average mortality rate is between 0 and 0.23% (Spotswood et al. 2011). While rare, it has been suggested, although without scientific studies, that larger birds may be more prone to leg injuries and internal bleeding while smaller birds, if they have problems it is with tangling issues and wing injuries. Factors that affect the injury and mortality rate are human error while handling the species, time of year caught, time of day caught, predators in the area, and size/material of the mist net.
Humans that deal with the species caught in mist nets are called banders in the United States. Banders are responsible for banding the species caught in the net so they can be tracked. In the United States, in order to band a bird, one must have a banding permit. Banding permits are given to people who have gone through training and whose projects contribute to the conservation and management of the bird population. Banders are responsible for the animals caught and thus apply their training by paying attention to stress cues such as panting, tiredness, closing of eyes, and raising of feathers. If not, the animal can severely injure itself. There are different types of banding permits, the Master Permit and the Sub permit. Master Permits are given to individuals who band on their own. Sub permits are given to individuals who will be supervised while banding by a person with a Master Permit. In order to receive a permit, one must fill out an application and return it to the nearest banding office. Banders must ask for special authorization in their application in order to use mist nets, cannon nets, chemicals, or auxiliary markers (North American Bander’s Study Guide 6).
- Bal-chatri traps to catch birds of prey (raptors)
- Spotswood, E. (2011). "How safe is mist netting? evaluating the risk of injury and mortality to birds". Methods in Ecology and Evolution. doi:10.1111/j.2041-210X.2011.00123.x. Retrieved 2011-10-07.
- J. V. Remsen, Jr., And David A. Good. 1996. Misuse of data from mist-net captures to assess relative abundance in bird populations. The Auk 113(2):381-398
- C. John Ralph and Erica H. Dunn, 2004 Editors Monitoring bird populations using Mist nets. Studies in Avian Biology No. 29
- Bierregaard, R.O.; Lovejoy T. E. (1989). "Effects of forest fragmentation on Amazonian understory bird communities.". Acta Amazônica 19: 215–241.
- Dunn, Erica H.; C. John Ralph (2004). "Use of Mist Nets as a Tool for Bird Population Monitoring". Studies in Avian Biology 29: 1–6.
- Spotswood, Erica N.; Kari Goodman; Jay Carlisle; Diana L. Humpie; Josee Rousseau; Susan L. Guers; Gina B. Barton (2011). "How Safe is Mist Netting? Evaluating the Risk of Injury and Mortality to Birds". Methods in Ecology and Evolution.
- "North American Banders Study Guide". North American Banding Council: 1–69. 2001.