The Indicator

This indicator describes unusual mortality among fish, aquatic mammals (such as otter or beaver), waterfowl (i.e., ducks, geese, and swans), and amphibians, along with the incidence of deformities among amphibians. Unusual mortality generally involves the death of multiple animals in a relatively small area over a relatively short period of time. That is, one dead bird would not be considered an “unusual mortality event,” but if one dead bird was found every day for a week, in the same location, it might be. In addition, a single death might be considered for inclusion here if the particular circumstances warranted it—for example, if the bird was part of a flock that was known to have fed at a contaminated site.

This indicator reports mortality events according to the number of individuals killed. When data for different species groups become available, it may be necessary to use categories (such as serious, severe, catastrophic) rather than numbers of individuals. This would facilitate comparison of mortality events affecting different species. For example, an event affecting 100 individuals would be viewed with different levels of seriousness if it affected 100 waterfowl, 100 fish, or 100 mammals such as otters.

The Data

Data Source: Data on waterfowl are collected by the Department of the Interior, U.S. Geological Survey, Biological Resource Division, National Wildlife Health Center (NWHC). They were supplied especially for this report.

Data Collection Methodology: NWHC is a research and diagnostic laboratory, with a primary focus on disease prevention, detection, and control in free-ranging wildlife. NWHC maintains a database of outbreaks of wildlife disease and unusual mortalities, usually affecting multiple animals at the same time. The database covers all 50 states, Puerto Rico, and the U.S. Virgin Islands, and covers wildlife disease and mortality events over the past 25 years. The database contains information on avian, mammalian, and amphibian mortality events. Information in the database is provided by various sources, such as state and federal personnel, diagnostic laboratories, wildlife refuges, and published reports.

Data Quality/Caveats: As noted, the NWHC database covers mammalian and amphibian mortality events, as well as avian events. For freshwater reporting, the avian component was selected as the most complete and most likely to provide representative information at this time. Even for birds, however, the database may not accurately reflect all causes or cases of mortality since NWHC is not informed of every mortality event. Smaller events, in particular, may be handled locally and may not be reported to NWHC. The decision whether or not to include a reported event in the database is made by NWHC specialists. The data reported mortality events primarily affecting anseriformes (ducks, geese, and swans); however, other types of birds that died in an event would have been counted. In addition, the database was not developed as a tool for reporting on national trends; it was intended for use by NWHC as a tool for tracking epidemiological information over time. The information is generally not from specifically defined surveillance and monitoring systems; rather, information is provided as events are discovered or reported.

Data Access: Data are reported quarterly in NWHC online reports. See http://www.nwhc.usgs.gov/pub_metadata/qrt_mortality report.html. These reports also include information on mammal and amphibian mortality. Data reported here were prepared by NWHC staff specifically for this project.

The Data Gap

Mammal and Amphibian Mortality: As noted, the NWHC collects data on amphibian and mammal mortality. These data are less complete than for waterfowl. Reporting on these groups would be possible if additional resources were available to ensure that reports of amphibian and mammal deaths were reported to NWHC on a regular basis from all regions of the country.

Fish: There is no program in place to collect information about freshwater fish die-offs.

Amphibian Deformities: The North American Reporting Center for Amphibian Malformations (NARCAM; see http://www.npwrc.usgs.gov/narcam/) is a project of the U.S. Geological Survey’s Northern Prairie Wildlife Research Center. The NARCAM database receives data from a wide variety of sources. NARCAM is not part of a structured monitoring system, but it cooperates with and receives information from several such monitoring programs, among them NAAMP (North American Amphibian Monitoring Project), Frogwatch USA, ARMI (Amphibian Research and Monitoring Initiative), and A Thousand Friends of Frogs. Wildlife refuge personnel, state fish and game agency staff, university students and researchers, and others who have conducted field surveys of amphibians also submit reports, as do members of the general public, who are able to use NARCAM’s Web site to submit their reports directly online. Unless the reporter is thought to have sufficient expertise, the submission is forwarded to a verifier (a professional herpetologist or other expert) who can go to the original site and confirm the report.

As of July 2001, more than 2,000 verified reports, from 47 states and 4 Canadian provinces, had been included in the NARCAM database (see http://www.npwrc.usgs.gov/narcam/reports/reports.htm and http://www.nwhc.usgs.gov/amph-dc.html). However, reports are not evenly distributed among the states: Minnesota, where large numbers of malformed amphibians were first reported, accounts for 21.7% of all reports, Wisconsin for 12.2, and Vermont for 12.0. Another nine states account for 26% of all verified reports. According to NARCAM, it is often difficult to find trained volunteers (and funds) for amphibian surveying programs.