The Effects of Weather on Radio Telemetry Accuracy and Signal Strength

Frank Parisio

Introduction
My research was focused upon the role of weather in radio telemetry data collection.  Varied topography and dense vegetation can cause signal weakening and increase error, but weather variables have less well-known effects on telemetry.  Interferences with the radio signal can alter the recorded direction and strength and create problems in estimating animal locations.  I attempted to identify the relationship between weather variables (precipitation, cloudiness, wind, and temperature) and signal variables (strength and activity), and made recommendations to improve telemetry in light of weather disturbances.

Methods
I used summer 1991-1995 data from a radio telemetry study of white-tailed deer (Odocoileus virginianus) at Huntington Wildlife Forest (HWF) in the central Adirondacks.  I used observer-recorded weather variables, and used daily temperature and precipitation data collected at the HWF weather station.  Signal strength was based on a scale of 1-5 (1 being the loudest).  Radio collars were not equipped with an activity sensor.  A signal was recorded as active if the signal intensity changed when the antenna was no longer being rotated. 

Results and Discussion
Greater cloud cover was correlated with a stronger signal.  This makes sense because a radio signal will bounce off of clouds as the signal projects out into the environment (Marshall Radio Telemetry 2003).  However, temperature and precipitation were both positively related to signal strength.  Wetter objects reflect signals better (Marshall Radio Telemetry 2003).  Humidity, which can often accompany high temperatures, may lower signal strength as the moisture in the air absorbs passing waves (Resources Inventory Committee 1998).  Therefore, it seems counterintuitive that temperature and precipitation should be related to greater signal strength. 

Windy conditions were related to weaker signal strength.  Vegetation can absorb or deflect signals, and wind can play an important role in shifting plants in different directions creating the illusion that the animal is moving when it may not actually be at all (Cochran 1980).  Windiness was the only weather variable related to signal activity, with greater signal activity during calm conditions.  Deer often seek shelter in heavy forest cover when faced with strong winds, particularly when it is cold (Dasmann 1981).

Conclusion
I concluded that weather variables can affect accurate location of collars, but the relationship is complex and the severity of these interferences to signals is still not fully known.  Minimizing radio telemetry error is important because the more closely we are able locate an animal’s location, the more information can be gathered on the health and activity of the species.  It would be valuable to determine whether changes in signal strength and activity are due to weather variables, the animal’s movements, or other factors.  

Literature Cited
Cochran, W. W.  1980.  Wildlife telemetry.  Pages 507-520 in S. D. Schemnitz, ed.  Wildlife Management Techniques Manual, 4th ed.  The Wildlife Society, Washington, D. C.  686pp.

Dasmann, W. 1981. Deer range: improvement and management. McFarland and Co., Inc. Jefferson, N.C.: 168pp.

Marshall Radio Telemetry.  2003.  Frequently Asked Questions.  Accessed June 6, 2003 online at: http://www.marshallradio.com/pointer/psupport_faq.asp

Resources Inventory Committee.  2003.  Accessed online 16 July, 2003 at http://srmwww.gov.bc.ca/risc/pubs/tebiodiv/wildliferadio/index.htm#table_of_Contents.

Contact Information
Adirondack Ecological Center- aechwf@esf.edu

About The Author:  I attend Plattsburgh State University and major in Environmental Science, and will graduate in 2005.  My experience includes environmental education for the Department of Environmental Conservation as well as several years of volunteering.