by Whit Gibbons

October 2, 2011

Q. Detectives use special techniques on invisible clues such as fingerprints, ballistics, and DNA to unravel the full story of what happened in a crime. Ecologists use visible clues such as footprints, tree rings, and hidden camera footage to reveal information about particular plants or animals. Do they also have procedures for investigating less obvious evidence?

A. Like crime fighters, medical professionals, and military personnel, ecologists use a suite of tactics and techniques to acquire information about a subject of interest. In fact, ecological research relies on many of the methodologies developed in these other arenas, including molecular DNA analyses, x-radiology, and satellite imagery.

The most basic environmental clues, known as spoor, were used in the earliest primitive human societies and are still used by modern-day ecologists and hunters. A footprint in the sand, deer tracks in the woods, feathers on the ground all are spoor that provide information to confirm that a certain type of animal was present. Such clues can be used to assess how long ago the animal was there and what activity it might have been engaged in. Dead leaves on a forest floor offer evidence of the presence of vines or shrubs that might not be readily observed when they are leafless in fall and winter. Scat (animal droppings) can be an especially valuable environmental clue. Not only does it reveal the existence of the animal itself but the contents may include fur, berries, or scales that denote the presence of other unseen animals and plants in the vicinity.

The use of modern technology is widespread in many fields of ecology. Environmental chemists use highly sensitive laboratory equipment to determine what compounds and isotopes are in contaminated soils and polluted waters, as well as in plants and animals themselves, such as fish with dangerously high levels of mercury. High mercury content in bottom sediments, water, and fish cannot be revealed by human sight, touch, smell, or taste. Mass spectrometry and other sophisticated procedures uncover otherwise invisible environmental clues that lead to public protection thanks to EPA regulatory guidelines. Advisory warnings from the EPA not to eat fish from certain rivers are based on such analyses.

Ecologists use the standard medical tool of x radiography to study reptile egg shells that contain sufficient calcium to be detected by x-ray photography. All crocodilians and turtles and most snakes and lizards lay eggs. Research ecologists use portable x-ray machines in the field that enable them to gather pertinent data about the number and size of eggs, and then return the animal unharmed to its habitat. The nondestructive sampling technique is especially important in ecological studies in which the loss of a single specimen of an endangered species is undesirable. Studies in New Zealand on the internationally endangered tuatara, which looks like a large lizard, relied on x-ray photography to obtain information on egg production. Investigators used x-ray photography to gather critical information on egg production necessary for understanding population growth patterns in these unusual animals that are on the verge of extinction.

Global positioning and geographic information systems that are essential for military operations worldwide are now commonly used by ecologists in a variety of studies. Combining these techniques with radiotelemetry, in which the location of individual research animals can be tracked, allows researchers to plot movement patterns over particular time periods. A GPS unit permits precise pinpointing of locations that can then be examined on GIS maps constructed from satellite imagery. The ecologist can identify critical habitats where mobile species such as deer, coyotes, and tortoises spend the most time. Land-use patterns and changes in ground cover and habitats due to forest fires, floods, pathogens, or other landscape-level phenomena can also be determined.

Sophisticated instrumentation and gadgetry are valuable in studying nature, but basic environmental clues--finding a shed snake skin, seeing a tree gnawed by a beaver, identifying the footprint of a bobcat--offer a gratifying wildlife experience. And even the simplest environmental clues can tell us something about the animals and plants in the world around us.

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