Spot mapping is a relatively simple but efficient method of covering an area of study during a field experiment. Requiring only a GPS and a map of the surrounding area, it allows for marking out of specific locations of interest and determination of more general regions such as territories. As such, learning the proper techniques for effective spot mapping was one of our first objectives as a group. This was true of both the local Tompkins County crew as well as the group signed on for the Borneo trip. In fact, the job fell to us to “train” the Borneo crew during the brief period they stopped in Ithaca between their respective vacations and the start of the expedition. This skill is a valuable one for field biologist everywhere, and after taking a short time to familiarize ourselves with the necessary equipment and techniques it begin our primary means of keeping tabs on our study nests.
Our TOCO crew was supplied with several GPSes for use in spot mapping. These pocket-sized devices were outfitted with a variety of options, but the feature we were most interested in was their ability to take measurements on the Universal Transverse Mercator coordinate system, commonly abbreviated as UTM. Unlike latitude and longitude, UTM measurement takes the distance from set x- and y-coordinates laid out in a grid across the earth. These measurements are referred to as easting and northing, and the GPS has a page that shows these precise measurements. A master map back at our “home base” showed the UTM grids laid out over an aerial view of our study area. This map was then scanned and copied multiple times, then split up into page-sized “zones” for use in the field. To spot map, we would take a GPS and zone maps for the sections of the woodlot we intended to visit, along with a writing implement. At any point of interest, we would simply take the last 3 digits of both measured coordinates and mark them with respect to our gridlines on the map.
This, of course, begs the question of what qualifies as a “point of interest”? The obvious answer is “a nest”, and discovering a nest is definitely grounds for a mark on the map, taking the coordinates from as close to the nest tree as possible for the sake of accuracy. However, as we’ve previously covered, nests can be difficult to find on their own. As such, we used our spot mapping trips to gradually build up an in-depth map of the region, showing us the important “who, what, when, where, and why” of our study subjects. Any observation of a target bird is denoted on the map with its four-letter band code (RBGR for Rose-breasted Grosbeak, SCTA for Scarlet Tanager, etc.). The point for marking it should be measured as accurately as possible, estimating the distance in meters and direction from the observation point to the target. A singing bird is indicated by a circle around the code, while a calling bird is underlined. If the bird is off in a direction where it is difficult to ascertain its exact location, the circle or underline are drawn dashed instead of full. Any additional notes, such as movement, behavior, individual identifiers, and sex are to be noted on the map as well. One behavior that provides us with particularly useful information is the observation of countersinging between rival males. This behavior, where two males in opposing territories sing to each other to defend their turf, indicates a clear territorial boundary. These behaviors and map observations, over time, provide us with a very clear picture of the territories and home ranges of the birds in our research area. Multiple observations on different days help us build a map of the territories these birds defend, providing us with a much more focused starting point for our nest searches.