Survey Instructions: An Introduction

Counting and monitoring the breeding activity of forest birds can be difficult because they are often hard to detect in thick foliage, and some species are secretive during the breeding season. Although nothing replaces good observation skills and patience, there are methods that make the job easier. The BFL protocol uses several tactics to increase the probability of detecting a species if it is present and simplify the determination of breeding status by honing in on easily recognized behaviors. These methods are derived from techniques used by professional field biologists and the coding systems developed by Breeding Bird Atlas coordinators.

Song

Birds make a variety of sounds -- some vocal, some mechanical -- that serve many purposes. The sound that is most important to the BFL protocol is "song" -- the noise used mainly by males to attract females and defend territories. Broadcasting a song within a bird's territory elicits a strong response, because the territory holder is coming to drive off the intruder.

However, birds "sing" in different ways, some of which are not typically thought of as songs. For example, a woodpecker's "song" consists of drumming, a mechanical sound made by rhythmically hammering the bill against a hollow tree or other object. Hawks use screeches and calls to defend their territories. It's important to learn which sounds represent a given species' territorial "song". Again, what defines a "song" is the function of the sound, not how it is made. (See Species Guidelines for more species-specific information about songs, calls, and drums).

Audio Recordings

Professional field biologists frequently broadcast audio recordings of "songs" to elicit a response from local birds. Broadcasting conspecific sounds (vocalizations by a bird's own species) often causes territorial males, and sometimes females, to respond by countersinging (singing back to the broadcast) or flying toward the source of the sound. The theory is that most males of your target species will respond if you are in or near their territory, making their presence known. Once a bird has been drawn into view, there are several behavioral cues that indicate its breeding status. The codes or terms for these behaviors stem from the need of Breeding Bird "Atlassers" to quickly and accurately determine a bird's breeding status with some measure of certainty.

Breeding Behaviors

Breeding Bird Atlas terms have been developed for breeding behaviors exhibited by a wide range of bird species. For example, the term "Carrying Food" , which is used when an adult bird has been seen carrying food presumably toward a nest, can apply to many taxonomic groups, including hawks, flycatchers, and warblers.

Terms are often standardized for all Breeding Bird Atlases, and each falls into one of three diagnostic categories: Possible, Probable, or Confirmed. For example, "Song Heard" or "Adult Seen" is classified as possible breeding, seeing a "Courtship/Display" is classified as probable breeding, and finding an "Occupied Nest" is classified as confirmed breeding. BFL uses about 20 breeding terms to identify the breeding status of species at each study site.

Mobbing

Even with this Breeding Bird Atlas system, if you can't hear or see your study species, there is no way to determine its presence or breeding status. Using our knowledge of bird behavior, particularly when it comes to predators, we can sometimes elicit the response needed to see the bird and determine its breeding status. Whereas territorial or breeding males will often respond to audio broadcasts of conspecific songs, calls, and drums, females and non-territorial males are much less responsive. An effective way to provoke a response from the later groups is to simulate a predator mobbing event.

Mobbing is an defensive behavior that occurs when birds locate an avian predator in their midst. For example, a mixed species flock of forest birds might mob a roosting Great Horned Owl. Mobbing consists of loud vocalizations and sometimes diving flight directed toward the predator. As mobbing calls are given, more and more individuals are attracted to the predator's location and the mobbing flock grows in number.

Regardless of why birds mob, the behavior gives us an added opportunity to observe individuals and assess their breeding status. The BFL survey protocol uses a 10-minute Behavior Watch Period that incorporates an audio broadcast of chickadee mobbing calls with a calling Eastern Screech-Owl for the eastern version and a Northern Pygmy-Owl for the western version. Broadcasting mobbing calls greatly increases the probability of detecting breeding birds at or near your study site.

Next: General Protocol