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degree
of longitude). Texas spans 12 degrees of latitude and 14 degrees of longitude and contains
over 5,000 quadrangles. Data were gathered from at least one out of every four
quadrangles. In order to produce a map with discrete data points, the mapping unit was a
block of 4 quadrangles (or a square 15-minutes on a side). Each data point on a TBBA range
map represents at least one, but more likely several, record(s) for that 4-quadrangle
block. A
bird was recorded as a Possible, Probable or Confirmed breeder depending on the evidence
observed. Possible evidence included "species observed in suitable habitat during the
breeding season" and "singing male present in suitable habitat during the
breeding season". Probable evidence of breeding included "multiple singing males
in one quadrangle on one visit", "pair observed", "territory
maintained", "courtship behavior or copulation", "visiting probable
nest site", and "agitated behavior or anxiety calls from adult birds". The
most certain category of evidence, Confirmed, required that the observer see "nest
building", "distraction displays", "an occupied nest or a recently
used nest identifiable to species", "adults carrying food or fecal sacs",
"nests with eggs or nests with young" ,"recently fledged young" or to
note "physiological evidence of breeding on a bird in hand". Approximately
92,000 records were collected and entered into the database. By 1995, preliminary maps had
been generated from these records. These maps were made available to researchers
investigating Texas birds and to individuals wishing to serve as authors of the species
accounts. Authors were found for more than half of the species and artwork was donated to
illustrate almost all of the species. But the rapid explosion of information technology
and the World Wide Web made traditional publication of the maps and species accounts less
and less satisfactory. Thus the decision was made to produce a website for the Texas
Breeding Bird Atlas as a means to disseminate the range maps and accompanying texts. All
of the species found to show evidence of breeding have been mapped and the maps are
available here. Just click on Range Maps. Written accounts (and artwork) will be placed on
the website on an account by account basis as soon as the permissions have been secured. |