Northern Prairie Wildlife Research Center
A clear record of the number and spatial distribution of breeding pairs is the chief foundation for reproductive monitoring.
Methodology for censuses of breeding pairs is detailed in the Great Lakes/Northern Great Plains Recovery Plan (FWS 1988), and is covered here mainly as it relates to the assessment of reproductive success.
Most piping plovers arrive at breeding sites on alkali lakes by late April or early May (Appendix A). At this time, a brief visit to selected breeding sites to note habitat availability and initial locations of plover pairs is helpful.
Wherever reproductive success is to be assessed, two formal censuses of breeding pairs are recommended. The first should be conducted during mid-May, by which time first nests likely have been initiated. It is possible for breeding pairs to attempt nesting, fail early, and abandon territories by the end of May. The second census should be conducted during early June, coinciding with early to mid-incubation for most breeding pairs; this also is the "official" census period for northern Great Plains plovers (Haig and Plissner 1993).
Some plover pairs may arrive at a breeding site after the mid-May and early June counts. These late arrivals can be detected wherever regular (at least weekly) visits are made to monitor reproductive success.
A third census, in late June, may be needed in areas of high nesting density to pinpoint late-arriving adults.
A breeding-site map is an excellent medium for recording locations of adult plovers during a census (example, Appendix B). Clear notation of breeding pairs and associated nests, as well as locations of what appear to be single, territorial adults and non-territorial plovers (e.g., at feeding sites) forms an unambiguous record for which there is no substitute. Ancillary notes can be recorded (e.g., on data forms), but assignment of numbers, letters, or other descriptions to identify individual pairs invariably result in errors and lost data if not accompanied by a reference map. Field maps also supply plover distribution records that will be critical to future management decisions.
Field map records should also indicate observer name, date and time, weather conditions, the approximate water level relative to the high water line, direct and indirect (i.e., tracks) observations of potential predators, and locations of other territorial shorebird species such as American avocets (Recurvirostra americana).
Investigators can use behavioral cues to help identify breeding pairs and define territorial boundaries. Persons responsible for censuses of breeding plovers should be familiar with basic species behavior and breeding biology as described by Cairns (1982) and Haig (1992) and should be able to recognize potential breeding habitat on alkali lakes (Prindiville Gaines and Ryan 1988).
Aerial courtship flights by males over territories and threat displays and "parallel runs" at territorial boundaries (Cairns 1982) are of particular importance. These behaviors are best viewed when plovers are relatively undisturbed; investigators should remain low, quiet, and still or observe from a remote point.
Vocalizations (e.g., alarm call, courtship flight call, Haig 1992) are helpful when assessing breeding status and delineating territories. On rare occasions, adults may defend feeding territories, such as at spring inlets on alkali lakes, but such defense is relatively weak and shortlived (R. Murphy and K. Smith, pers obs.).
Whatever the specific census strategy, breeding plovers seem tolerant of investigators who move slowly and quietly and stay away from their territories.