Piping Plovers and Least Terns of
the Great Plains and Nearby
A draft protocol for assessing piping plover reproductive success
on Great Plains alkali lakes
Methodology -- Section E
Determining nest success in the field
Nest success is a frequently used measure of avian reproductive performance (Johnson 1979). However, it is not always easy to determine whether eggs have hatched in piping plover nests.
Once a nest is marked and its contents noted, it should not be necessary on subsequent visits to approach closely unless adults are either absent or present but not tending their nest. An exception to this is that nests might be checked 2-3 days before anticipated hatching dates or quickly count eggs and look for signs of pipping, if clutch reduction is a huge concern or if a hatching date must be pinpointed.
Otherwise, nest status usually can be checked remotely by confirming the presence of an incubating adult. If adults are present but not tending a nest near hatching, investigators should observe remotely for ≥20 min. Chicks obviously indicate a successful nest, as long as assignment to a breeding territory is unambiguous.
Sometimes it is nearly impossible to check nesting status without getting close enough to cause an adult to leave its nest. Disturbance also is inevitable when looking for nests or checking nest fate in adjoining breeding territories.
Although investigator-caused disturbance does not appear to influence survival of nests or adults on parts of the Atlantic Coast (MacIvor et al. 1990), its effects are unstudied in the Great Plains and should be minimized.
Evidence of nest failure is mainly based on eggshell remains, predator sign, and especially the timing of loss in relation to hatching date. Any full clutch of eggs incubated <23 days should be considered failed (Mabee 1997).
Nests should be approached cautiously when failure is suspected, in case small chicks actually are present or a new nest has already been initiated. An area within at least 10 m of the nest should be inspected for signs of predators and remains of eggs, chicks, or adults. Nest bowl contents should be scrutinized by using a probe such as a pencil tip to tease through pebbles that form the lining.
Several clean eggshell fragments (≤1-2 mm) remain from pipped eggs at nests visited after hatching (Smith et al. 1993, Mabee 1997). Eggshell caps may be found nearby, which also suggest hatched eggs when they are symmetrical, with equidistant length from the center to the broken edge of the shell, and have a membrane not tightly adhering to the eggshell (Mabee 1997).
At destroyed nests, eggshell fragments tend to be larger (>4 mm), without intact caps; membranes adhere tightly to eggshell fragments and may be heavily stained with yolk or bloody residue. Due mainly to wind or hard rain, all forms of plover eggshell evidence tend to be shortlived (<<1 wk).
Predator sign is difficult to detect on alkali lakes because by early summer the substrate usually is dry, hard, and does not hold tracks well.
Evidence of nest predation may include digging at the scrape, nearby feces, or punctures in remaining eggs. Tracks found in damper substrates nearby may be of species not necessarily responsible for nest loss.
Information on predator communities may be more helpful in explaining temporal or spatial trends in plover reproductive success. For this, simple observational surveys of potential predators (Sargeant et al. 1993) can be conducted in conjunction with regular site visits.
Investigators should be cautious when classifying nest fate as "abandoned," which seems rare on Great Plains alkali lakes in central and northwestern North Dakota (B. Root, unpubl data; R. Murphy and K. Smith, unpubl data), vs. about 10% of nests on the Atlantic Coast (Vaske et al. 1994).
If a nest appears abandoned, an egg within the nest should be repositioned in a unique way and rechecked perhaps 1 day later for evidence of movement by an incubating adult (note: FWS Section 10 permits allow handling of untended eggs). Plovers have been known to incubate viable eggs for as long as 38 days (Cairns 1982). Investigators should also closely inspect the abandoned area for signs of predation on adults. Plovers at nests protected by predator exclosures may be particularly vulnerable (R. Murphy and K. Smith, unpubl data).
Once it is clear that a clutch is no longer being tended by adult plovers, eggs should be checked for presence of embryos. Abandoned clutches consist of ≥1 egg with a dead embryo. Clutches composed entirely of infertile eggs should be classified as "sterile" rather than abandoned.
In summary, nest fate can be listed in the field as one of the following:
- (1) successful
- (a) ≥1 chick is observed and clearly ascribed to the nest, or
- (b) there is eggshell evidence of ≥1 hatched egg, or
- (c) eggs are missing after the anticipated hatch date adults associated with the nest exhibit persistent, intense distractive displays
- (b) there is eggshell evidence of ≥1 hatched egg, or
- (2) unsuccessful
- (a) all eggs are missing >5 days before the anticipated hatch date,
or
- (b) no chicks are observed and eggshell and/or predator sign indicates a depredated nest, or
- (c) the clutch is abandoned (eggs fertile based on presence of dead embryos), or
- (d) all eggs are sterile
- (b) no chicks are observed and eggshell and/or predator sign indicates a depredated nest, or
- (3) unknown -- if it cannot otherwise be classified.
Previous Section -- Section D - Nesting chronology: initiation, hatching, and fledging dates
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Next Section -- Section F - Monitoring chick survival and fledging
