Northern Prairie Wildlife Research Center
Artificial nest - Depression scraped in soil and usually lined with nest material (to simulate the appearance of a natural nest) by an investigator in which eggs (always 6 in the present study) were placed by the investigator.
Cached egg - Egg deliberately hidden in vegetation, buried, or otherwise partially or completely covered with soil and/or debris by a predator.
Chip of shell - Single detached piece of shell <1 cm diameter.
Depredated egg - Egg completely or partially eaten, cached, or removed from a nest by a predator.
Depredated nest - Nest with ≥1 egg known depredated.
Destroyed nest - Nest with all eggs depredated, or nest abandoned by attendant hen after ≥1 egg was depredated.
Displaced nest material - Nest material pulled or otherwise removed from a nest by a predator and located >5 cm outside the original nest edge established by the attendant hen or the investigator. Nest material >5 cm outside the original nest edge but connected to the nest is displaced. Nest material rearranged or matted in the nest is not displaced.
Eggshell - Single piece of shell or pieces of shell connected by membrane that represent >50% of the total shell of an egg.
Eggshell that is crushed - Eggshell of egg crushed within the mouth of a predator resulting in a cylindrical or spherical mass of connected shell pieces, but with <25% of the original shape of the egg intact.
Eggshell that has large hole - Eggshell with ≥1 opening and >50% but ≤75% of the original shape of the egg intact.
Eggshell that has small hole - Eggshell with ≥1 opening and >75% of the original shape of the egg intact.
Eggshell that is fractured - Eggshell with ≥1 opening and 25-50% of the original shape of the egg intact.
Eggshell that is severely damaged - Eggshell with ≤50% of the original shape of the egg. Includes crushed, fractured, and trampled eggshells.
Eggshell that is trampled - Eggshell of egg that was trampled or otherwise smashed and looks flattened, and has <25% of the original shape of the egg intact.
Eggshell with opening in an end - Eggshell with >50% of original shape of the egg intact in which all openings in the egg were in 1 or both ends of the egg.
Eggshell with opening in the side - Eggshell with >50% of original shape of the egg intact in which all openings in the egg were in the side of the egg.
Eggshell with opening in a side-end - Eggshell with >50% of original shape of the egg intact in which the opening extended from the side into an end or there was an opening in the side and another in an end.
Exposure-day - One nest at risk of depredation during all or part of a 24-h period.
Fragment of shell - Single detached piece of shell or connected pieces of shell that represent ≤50% of the shell of an intact egg. Shell chips are small shell fragments.
Loose egg(s) - Individual egg or small number of eggs placed on the ground surface to attract predators but with no attempt to simulate a clutch in a nest. All loose eggs offered to predators in this investigation were duck eggs.
Membrane of egg - Thin pliable lining separating the embryonic content of an egg from the outer calciferous shell.
Missing egg - Egg that is no longer present or represented by an eggshell at the nest, but may be represented by shell fragments at the nest.
Nest depredation record - The record of information describing evidence of depredation found at a nest destroyed by predators.
Nest material - Vegetation, down, and other small feathers used by a hen to construct its nest.
Nest record - The record of information describing the species, location, history, and fate of a nest.
Nest site - The 3-m radius zone around and including an artificial or natural duck nest (synonymous with "at nest").
Nest success - The probability that ≥1 egg of a clutch hatches (Cowardin and Johnson 1979).
Offending predator - Individual predator that depredated or destroyed a nest.
Principal predator - One of 9 species and 2 groups of congeneric species with potential to destroy significant numbers of duck nests in the Prairie Pothole Region.
Puncture hole - Small hole (≤1 cm diameter) punctured through the shell and membrane of an egg by a predator but which is not the main opening in the eggshell.
Puncture mark - Small visible indentation in the shell of an egg that was made by a predator when biting, pecking, or grasping the egg but which does not penetrate the membrane.
Retreat - Site used by a mammalian predator for resting.
Verification data - Data describing nest depredations for which the offending predator species was known or presumed known.