Northern Prairie Wildlife Research Center
Techniques for Studying Nest Success of Ducks in Upland Habitats in the
Prairie Pothole Region
Instructions for Recording Data and Calculating Nest Success
- Nest. A scrape or bowl containing one or more eggs. The
terms "nest" and "clutch" are often used interchangeably in this and other
duck nesting study reports. Only nests tended by hens (not destroyed or abandoned)
when found are used to compute nest success by the methods described.
- Age when Found. Number of eggs plus incubation stage in
days. (Assume that one egg is laid each day.)
- Exposure Days. The number of days a clutch of eggs is under
observation and vulnerable to loss to predators or other decimating factors.
- Full Clutch. Clutch size of incubated nests that have no
history of destroyed or missing eggs.
- Mean Age at Hatching. Mean clutch size plus mean incubation
term in days.
- Terminated Nests. Nests, successful or unsuccessful, no
longer tended by a hen.
- Nest Fate. The success or failure of a nesting attempt.
- Abandoned. Intact clutches that are deserted by the hen.
True abandonment rates are difficult to estimate because some untended clutches
result from the death or injury of hens and some abandoned clutches are destroyed
before their true fate can be determined. Abandoned clutches (other than those
abandoned because of investigator disturbance on the day found) are combined
with destroyed clutches to compute survival rates.
- Destroyed. A nest in which one or more eggs are missing
or destroyed and none hatched.
- Fate Unknown. The fate of the clutch was not determined
because of inadequate evidence at the nest site or because the nest was not
- Nonviable. All eggs are infertile, addled, or contain dead
- Successful. One or more eggs hatched even if young are
found dead at nest sites.
- Nest Success. The probability that a nesting attempt will
result in the production of one or more ducklings, as opposed to hen success
- the probability that a hen will succeed in hatching at least one duckling
in one or more nesting attempts.
- Mayfield Method for Computing Nest Success. A method that
uses the interval during which a nest is under observation and exposed to
decimating factors (see Exposure Days).
- Shortcut Method for Computing Nest Success. A quick method
for obtaining preliminary results or for checking calculations used for the
- Traditional Method for Computing Nest Success. The number
of nests in which one or more eggs hatched divided by the total number of
nests of known fate that were found; reported as apparent nest success.
Estimates by this method are almost always extremely biased.
Sample Field Form for Recording Nesting Data
The sample Nest Record (Fig. B-1) contains
space for entering the data necessary for computating nest success rates, and
supplementary data on vegetation at the nest site and the fate of hens and eggs.
Some investigators will need other data to meet the objectives of their studies.
If so, additional data can be systematically recorded on a supplementary form
cross-referenced to the basic record described here.
A computer program is used at Northern Prairie Wildlife Research Center to
calculate exposure days for each clutch and to generate tables of clutch survival
for such variables as species, study area, and habitat. The Nest Record was
designed to facilitate direct computation of exposure days by those who want
to process small batches of data without a computer.
Columns 2-19 are used for data control, columns 27-47 are used to compute
nest success with a computer, and columns 20-26 and 48-51 are used to record
supplementary data on the nest site, hen mortality, unhatched eggs, and parasitism.
Uncoded space is provided to record observations made at each visit to the nest
(Nest Visitation Record) and for calculating exposure days when a computer is
not used. Entries are made in columns 2-27 on the day the nest is discovered.
Data in the Nest Visitation Record are used to complete columns 28-51 after
the last visit to the nest. Instructions for making entries needed to compute
nest success (columns 27-47) follow.
- Col. 27
- Nest Status on Day Found: Nests coded greater than 0 are
usually not used to compute survival rates. Nesting attempts disrupted by
investigators after the first visit may be used in nest survival computations.
0 - Normal
1 - Eggs destroyed or hen injured or killed by investigators
2 - Some eggs cracked or broken by investigators
3 - Any other major disturbance by searchers that would jeopardize nest
4 - Nest abandoned because of investigator disturbance on day found; determined
on second visit
5 - Partially destroyed when found
6 - Terminated when found
7 - Parasite eggs present when found
- Cols. 28-29
- Number of Eggs When Found: Record number of whole eggs.
If nest contains parasite eggs, record only the number of eggs of host species.
- Cols. 30-31
- Incubation Stage When Found:
nn - Number of days incubated (00 = laying stage)
44 - Pipping
55 - Hatched (young in nest)
77 - Nesting attempt terminated when found
88 - Unknown
99 - All eggs addled or contained dead embryos
- Cols. 32-33
- Full Clutch: If nest was not observed during incubation
or has a history of parasitism or destroyed or missing eggs, code . (dot)
in Col. 33. Do not assume Full Clutch from broken eggs or membranes in terminated
- Col. 34
1 - Successful
2 - Abandoned - if abandonment was caused by observer on the day the nest
was found, code 4 in Col. 27
3 - Destroyed
4 - Nonviable eggs
5 - Unknown
- Col. 35
- Cause of Loss: Data in this column are not used to estimate
nest success therefore codes are not presented.
- Cols. 36-38
- Date Found:
- Cols. 39-41
- Date of Last Visit on Which Nest Was Still Viable: Same
as Date Found when nest was terminated between the first and second visit,
date of second visit when the nest was terminated between second and third
visit, etc. May be left blank if nesting attempt was successful.
- Cols. 42-44
- Date Fate Determined: Usually the last visit to the nest.
Code . (dot) in Col. 44 if fate not determined, e.g, if nest could not be
- Cols. 45-47
- Date of Termination Known: For some nests the exact day
of termination is known. For example, hatched young were observed in the nest;
the nest was destroyed or abandoned because of investigator activity; the
date the nest was abandoned was determined from the increase in number of
eggs, advance in stage of incubation, or both of these; the date of a destructive
event such as a storm or tillage operation is known. Do not confuse with estimated
hatch date. Leave blank if unknown.
Computation of Nest Success
Data in columns 27-47 are sufficient for calculating nest success rates by
computer. If a computer is not used, complete the following in the uncoded section
of the Nest Record and calculate nest success as described on page 24.
- Age When Found: Number of Eggs When Found plus
Incubation Stage When Found. If nest is found when eggs are pipping
(Cols. 30-31 = 44), use average incubation term minus 1 for incubation stage.
A nest record is not used to calculate nest success if the age at discovery
- Estimated Initiation Date: Date Found minus
Age When Found.
- Estimated Hatch Date: Initiation Date plus Full Clutch
plus Average Incubation Term (Table B-1). Use mean clutch
size (Table B-1) if Full Clutch is not known. (Exception: If eggs are observed
while pipping, the estimated hatch date is the following day.)
- Exposure Days: Exclude abnormal nests (Col. 27 > 0)
and those with Age When Found unknown; then determine exposure days as follows:
- TERMINATION DATE KNOWN (Table B-2, nest 1): Exposure = Known Termination
Date minus Date Found
- TERMINATION DATE UNKNOWN:
* Nesting attempt successful (Table B-2, nest 2): Exposure = Estimated
Hatch Date minus Date Found.
* Fate of nest is unknown (Table B-2, nest 3): Exposure = Last Visit Date
When Clutch Was Viable minus Date Found .
* Nesting attempt unsuccessful (Table B-2, nests 4-7): Exposure = Known
Exposure plus Probable Exposure where Known Exposure
= Last Date Nest Viable minus Date Found and Probable
Exposure = half the interval between Last Date Nest Viable and
the lesser of Date Fate Determined and Estimated Hatch Date
(Multiply by 0.4 instead of 0.5 if this interval is > 14 days; table B-2,
- Nest Success: Two methods for calculating nest success
- the Mayfield method and a shortcut method - are described. Examples of calculations
by both methods are presented in Table B-3.
- MAYFIELD EXPOSURE METHOD.
Usable records. Nest survival rates are calculated from nests for
which exposure days are available.
Number of nesting attempts that failed (Nu). Tally number
of nesting attempts that failed (Col. 34 = 2, 3, or 4). Exception: Do not
include losses due to investigator disturbance that occurred after the first
visit, but do include exposure daya.
Total exposure days (E). Sum of exposure days for all usable records.
Mean age at hatching (h). From Table B-1.
Estimated nest success (P2). Calculate as in Table B-3.
- SHORTCUT METHOD.
Usable records. Exclude abnormal nests (Col. 27 > O) and those
with unknown fate and unknown age when found.
Apparent nest success (P1). Number of successful nests
divided by all usable nests.
Mean age at hatching (h). From Table B-1.
Mean age of nests when found (f). Calculate mean age of nests when
found from usable nest records.
Estimated nest success rate (P3). Calculate as in Table
Previous Section -- Appendix A
Return to Contents