Northern Prairie Wildlife Research Center
Nesting chronology varies by species, locality, and year. Data from previous studies in your local area may provide useful guidelines for scheduling searches. For example, data in Table 1 portray the relative efficiency of varied search numbers and schedules for finding nests with a cable-chain drag on a 250-ha study area in south-central North Dakota in 1976. A total of 523 duck nests of five upland nesting species were found during 12 searches conducted at weekly intervals. Each entry shows the percentage of all nests found - for three species or all species combined - with a specific search schedule.
Results of this study indicated that if only a single search could be made, late May would be the optimal time for locating nests of mallard, blue-winged teal, and all species combined. A single search in mid-June would be optimal for locating gadwall nests. Wetland conditions in June 1976 were poor and relatively few nests were found during the early July search.
The number of additional nests found per search decreases with each new search. For some studies this would indicate that it would be more efficient to conduct one or two searches in each of a larger number of similar habitats than to search fewer units many times. An advantage of multiple searches is that larger samples of nests of all species can be found in habitat units of special interest. Searches conducted at regular intervals throughout the nesting season also increase the probability of including variation in mortality related to seasonal effects. Again, we emphasize that the search schedule is part of the study design and depends on the study objectives.
If nest success rates are to be compared we recommend that the same search schedule be used for each habitat unit. (Sample size considerations are presented on page 12.)
A recommended search schedule for monitoring nest success in south-central North Dakota is three searches at 3-week intervals starting the first week in May (Table 1, searches 3-6-9). In 1976 the sample of nests found with this schedule included 61% of the total nests found with 12 searches. When prolonged nesting activity occurs during years of favorable wetland conditions, an additional search in late June or early July is recommended.
The amount of nesting cover that can be searched in a day should also be considered. The area that can be searched by a drag crew depends on the cover type, terrain, and number of nests found. Usually a 65-ha tract of herbaceous nesting cover can be searched with a cable-chain in about 4 or 5 h. When practical, searches should be completed by noon because laying hens are more likely found on the nest in the morning hours.