Duck Recruitment Research
Mallard Recruitment in the Sandhills of Nebraska

The Sandhills of Nebraska comprise approximately 20,000 square miles of continuous native grassland habitat and are important to a diverse group of wildlife species. This region provides critical habitat for many grassland-dependent species such as prairie chickens, ferruginous hawks, and long-billed curlew. Furthermore, the abundant groundwater-fed wetlands and expansive grasslands of the Sandhills provide migration and breeding habitat for waterfowl as well. Nebraska Game and Parks commission biologists have counted up to 250,000 ducks in the Sandhills during their May waterfowl survey. Many of those ducks are thought to nest and raise broods in the sandhills, providing an opportunity for biologists to investigate relationships between waterfowl reproduction and landscape characteristics in a relatively intact prairie ecosystem.

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Sandhills Mallard Study 2005 Field Season Summary
Johann Walker, Regional Biologist - Research

August 1st, 2005

The last active nest initiated by a radio-marked mallard hatched on 19 July. The successful female (this was her second nest) and her brood were briefly seen on a small, cattail-covered wetland two days later. Most of the other mallards that we marked were not so lucky. The 2005 breeding season was characterized by late freezes, pouring rains, and high rates of nest predation. Nonetheless, our preliminary research effort in the Sandhills ended on a pleasant note-with ducklings.

We marked 266 mallards (Fig. 1) and one gadwall during the study. The bulk of the mallards (234) were males that we banded with US Fish and Wildlife Service aluminum leg-bands and released. When these birds are recovered and reported by waterfowl hunters, we will receive valuable information about movements and survival. We captured the gadwall on her nest shortly before the eggs hatched and monitored her brood for two weeks.

The 32 female mallards that we captured and marked with radio-transmitters initiated 28 nests. The nests gave us useful information about re-nesting and nest survival on our study area. The marked mallards re-nested up to three times following failure of an earlier nest. We also observed that mallards in the sandhills nest in a wide range of habitats-from wetland margins to blown-out sand dunes covered with yucca. Nest survival probability, however, was very low (3%) in all habitats, and only three nests produced ducklings. Most of the nests that failed (17) were destroyed by unidentified predators. Overall, we think that recruitment of mallards was relatively negligible on our study area this year.

Climatic conditions, for the most part, appeared ideal for breeding ducks. Most of the temporary and seasonal wetland basins on our study area were filled by ample rains in late April and early May. Surprisingly, the mallards that we marked appeared to initiate nests about one week later than mallards in North Dakota. The median nest initiation date on our study area was 21 May. A week of frigid temperatures in mid-April froze many of the wetlands. Perhaps this unusual event delayed and interrupted the nesting effort. On the other hand, we cannot be sure that we failed to detect many nests that were initiated earlier and were destroyed early in laying. This detection problem is all the more likely when nest survival probability is low.

The mallards that we marked also abandoned their nests much more readily than we expected. Of the 25 nests that failed, 7 were abandoned by the female immediately after discovery. Nest abandonment is not uncommon when researchers encounter females early in the nesting cycle (i. e., during laying or early incubation), however, many of our radio-marked females abandoned nests with a full clutch of eggs and several days of incubation. This is unusual. For comparison, we nest trapped over 40 mallards in North Dakota at varying stages of incubation (4-24 days) during the same time period and only one of them abandoned her nest.

We also experienced considerable difficulty when we tried to observe broods. The first brood that hatched was never seen despite our best efforts and considerable investment of time. This female, and, presumably, her brood, remained on a small wetland with heavy emergent cover for nearly three weeks. Then she moved to a much larger wetland, was seen once with no ducklings, and then left the study area. We are unsure whether or when she lost her brood. The second nest that hatched was associated a female whose radio-transmitter failed near the end of incubation, and thus we had no way of tracking her during brood-rearing. Some radio failure occurs in most radio-telemetry studies, but it is much more disappointing when there are only three broods to monitor. The third mallard brood was described earlier; we successfully observed this brood once at the end of the season. In contrast, the gadwall brood was easy to find, see, and count. Research assistants successfully counted this brood three times over 14 days.

The surprises and challenges that we encountered revealed the need for caution when making generalizations about waterfowl production. Although we had ample wetland habitat and nesting cover on our study area, these ingredients proved to be insufficient during 2005. Nonetheless, we cannot know whether 2005 was an unusually poor year for duck production on our study area without returning for at least one more season. Therefore, armed with the knowledge that we gained in 2005, we will return to the Sandhills in 2006 and radio-mark mallards again. We will be prepared for low nest survival, and thus we expect to detect more nests. We will observe more mallard broods if nest survival is higher. Otherwise we plan to mark an additional sample of gadwalls to improve our description of brood survival. We expect to be far more confident in our conclusions at the end of the 2006 nesting season.

We were fortunate to be allowed to do this research on private lands in the Nebraska Sandhills. Our study area was representative of the grassland and wetland habitat as well as land-use practices in the sandhills region. We would like to extend our thanks to the private landowners who allowed us to work on their property and trusted us to button up their gates. Specific thanks are due to the Lackaff family for their hospitality and sincere interest in our research. We also wish to thank our cooperators and funding sources, and the field assistants who collected these data. The Sandhills Task Force and the Nebraska Game and Parks Commission (NGPC) provided funding and support. Thanks to the staff at the Bassett office of NGPC for their assistance with logistics. Finally, thanks to Lindsay Ware and Zach Cunningham who worked long hours in the field under challenging conditions to gather this information. Their expertise and dedication contributed substantially to the success of our effort in the Sandhills.

Thanks for your interest in our research in the sandhills. Check in with us as we prepare for the 2006 field season. We will be capturing birds again in mid-April 2006. We hope you return with us!


Figure 1. The number of females radio-marked and the number of nests, re-nests, and broods observed in the Nebraska Sandhills during April-July 2005.