Habitat selection by postbreeding female diving ducks: influence of habitat attributes and conspecifics

Abstract

Habitat selection studies of postbreeding waterfowl have rarely focused on within-wetland attributes such as water depth, escape cover, and food availability. Flightless waterfowl must balance habitat selection between avoiding predation risks and feeding. Reproductively successful female ducks face the greatest challenges because they begin the definitive prebasic molt at or near the end of brood rearing, when their body condition is at a low point. We assessed the relative importance of habitat attributes and group effects in habitat selection by postbreeding female lesser scaup Aythya affinis on a 2332-ha montane wetland complex during the peak flightless period (August) over seven years. Hypothesis-based habitat attributes included percent open water, open water:emergent edge density, water depth, percent flooded bare substrate, fetch (distance wind can travel unobstructed), group size, and several interactions representing functional responses to interannual variation in water levels. Surveys of uniquely marked females were conducted within randomly ordered survey blocks. We fitted two-part generalized linear mixed-effects models to counts of marked females within survey blocks, which allowed us to relate habitat attributes to relative probability of occurrence and, given the presence of a marked female, abundance of marked individuals. Postbreeding female scaup selected areas with water depths  40 cm, large open areas, and intermediate edge densities but showed no relation to flooded bare substrate, suggesting their habitat preferences were more influenced by avoiding predation risks and disturbances than in meeting foraging needs. Grouping behavior by postbreeding scaup suggests habitat selection is influenced in part by behavioral components and/or social information, conferring energetic and survival benefits (predation and disturbance risks) but potentially also contributing to competition for food resources. This study demonstrates the importance of incorporating group effects and interannual variability in habitat conditions when investigating habitat selection, particularly for seasons when waterfowl are aggregated.

Habitat Associations of Migratory Waterbirds Using Restored Shallow Lakes in Iowa

“…Additionally, some degree of open water improves visibility of potential predators, while emergent vegetation provides protection against other disturbances, such as weather and human disturbance. (Kaminski and Prince 1981;Austin et al 2017).…”

Measuring habitat quality for waterbirds: A review

“… Predation can be the leading cause of waterbird nest failure (Riecke et al, 2019 ) Predation risk is evaluated by waterbirds and trade‐offs made that may reduce other components of fitness (e.g., foraging rate) (Austin et al, 2017 ; Fernández & Lank, 2010 ; Maslo et al, 2012 ; Zharikov et al, 2009 ) Nest predation rate increases with the abundance of avian nest predators (Manton & Angelstam, 2021 ), and conversely, predator control (mammal and avian) increased the percentage of pairs that successfully raised young (Fletcher et al, 2010 ) …”

Prefledging Growth and Recruitment of Female Lesser Scaup

“…We subtracted these depth measurements from August lake-level values in each year of the study to estimate elevation and interpolated between stations with inverse distance weighting to produce a continuous surface of lake bottom elevation (O'Neil et al 2014). To calculate the area of the lake with depths suitable for duckling foraging, we considered 2 minimum depth thresholds, 0.35 m and 0.5 m, based on previous research at the lake (Austin et al 2017) and elsewhere (Fast et al 2004). Because lake depth does not exceed 1.5 m in an average year and submerged vegetation may further reduce effective water depth, we assumed ducklings could potentially forage in any part of the lake exceeding the minimum depth thresholds.…”