THE HONEYMOON PHASE: BREEDING DUCK HABITAT SELECTION AND ITS ASSOCIATED EFFECTS ON NEST SURVIVAL IN THE PRAIRIE POTHOLE REGION OF CENTRAL SASKATCHEWAN, CANADA

Abstract

The order of waterfowl includes some of the most extensively studied organisms in the world due to their global importance and the ecosystem services they provide (Koons et al. 2014, Bagstad et al. 2019, Green and Elmberg 2014). Most species are in the family Anatidae, which includes ducks, geese, and swans (Baldassarre 2014). Anatidae have evolved a range of life history strategies that span the slow-fast continuum. The slow-fast continuum theory states that organisms with fast-paced life histories tend to have relatively low survival but high fecundity, and organisms with slow-paced life histories tend to have relatively high survival yet low fecundity (Koons et al. 2014, Stearns 2000, Ricklefs and Wikelski 2002). These act as trade-offs where, species that are long-lived, like swans, delay reproduction and invest in offspring slowly throughout their life and short-lived species, like teal, reproduce early in life to optimize fitness (Koons et al. 2014). Slow-paced species tend to have population growth rates that are more sensitive to changes in adult survival, whereas fast-paced species are generally more sensitive to changes in recruitment (Koons et al. 2014, Robinson et al. 2010, Linden and Møller 1989). Hoekman et al. (2002) conducted a sensitivity analysis on the life cycle of midcontinent mallards, a focal species of waterfowl, and found that nest success, duckling survival, and adult female survival were the most important drivers of variation in population growth. Together these metrics accounted for 76% of the variation in mallard population growth rates where as, winter survival, including harvest mortality, only explained 9% (Hoekman et al. 2002). These findings imply that vital rates during the breeding season play a critical role in duck population dynamics, and therefore, research and conditions on the breeding grounds are important for understanding the drivers of duck populations (Nichols et al. 1995, Hoekman et al. 2002, Greenwood et al. 1995, Klett et al. 1988, Beauchamp et al. 1996). The Prairie Pothole Region (PPR) is one of the most unique wetland-grassland ecosystems in the world because of its characteristic depressional wetlands, termed “potholes”. (Doherty et al. 2018, Thogmartin et al. 2023, Krapu and Duebert 1989). The PPR is located in the interior of North America, straddling the Canada/US border with about 80% of the region in Canada (Greenwood et al. 1995). Climate of the PPR is variable as it fluctuates between wet-dry cycles, undergoing extended periods with high precipitation followed by years of drought (McLean et al. 2022, Millett et al. 2009, Doherty et al. 2018). Precipitation and these wet-dry cycles ultimately determine the amount of water that enters, stays, and leaves wetland basins, influencing many of the important ecosystem services that prairie wetlands provide (Millett et al. 2009, Doherty et al. 2018). The PPR provides habitat to a diverse number of species including mammals (Clark 2000), amphibians (Lehtinen et al. 1999), and migratory birds (Steen et al. 2018) with over 50% of the continental breeding duck population migrating there annually (Adde et al. 2021, McLean et al. 2022, Thogmartin et al. 2023). Although, the PPR historically consisted of vast grasslands interspersed with depressional wetlands it is now a landscape characterized by high habitat fragmentation (McLean et al. 2022, Rashford et al. 2016). Agriculture has greatly altered the landscape through large-scale farming practices, and up to 90% of native grassland has been converted to crop (wheat, barley, corn, and canola) and other cover types (alfalfa, sweet clover, and brome grass; Mclean et al. 2022, Doherty et al. 2018, Stephens et al. 2005, Knutsen and Euliss 2001, Greenwood et al. 1995, Higgins 1977). The conversion of native grasslands to agricultural production has been associated with declines in wetland-dependent species, specifically ducks (Anas, Spatula, Mareca, and Aythya spp.; Knutsen and Euliss 2001, Beauchamp et al. 1996). After the second industrial revolution of the 1950’s duck populations suffered substantial declines due to a period of drought and habitat loss (Greenwood et al. 1995, Doherty et al. 2018, Higgins 1977). These declines were the primary motivator for developing the North American Waterfowl Management Plan (NAWMP) (Williams et al. 1999). The NAWMP was established in 1986 with the intention of restoring waterfowl populations to levels recorded in 1970 (Williams et al. 1999, Banks and Springer 1994). Efforts focused on increasing population growth rates by improving vital rates through implemented management of habitat and predator communities in breeding areas (Hoekman et al. 2002, Williams et al. 1999, Prairie Pothole Joint Venture 2017). Since the initiation of NAWMP, duck populations have increased and have remained around the long-term average. The 21st century presents new challenges to duck populations, especially related to climate change (Mclean et al. 2022, Millet et al. 2009, Thogmartin et al. 2023). Predictive models suggest under climate change scenarios there will be fewer ducks (Rashford et al. 2016). Koons et al. (2016) published an overview of our current understandings of waterfowl population dynamics and discussed how other than direct effects of exposure, climate change can indirectly effect duck populations through top-down predation, bottom-up food resources and density dependant interactions. I used 2 years (2023-2024) of nest monitoring data from the Central Saskatchewan, Canada (Figure 1-1) and hierarchical modeling to examine the influence of duck habitat selection (Chapter II) and its associated effect on the nest survival of upland nesting ducks (Chapter III). I also evaluated the use new technology to conduct breeding pair count surveys and demonstrated its application in local studies (Chapter II). These studies allow us to 1) demonstrate the potential to improve breeding pair surveys and 2) explore how habitat characteristics influence nest survival, particularly in relation to predator dynamics. Although seemingly separate, both studies allowed me to improve how we manage our duck populations in the future. The following chapters were prepared separately for submission to peer reviewed journals, therefore, information among chapters may be redundant and formatting of each chapter may differ based on journal requirements. I was responsible for data curation, analysis, and manuscript preparation for all chapters, with valuable input and feedback from coauthors that are listed on the first page of each chapter. Due to the collaborative effort of the following works, the pronoun “we” is used throughout.