DOI: 10.5061/dryad.rjdfn2zn7
title: Agricultural mosaics offer nesting habitat to dabbling ducks in the arid Intermountain West of the United States

description: The debate over the best agricultural practices for biological
 conservation often focuses on the degree to which agricultural lands
 should be interspersed with desirable habitats versus protecting lands
 entirely from production. It is important to understand the benefits
 agriculture provides for wildlife because it is consuming an increasing
 proportion of the landscape. We evaluated the nesting ecology of breeding
 ducks within a mosaic of flood-irrigated conservation areas and
 agricultural lands in hay production. We assessed how habitat features at
 two spatial scales across these lands were related to nest site selection,
 nest density, and nest survival of multiple duck species. Birds selected
 nest sites with higher visual obstruction, a higher proportion of shrubs
 around the nest, and less bare ground, but we did not detect evidence of
 selection per se at larger spatial scales. Nest density was marginally
 higher along linear features, including irrigation ditches and riparian
 stretches, but nest survival remained similar across land-use types and
 habitat features. This system is representative of many agricultural
 landscapes around the globe and highlights the ways agroecosystems can be
 managed to maintain habitat suitability for wildlife on working lands.
description: <em>Study System</em> We studied a
 system of flood-irrigated basins in north-central Colorado, USA, to
 evaluate duck reproductive success across agricultural working lands
 (Figure 1). The North Platte Basin (hereafter North Park) is a
 high-elevation (2500 m on average) intermountain basin characterized by
 sagebrush (<em>Artemesia </em>spp.) steppe and riparian
 corridors used as sources of water to flood irrigate hay meadows (by
 diverting water into irrigation ditches). The Intermountain West of North
 America spans 11 states and is comprised of many of these high-elevation
 basins associated with river and groundwater-fed wetlands. While many are
 still associated with flood irrigation, some have predominantly
 transitioned to sprinkler-based irrigation systems to use water more
 efficiently (e.g., the San Luis Valley of Colorado). Agricultural
 production is typically comprised of large cattle ranches that also
 actively produce high-quality, flood-irrigated hay that is harvested each
 year. In North Park, harvested meadows consist primarily of Timothy hay
 (<em>Phleum pretense</em>), and are flooded in May, dried
 anywhere from July to August, and then harvested from July to September.
 Because of the short growing season, a single cut of hay each year is
 typical. The system also has public land parcels along riparian areas that
 are spared the annual harvest of typical agricultural operations,
 primarily Arapaho National Wildlife Refuge (NWR). This NWR was created in
 1967 to benefit migratory and breeding ducks as mitigation for the
 conversion of high-quality duck breeding habitat in the Prairie Pothole
 Region of North America to high-intensity agriculture production in the
 1960s and 1970s (Doherty et al. 2018). The NWR flood-irrigates wet meadows
 that are not cut, and that typically exhibit more diverse vegetation
 communities than Timothy hay meadows, including forbs, sedges, rushes, and
 grasses interspersed by small areas of greasewood shrubs
 (<em>Sarcobatus vermiculatus</em>) and sagebrush. In addition
 to the NWR, there are also state wildlife areas (SWAs) on which managers
 flood irrigate to create wetland habitat, as well as waterfowl management
 areas (WMAs) managed by the Bureau of Land Management (BLM) specifically
 for breeding ducks. Wetland habitats on the parcels of public land
 included in the study are comprised of large water storage reservoirs with
 variable amounts of submerged aquatic vegetation, basin wetlands with
 rings of emergent vegetation, and irrigated meadows consisting of
 graminoids and occasionally robust emergent vegetation (e.g., cattails
 [<em>Typha </em>spp.] and bulrush
 [<em>Scirpus</em> spp.]). <em>Data
 Collection</em><em> and Processing</em>
 We searched systematically for duck nests from 20 April until 1
 August 2018-2023. Study sites included five private ranches on which
 agricultural production was predominantly focused on cattle and hay.
 Additionally, we included Arapaho NWR, Lake John SWA, and Hebron WMA,
 which are multi-use parcels of public land spared from extractive
 agricultural production but subject to light cattle grazing. We searched
 randomly selected nest plots across land-use types in addition to
 searching opportunistically between plots. After overlaying a grid with
 8-ha grid cells on the wet meadows of Arapaho NWR using a geographic
 information system (GIS; Esri ArcGIS Pro 2.8.0), we randomly selected 16
 square plots to sample portions of the large expanses of the irrigated
 meadow. However, plots on private lands followed the natural boundaries of
 hay meadows, which were often smaller and more easily definable (Figure
 2). As a result, plots on private land varied in size and number, but we
 still delineated them based on landscape features in a GIS and randomly
 selected a subset to search each year. Access to ranches also varied
 across years, which altered the number of plots we could search. The
 number of plots we searched on private ranches varied from five during a
 pilot year to 131, and plots ranged in size from 0.14-35.83 ha, averaging
 6.44 ha. Additionally, we randomly selected 500-m length sections of
 riparian areas (n=40) and irrigation ditches (n=25) across the study area,
 searching within a 200-m buffer of the edges, and systematically searched
 the perimeter of all basin wetlands out to a radius of 200 m. We display
 an example ranch in Figure 2, which shows the layout of selected plots of
 several wetland habitats. We report the total area (ha) of each habitat
 type in the study area in Table 1 alongside the area of each habitat in
 our sampling frame, including land associated with accessible ranches and
 focal parcels of public land. Finally, we report the area within that
 sampling frame that we searched annually to illustrate which habitats were
 represented in our search plots relative to the area available. We
 searched plots 1-5 times per year and used a combination of rope drags (on
 foot; Higgins et al. 1969) and systematic foot searches to flush laying
 and incubating hens off of the nests, marking the location with a global
 positioning system (GPS) device. We recorded search effort each year (date
 searched and the number of people searching a plot) and used a GIS
 framework to compute the area in ha of each plot, whether the plot
 contained or its centroid was within &lt; 200 m of
 a basin wetland, and the composition of rasterized habitat classes within
 each plot based on the 2021 National Land Cover Database (NLCD) layer. We
 identified the species incubating each nest as the hen flushed and used
 the size and color of the eggs to verify the identification. We candled
 several eggs in each nest to calculate the nest initiation date by
 backdating from the date the nest was located based on the embryonic stage
 of development and the number of eggs in the nest (Klett et al. 1986). As
 incubating hens typically cover their eggs with down feathers upon leaving
 the nest, we also covered eggs after each nest visit and placed two pieces
 of grass across the top of the nest in an “x” shape to determine whether
 the hen returned to the nest or abandoned after disturbance. We monitored
 each nest approximately every five to seven days, noting its incubation
 status, hen presence or absence, full clutch size, and ultimately nest
 fate. Regardless of whether a nest failed (i.e., all
 eggs were eaten by a predator or abandoned by the hen) or was successful
 (i.e., at least one egg hatched), we conducted vegetation surveys on the
 estimated or actual hatch date (McConnell et al. 2017). We calculated the
 hatch date based on the stage of embryonic development of the eggs during
 each nest visit and the average incubation time for each species. For
 successful nests, we conducted surveys the day after ducklings left the
 nest. Vegetation surveys occurred at the nest bowl and at four randomly
 selected points within a 200-m radius of the nest bowl to evaluate
 fine-scale (i.e., third-order; Johnson 1980, Eichholz and Elmberg 2014,
 Kaminski and Elmberg 2014) metrics of habitat selection. Surveys included
 visual estimation of percent cover within a 1-m Daubenmire frame
 (Daubenmire 1959). We estimated the percent cover of bare ground, litter
 (dead vegetation from the previous growing season), water, grasses, forbs,
 shrubs, sedges, and rushes, and we allowed the total percent cover to sum
 to more than 100% because the vegetation was often layered vertically. We
 also assigned each nest to a categorical habitat type at the time of
 measurement and measured visual obstruction by noting the lowest decimeter
 visible on a 1-m Robel pole from each cardinal direction and averaged the
 four values (Robel et al. 1970). Habitat types were classified based on
 the dominant vegetation within 200 m of the nest and included riparian,
 shrub-scrub, emergent marsh (dominated by robust vegetation like
 cattails), graminoid meadow, graminoid meadow interspersed by shrubs,
 Timothy hay meadow, and irrigation ditch, which was used when a nest was
 within 3 m of the inner channel of an irrigation ditch. We separated
 graminoid meadows from graminoid meadows interspersed with shrubs because
 shrubs may provide perches for avian predators from which duck nests may
 be more easily located (Thompson et al. 2012, Coates et al. 2021, Peterson
 et al. 2022). We measured broad-scale habitat
 characteristics using a GIS to evaluate the drivers of nest site selection
 at a larger scale. We created ~10000 random points across the study area
 (i.e., within the sampling frame indicated by the delineated boundaries in
 Figure 1) in all habitats where we consistently searched for nests. We
 calculated the distance of each random point and nest site to the nearest
 irrigation ditch, river, open water (i.e., ponds, marshes, or reservoirs),
 road, harvested hay meadow, and uncut irrigated meadow using NLCD land
 cover types. We refer to this as the “patch scale.” We also created
 circular buffers around each nest point and random point with a radius of
 200 m. This allowed us to tabulate the number of 30 x 30 m pixels within
 each 200-m radius buffer plot assigned to each NLCD land cover category,
 and from that the area in ha of each habitat. We refer to this as
 “landscape composition.”  We could not include the year as a random effect
 because the GIS layer was not year-specific, but changes in the
 patch-level GIS variables used were minimal over the study period. This
 differing random effect structure precluded the comparison of models of
 fine-scale vegetation metrics to models of patch-scale metrics, so we
 considered nest site selection at the two scales separately.
description: # Agricultural mosaics offer nesting habitat to dabbling ducks in the arid
 Intermountain West of the United States
 [https://doi.org/10.5061/dryad.rjdfn2zn7](https://doi.org/10.5061/dryad.rjdfn2zn7) ## Description of the data and file structure This dataset is part of a long-term study by Colorado Parks and Wildlife and Colorado State University focused on waterfowl productivity in flood-irrigated agricultural lands in northern Colorado. Data collection methods are described in the methods section of this file, and all files and variables are described below. Specific UTMs of nest locations have been removed and properties have been anonymized. ### Files and variables #### File: nestbuffer200nlcd\_dryad.xlsx **Description:** Located dabbling and diving duck nest sites in North Park, CO from 2018-2023 with the amount of each National Land Cover Database (NLCD) cover class in sq. meters in a 200-m radius around the nest site. ##### Variables * NESTID: unique nest identification code * All other column headings correspond to NLCD cover classes #### File: nestsurvival\_dryad.csv **Description:** Nest data for dabbling and diving duck nests located in North Park, CO from 2018-2023. Unless otherwise noted in this README file, NAs indicate missing data. ##### Variables * NestID: Unique code given to each nest * DateFound: Date the nest was located * FirstFound: Date the nest was located in a given year using Day of Year as the unit * LastPresent: Day of year the nest was last checked alive (i.e., still active and not depredated or abandoned) using Day of Year as the unit * LastChecked: Day of year the nest was last checked to determine fate using the Day of Year as the unit * Fate: 0 = failed, 1 = successful (hatched at least one duckling) * Reason: If the nest failed, this column indicates the reason it failed * Max Clutch Size: The total size of a full clutch. Only filled out for nests that reached a full clutch and entered incubation, so NA indicates nests that failed before reaching a full clutch. Unit is the number of eggs. * AgeFound: Age of the nest when it was located. Calculated based on the number of eggs in a nest during the laying stage (1 day per egg) or the developmental stage of the embryo (via candling) during the incubation stage. Unit is age in days. * NID: Nest initiation date. Back-calculated based on the age of the nest when it was located. Unit is the day of the year. * Species: Four-letter AOS code indicating the duck species * Guild: Dabbling duck or diving duck * PlotName: Specific plot in the study area * Habitat Category: Rip = riparian, GSM = graminoid-shrub meadow, Ditch = irrigation ditch, GM = graminoid meadow, EM = emergent marsh, Hay = cultivated Timothy hay meadow, SS = shrub-scrub * Included in Density?: Whether the nest was included in the computation of nest density. Some nests were located incidentally rather than during systematic searches, and could not be used in the estimation of nest density. * Year: Study year * Property: Anonymized property within the study area * Private: 1 = private property, 0 = public land * SpAtNest: Vegetation species code the nest bowl was made out of/in * DistWater: Distance to water in meters * TallestVeg: Height of tallest vegetation within 1 m of the nest bowl in cm * Robel: average visual obstruction rating (cm) estimated using a modified Robel pole and measured in all four Cardinal directions * BG: Percent bare ground within a 1-m Daubenmire frame centered on the nest bowl * Litter: Percent litter within a 1-m Daubenmire frame centered on the nest bowl * Water: Percent water within a 1-m Daubenmire frame centered on the nest bowl * Grass: Percent grass within a 1-m Daubenmire frame centered on the nest bowl * Forb: Percent forbs within a 1-m Daubenmire frame centered on the nest bowl * Shrub: Percent shrubs within a 1-m Daubenmire frame centered on the nest bowl * Sedge: Percent sedges within a 1-m Daubenmire frame centered on the nest bowl * Rush: Percent rushes within a 1-m Daubenmire frame centered on the nest bowl * RE: Percent robust emergent vegetation (e.g., cattails, bulrush) within a 1-m Daubenmire frame centered on the nest bowl #### File: density\_dryad.csv **Description:** Nest density data from North Park, CO 2018-2023. Unless otherwise noted in this README file, NAs indicate missing data. ##### Variables * Date: Date nest plot was searched * Year: Study year * Property: Anonymized property of the nest search * Private: 1 = private property, 0 = public land * PlotName: Unique code given to each search plot * Basin: Basin = plot contained or was within 200 m of a basin wetland, NA = plot did not contain or was farther than 200 m from a basin wetland * Habitat.Type: Rip = riparian, GSM = graminoid-shrub meadow, Ditch = irrigation ditch, GM = graminoid meadow, EM = emergent marsh, Hay = cultivated Timothy hay meadow, SS = shrub-scrub * Nests.in.Plot: Number of unique nests located during that specific search * Species: Nest ID code or species of duck. NA = no nests located during that search. * No.People.Searching: How many people were searching during that specific event * Hectares: Plot size in ha #### File: nss\_dryad.csv **Description:** Nest data used to evaluate nest site selection of dabbling ducks in North Park, CO from 2018-2023. Unless otherwise noted in this README file, NAs indicate missing data. ##### Variables * Location: Anonymized property within the study site * Year: Study year * Date: Date vegetation measurements were taken * Species: Duck species four-letter code * Guild: Dabbling duck or diving duck * Nest: Unique nest ID code * Choice: 1 = nest point, 0 = random point within 200 m of the nest location * Obs: Observer initials * HabCat: Rip = riparian, GSM = graminoid-shrub meadow, Ditch = irrigation ditch, GM = graminoid meadow, EM = emergent marsh, Hay = cultivated Timothy hay meadow, SS = shrub-scrub * Wdepth: Depth of the water at the point in cm * DistW: Distance to the nearest open water body in m * SpAtNest: Vegetation code for species at the point * DOY: Day of year * TallestVeg: Tallest veg within 1 m of the point in cm * Robel: average visual obstruction rating (cm) estimated using a modified Robel pole and measured in all four Cardinal directions * BG: Percent bare ground within a 1-m Daubenmire frame centered on the point. We allowed the total percent cover to sum to more than 100% because the vegetation was often layered vertically. * Litter: Percent litter within a 1-m Daubenmire frame centered on the point * Water: Percent water within a 1-m Daubenmire frame centered on the point * Grass: Percent grass within a 1-m Daubenmire frame centered on the point * Forb: Percent forbs within a 1-m Daubenmire frame centered on the point * Shrub: Percent shrubs within a 1-m Daubenmire frame centered on the point * Sedge: Percent sedges within a 1-m Daubenmire frame centered on the point * Rush: Percent rushes within a 1-m Daubenmire frame centered on the point * RE: Percent robust emergent vegetation (e.g., cattails, bulrush) within a 1-m Daubenmire frame centered on the point * Moss: Percent moss within a 1-m Daubenmire frame centered on the point * Lichen: Percent lichen within a 1-m Daubenmire frame centered on the point * Shared: 0 = public land, 1 = private property #### File: PatchCovariates\_dryad.csv **Description:** Landscape metrics of nest locations and random points for dabbling/diving duck nests in North Park, CO from 2018-2023. All distances were measured using a GIS. ##### Variables * OBJECTID: Row number * NestID: Unique nest code. NA = random points generated for comparison to nests. * species: Four-letter duck species code. NA = random points generated for comparison to nests. * year: Study year. NA = random points generated for comparison to nests. * nestorrandom: 1 = nest location, 0 = random point * River: Distance to the nearest river in m * Ditch: Distance to the nearest irrigation ditch in m * Flow: Distance to the nearest flowing water in m (i.e., the lower of the two columns River or Ditch) * OW: Distance to the nearest open water in m * Roads: Distance to the nearest road in m * hay: Distance to the nearest cultivated Timothy hay meadow in m * nwrhay: Distance to the unharvested graminoid meadow on Arapaho NWR in m * Irr: Distance to nearest irrigated meadow of any type of vegetation in m. NA = missing data. ## Access information NA