DOI: 10.5061/dryad.gqnk98skv
title: Nesting White Ibis prey use in Everglades National Park in 2017 and 2018

description: As avian reproductive success is generally prey limited, identifying
 important prey types or sizes, and understanding mechanisms governing prey
 availability are important objectives for avian conservation ecology.
 Irruptive White Ibis (Eudocimus albus) nesting at coastal colonies in the
 southern Everglades numbered over 100,000 nests in the 1930s. A century of
 drainage and altered hydrologic patterns reduced aquatic prey availability
 and eliminated large nesting events; nesting activity in recent decades
 has been typically &lt;5% of historical peaks. Hydrologic restoration
 is expected to increase ibis nesting activity, but which prey types will
 support high nesting effort is less clear. In 2017 and 2018 we collected
 food boluses from White Ibis chicks at coastal colonies in Everglades
 National Park. We also monitored regional nesting activity from 1999-2018.
 In 2017 the region had 1,075 nests, typical of the past several decades,
 but in 2018 there were 30,420 nests, representing the highest recorded
 nesting activity in 87 years. Prey composition varied between years;
 estuarine crabs dominated nestling boluses in 2017 while crayfish and fish
 were dominant prey in 2018. Crayfish, especially Procambarus alleni, were
 heavily exploited by ibis early in the 2018 breeding season while fish
 were used more at the end. Crayfish abundances in wetlands near the
 colonies were higher prior to 2018, and more crayfish-producing
 short-hydroperiod wetlands remained available for ibis foraging in 2018.
 Our results support previous studies indicating that crayfish are
 important prey for breeding ibises and suggest that unprecedented,
 extensive flooding of seasonal wetlands promoted crayfish production and
 initiated the irruptive breeding in 2018. Our observations indicate
 re-hydration of the southern Everglades could restore ibis nesting
 activity at coastal colonies, but further investigations of hydrologic
 variation, crayfish production, and ibis foraging and nesting activity
 will be helpful to understand these dynamics and the importance of
 short-hydroperiod wetlands.  
description: <strong>Prey composition of White Ibis nesting in
 Everglades National Park in 2017 and 2018 </strong>
 We quantified prey use of ibises nesting in the ecotone of
 Everglades National Park in 2017 and 2018 by examining the contents of
 regurgitated food boluses collected from nestlings. We collected boluses
 weekly for ~5 weeks each year during the peak provisioning period when
 chicks are between 12 and 28 days old. Most boluses (~90%) were collected
 from the ground or nesting substrates following voluntary regurgitation
 and the rest were collected via esophageal massage.Each bolus was picked
 through twice, and all useful prey parts were recorded, counted, and
 sorted into vials of 70% ethanol similar to methods used in previous diet
 studies (Boyle et al. 2014). We measured lengths of prey parts and
 back-calculated dry masses of fish and most invertebrates with regressions
 developed for previous assessments of ibis diets (Boyle et al.
 2014). <strong>White Ibis nesting
 activity</strong> We conducted aerial surveys of
 nesting ibis at seven historical colonies in the ecotone of Everglades
 National Park from 1999 and 2018. We monitored active nesting colonies
 monthly from January through June using fixed-winged aircraft and
 helicopters flown at an altitude of 150-250 meters above ground level.
 During each flight, we took photos of the entire colony using a
 high-resolution DSLR camera and telephoto lens. We examined the photos to
 determine the stage of nesting and number of nests. We counted nests
 during the incubation stage, when the white incubating adult could be
 detected against the darker background of the nesting colony; we assumed
 each horizontally sitting (incubating) adult equated to one nest. We
 estimated total nest counts by rounding the number of nests up to the
 nearest 5, 50, or 100 nests for colonies with &lt;100, 100-1000, and
 &gt;1000 nests, respectively. We used the total nest count for each
 colony as a measure of colony-level nesting effort. We summed total nest
 counts for all colonies in the ecotone each year to examine temporal
 trends of total nesting effort in the coastal ecotone of Everglades
 National Park. <strong>Crayfish
 Production</strong> We quantified wet-season
 crayfish (<em>Procambarus alleni</em> and <em>P.
 fallax</em>, combined) catch rates at five spatially-fixed sampling
 sites in marl prairies and sloughs east of the colonies in each October
 preceding the 2017 and 2018 dry seasons (i.e. October 2016 and 2017). At
 each of the five sites we set six non-baited minnow traps (three 3.0 mm
 and three 6.4 mm wire mesh traps) for 22-24 hr. We considered the
 aggregate catch of six traps at each site a single effort. Crayfish were
 identified to species and measured (mm carapace length), and dry weights
 were calculated using length-weight regressions (Boyle et al. 2014). We
 compared mean crayfish catch rates (crayfish
 effort<sup>−1</sup>) and biomass (g dry mass
 effort<sup>−1</sup>) between 2016 and 2017 with paired
 one-tailed t-tests. Crayfish biomasses were natural log transformed to
 help meet assumptions of the analyses.
description: Biomasses (in mg) for White Ibis boluses are summed for all prey
 types per bolus. Aggregate crayfish biomasses and
 abundances in traps set in October 2016 and 2017 (DW2016 and DW2017) are
 provided in two separate files.