Nesting White Ibis prey use in Everglades National Park in 2017 and 2018

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 <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.