Water Level Fluctuations Influence Wading Bird Prey Availability and Nesting in a Subtropical Lake Ecosystem

Abstract

Food availability affects the reproductive success of animal populations. However, food availability includes both prey abundance and its accessibility, which are regulated by different environmental processes. The match-mismatch hypothesis links reproductive success to annual variability in food availability, but the threshold hypothesis suggests that changes in prey abundance can reduce or intensify the effects of a mismatch event. From January-June 2011-2013, food availability and wading bird (Pelecaniformes) reproduction were measured amidst different environmental conditions at Lake Okeechobee, Florida, USA. Mean prey density was 165 ± 21 prey/m2 (2011), 87 ± 7 prey/m2 (2012), and 104 ± 9 prey/m2 (2013) while 34% (2011), 36% (2012), and 77% (2013) of the landscape became available for foraging. Two generalized linear mixed models were constructed to quantify the relationship between fledging success and total productivity using prey density and foraging habitat availability as independent variables. The interaction of prey density and habitat availability was significant and positive in both models. Fledging success and total productivity increased with increasing prey density, the effects of which were more pronounced when habitat availability was low. Saturation thresholds existed for both fledging success (147 prey/m2) and total productivity (189 prey/m2), above which high concentrations of prey could sustain nesting when habitat availability was low.