Reproductive Declines in an Endangered Seabird: Cause for Concern or Signs of Conservation SuccessReport as inadecuate




Reproductive Declines in an Endangered Seabird: Cause for Concern or Signs of Conservation Success - Download this document for free, or read online. Document in PDF available to download.

Collection and analysis of demographic data play a critical role in monitoring and management of endangered taxa. I analyzed long-term clutch size and fledgling productivity data for California least tern Sternula antillarum browni, a federally endangered subspecies that has recently become a candidate for down-listing. While the breeding population grew from approximately 1,253 to 7,241 pairs 578% during the study period 1988–2009 both clutch size and fledgling productivity declined. Clutch size decreased by approximately 0.27 eggs 14% from 1990–2004 then showed a moderate increase of 0.11 eggs from 2004–2009. Estimates of fledgling productivity showed a similar pattern of decline and moderate increase even after controlling for clutch size. Sea surface temperature anomalies, an index of El Niño-Southern Oscillation activity, did not influence clutch size but were associated with fledgling productivity through a non-linear relationship. Both clutch size and fledgling productivity increased with latitude, potentially indicating a gradient of life-history trade-offs. Random site effects explained little of the overall variation in clutch size 3% or fledgling productivity <1% suggesting that site characteristics beyond those associated with latitude had little bearing on either measure of reproduction. Despite intensive monitoring and management, causes of variation in key demographic parameters remain poorly understood. Long-term declines in clutch size and fledgling productivity may reflect: 1 reduced food availability, 2 increased density-dependent competition, and-or 3 age-dependent reproduction coupled with a shifting population age-structure. Until the mechanisms shaping demographic parameters and population change are better understood, the success of past management and the probability of ongoing recovery will remain difficult to characterize.



Author: Justin Schuetz

Source: http://plos.srce.hr/



DOWNLOAD PDF




Related documents