Population trends in a substantial colony of Little Penguins: three independent measures over three decades

Biodivers Conserv (2014) 23:241250

DOI 10.1007/s10531-013-0597-y

BRIEF COMMUNICATION

Duncan R. Sutherland Peter Dann

Received: 15 October 2012 / Accepted: 20 November 2013 / Published online: 28 November 2013 Springer Science+Business Media Dordrecht 2013

Abstract Estimating long-term population trends is vital for the conservation and management of species, yet few trends exist and fewer still are veried with independent measures. We compared three independent measures of change in population size over 27 years (19842011) for a signicant Little Penguin Eudyptula minor colony in southeastern Australia: (1) a series of 13 colony-wide surveys conducted in eight separate years,(2) mean nightly counts of penguins returning to breeding sites (365 counts 9 27 years) and (3) population growth rates from a demographic model based on survival and recruitment rates measured at three sites each year. Colony-wide surveys of burrows were used as a benchmark of change in population size in the 8 years they were conducted as they were a robust measure of population size corrected for intra-annual variation in burrow occupancy using mark-recapture modelling at six reference sites. However, the demographic model matched the trend from colony-wide surveys with greater resolution in years and with less effort. Beach counts were unreliable for monitoring trends for the entire population due to its singular and peripheral location in the colony. Trends indicate a doubling of the population from 1984 to 2011 despite a marked population contraction linked to a mass mortality of a key prey species. The colony appears secure but remains subject to changes in the marine and terrestrial environments in the longer term.

Keywords Burrowing seabirds Eudyptula minor Colony size Long-term

study Mark-recapture modelling Population growth rate Recruitment

Introduction

Estimates of population size and identifying population trends through time are key criteria for assigning conservation status for a species (IUCN 2010) and for initiating management

D. R. Sutherland (&) P. Dann

Research Department, Phillip Island Nature Parks, PO Box 97, Cowes, VIC 3922, Australia e-mail: [e-mail]

Population trends in a substantial colony of Little Penguins: three independent measures over three decades

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actions (Rodrigues et al. 2006; Possingham et al. 2002). Seabirds are subjected to multiple anthropogenic threats from sheries, land-based predation, pollution and habitat modication; hence the ability to accurately detect population...