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Type: Thesis
Title: The life history characters, reproductive constraints and foraging strategies of a neritic seabird, the crested tern.
Author: McLeay, Lachlan J.
Issue Date: 2010
School/Discipline: School of Earth and Environmental Sciences
Abstract: This thesis examines the functional relationships between the diet, foraging behaviour and life history traits of crested tern populations in South Australia between 2004 and 2008. Diet analyses indicated that crested terns are a generalist predator on surface-schooling fishes. Clupeiform fish (Australian anchovy Engraulis australis, sardine Sardinops sagax) comprised a large component of the diet of crested terns. Ontogenetic differences in prey size indicated that adults selected small prey for their chicks during early provisioning but increased the size and rate of prey delivered throughout the breeding season as chicks grew. Adults also selected higher quality prey for their chicks compared to what they consumed themselves. Chick and adult diets may have reflected spatial differences in the species composition of prey assemblages near colonies and a North-South gradient in prey size. I also investigated the provisioning patterns of crested terns and how reproductive timing and adult body condition affect the growth and survival of crested tern chicks. Provisioning rates were related to the daily mass change of chicks, and chick growth was correlated with asymptotic mass, suggesting that prey availability and adult foraging proficiency influences fledgling size. Parental ‘quality’ affected reproductive performance. Adults with good body condition hatched chicks earlier and early breeding was positively related to hatchling mass, fledgling condition and chick survival. Adults aged <7 years had significantly poorer body condition and hatched their chicks later compared to adults ≥7 years. However, adult body condition also varied within cohorts, indicating that reproductive performance is affected by phenotypic differences in parental quality. Consequently, the growth of crested tern populations may be most sensitive to the foraging behaviour and reproductive output of high quality adults ≥7 years old. Disease-related mortality events in 1995 and 1998, which killed ~ 70% of adult sardine Sardinops sagax biomass, provided an opportunity to assess whether crested tern populations were affected by decreases in prey abundance. Age-specific information collected from adults indicated that chicks reared during poor prey conditions caused by the first sardine mortality event in 1995 exhibited lower rates of recruitment to the breeding colony. Females from cohorts reared <1 year after the end of each sardine mortality event also had smaller morphology compared to other age classes indicating that chick growth was reduced during periods of low sardine abundance. Analyses of foraging behaviour using GPS indicated that adults generally commuted to foraging grounds <40 km from the colony where they accessed prey from warm, shallow, near-surface waters that were relatively high in Chl-a (> 0.5mg.m⁻³). Intra-specific variations in foraging behaviour reflected either prior knowledge of where prey aggregations exist, distinctions in individual niche use driven by the types or sizes of prey available, and/or alternate behavioural states (self feeding and provisioning). The restricted foraging range of crested terns while breeding may make them sensitive to competition with fisheries that operate within their foraging range. Diet and demographic information collected from crested tern populations may provide ecological performance indicators to enhance conservation strategies for crested tern populations and augment current fisheries management approaches.
Advisor: Goldsworthy, Simon D.
Ward, Timothy Mark
Paton, David Cleland
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2010
Keywords: seabird; demography; reproduction; foraging; tern; life-history; performance indicator; fisheries
Provenance: Copyright material removed from digital thesis. See print copy in University of Adelaide Library for full text.
Appears in Collections:Research Theses

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