Many studies of parental provisioning focused on pelagic procellariiformes have been conducted in the absence of reference to oceanographic conditions. However, the ability of an adult seabird to maintain its body condition is expected to change with oceanographic conditions. Consequently, resource levels are expected to limit reproductive participation and success, potentially define the quality of participants, and also influence the overall ability of a colony to provide for their offspring. The Western Australian coast provides a suitable place to study adult behaviour in the context of oceanographic conditions, given the inter and intra annual fluctuations in
oceanic conditions experienced as a result of variations in the strength of the Leeuwin Current, whose rate of flow is determined by global climatic events (section 1.4.4). Here, variations in climatic conditions have been found to affect both the breeding participation and success of summer breeding tropical seabirds, especially that of the Wedge-tailed Shearwater (Wooller et al. 1991, Dunlop et al. 2002, Integrated
Shearwater Monitoring Program 2003, 2006) (section 1.4.5). Although, no three-year study can explore the trends in seabird reproduction in relation to such factors, the existence of an ongoing long-term study of Wedge-tailed Shearwaters provided an index of oceanographic resource levels and allowed the interpretation of findings within a wider context.
Fortunately, this study encompassed one year of strong current flow (2000), one transitional year (2001) and a year (2002) associated with weak Leeuwin Current flow when cooler waters prevailed offshore. In addition to easily measured outcomes such as reproductive participation, failure or success, which have been monitored in other studies on the Western Australian coast (Wooller et al. 1991, Dunlop et al. 2002, Integrated Shearwater Monitoring Program 2003, 2006), more subtle effects of climate upon parental provisioning were investigated – such as nestling weights which reflect the adults ability to provide food. The expansion of existing work will increase our understanding of potential mechanisms, the effects of climate change on seabirds and may help to explain the southwards range expansion documented for several species of tropical seabirds along the Western Australian coast (Dunlop and Goldberg 1999, Dunlop and Mitchell 2001, Bancroft et al. 2004)
Traditional models denote that long-lived K-strategists reproduce in stable conditions. The oceanographic variability recorded along the Western Australian coast, suggests that seabirds reproduce in unstable conditions. This study will comment upon life- history strategies of long-lived seabirds and their successful radiation in relatively unstable and unpredictable environments. The level of parental care provided by the K-strategist during variable oceanographic conditions will be investigated, especially the amount and frequency of food delivered, whilst also focusing on constraints which may affect parents, including adult body weight, immediate weather and regional oceanographic conditions.
The interaction between seabird provisioning and immediate weather conditions will be examined. Obviously, seasonality has a predictable effect upon the weather patterns experienced along the Western Australian coast. Whilst, the variable flow of the Leeuwin Current between different years has the potential to produce subtle inter- annual variations in climate. During years when the warm Leeuwin Current flows strongly in autumn elevated sea surface temperatures are maintained which sustain active or dissipating tropical cyclones for longer, and provide opportunity for such system to travel to higher latitudes. The effect of dissipating tropical cyclones on the relatively broad-winged Wedge-tailed Shearwater provisioning will be examined during the study. Given the species tropical breeding distribution and comparatively broad wings it is expected to be relatively tolerant of low wind conditions. Similarly, the study will examine the interaction between the weather experienced in winter and Little Shearwater provisioning patterns. The southern breeding distribution of the Little Shearwater and its comparatively narrow wings suggest it is a species suited for
high wind conditions. Weather systems have the potential to alter travel costs, given that pelagic seabirds often utilise them for locomotion.
Traditionally, studies of parental provisioning and nestling obesity in
Procellariiformes have focused on species breeding at higher latitudes or dependent on distant high latitude resources that are temporally limited as a result of predictable seasonality (1.3.3). Following the sharp seasonal decline of high latitude resources many of these species undergo trans-equatorial migrations and often nestling obesity and a period of nestling desertion was recorded (Warham 1990; Warham 1996). Less research has focused on species breeding at lower latitudes. In this study at
approximately 30 º latitudes it was expected that nestlings would not be deserted before fledging. If obesity served to overcome a period of pre-fledging desertion associated with a seasonal decline in resources it should not occur at mid latitudes, where seabird reproduction occurs in both winter and summer indicative of ongoing resource availability.
Obesity has also been proposed to be a by product of chronic overfeeding in the absence of a reliable feedback mechanism (section 1.3.2 and 1.3.3). Literature suggests that both species feed their nestlings regularly and are therefore expected to have sufficient opportunity to obtain feedback about nestling condition, which should prevent chronic overfeeding and resultant obesity. Consequently, obesity is not expected to occur in either species. Respirometry and supplementary feeding of Wedge-tailed Shearwaters will be used to investigate aspects of parental provisioning and pre-fledging weight loss to supplement the field data collected.
The breeding biology of the Little Shearwater has not been extensively examined at a subtropical location in the southern hemisphere. Results will contribute towards the understanding of seabird biology along Western Australian coast and serve as a comparison to existing studies of the species at other locations. The Little Shearwater is the smallest shearwater (Harrison 1985) and is therefore expected to have a higher resting metabolic rate and its threshold weight would be reached after a smaller weight loss than in larger species. This suggests that the Little Shearwater is an ideal species in which to study parental behaviour, especially how the ability to maintain adult body condition may affect continuity of parental care during incubation and nestling feeding.
Little is known about the foraging behaviour of the Little Shearwater breeding at lower latitudes of the Western Australian coast. Common belief prevails that its foraging was likely to be size restricted and it was predicted that it would forage near the breeding sites. The distribution of the Little Shearwater suggests that it is adapted to forage in cold water, whereas Wedge-tailed Shearwaters are associated solely with tropical waters. Based upon observations of birds in association with sea surface temperatures (Brooke 2004) it may be deduced that Little Shearwaters are more likely to excel in years of reduced sea surface temperatures or forage in zones dominated by cool water. Zones of cooler water are often found inshore along the Western Australian coast, where a northwards flowing counter current exists (Pearce 1997). Given its southern distribution of the Little Shearwater, it was also thought that the species was more likely to forage in cool inshore shelf waters. Opportunistic voyages on fishing and charter vessels and feedback from the skilled observers during the Little Shearwater breeding season will be used to locate Little Shearwaters at sea.
Observations of seabirds at sea provide an insight into the foraging behaviour of adults at sea. It however is often difficult and time consuming to collect direct observations at sea. Consequently, indirect methods of approximating adult
behaviour at sea were employed. Since, little was known about dive depths in Little Shearwaters maximal depth gauges were utilised to examine foraging behaviour during incubation and nestling feeding. The potential use of stable isotope analysis to elucidate the behaviour of pelagic seabirds at sea will also be examined.
Stable isotope analysis focuses on the time specific materials, such as egg membranes and nestling plumage to comment on foraging behaviour (Bearhop et al. 2001). Here materials will be used to draw comparison between species engaged in similar
behaviours and within a species at different locations and times in the breeding season. The technique was used to question the ability to directly compare the mass of food delivered to nestlings over time, as composition of meals may change in terms of energy and nutritional values with seasonal changes in diet. Nonetheless, meal sizes based on mass alone are often directly compared in seabird research, including meal sizes delivered within a species over time, between different locations and between subspecies and between species. Stable isotope analysis will be used to detect potential changes in diet with season in Wedge-tailed Shearwaters. The potential applications of this indirect technique will be examined with focus on its ability to track the changing behaviour of adults at sea, that can otherwise be time consuming to understand.