Abstract
This thesis centres on methods and studies designed to increase knowledge surrounding the at sea distribution of seabirds during various periods in their annual cycle (i.e., breeding, migration, over-wintering). Following a brief introduction in Chapter 1, in Chapter 2, “Effects of archival tags on Sooty Shearwater (Puffinus griseus)”, I report the effects of global location sensing (GLS) tags applied to provisioning adult Sooty Shearwaters captured on Whenua Hou (Codfish Island, New Zealand). Specifically, I assessed effects on chick size, chick mass, and estimated post-fledging recruitment by comparing two groups: chicks reared by parents where one or both members of each breeding pair were outfitted with GLS tags versus chicks reared by non-handled and non-tagged adult pairs. Deployment of tags on adults resulted in 35% reduction in chick body mass and significantly reduced chick skeletal size preceding fledging. Chick mass was negatively related to the duration that adults carried tags. In this study, none of the chicks reared by pairs where both parents were tagged, 54% of chicks reared by pairs where one parent was tagged, and 83% of chicks reared by non-handled and non-tagged parents achieved a pre-fledging mass threshold of 564 g related to successful recruitment at age >1 yrs. Body mass of adults carrying tags and returning from transequatorial migration the following year were 4% lighter on average than non-tagged birds, but this difference was not statistically significant. I suggest that the ethics and potential risks of deployment of tags must be balanced against risks of not deploying them and thereby missing crucial information for understanding biological adaptations and informing conservation efforts. The designs and attachment methods for such devices continues to be modified to minimise disruption and effects to individuals. The placement and streamlining of tags in future studies on shearwaters and other seabirds should be considered to minimize efficiency penalties incurred by the reduction in hydrodynamic drag or displacement of mass. Caution is required especially when deploying tags on threatened species.
The Sooty Shearwater exists in a perpetual summer and completes one of the lengthiest annual avian migrations (>28,000 km roundtrip). Previously, knowledge of shearwater movements came from opportunistic ship-based observations of the flight direction of individual birds along their vast migration route, and from serendipitous recoveries from beaches and fishery by-catch of individuals banded at colonies in New Zealand. In Chapter 3, “Wings over waves: the extraordinary trans-Pacific migration of the Sooty Shearwater”, I describe the first continuous satellite-tracking of the fall (boreal) trans-Pacific migration of the Sooty Shearwater from foraging areas off central California back to the South Pacific. Individual tracks were very consistent, with all birds closely following the shortest possible great circle route toward New Zealand. From departure to the first location south of the Tropic of Capricorn, individual shearwater paths were 10.1 ± 4.6% greater than respective great circle routes. Shearwaters traveled at 25 ± 6 km hr-1, slower than the instantaneous flight speeds recorded from ships. Traveling at 25 km hr-1 along the most direct possible route, a shearwater could leave San Luis Bay (California), traverse the Pacific, and reach the colony at Taiaroa Head (New Zealand) in 16.5 days.
In the absence of information regarding the actual distribution, abundance, and hence, availability of zooplankton prey for seabirds, environmental factors can serve as proxies to help understand seabird habitats. In Chapter 4, “Oceanographic factors influencing the at sea distribution of Cassin’s Auklets that breed in the Channel Islands, California”, I used radio-telemetry data collected in 1999-2001 to evaluate at-sea habitat use among Cassin’s Auklets Ptychoramphus aleuticus breeding at Prince Island off southern California. I examined logistic regression between paired radio-telemetry (presence) versus random (pseudo-absence) location-associated habitat variables derived from satellite remote-sensing of sea surface temperature and chlorophyll a concentration, and digital bathymetry. In this chapter, I used a Baysian model-ranking approach to examine the predictive capacity of these oceanographic variables. Compared with random locations within their foraging area and after controlling for distance to colony, odds ratios indicated that auklets provisioning chicks occurred in relatively shallower, warmer, chlorophyll-rich water characterized by chlorophyll fronts near the insular shelf break.
In Chapter 5, “Summer-time use of West Coast U. S. National Marine Sanctuaries by migrating Sooty Shearwaters (Puffinus griseus)”, I used a similar model-ranking approach that I developed in Chapter 4, to evaluate oceanographic factors that could potentially help predict the annual distribution of over-wintering Sooty Shearwaters in the California Current Large Marine Ecosystem (CCLME). During 2008 and 2009, I used satellite telemetry to evaluate shearwater ranging patterns among birds captured at three locations: Columbia River Plume, WA; Monterey Bay, CA; and Santa Barbara Channel, CA. Within the U. S. Exclusive Economic Zone (EEZ) during 2008 and 2009, shearwaters spent 68% and 46% of time over the shelf (<200 m), 27% and 43% of time over the slope (201–1000 m), and 5% and 11% of time over the continental rise and abyssal regions (>1000 m), respectively. In 2008 and 2009, shearwaters spent 22% and 25% of their time in the EEZ within the five west coast National Marine Sanctuaries; high utilization occurred in non-Sanctuary waters of the EEZ. Individual birds from three discrete capture locations overlapped substantially in space and we identified several regional “hotspot” areas, including the Columbia River Plume, Cape Blanco, Monterey Bay, Estero/San Luis Obispo Bays, and the Santa Barbara Channel. After accounting for bathymetry, shearwater utilization in both years was positively associated with long-term mean chlorophyll a (range in estimated R2 = 0.13–0.20).
Wind strength and direction are important factors related to the overall movements that delineate the distribution of petrels at sea. Consistent with the theme of exploring oceanographic habitat associations among tracked seabirds in Chapters 4 and 5, in Chapter 6, “Correlating seabird movements with ocean winds: linking satellite telemetry with ocean scatterometry”, I present a new method for quantifying the movements of far-ranging seabirds in relation to remotely-sensed ocean winds measured by the SeaWinds scatterometer onboard the QuikSCAT satellite. Individual seabirds (Sooty Shearwater, Pink-footed Shearwater, Hawaiian Petrel, Grey-faced Petrel, and Black-footed Albatross) all traveled predominantly with oblique, isotropic crossing to quartering tail-winds (i.e., 105° to 165° in relation to birds’ trajectory). For all five seabirds, entire track line trajectories were significantly correlated with co-located winds. I suggest that vector correlation can be used to quantify movements for any marine vertebrate when tracking and environmental data (winds or currents) are of sufficient quality and sample size. Vector correlation coefficients can then be used to assess population- or species-specific variability and used to test specific hypotheses related to how animal movements are associated with fluid environments.