WEDGE-TAILED SHEARWATER FORAGING BEHAVIOUR IN THE EXMOUTH REGION

Dr Belinda Cannell, Sheryl Hamilton, Joris Driessen

May 2019

ACKNOWLEDGEMENTS

This research was supported by funding from the Woodside-operated Greater Enfield Project, a Joint Venture between Woodside Energy Ltd and Mitsui E & P Australia Pty Ltd.

This report may be cited as:

Cannell, B., Hamilton, S and Driessen, J (2019) Wedge-tailed shearwater foraging behaviour in the Exmouth region. Report for Woodside Energy Ltd. University of Western Australia and Birdlife Australia, 36pp http://birdlife.org.au/documents/wedge-tailed shearwater foraging behaviour.pdf

TABLE OF CONTENTS

Summary ............................................................................................................................................................. 3

Introduction ........................................................................................................................................................ 3

Wedge-tailed shearwater distribution and important areas in Western Australia ........................................ 3

Breeding and foraging behaviour of WTS ....................................................................................................... 5

WTS at the Muiron Islands ............................................................................................................................. 7

Methodology ...................................................................................................................................................... 8

Results .............................................................................................................................................................. 14

Discussion ......................................................................................................................................................... 31

References ........................................................................................................................................................ 33

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SUMMARY

The foraging habitat of Wedge-tailed Shearwaters (WTS) at the Muiron Islands was investigated. Either satellite or GPS tags were deployed on adult shearwaters incubating eggs in November 2018. A total of 30 birds were tagged (20 Satellite, 10 GPS). Data from the satellite tags were downloaded from ARGOS, whereas data from the GPS tags offloaded to a base station when a bird returned to its nest, providing 1) the tag was still attached upon its return and 2) that the bird was on the surface for sufficient time for the data to offload. These data were then retrieved from the base station.

The tags logged locational data for different durations, ranging from 11 - 64 days. From the trip characteristics it was likely that five different behaviours were observed 1) short trips during incubation during which the eggs were likely to have been temporarily abandoned 2) foraging trips during incubation, 3) short foraging trips during chick rearing, 4) long foraging trips during chick rearing, and 5) trips where the bird was likely to have abandoned the egg for long durations.

The birds used an area that extended from the Muiron Islands to just south of the Indonesian Archipelago. The longitudinal range extended from 100 ° E to 120 °E. The maximum distance the birds travelled to from the colony ranged from 9 – 1,854 km. The home range (95% KUD) of all the WTS deployed with satellite tags covered 1,266,516 km2, but the core foraging habitat (50% KUD) composed only approximately 20% of the home range.

For the incubation trips, there was a strong consistency for the birds to travel towards seamounts, typically located north-west of the Muiron Islands, between Australia and Indonesia. A bimodal foraging strategy during chick-rearing was observed, with the Wedge-tailed Shearwaters undertaking long foraging trips after a series of short foraging trips.

INTRODUCTION

WEDGE-TAILED SHEARWATER DISTRIBUTION AND IMPORTANT AREAS IN WESTERN AUSTRALIA

Wedge tailed shearwaters (Ardenna pacifica) (WTS) are pelagic, migratory seabirds that typically occur in tropical and sub-tropical oceans across the Pacific and Indian Oceans (Marchant and Higgins 1990), but are also found in temperate waters (Johnstone and Storr 1998, Dunlop et al. 2002, Peck and Congdon 2005). In Australia, they are listed as a marine and migratory species in the Australian Environmental Biodiversity and Conservation Act 1999, and are protected under the Japan-Australia Migratory Bird Agreement (Department of Foreign Affairs 1981). They are listed as a species of Least Concern in the IUCN Red List and there is no approved Conservation Advice, no Listing Advice, and no

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adopted or made Recovery Plans for the WTS (http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=1027). However, they have been identified as of conservation value in the south-west, north-west and temperate east of Australia (http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=1027). In Western Australia (WA), they breed on multiple offshore islands between Ashmore Reef (12.255° S, 123.038° E) and Carnac Island (32.121° S, 115.662° E) (Dunlop et al. 2002), and over one million pairs are estimated to breed across these sites (Burbidge et al. 1996).

Several Biologically Important Areas (BIA) have been identified for WTS by the Department of The Environment and Energy (DOEE) (https://www.environment.gov.au/marine/marine-species/bias). BIA are “areas that are particularly important for the conservation of protected species and where aggregations of individuals display biologically important behaviour such as breeding, foraging, resting or migration. They have been identified using expert scientific knowledge about species’ distribution, abundance and behaviour in the region” (DSEWPaC 2012). One BIA in WA is located in the Pilbara region. It extends north-east from the Cape Range National Park to approximately the North Turtle Island Nature Reserve (north of Port Hedland), and includes the Muiron Islands and surrounding waters (Fig. 1).

The Muiron islands, composed of North and South Muiron Islands, are located 35 km north of Exmouth and lie within the Pilbara Offshore Region (IMCRA 1998). North and South Muiron Islands are 465 and 450 ha respectively. They form part of the Ningaloo World Heritage Area and hence have World Heritage listing under the Convention Concerning the Protection of the World Cultural and Natural Heritage (Woinarski et al. 2018). They are also a state Marine Management area and join with the northern end of the Ningaloo Marine Park (http://www.fish.wa.gov.au/Sustainability-and-Environment/Aquatic-Biodiversity/Marine-Protected-Areas/Pages/Recreational-fishing-in-Muiron-Islands-Marine-Management-Area.aspx). Both islands are a significant nesting site for WTS, with 292,844 breeding pairs observed between March 2013 and January 2014 (Surman and Nicholson 2015).

Important Bird and Biodiversity Areas (IBA) are internationally recognised important areas for bird conservation. For species that are neither threatened or have a restricted range, an IBA represents an area where >1% of the global population is located (http://datazone.birdlife.org/site/ibacritglob, accessed April 2019). Only one site, the Houtman Abrolhos, has currently been proposed as an IBA for WTS in WA (https://maps.birdlife.org/marineIBAs/default.html). More than 1,000,000 WTS burrows have been documented on three of the islands in this group (http://datazone.birdlife.org/site/factsheet/houtman-abrolhos-iba-australia).

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BREEDING AND FORAGING BEHAVIOUR OF WTS

Globally, WTS are synchronous breeders, with egg lay typically occurring over a two week period (Byrd et al, 1983, Surman et al. 2012). On the WA coast, the date of peak egg lay varies between colonies, with an increasing temporal gradient from north-west to south-west (Garkakalis et al. 1998, Dunlop et al. 2002, Nicholson 2002, Surman et al. 2012). For example, peak egg lay at Varanus Island (20.652° S, 115.579° E) is in early November (Nicholson 2002), whilst it occurs in late November on Rottnest Island (32.006° S, 115.512° E) (Garkakalis et al. 1998). The birds begin arriving at their WA colonies around August to dig

Fig. 1 Biologically Important Areas for Wedge-tailed Shearwaters in Australia, obtained from the Conservation Values Atlas, with the approximate location of the Muiron Islands indicated. Source: http://www.environment.gov.au/topics/marine/marine-bioregional-plans/conservation-values-atlas

Muiron Islands

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out burrows (Garkakalis et al. 1998, Nicholson 2002). By September the majority of freshly dug burrows are occupied by adults in the evening, but thereafter the number of adults in the colony decreases until egg lay commences (Garkarkalis et al. 1998, Nicholson 2002).

Regardless of colony location, WTS lay a single egg which is incubated for an average of 53 days (Byrd et al. 1983). Both parents share incubation duties. To our knowledge, tags have not been deployed on WTS during the incubation period, and hence foraging behaviour during this period is unknown.

The duration from hatching to a chick fledging and departing the nest is protracted in all WTS colonies that have been studied globally, with chicks fledging at approx 110 days (Byrd et al. 1983). Chicks are fed only at night time by the adults, but are not necessarily fed every night (Smithers et al. 2003), and hence have a slow growth rate (Nicholson 2002).

Adults in colonies in both Hawaii and Eastern Australia have been found to engage in one of two foraging strategies during chick rearing, either consistently performing short foraging trips of typically 1-2 days but up to 4 days (i.e. unimodal) or short trips interspersed by a longer foraging trip of 6-14 days duration (bimodal foraging) (Baduini 2002, Peck and Congdon 2005, Congdon et al. 2005, McDuie et al. 2015). During bimodal foraging, adults will generally perform multiple short trips consecutively before undertaking a long trip (Congdon et al. 2005). Longer trips are associated with improvement in body condition of the adults, whereas they often lose body condition during the short trips (Congdon et al. 2005). Participation in unimodal-only foraging during chick rearing appears to be related to abundant and predictable prey close to the colony (Baduini 2002, Peck and Congdon 2005). There is no tracking information on the foraging distance from a colony during the short trips, however maximum distances from the colony during longer trips have ranged from 385-1150 km (McDuie et al. 2015). As the maximum speed of WTS has been found to be 30 km/hr, it is expected that they remain within 300 km radius of the colony during short trips (McDuie et al. 2015).

Following breeding, WTS migrate from their colony for some five months (Garkaklis et al. 1998, McDuie and Congdon 2016). Migration from the colony is very synchronous, but the return is less so (McDuie and Congdon 2016). Tags have been deployed on WTS from the Houtman Abrolhos and Pelsaert Island, the Great Barrier Reef and the Seychelles during the migration period (Catry et al. 2009, McDuie and Congdon 2016, Surman et al. 2018). WTS from the Houtman Abrolhos and Pelsaert Island migrated 4200 km north-west into the Indian Ocean (Surman et al. 2018), and those from Great Barrier Reef migrated to the northern hemisphere, approximately 6000 km northwards to Micronesia (McDuie and Congdon 2016). However, WTS from the Seychelles were less consistent in their migratory stop over areas, ranging from approximately 500-3000 km east of the colony (Catry et al. 2009).

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WTS use several methods for obtaining prey; contact-dipping (where only the head, bill or breast make contact with the water), surface-seizing (a bird grasps prey in its bill when settled on the surface), and plunge diving (a bird plunges from the air and descends the water column). Diving depths when plunge diving have ranged from 2-12 m (Lord Howe Island, Australia: Peck and Congdon 2006), to 1-66 m (Cousin Island, Seychelles: Burger 2001). Dietary studies of WTS are scarce, however research on WTS in WA has shown that they feed on cephalopods, fish crustaceans and jellyfish (Nicholson 2002, Surman and Nicholson 2009).

WTS AT THE MUIRON ISLANDS

Despite the significance of the Muiron Islands for the WTS, there is very limited information on their breeding and foraging behaviour at this colony. Aerial surveys conducted during the breeding season (February and July 2013, March 2014 and January 2015) have demonstrated the presence of the shearwaters within the limit of the surveys, which covered a width of 60 km from the northern edge of the islands (Surman and Nicholson 2015).

The objectives of this study therefore were to obtain baseline information on the foraging behaviour and spatial and temporal patterns of shearwater foraging movements when resident on the Muiron Islands during the incubation, and potentially early chick-rearing period. Results from the study will assist BLA and UWA to fill knowledge gaps in the ecology and conservation management of the WTS population of the Muiron Islands during the breeding stage. Such information will support the refinement of BIA for this species in the Pilbara region. Additionally, there will be improved knowledge on the likely impacts faced by WTS during these breeding stages. Such information will assist in developing measures to mitigate potential threatening processes including interaction with fisheries, marine debris, light pollution, oil spills and climate change.

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METHODOLOGY

Fieldwork was undertaken from 27/11/2018 - 3/12/ 2018, on North Muiron Island (21.3686° S, 114.3728° E). Specifically, burrows located on the southeastern corner of the island were utilised for tag deployment (Fig. 2). This area was chosen based on 1) the density of burrows observed in a transect survey undertaken by Birdlife in January 2018, 2) access between the mother vessel and the island and 3) access to the study site within the island whilst limiting trampling of burrows.

Burrows were checked for 1) occupancy by WTS, 2) presence of an egg and 3) burrow length. Burrows where a shearwater was on an egg but more than an arm’s length from the entrance were deemed unsuitable as the bird could not be reached.

Fig. 2 North and South Muiron islands, Exmouth region: green dots indicate location of burrows and size of dots indicating density of burrows/m2, determined in January 2018 by BirdLife Australia. The white box on the southeastern end of North Muiron Island indicates the area of burrows utilised for both satellite and

GPS tag deployment on Wedge-tailed shearwaters.

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Shearwaters were removed from their burrow and placed in a shadecloth cone. They were weighed using a spring balance (± 5 g). If the birds met a minimum mass criteria for tag attachment, then either a satellite tag (Microwave Telemetry, Solar 9.5g PTT, 38.9 mm*17.8 mm*13 mm high) (Fig. 3a.) or a GPS tag (Pathtrack, Nanofix GEO+RF, 6.6 g, dimensions tag + baseplate: 50 mm*16 mm * 11 mm high) (Fig. 3b) was taped at the base of the three central tail feathers using TESA tape (Figs. 4a and b). A technique was developed to isolate the three feathers using a foam platform to prevent other feathers from being incorporated within the tape/tag and to reduce handling time (Cannell, unpublished Fig. 5). WTS are monomorphic and hence it is not possible to identify gender without using molecular techniques from blood samples. However, given that this is seemingly the first time that WTS have been deployed with tags during incubation, the likelihood of egg abandonment was unknown. Therefore, it was decided that minimal handling of the bird would decrease the likelihood of abandonment, and hence a blood sample was not obtained. To ensure that the burrows of shearwaters deployed with tags were not trampled, there was no backtracking over areas, and all the satellite tags were deployed before deploying the GPS tags.

Fig. 3 Tags deployed on Wedge-tailed shearwaters at North Muiron Island in Nov/Dec 2018, a) Microwave Telemetry Solar PTT 9.5g and b) Pathtrack Nanofix GEO +RF tag and base

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Fig 4. Attachment of a) satellite tag and b) GPS tag on Wedge-tailed Shearwaters at North Muiron Islands, Nov/Dec 2018. Note that the birds are placed within a shadecloth cone throughout the attachment to reduce their capacity to wriggle and hence reduce handling

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The satellite tags were programmed to have a 6 hour duty cycle, and were set to be ON from 1700-2300 h and 0500-1100 h. One of the OFF duty cycles was timed to coincide with a period of no satellite passes in the northwest of Australia, i.e. from 1100-1500 h. Data from the GPS tags offloaded to a base station when a bird returned to its nest, providing 1) the tag was still attached upon its return and2) that the bird was on the surface for sufficient time for the data to offload. Data were downloaded from the base station on three occasions: mid-January 2019, late February 2019 and late March 2019. The base station was placed on a 3 m wooden pole and erected within a 200 m radius of the burrows of those WTS with an attached GPS tag (Fig. 6).

Fig. 5. A foam platform was used to isolate the three tail feathers when attaching a tag on Wedge-tailed Shearwaters at North Muiron Island, Nov/Dec 2018

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DATA ANALYSIS

Analyses of the habitat used by the WTS have been based on established methodologies using various R packages (e.g. Meier et al. 2015, Pickett et al. 2018, Fisher et al. 2018)

To characterise the spatial distribution of the WTS, the data were first organised into separate trips for each bird. Trips were defined as starting and finishing on the island. However, for the data obtained from the satellite tags, the first and last location of a trip was often not recorded on the island, based on the satellite pass times. Therefore, we used the average speed of departure based on data from the GPS tags deployed (this project-30 km/hr), and obtained the time of departure based on this speed and the first location obtained. This assumed a direct flight path from the colony to the first location. Similarly, the time of day a bird returned to the colony was predicted based on the last location of a trip before the colony and the speed of return (13 km/hr). Location data from the satellite tags were then interpolated at hourly intervals using the R package “Crawl” (Johnson et al. 2008). Any spurious locations were removed using a speed filter of 75 km/hr, based on McDuie et al. (2018). Using the R package “Trip” (Sumner 2016) we obtained three trip metrics for each trip undertaken 1) trip duration (hours), 2) overall trip length (km), and 3) maximum distance from the colony (km). Five types of trips were identified 1) short trips during incubation during which the eggs were likely to have been temporarily abandoned 2) foraging trips during incubation, 3) short foraging trips during chick rearing, 4) long foraging trips during chick rearing, and 5) trips where the bird was likely to have abandoned the egg for long durations. The first trip was assumed to be during incubation based on the number of days since tag deployment, the known average lay date for the closest colony (at Varanus Island, 140 km north-east of the Muiron Islands), the known average incubation period for

Fig. 6. The base station located within 200 m of Wedge-tailed Shearwaters with deployed GPS tags. Data will download from the tags to the base station when the birds return to their burrows.

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WTS (53 days), and the length of the trip. Short foraging trips (1-3 days) following a long incubation foraging trip were assumed to be during chick rearing phase. A long trip that followed one or more short trips was assumed to be during the chick rearing phase.

Next, the 50 and 95% kernel utilisation distributions (KUD) were calculated for the WTS deployed with satellite tags only. The 50% KUD represents the core foraging area, and 95% KUD represents the home range. The KUDs were obtained for four different groups of WTS 1) all WTS combined, 2) those incubating eggs, 3) those likely rearing chicks, and 4) those that likely abandoned eggs. They were also calculated for each individual WTS. The hplugin value implemented in the function “kde” of the R package “ks” (Duong 2017) was used, and the volume of the kernel densities were calculated by implementing the function “getvolumeUD” of the R package “adehabitatHR” (Calenge 2006).

A generalised additive model with full-subsets analyses were used to determine the relationship between core foraging habitat and the key physical habitat variables, using the R package “FSSgam” (Fisher et al. 2018). The dependent variable was the location-based density value within the 50% kernel utilisation distribution. Explanatory variables were bathymetry, rugosity (log-transformed), aspect and slope (Table 1). Breeding stage (incubation, short trips during chick rearing and long trips during chick rearing) was included as a factor. The analyses were conducted in R 3.4.4 (R Core Team 2018).The location based density value was modelled using a Gaussian distribution, implemented via a call to gam (mgcv). No random effects were included. Smoothers were applied to all the explanatory variables.

Table 1. Physical habitat variables used to investigate the spatial distribution of breeding WTS from the Muiron Islands.

Variable Description Source

Bathymetry Seabed Water Depth https://ecat.ga.gov.au/geonetwork/srv/eng/catalog.search?node=srv#/metadata/67703

Rugosity Topographic relief Obtained using the Focal Statistic tool “Range” in ArcGis 10.3.1. Input raster is Australian Bathymetry and Topography Grid (see Bathymetry source)

Aspect The direction a slope faces, measured in degrees from 0 (due north), counter clockwise to 360 (again due north)

Obtained using the 3D Analyst Tool. Input raster is Australian Bathymetry and Topography Grid (see Bathymetry source) “Aspect” in ArcGis 10.3.1. Input raster is Australian Bathymetry and

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Topography Grid (see Bathymetry source)

Slope The steepness at each cell of a raster surface. The lower the slope value, the flatter the terrain

Obtained using the 3D Analyst Tool “Slope” in ArcGis 10.3.1. Input raster is Australian Bathymetry and Topography Grid (see Bathymetry Source)

RESULTS

Three hundred and eighty two burrows were checked from 27/11/18 - 2/12/18. Less than 20% of those were occupied by incubating shearwaters in burrows from which the bird could be extracted. Only 30% of these burrows were occupied by shearwaters that were heavy enough to deploy with satellite tags (Fig. 7). All the satellite tags were deployed by 1/12/18 (Table 2).

The GPS tags were all deployed at the northeastern margin of the study area, based on our decision to not back track over nesting areas where birds had been deployed with satellite tags. Burrows were checked for suitability before a site for the base station was confirmed. Shearwaters that met the minimum weight for the GPS deployment were found in only 55% of those suitable burrows, and all GPS tags were deployed by 3/12/18 (Table 2).

Location data were retrieved from all 20 satellite tags and 2 of the 10 GPS tags (Table 2). We recorded 61 foraging trips, 57 from the satellite tags and 4 from the GPS tags. A mixture of complete and incomplete (i.e. the tag stopped transmitting before the bird returned to the island) trips were obtained for the WTS deployed with satellite tags. Complete trips were obtained for 16 of the 20 birds. All but one of these 16 birds had data from multiple trips, but the final trip for 13 of these birds was incomplete. The GPS tags began recording data after both birds had left the colony, but thereafter recorded complete trips.

One to six trips were recorded for each bird. The trip duration ranged from 8 - 708 hours, trip distance ranged from 19 – 6,188 km and the maximum distance from the colony ranged from 9 – 1,854 km (Table 3, Fig 8). Not surprisingly, the trip metrics were greater for the incubation trips. The WTS covered an average of 3,284 ± 901 km during incubation, and 436 ± 286 km when completing short foraging trips during chick rearing (Table 4). There was a four-fold increase in the duration and distance of the long foraging trips during chick rearing compared to the short trips (Table 4). The trips during incubation in which the birds were likely to have temporarily abandoned the eggs were the shortest trips of all. The birds performing these trips typically returned on the same day that they departed the colony, and they travelled less than 100 km from the colony (Table 4).

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The birds used an area that extended from the Muiron Islands to just south of the Indonesian Archipelago. The longitudinal range extended from 100 ° E to 120 °E. For the incubation trips, there was a strong consistency for the birds to travel towards seamounts, typically located north west of the Muiron Islands, between Australia and Indonesia (Figs. 8 - 10). One bird however remained south-west of the islands, in the Cape Range Canyon. A similar pattern to utilise areas associated with sea mounts was also observed for the long foraging trips during chick rearing, though some of the foraging was concentrated in deeper waters. The WTS appeared to forage closer to the colony during these long trips when compared to the incubation trips (Table 3, Fig. 9), however they were incomplete trips so these parameters are potentially underestimated.

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Fig. 7 Location of the confirmed active Wedge-tailed shearwater burrows checked for Satellite or GPS tag deployments. Some of the shearwaters were too light for deployment with satellite tags whilst others were too light for deployment with either tag. However, due to our decision to not back track over areas where birds had been deployed with satellite tags, GPS tags were only deployed on the northeastern margin of our study area.

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Table 2. Tag deployment and number of trips obtained for each Wedge-tailed Shearwater tagged at the Muiron Islands in November - December 2018.

Tag ID Tag Type

Date Deployed

Date of Departure Duration of deployment

(days)

Number of trips (complete and

incomplete)

Number of complete trips

64649 Sat 30/11/18 10/12/18 43 6 5 64650 Sat 1/12/18 14/12/18 24 1 1 64651 Sat 1/12/18 15/12/18 28 4 3 64652 Sat 1/12/18 9/12/18 47 4 3 64653 Sat 29/11/18 13/12/18 24 4 3 64655 Sat 29/11/18 9/12/18 19 1 0 64656 Sat 1/12/18 8/12/18 34 2 2 64657 Sat 1/12/18 16/12/18 47 3 2 64659 Sat 28/11/18 12/12/18 13 1 0 64660 Sat 28/11/18 7/12/18 33 6 5 64664 Sat 28/11/18 6/12/18 64 4 3 64668 Sat 29/11/18 8/12/18 19 2 1 64686 Sat 30/11/18 30/11/18 35 2 1 64691 Sat 28/11/18 9/12/18 19 2 1 64693 Sat 30/11/18 10/12/18 22 4 3 64694 Sat 30/11/18 8/12/18 39 4 3 64706 Sat 1/12/18 10/12/18 31 4 3 64707 Sat 1/12/18 11/12/18 27 1 0 64708 Sat 29/11/08 11/12/18 11 1 0 64709 Sat 29/11/08 1/12/18 30 3 2

17584 GPS 2/12/18 Unknown as tag turned on

after bird left colony 13 1 1

17601 GPS 2/12/18 Only data while on land 0 0 17605 GPS 2/12/18 No data 0 0 17607 GPS 2/12/18 Unknown as tag turned on

after bird left colony 13 3 3

17609 GPS 2/12/18 No data 0 0 17611 GPS 3/12/18 No data 0 0

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17613 GPS 3/12/18 No data 0 0 17657 GPS 3/12/18 Only data while on land 0 0 17670 GPS 3/12/18 No data 0 0 17708 GPS 3/12/18 No data 0 0

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Table 3. The trip parameters for the foraging trips undertaken by breeding Wedge-tailed Shearwaters from the Muiron Islands during different presumed stages of breeding. Trip Type: AbdInc=Short trip during incubation, likely temporary abandonment of egg; Inc=Incubation; Gd=Short trips during Chick rearing (guard), LongGd= Long trip during chick rearing (guard); ?=uncertain of breeding stage. *-incomplete trips (trip parameters will be underestimated), a underestimated as GPS tag began recording after the birds had left the colony

Tag ID Trip Number

Trip type Trip Duration (hours)

Trip Distance (km)

Max Distance

from Colony (km)

64649 1 AbdInc 22 237 113 64649 2 Inc 405 3850 1290 64649 3 Gd 23 270 131 64649 4 Gd 17 156 103 64649 5 Gd 8 238 117

64649* 6 longGd 245 1549 760 64650* 1 Inc 503 4348 1341 64651 1 Inc 175 1661 451 64651 2 Gd 65 583 199 64651 3 Gd 41 452 197

64651* 4 LongGd 236 1951 934 64652 1 Inc 354 3092 1227 64652 2 Gd 18 213 106 64652 3 Gd 65 711 191

64652* 4 Abandon 605 4795 1601 64653 1 Inc 389 4096 1469 64653 2 Gd 17 290 137 64653 3 Gd 24 281 137

64653* 4 LongGd 145 1571 604 64655* 1 Inc 468 3942 1602 64656 1 Inc 277 1700 269 64656 2 Inc 303 2815 656 64657 1 Inc 435 3765 1125 64657 2 Abandon 360 4038 1187

64657* 3 Abandon 300 3585 1323 64659* 1 inc 319 1785 1027 64660 1 Inc 333 3532 1336 64660 2 Gd 72 627 246 64660 3 Gd 34 225 78 64660 4 Gd 47 462 155 64660 5 Gd 111 955 300

64660* 6 LongGd 184 2019 1072 64664 1 Inc 354 3446 1183 64664 2 Inc 349 4924 1798 64664 3 Abandon 522 6188 1854

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64664* 4 Abandon 170 1582 1168 64668 1 AbdInc 11 19 9

64668* 2 Inc 73 1153 1105 64686 1 Inc 406 3538 1291

64686* 2 ? 101 1109 732 64691 1 AbdInc 36 411 119

64691* 2 Inc 387 3220 1347 64693 1 Inc 431 3761 1462 64693 2 Gd 15 195 74 64693 3 Gd 17 380 269

64693* 4 Gd 40 408 218 64694 2 AbdInc 11 65 31 64694 3 Inc 409 3245 982

64694* 4 Inc 299 1366 1104 64706 1 Inc 314 2833 1010 64706 2 Inc 245 2280 687 64706 3 Gd 15 208 108

64706* 4 Gd 67 1117 483 64707* 1 Inc 657 3534 1415 64708* 1 Inc 281 2029 983 64709 1 Inc 425 3968 966 64709 2 Gd 113 1201 489

64709* 3 LondGg 110 1092 455

17584 1 Inc 315a 1891a 458 17607 1 Inc 327a 3349a 1380 17607 2 Gd 13 70 52 17607 3 Gd 15 178 78

Table 4. Mean (±SD) trip metrics for complete and incomplete (*) trips at different stages of the breeding cycle. Trip Type: AbdInc=Short trip during incubation, likely temporary abandonment of egg; Inc=Incubation; Gd=Short trips during Chick rearing (guard), LongGd= Long trip during chick rearing (guard). No SD if only a single trip, Data from satellite tags only

Trip Type Trip Duration

(hrs)

Trip Distance (km)

Max Distance

from Colony (km)

AbdInc 20 (12) 183 (179) 68 (56) Inc 350 (74) 3,282 (870) 1,081 (415)

Inc* 373 (175) 2,672 (1,235) 1,240 (218) Gd 41 (32) 436 (286) 181 (101)

Gd* 66 1117 483 LongGd N/A N/A N/A

LongGd* 184 (57) 1,636 372) 765 (247) Abandon 441 (114) 5,113 (1,520) 1,520 (472)

Abandon* 358 (224) 3,321 (1,623) 1,364 (220)

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Fig, 8. Foraging trips of 20 Wedge-tailed Shearwaters from Muiron Islands deployed with satellite tags in Nov 2018. Trips include those performed during incubation and chick rearing as well as some from adults likely to have abandoned their nest. Each bird represented by a different colour.

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Fig. 9. All foraging trips performed by Wedge-tailed Shearwaters deployed with satellite tags from the Muiron Islands in 2018. The trips likely to represent temporary abandonment of eggs were very close to the colony and are not visible at this scale.

incubation short trips chick rearing long trips chick rearing abandoned eggs

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The home range (95% KUD) of all the WTS deployed with satellite tags covered 1,266,516 km2, but the core foraging habitat (50% KUD) composed approximately 20% of the home

Fig. 10. Foraging trips performed by 2 Wedge-tailed Shearwaters deployed with GPS tags from the Muiron Islands in 2018.

incubation short trips chick rearing

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range (Tables 5 and 6, Fig. 11). The rugosity and an interaction between breeding stage and depth influenced the core foraging areas (Figs 12 a and b). The WTS were less likely to use areas of increased rugosity, and birds undertaking long foraging trips during breeding were more likely to use deeper waters. However, the model explained only 4% of the variance in the distribution of the birds within their core foraging habitat.

Table 5 Total area of the 50% and 95% kernel utilisation distribution (KUD-in km2) calculated from all the Wedge-tailed Shearwaters combined in each breeding stage. The data are likely underestimated due to the inclusion of incomplete trips.

WTS group Tag Type 50% KUD 95% KUD All birds Satellite 262,926 1,266,516

Incubation Satellite 205,902 962,280 Chick-rearing (short

and long trips) Satellite 51,452 366,528

Incubation GPS 30,618 188,082

Chick-rearing (short trips only)

GPS 567 1,944

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Table 6. Utilisation distributions (km2) calculated for individual Wedge-tailed Shearwaters using a data-based “plug-in” bandwidth selector determined for each trip separately. Mean(± SD) and range of the 50 and 95% utilisation distributions for each breeding stage (incubation, short trips during chick rearing, long trips during chick rearing, temporary abandoned eggs and abandoned eggs). Note that the utilisation distributions are likely to be underestimated for all breeding stages except for the short trips during chick-rearing and temporary abandoned eggs, due to incomplete trips.

Incubation Short-Trips Chick Rearing

Long Trips Chick Rearing

Temporary Abandoned eggs

Abandoned eggs

50 44,250 (47,759) 3,061 (4,250) 20,898 (5,697) 999 (866) 91,805 (90,650)

Range 2,187 - 245,997 162 – 15,764 14,094 – 29,403 243 – 1,944 18,306 – 249,399

95 201,734 (175,769) 12,568 (16,708) 100,132 (30,757) 4,050 (3,774) 489,953 (434,450) Range 13,851 – 914,571 486 – 61,884 68,526 – 149,364 972 -8,262 72,495 – 1,222,452

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Fig. 11. The 50% (green) and 95% (yellow) kernel utilisation distributions for all foraging trips undertaken by all 20 Wedge-tailed Shearwaters from the Muiron Islands deployed with satellite tags in November 2018.

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The 50% KUD of every trip undertaken by each WTS ranged from a few kilometres from the Muiron Islands up to 1900 km from the island (Figs. 13 - 15). They were generally located north-west of the colony, though areas west and south-west of the colony were also used. The core foraging areas of birds incubating eggs was generally much further from the colony, and encompassed a much larger area compared to the core foraging area of birds rearing chicks (Figs 14 and 15, Table 6). In contrast, the core foraging habitat of those birds that were likely to have temporarily abandoned their eggs was considerably smaller compared to the birds undertaking even short trips during chick rearing. This is not surprising given that that these birds used areas much closer to the colony and were absent for the least amount of time (Figs 14 and 15, Table 6). The core foraging habitat of those birds that likely abandoned eggs was larger than for all other birds, but was located within the overall region used by all the WTS.

Fig 12. Effect of individual smoothed continuous predictors on the location density of Wedge-tailed Shearwaters in the best-fitting, most parsimonious generalised additive mixed model (GAMM) a) rugosity and b) an interaction between breeding stage and water depth. The three breeding stages are incubation (red), short trips during chick rearing (blue) and long trips during chick rearing (black)

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Fig. 13. The 50% kernel utilisation distributions for all foraging trips undertaken by each of the 20 Wedge-tailed Shearwaters from the Muiron Islands deployed with satellite tags in November 2018. One to six foraging trips/bird. One colour used per bird, different shading per trip

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Fig. 14. The 50% kernel utilisation distributions for foraging trips by 20 Wedge-tailed Shearwaters from Muiron Islands during incubation phase. Short trips undertaken by birds temporarily abandoning eggs are included. The shearwaters were deployed with satellite tags in November 2018. One colour used per bird, different shading per trip

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Fig. 15. The 50% kernel utilisation distributions for short and long foraging trips by 8 Wedge-tailed Shearwaters from Muiron Islands during the chick rearing phase. The shearwaters were deployed with satellite tags in November 2018. One colour used per bird, different shading per trip

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DISCUSSION

The foraging habitat of WTS during both incubation and chick rearing periods was identified using both satellite and GPS tags. This is the first time that the foraging patterns and distribution of incubating WTS have been documented globally. Furthermore, it was shown that the WTS rearing chicks engaged in a bimodal foraging strategy, completing both short (< 4 day) and long (>7 day) trips. Whilst it was not possible to verify that the birds were rearing chicks, their behavioural patterns were similar to that identified for WTS raising chicks at the Great Barrier Reef (McDuie et al. 2015). Additionally, the short trips followed the initial long trip, and often a second one, undertaken by a WTS, and these log trips were > 10 days in duration (complete trips only). It is thus likely that trips performed by WTS rearing chicks have been captured.

The WTS used an area that ranged from 100°E to 120°E, and from the Cape Range Canyon to south of the Indonesian Archipelago. This same area also formed part of the extent used by migrating and non-breeding WTS from both Pelsaert Island and the Houtman Abrolhos (Surman et al. 2018). A consistent pattern for the WTS to forage near, but not necessarily directly on, seamounts, was identified. This pattern occurred during both the incubation and to a lesser extent during long foraging trips whilst chick rearing. Whilst the faunal assemblage of seamounts is not well known, they appear to have high productivity and support diverse benthic and pelagic consumers (Clark et al. 2010). Indeed, higher reef patch complexity is associated with increased fish biomass and abundance (Fisher et al. 2018). Seamounts are focal foraging areas for seabirds (Haney et al. 1995, McDuie et al. 2015), and appear to be particularly important for seabirds that forage in tropical waters, where prey are more patchily distributed compared to temperate and polar waters. The seamounts used by the WTS in this study appear to also be important for other marine megafauna such as whalesharks (Arrowsmith unpubl. data). As this area is devoid of other oceanographic features that are associated with increased prey availability, such as upwellings (Pattiaratchi pers. comm.), it is not surprising that the seamounts are used by a range of marine fauna.

The habitat used by WTS performing short foraging trips during chick rearing were < 300 km from the colony, and the trips were typically <3 days. This is similar to WTS from Lord Howe Island (Peck and Congdon 2005), and at the Seychelles (Catry et al. 2009). However, the WTS in this study also engaged in a bimodal foraging strategy, undertaking long foraging trips after a series of short foraging trips. Similar to the WTS at the Great Barrier Reef, this suggests that prey availability close to the colony are inadequate for the large numbers of breeding shearwaters to maintain a critical body mass necessary for continued breeding (Congdon et al. 2005). Local waters were also found to be important for those birds that seemingly temporarily abandoned eggs. Such temporary abandonment usually occurs if the partner feeding at sea has been gone too long, and the body condition of the incubating partner has reduced below a critical threshold. This pattern of behaviour and the

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requirement to use waters close to the colony has not previously been documented for WTS.

The consistency of the seamount habitats used by WTS during incubation indicates the significance of this habitat for the WTS. Unfortunately, these habitats have not been captured within the BIA for WTS. Nor are they likely to be, as they generally lie outside the Australian EEZ, and BIAs must lie within the EEZ. However, other areas used by chick-rearing WTS do lie within the EEZ. As such, it is recommended that the results from this study be used to refine the mapped BIA for WTS in this region.

Unfortunately, no data were obtained from the majority of the GPS tags. However, the data obtained were significant. Not only did they detail high resolution movements of the WTS, but they verified the interpolation performed for the satellite tag data. Thus, it is recommended that a combination of tags should be used in future tracking studies of WTS. This tracking study was performed during a single breeding season of WTS. To confidently conclude habitat preferences and, it is recommended that tracking studies of the WTS should be undertaken across multiple years. This is because the foraging behaviour and habitat of WTS, and other seabirds, has been shown to vary between years (e.g. Bogdanova et al. 2014), being influenced by changes in the distribution of their prey by natural and anthropogenic impacts (e.g. Peck et al. 2004, Crawford et al. 2008). Additionally, the degree of foraging plasticity inherent within a colony can have ramifications on the survival of the colony (e.g. Paiva et al 2014), particularly if their food resource in preferred foraging areas diminishes. This information can be pivotal for informing management strategies for WTS on the Muiron Islands.

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