J Ornithol (2010) 151:755–759 DOI 10.1007/s10336-010-0504-1
SHORT NOTE
A virgin flight across the Tasman Sea? Satellite tracking of post-fledging movement in the Australasian Gannet Morus serrator Stefanie M. H. Ismar • Colin Hunter Kevin Lay • Tamsin Ward-Smith • Peter R. Wilson • Mark E. Hauber
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Received: 31 October 2009 / Revised: 12 January 2010 / Accepted: 2 February 2010 / Published online: 27 February 2010 Ó Dt. Ornithologen-Gesellschaft e.V. 2010
Abstract New technologies enable tracking of the route, duration, and destination of previously unassessed longdistance movements. Fledgling Australasian Gannets Morus serrator from breeding populations in New Zealand had been reported to fly across the Tasman Sea to Australia, with this historic knowledge derived from the recovery of banded carcasses and from observations of initial flight direction. We deployed Argos satellite devices on ten M. serrator fledglings at Cape Kidnappers Gannetry, North Island, New Zealand, across 2 years. Birds that were tracked leaving the colony initially appeared to have landed on the sea. A male bird and two female birds were tracked moving along the east coast to the south tip of New Zealand. The two females then crossed the Tasman Sea to eastern Australian coastal waters in 4 and 5 days,
respectively. We suggest that, contrary to historic reports, the route via Stewart Island constitutes a realized migration path for fledglings from Cape Kidnappers, which might minimize the distance traveled across the open sea to southeastern Australia or Tasmania. Our results further imply that initial direction of flight needs not be indicative of the subsequent migration route taken by M. serrator. This highlights the importance of direct tracking technology for adequate assessment of dispersal and migration in seabirds and other highly mobile species. Keywords Seabird
Argos Migration route Satellite telemetry
Introduction Communicated by P. H. Becker. S. M. H. Ismar (&) M. E. Hauber School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1143, New Zealand e-mail:
[email protected] C. Hunter K. Lay SIRTRACK Limited, Private Bag 1403, Goddard Lane, Havelock North 4157, New Zealand T. Ward-Smith Cape Kidnappers and Ocean Beach Wildlife Preserve, 90 Kennedy Road, Napier, New Zealand P. R. Wilson 17 Mondena Crescent, Glendowie, Auckland, New Zealand M. E. Hauber Department of Psychology, Hunter College of the City University of New York, New York, NY 10065, USA
In recent years, applications of tracking technology have revolutionized the understanding of movement and migration in avian species (Gill et al. 2009), including the Northern Gannet Morus bassanus (Garthe et al. 2007; Lewis et al. 2002; Hamer et al. 2000). Comparative information is wanting for the post-fledging movements in the Australasian Gannet Morus serrator, as well as for fledglings of the related Northern Gannet. Australasian Gannet fledglings are reported to migrate from their New Zealand breeding grounds across the Tasman Sea to Australia when taking flight, supposedly either utilizing the Cook Strait or traveling around North Cape (Fig. 1a) (Nelson 1978; Wodzicki 1967; Wodzicki and Stein 1958). This would involve a journey across the open sea of up to 5,000 km (Nelson 1978). While the distances covered in this presumed ‘‘virgin flight’’ appear well within the range of fledgling flights in the related Northern Gannet of 4,000–6,000 km (Nelson 2002), so far there is no direct
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Fig. 1 a Supposed migration routes of Australasian Gannets Morus serrator banded at Cape Kidnappers; modified from Nelson (1978); b flightpath of an Australasian Gannet fledgling from Cape Kidnappers M-74705, male (circles) to Stewart Island 12.–8.03.2008; c migration routes of two female Australasian Gannet fledglings M-91208
(diamonds) and M-91209 (triangles) across the Tasman Sea to Australia tracked with Argos GIS device; full arrows signals within the same or from consecutive days; dashed arrows several days between transmissions; plots ArcMap 9.3
evidence from a live fledgling M. serrator of either its exact destination or course of movement. Historical evidence of post-fledging flight routes for the Australasian Gannet is based on the directions taken by fledglings when departing from their natal colonies (Nelson 1978; Wodzicki and Stein 1958). The eventual destinations, in turn, have been inferred from the recovery of banded carcasses of juveniles (Stein and Wodzicki 1955; Wodzicki and Robertson 1953). Much of the nestling banding work for these studies was carried out at two locations on the east coast of the North Island of New Zealand, at Horuhoru Gannetry and at the Cape Kidnappers Plateau Colony (Wodzicki and Stein 1958). A summary of the supposed fledgling migration routes in Australasian Gannets ringed at Cape Kidnappers (Fig. 1a) is provided by Nelson (1978). Here, we report the first direct flight
route data of New Zealand-hatched M. serrator fledgings from their natal colony using tracking through satellite tagging.
Methods To generate direct data on the initial movements of gannet fledglings, ten M. serrator nestlings were measured and equipped with Argos satellite tags (Nicholls and Robertson 2007; Nicholls et al. 2007) with five individuals each tagged on 12.03.2008 and on 06.03.2009, respectively, (Table 1) at Cape Kidnappers Plateau Colony (39°380 S, 177°050 E). For full details of methods and the study site see Ismar et al. (2010). Morphometric measurements of exposed culmen, bill width, bill depth, and right tarsus were taken to the
Table 1 Measurements (in mm), PCR sexing results and device IDs of ten satellite-tagged Australasian Gannet Morus serrator fledglings Bird
Argos no.
Sex
Bill Width
Depth
Length
Tarsus
Tail
Wing
Last signal on colony
Last signal
M-74710 M-74705
83089 83090
M M
26.50 25.43
32.94 33.30
85.57 89.18
61.81 60.61
141 152
473 461
20.03.08 12.03.08
21.03.08 28.03.08
M-74694
83091
F
25.66
31.76
90.39
59.57
182.7
474
14.03.08
16.03.08
M-74666
83092
M
26.74
32.55
87.51
64.72
182
483
15.03.08
23.03.08
M-74686
83093
M
25.99
32.72
91.62
63.22
154
466
19.03.08
24.03.08
M-91226
93334
M
23.52
28.67
83.86
58.88
156
349
16.03.09
26.03.09
M-91217
93331
F
24.14
29.59
87.92
55.52
184
391
15.03.09
15.03.09
M-91208
93333
F
24.75
29.42
90.00
62.61
173
410
11.03.09
22.03.09
M-91209
93335
F
23.82
30.78
90.33
64.92
163
417
13.03.09
25.03.09
M-91218
93332
M
24.52
30.08
87.01
60.25
126
396
13.03.09
14.03.09
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nearest 0.01 mm using callipers; the flattened wing chord of the right wing and tail length were measured to the nearest 0.5 mm using a wing ruler and ruler. The 55-g (*1.8% of fledgling weight) KiwiSat202 satellite tags were programmed with a 60-s repetition rate and transmission from UTC 0700–1100 hours daily, for a 215-day life. One location per hour can be expected at this latitude (Guan Oon, CLS Argos Australia, personal communication). In 2008, the tags were attached with Tesa tape (Ballard et al. 2001) to seven layers of lower back plumage, crossweaving the layers of tape around the device to cover its full length. In 2009, the underside of the tag was glued to three central rectrices, taped around these tail feathers with Tesa tape, and secured with two cable ties. Each fledgling was watched for 5 min after deployment to make sure the birds settled back on their nest sites within the colony. The average time between deployment of the devices and fledging was 7 days (range 1–11 days), followed by an average obtained tracking time of 7 days at sea (range 1–17 days; Table 1). The selected birds had been blood sampled and individually marked with metal bands previously between 18.02 and 20.02 amongst 40 handled fledglings in 2008, and between 16.02 and 18.02 amongst 32 fledglings with relatively well-developed flight plumage in 2009. The sex of the gannets was identified from DNA samples following Daniel et al. (2007). Argos satellite data were downloaded daily, and checked for quality. Only signals with a quality attribute of 2, corresponding to an error radius of\500 m, or better were selected for analyses in the 2008 dataset; for analyses of cross-Tasman migration in 2009, lower quality signals were also included if the error radius did not exceed 10 km. Data were plotted in ArcGIS after conversion to the New Zealand Map Grid to achieve high precision for Hawke Bay and New Zealand coastal tracks in 2008 (Fig. 1b), and plotted on an ArcGIS worldmap after ITRF2005 calculation of coordinates of cross-Tasman flight routes in 2009 (Fig. 1c). Tagged fledgling M-74666 was seen to be crop-fed once (on 20.02.2008) by a marked hybrid son [M-77260 (right foot), B60 (left foot); Robertson and Stephenson 2005] of a Cape Gannet M. capensis male and an Australasian Gannet female, observed breeding at a neighboring nest site at Cape Kidnappers throughout the 2007–8 season (S.M.H. Ismar et al., unpublished data), and thus incidentally may be an F2 hybrid offspring; no data on migration were received from this fledgling’s tag. To test for possible correlations between morphometric parameters and deployment or survival times, linear regression analyses were conducted in SigmaPlot 11.0 with culmen, bill width, bill depth, tarsus, and wing chord, each as an independent variable respectively, and deployment time as days from fledging to last transmission from the device as the dependent variable.
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Results In 2008, a male Australasian Gannet fledgling banded as M74705 took flight within 1 day of deployment in a northward direction, then turned west into Hawke Bay and appeared to settle on the water overnight, with the track showing the drift patterns of tidal currents. This bird consequently followed the shoreline northward over 4 days, showing drift with tides again within Hawke Bay before starting a southward flight along the North Island eastern coastline on 17.03.2008. This bird passed East of Cook Strait on 18.03.2008, continuing to head south along the east coast of the South Island. Two transmissions received on 20.03.2008 showed it off Banks Peninsula, and a final transmission 8 days later, at 10:45 GMT 28.03.2008, located the bird on the Foveaux Strait, between the southern tip of the South Island and Stewart Island (43°140 S, 174°540 E; Fig. 1b). A position at sea, about 2 km east of Cape Kidnappers Gannetry, was transmitted from a second male fledgling M-74710 on 20.03.2008 following previous signals from the colony itself. The bird was still located on the water the following day, yet closer to its fledging site, south of Sharks Tooth, Cape Kidnappers Peninsula. Positions from the Argos devices on one female (M-74694) and one male (M-74666) fledgling each were lost after first transmissions from Hawke Bay waters on 16.03.2008 and 18.03.2008, respectively, after previous signals from the colony site on land. Low quality transmissions from M-74666, which did not detail position, were received until 23.03.2008. The last reliable transmission from a fifth male fledgling M-74686 was received on 19.03.2008, with all reliable signals of position within the natal colony on land. In 2009, two female fledglings (M-91208, M-91209) took flight on 11.03 and 13.03, respectively. No signals were received from either device during the following days, which might be indicative of the birds sitting on the water, resulting in submerged aerials with the tail-deployment used in 2009. M-91208 was then tracked south of the Cook Strait on the New Zealand east coast (41°460 S 174°270 E) on 15.03.2009. Signals from both tags were again received from east of Stewart Island, 45°450 S 166°040 E and 45°590 S 166°280 E on 18.03 and 22.03.2009, respectively. Consequently, both Australasian Gannets were tracked on their migration to southeastern Australian and Bass Strait coastal waters north of Tasmania on 22.03.2009 (37°500 S, 151°060 E) and 25.03.2009 (40°110 S, 149°550 E). Thus, these fledglings crossed the Tasman Sea covering 1,928 and 1,687 km in 5 and 4 days, respectively. In total, the migration routes these two birds took allowed them to reach Australian waters by traveling 3,069 and 2,811 km from their fledging site. Tags of the other three 2009 fledglings transmitted last reliable signals from the colony on 15.03, 13.03 and 16.03.2009.
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None of the measured morphological parameters were correlated with duration of deployment for our limited sample sizes combined across 2 years (n = 10; culmen: R2 \ 0.01, P = 0.93; bill width: R2 = 15, P = 0.22; bill depth: R2 = 0.01, P = 0.65; tarsus: R2 = 0.05, P = 0.64; wing chord: R2 = 0.05, P = 0.36).
Discussion Our observations present the first tracks of a post-fledging migration across the Tasman Sea in New Zealand-hatched M. serrator. The loss of reliable signals from four of five fledglings in 2008 within the first day of landing on the sea is consistent with the possibility that back feathers are unsuitable for deployment, as has been found with adults of the related Cape Gannet (Ralf Mullers, personal communication). Alternatively, if lost signals represent deaths rather than lost transmitters, we had indeed expected high postfledging mortality in the Australasian Gannet, because estimates are at the scale of approximately 60% of fledglings dying within their first year (Nelson 1978, quoting C. Robertson), with the majority of these deaths occurring in the first few weeks after fledging. Transmissions were lost from all devices within a month of deployment, which is much less than the 215 days of expected battery life. We cannot resolve from these findings if losses of signal were due to eventual detachment of the devices from the birds’ plumage, to eventual failure of the devices, possibly through repeated water impact of high-speed diving, or to the death of the birds, which could indicate a potential negative impact of the deployment on survival. The Australasian Gannet is suggested to typically fledge with sustained flight rather than simply landing on the waters off the colony, contrary to the congeneric M. bassanus (Nelson 1978). In contrast to these reports, all four birds tracked away from the colony in 2008 appeared to have first landed on the water. The lack of transmissions in the first days of tracking in the two fledged females in 2009 is also in line with submerged aerials, indicating these birds also first landed on the water. We thus conclude that Australasian Gannet fledglings, as those of other gannet species, spend time on the water after leaving the colony. With flights to Stewart Island at the southern tip of New Zealand, our data provide examples of a supposedly rarely taken initial route or destination for an Australasian Gannet fledging from Cape Kidnappers (Nelson 1978; Wodzicki and Stein 1958). Indeed, for both gannet fledglings tracked to Australian waters, the migration route via Stewart Island shortened the distance across the Tasman Sea to reach the closest point on the Australian (*2,050 km) or Tasmanian (*2,000 km) Coast by 10–20%, from a minimum of
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2,200 km from the North Cape and 2,400 km from the Cook Strait to reach the closest point on the coast of east Australia. Additionally, this southern route circumvents the reportedly disadvantageous strong winds prevailing in the Cook Strait region (Nelson 1978). Thus, the route over Stewart Islands appears to be a realized migration path amongst the potential range of routes to Australian waters for Australasian Gannet fledglings from Cape Kidnappers. Our results also imply that initial flight direction at fledging does not necessarily conform with a predominantly northward migration route in Australasian Gannets that would be eventually traveling west over the North Cape (Wodzicki and Stein 1958), as previously suggested. These findings hence underline the importance of applying sophisticated tracking technology to assess post-fledging migratory behavior, route, speed, and destination in this and other seabirds, as well as other long-distance migrants.
Zusammenfassung Ein Jungfernflug u¨ber die Tasmanische See? Satellitenverfolgung der Bewegungen nach dem Ausfliegen bei Australto¨lpeln Morus serrator Neue Technologien ermo¨glichen ein Verfolgen von Route, Dauer und Ziel zuvor nicht erfasster Langstrecken-Bewegungen. Es war berichtet worden, dass flu¨gge Australto¨lpel Morus serrator aus neuseela¨ndischen Brutpopulationen u¨ber die Tasmanische See nach Australien fliegen; diese historischen Kenntnisse stammten von Todfunden beringter To¨lpel sowie Beobachtungen der Anfangsflugrichtung. Wir haben u¨ber zwei Jahre Argos-Satellitensender an zehn M. serrator-Flu¨gglingen aus der Cape Kidnappers To¨lpelkolonie auf der Nordinsel Neuseelands befestigt. Vo¨gel, die verfolgt wurden, als sie die Kolonie verließen, schienen zuna¨chst auf dem offenen Meer gelandet zu sein. Ein ma¨nnlicher und zwei weibliche Vo¨gel wurden verfolgt, wa¨hrend sie entlang der Ostku¨ste zum Su¨dzipfel Neuseelands flogen. Die beiden Weibchen u¨berquerten dann die Tasmanische See bis in ostaustralische Ku¨stengewa¨sser in vier beziehungsweise fu¨nf Tagen. Wir schlagen vor, dass entgegen historischer Berichte die Route u¨ber Stewart Island einen realisierten Zugweg fu¨r Flu¨gglinge von Cape Kidnappers darstellt, der die Entfernung, die u¨ber die offene See nach Su¨dost-Australien oder Tasmanien zuru¨ckgelegt wird, minimieren ko¨nnte. Unsere Ergebnisse deuten außerdem darauf hin, dass die anfa¨ngliche Flugrichtung nicht unbedingt die nachfolgend von M. serrator gewa¨hlte Zugroute anzeigen muss. Dies unterstreicht die Bedeutung direkter Verfolgungstechnologie fu¨r die ada¨quate Einscha¨tzung von Ausbreitung und Zug bei Seevo¨geln und anderen sehr mobilen Arten.
J Ornithol (2010) 151:755–759 Acknowledgments This study received funding from Education New Zealand to S.M.H.I., and from the University of Auckland to M.E.H. The project was subvented by SIRTRACK in the frame of work at the Cape Kidnappers and Ocean Beach Preserve, and was carried out under government and institutional research permits. Our thanks go to the Napier DoC Office for their kind permission to use their field facility and to Cape Kidnappers landowners and farm managers for friendly admission to their property. We would like to acknowledge N.L. Chong, D. Dearborn, A. Gager, I. Richling, W. Boeckeler, and G. Machovsky-Capuska for help in the field, and G. Ballard, T. Landers, J. Mackay, B. Igic, R. Mullers, M. Rayner. and anonymous reviewers for helpful discussions.
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