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Trull et al.: Catching Wilson’s Storm Petrels at sea 125

Marine Ornithology 46: 125–127 (2018)

125

INTRODUCTION

Several species of oceanic birds in the order Procellariiformes migrate annually from their polar and subpolar Southern Hemisphere breeding grounds to Northern Hemisphere waters for the non-breeding period. Studying these species at sea is inherently challenging due to the complex logistics of working in pelagic marine environments. Moreover, catching seabirds undergoing challenging life-history phases (i.e., migration, molting) and subjecting them to potentially harmful capture stress and handling (Smith et al. 1994, Deguchi et al. 2014) presents ethical concerns, especially since global seabird populations declined up to ~70% between 1950 and 2010 (Paleczny et al. 2015).

Previous methods for catching live birds at sea (e.g., Gill et al. 1970, Bugoni et al. 2008, Ronconi et al. 2010) include the use

A NEW METHOD FOR CATCHING WILSON’S STORM PETRELS OCEANITES OCEANICUS AT SEA

PETER F. TRULL1, SUSAN FINNEGAN2 & AUSTIN J. GALLAGHER3,4

1Cape Cod Lighthouse Charter School, Harwich, MA 02645, USA 2Cape Cod Museum of Natural History, Brewster, MA 02631, USA

3Beneath the Waves, PO Box 126, Herndon, VA 20172, USA ([email protected]) 4Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33146, USA

Received 14 May 2018, accepted 03 July 2018

ABSTRACT

TRULL, P.F., FINNEGAN, S. & GALLAGHER, A.J. 2018. A new method for catching Wilson’s Storm Petrels Oceanites oceanicus at sea. Marine Ornithology 46: 125–127.

Catching oceanic birds is challenging for researchers interested in studying migration and feeding dynamics. To address that challenge, we evaluated a new method for catching Wilson’s Storm Petrels Oceanites oceanicus at sea. Using an extended butterfly net and a sweeping technique, we successfully captured 50 sub-adult and adult storm petrels offshore in the Northwest Atlantic with a 94% success rate. All were processed without sign of physical trauma or injury; 100% flew off in apparently good condition. This method provides a cost-effective and safe approach for the capture and study of small oceanic birds attracted to fish slicks.

Key words: capture, net, oceanic bird, petrel, seabird

of modified hoop-nets with 2–3 m of line attached thrown from a vessel to catch shearwaters and petrels nearby. Other researchers have captured shearwaters and alcids at sea after dark using a combination of spotlights and dipnets (Whitworth et al. 1997, Adams et al. 2012) or collected storm petrels using a net-gun (Stephenson et al. 2008). These methods put birds at risk of becoming at least partially submerged in water, physical injury from entanglement (particularly the wings; Løkkeborg 2011), or capture- induced physiological stress (Smith et al. 1994); such methods also pose a lethal risk of drowning. Therefore, less invasive and more efficient methods would be advantageous.

Wilson’s Storm Petrels Oceanites oceanicus breed on Antarctic/ sub-Antarctic coasts and islands, and they migrate to the western North Atlantic Ocean, arriving off the coast of Massachusetts (USA) in May and June (Nisbet et al. 2013). Here we discuss a

Fig. 1. (a) Modified butterfly net and sweeping posture used offshore when catching Wilson’s Storm Petrels. (b) A live petrel is caught mid-air. Note the small area, size of mesh, and protective modifications around the perimeter of the net. (c) A petrel is processed after being removed from the net.

(a) (b) (c)

126 Trull et al.: Catching Wilson’s Storm Petrels at sea

Marine Ornithology 46: 125–127 (2018)

previously undescribed, safe, and effective technique for catching this species at sea, which will allow further investigation of their wintering ecology.

METHODS

On 07 and 10 July 2011, we drifted in a 12 m commercial fishing vessel on the continental shelf 10 km east of Chatham, Massachusetts in a known corridor for storm petrel austral migration. Sea conditions on both occasions were 1 m swells and winds of 10–15 knots (19–28 km/h) with warm, clear skies. Once at the site, we used mashed livers from spiny dogfish Squalus acanthias to create an oily slick on the water’s surface. Within five minutes, this attracted a variety of seabirds, including gulls (Larus spp.), shearwaters (Ardenna spp., Puffinus spp., and Calonectris spp.), and Wilson’s Storm Petrels. At any given time, 5–10 storm petrels were observed around the boat. We targeted them with a long-handled (200 cm), circular-rimmed (40 cm circumference) Cumings dipnet (Fig. 1a), which had a net made of 0.6 mm Micromesh insect netting. The metal rim and wooden handle of the net were wrapped with Thermo King foam pipe insulation to protect birds in case of contact during capture (Fig. 1b). As petrels were attracted by the chum, we used a sweeping technique to capture the birds while they hovered and fed close to the boat (Fig. 1b). Birds were gently removed from the net (Fig. 1c) and placed in small cotton bags (attached to a line with a clothespin) to await processing.

For processing, each bird was banded with a US Fish and Wildlife size 1A stainless steel band; pictures were taken of the wing, tail, and claws; ages were determined based on the shape of their primary and tail feathers (Pyle 2008, Table 1); and feather samples were collected for a separate study using stable isotopes to infer feeding and molting. All birds were then released and were given a release condition score ranging from one to three: (1) poor, bird unable to fly; (2) fair, bird can fly but shows signs of distress or impairment; or (3) good, bird flew off unabated.

RESULTS

A total of 53 sweeps at petrels was attempted over two days, resulting in 50 individually captured birds—a 94% success rate. Only one bird was captured at a time, and no birds escaped the net. Our bycatch rate was 0%, meaning no other species were incidentally captured. Average handling time, defined as the time measured from when a bird was captured to when it was removed for pre-processing, was 10 seconds. We captured 5–10 birds at a time and would start chumming again while working on the last bird. Age analysis revealed that 50% of individuals were adults (25 birds), 42% were immature (21 birds), and 6% were of unknown age (3 birds). We observed no injuries or signs of physiological stress, such as rapid vibration or shaking; all birds showed movement and signs of vitality during and after capture. Upon release, all birds consistently demonstrated characteristic flight behaviors (i.e., shallow wingbeats and immediate robust fluttering flight), with 100% of birds scoring a class 3 release condition.

DISCUSSION

When banding birds, researchers must assess the capture method to ensure it is done safely and effectively. Previous methods for capturing waterbirds or birds at sea required close supervision to prevent injury or drowning. These methods had variable effectiveness and affected both target and non-target species.

One difficulty with daytime sampling is easy evasion by birds, which is less of an issue when spot-lighting at night. In one of the earliest described methods of capturing Procellariiformes at sea during daylight hours, Gill et al. (1970) used a “hoop” net thrown from a vessel. The circular plastic tubing, about 1.3 m in diameter and covered with mist netting, would land over swimming or flying birds. Upon retrieval, birds often rolled out of the net and escaped, thereby limiting the reliability of the method. Bugoni et al. (2008) described a method for catching pelagic seabirds away from nesting areas using a weighted hand-thrown net like those used in shallow tropical waters for catching small fish. This type of net, secured to the thrower by a line, is cast from a vessel and falls over the target birds, which are entangled and brought to the boat. This method was effective in catching a high number and a diverse selection of birds, but it was not completely selective and produced high bycatch. Birds caught with this method became wet and risked both hypothermia and drowning. The authors concluded that this was not an effective way to catch Wilson’s Storm Petrels because the species rarely sits on the water.

Our “butterfly net” method solves the abovementioned issues of effectiveness, safety to target species, and bycatch. We were able to limit the number of captures so that we could process the birds

TABLE 1 Summary of age classes and release condition scores for Wilson’s

Storm Petrels captured using the “butterfly net” method

Bird ID

Age Classa

Release Condition

Bird ID

Age Class

Release Condition

001 SY 3 026 AHY 3

002 AHY 3 027 HY 3

003 HY 3 028 HY 3

004 SY 3 029 HY 3

005 AHY 3 030 AHY 3

006 AHY 3 031 AHY 3

007 AHY 3 032 AHY 3

008 AHY 3 033 AHY 3

009 HY 3 034 HY 3

010 HY 3 035 AHY 3

011 HY 3 036 HY 3

012 AHY 3 037 HY 3

013 AHY 3 038 AHY 3

014 AHY 3 039 AHY 3

015 HY 3 040 AHY 3

016 HY 3 041 AHY 3

017 AHY 3 042 AHY 3

018 HY 3 043 U 3

019 AHY 3 044 U 3

020 AHY 3 045 HY 3

021 HY 3 046 AHY 3

022 HY 3 047 HY 3

023 HY 3 048 HY 3

024 HY 3 049 HY 3

025 AHY 3 050 U 3 a SY/AHY (Second Year/After Hatch Year) = adult, HY (Hatch

Year) = immature, U = unknown age

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Marine Ornithology 46: 125–127 (2018)

in a timely manner, and no birds ever escaped the net. Since the birds were captured in flight and never submerged, they faced no drowning risk and were not waterlogged, allowing immediate release and alleviating the need to hold birds for an extended period until their feathers dried. In addition, no bycatch occurred. We recognize that we tested this method for only one species of oceanic bird across a limited morphological size range. However, given the general lack of information on Wilson’s Storm Petrels, our approach may prove useful for future studies seeking to capture storm petrels attracted to fish slicks.

ACKNOWLEDGEMENTS

We thank Teddy Ligenza for logistical support. Funding for this research was provided by the Blake-Nuttall Fund from the Nuttall Ornithological Club. PT and SF conceived the study and performed the field work; PT, SF, and AJG wrote and prepared the manuscript. All research was approved under master permit #23076 to SF. The paper was improved by addressing comments from Josh Adams and David Ainley.

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