Australian Field Ornithology 2021, 38, 49–55http://dx.doi.org/10.20938/afo38049055

Introduction

The Australian Fairy Tern Sternula nereis nereis (hereafter Fairy Tern) is a gregarious, coastal seabird whose small populations are widely dispersed over a vast stretch of the Australian coastline (Commonwealth of Australia 2019). It exploits a variety of coastal breeding habitats, but most commonly selects coarse-grained sandspits and beaches of the mainland, river mouths, salt lakes and nearshore islands (Higgins & Davies 1996; Johnstone & Storr 1998; Greenwell et al. 2021). It was listed as threatened (Vulnerable) under the Environment Protection and Biodiversity Conservation Act 1999 in 2011, having suffered an estimated 24% population decline over the three decades preceding 2007 (DSEWPC 2011; Threatened Species Scientific Committee 2011).

Regular monitoring is critical to determine breeding success and identify site threat profiles, and is a key action to measure the success of recovery actions under the Draft National Recovery Plan for the Australian Fairy Tern (Sternula nereis nereis) (Commonwealth of Australia 2019). The tendency of Fairy Terns to frequently shift colony locations (Dunlop & Greenwell 2020; Greenwell et al. 2021) adds to the difficulty of regular monitoring of colonies, particularly when efforts are limited to coastal public land and wildlife agencies or non-government organisations with limited resources. To support management efforts and expand opportunities for the monitoring of colonies, citizen science programs, e.g. the Beach-nesting Birds Program (BirdLife Australia 2020) and Western Australian Fairy Tern

Network (Conservation Council of Western Australia 2020) have been established in several Australian states. As part of these programs, training and monitoring protocols are required for key stakeholders to promote best practice and ensure that consistent measurements are recorded over time.

Bird-banding studies are often used to gather information about the habits, life histories, plumage development and movement patterns of birds, and to provide data to inform species conservation and management (Lowe 1989). Although readable bands and colour-bands enable information about individuals to be collected without the need for recapture, these longer-term marking techniques may not be appropriate for short-term field studies or the banding of pulli, which are unable to carry large or multiple bands.

The objectives of this study are to (i) describe plumage development and general age-related behaviour in juvenile Fairy Terns, from hatching through to early moult, using direct observations and photographic recapture of individually marked birds; and (ii) assess the effectiveness of nail varnish painted on Australian Bird and Bat Banding Scheme (ABBBS) bands as a temporary colour-marking method for recognising individual birds in the field and describing development of juvenile plumage. Higgins & Davies (1996) described juvenile plumages but recognised the need for more thorough studies of plumage development.

Application of a novel banding technique and photographic recapture to describe plumage development and behaviour of

juvenile Fairy Terns

C.N. Greenwell1,2*, D. Sullivan3, N. Goddard4, F. Bedford5 and T.K. Douglas3

1Environmental and Conservation Sciences, College of Science, Health, Engineering and Education, Murdoch University, 90 South Street, Murdoch WA 6150, Australia

2Centre for Sustainable Aquatic Ecosystems, Harry Butler Institute, Murdoch University, 90 South Street, Murdoch WA 6150, Australia3BirdLife Australia, Suite 2–05, 60 Leicester Street, Carlton VIC 3053, Australia

4Western Australian Fairy Tern Network, Conservation Council of Western Australia, Lotteries West House, 2 Delhi Street, West Perth WA 6150, Australia

5Department of Environment, Land, Water and Planning, 574 Main Street, Bairnsdale VIC 3875, Australia*Corresponding author. Email: cgreenwell@iinet.net.au

Abstract. The Australian Fairy Tern Sternula nereis nereis is a seabird that breeds along the coast and whose small populations are dispersed over vast stretches of the Australian seaboard and nearshore islands. In recent years, citizen science programs have been developed to bolster monitoring efforts to better understand breeding success and identify site threat profiles. The development of protocols that facilitate the collection of consistent measurements is important for long-term monitoring of this threatened (Vulnerable) species. This study describes plumage development and age-related behaviour in juvenile Australian Fairy Terns using direct observations and photographic recapture of individually marked birds. This information may be used as the basis for the development of a field ageing guide, enabling the collection of standardised information on colony demographics and juvenile development. A temporary colour-banding study was trialled by painting nail varnish onto 15 Australian Bird and Bat Banding Scheme (ABBBS) incoloy bands, avoiding the need to band nestlings with additional readable or PVC colour-bands. The varnish remained intact, albeit chipped, on four surviving birds that were resighted ≤80 days after banding, enabling the identification of individuals away from the colony site, without the need for recapture. The temporary marking of ABBBS bands using nail varnish offered an effective short-term solution for identifying individual juvenile Fairy Terns in the field and for describing plumage changes over a period of c. 3 months.

50 Australian Field Ornithology C.N. Greenwell et al.

Study site and methods

This study combines structured and opportunistic field observations, bird-banding and photographic recapture to describe feather development and age-related behaviour in juvenile Fairy Terns. Photographs of typical plumage stages were used to describe changes in feather development at the colony site, and successive sightings of banded birds away from the breeding colony were used to compare and describe plumage changes over time when fledged juveniles were found ~30 km south of the natal colony. The information and images collected from breeding sites of Fairy Terns in Western Australia were compared with data collected in Victoria (Department of Environment, Land, Water & Planning unpubl. data) to confirm consistency between states and have been used as the basis for the development of a field ageing guide, enabling the visual assessment of colony demographics.

To investigate the prevalence of plumage colour at the time of hatching, observations of chick coloration were made at North Fremantle, Western Australia (Rous Head, 32°02′27″S, 115°44′23″E) in December 2018. The colour of chicks (n = 63) from 47 nests was recorded soon after hatching, but once completely dry, as either silver (i.e. white/grey) or gold (i.e. sandy/yellow). Supplementary observations of chick coloration (n = 30) were made at Penguin Island, Shoalwater Bay (32°18′21″S, 115°41′35″E), in January 2020, while chicks remained in their nest-cups.

To describe feather development in Fairy Terns, 15 1–4-day-old Fairy Tern chicks, from one-egg (n = 5) and two-egg (n = 5) clutches, were banded on Penguin Island between 7 and 10 January 2020 as part of a broader study investigating the ecology, behaviour and substrate preferences of the Fairy Tern, in four colonies around Perth, Western Australia, between 2018 and 2020 (see Greenwell et al. 2021).

To identify individual Fairy Terns at the colony site, size 4 incoloy metal Australian Bird and Bat Banding Scheme (ABBBS) bands were painted with nail varnish of one of 15 different colours. Incoloy is a durable alloy of nickel, chromium and iron, used for seabird bands (Kadlec 1975). Nail varnish was painted onto each band and allowed to air dry before a second coat was applied. Ten of the painted bands were cured for 7 days and a further five were cured for <7 hours. A range of brands of nail varnish was utilised for the study, selected to provide a broad spectrum of easily differentiated colours. No band preparation (e.g. sanding) was undertaken before painting the bands.

Since the initial objective of this banding study was only to follow individual, juvenile Fairy Terns whilst they remained at the colony site, longer-term marking methods (e.g. readable bands, PVC colour-bands) were not needed. This also ensured consistency with a pre-existing, ongoing cohort banding study of Western Australian Fairy Terns (Dunlop & Greenwell 2020), and there were no possible welfare issues of additional encumbrance to very small chicks.

An attempt to photograph banded juveniles was made each day (except 13 and 20 January 2020) from the outskirts of the colony, until the last individual left the island on 5 February 2020. Because of the tendency of juveniles to hide in vegetation or within chick shelters, and also to minimise colony disturbance, not every individual was

photographed each day. Ten of the 15 banded juveniles successfully fledged and left the colony site 4–8 days after fledging.

On 6 February 2020, one banded juvenile was photographed on the Peel–Harvey Estuary, Mandurah (32°31′14″S, 115°43′00″E), ~24 hours and ~30 km south of the last sighting of this individual on Penguin Island, where it was tended and fed by adults. Subsequently, opportunistic surveys were made of other locations within the Peel–Harvey Estuary, by foot around Nairns, Coodanup, and by kayak around Creery and Boundary Islands and the exposed sandbanks surrounding these estuarine islands, between 7 February and 23 April 2020. Any banded juvenile sighted during these surveys was photographed.

Results and discussion

Two variations of colouring of the dorsal feathers were recorded on the Fairy Tern chicks, silver and gold (as recognised by Higgins & Davies 1996), but all chicks had white underparts. At North Fremantle, silver-morph chicks (70%, n = 44) outnumbered gold-morph chicks (30%, n = 19), and in 16 nests where two chicks were recorded, there was one of each morph in 44% (n = 7), two silvers in 44% (n = 7) and two golds in 12% (n = 2). At Penguin Island, the proportions of silver (47%, n = 14) and gold (53%, n = 16) morphs were nearly equal. Of the subset of nests (n = 24) where chicks hatched, six contained two chicks, and a single chick was observed in the remaining 20. From this small sample, there was one of each morph in 50% (n = 3), two golds in 33% (n = 2) and two silvers in 17% (n = 1). The degree of dorsal patterning varied considerably among individuals at both sites, ranging from almost none through to heavy dark-coloured patterning (Figure 1a).

Development of juveniles

On hatching, the feet and legs of Fairy Tern chicks were pinkish, the body was covered in down and the bill was brown with a prominent white egg-tooth at the tip of the upper mandible (Figure 1a). Residue from the egg-membrane was often visible on the down, particularly around the mantle, for the first 2 days after hatching, giving a slightly matted appearance, but this feature was less obvious when observing from a distance. Chicks and adults exhibited strong site-fidelity during this period, although adults moved nestlings between scrapes or to nearby colony landmarks where they were well-camouflaged (e.g. edge of vegetation, seagrass wrack or rocks), making full use of their cryptic plumage. Chicks were diligently brooded by the adults, which regularly tented their wings to provide protection, but chicks were occasionally left unattended for brief periods while the adults went fishing (see also Greenwell et al. 2021). From a young age, juveniles dug scrapes in the sand with their feet and largely remained quiet and still except when being fed, as described for the Little Tern Sternula albifrons in the United Kingdom (Davies 1981).

The primary pin-feathers were first visible when the chicks were c. 4 days of age, although pins were difficult to observe when the wings were held against the body (Figure 1b). However, a dark patch at the tip of the flight-

Juvenile Fairy Terns studied by novel banding and photography 51

Figure 1. Fairy Tern typical plumage states from 1 to 23 days of age. Individuals are identified by the colour of their leg-bands, as indicated. (a) One- and 2-day-old siblings, each with a white egg-tooth visible at the tip of the upper mandible (Orange, Mint); (b) primary pin-feathers visible (see left wing) at 4 days (White); (c–d) feathers on the scapular, wing, mantle and back, and primary and secondary feathers starting to break from pins at c. 9 days (Orange); (e–f) distinct rufous crown visible, primaries and secondaries well developed, tail roughly equal in length to resting wing, and brownish chevron markings on coverts, which have rufous margins, at c. 16 days (Red); (g) completely feathered upper and lower body, with little down around nape and crown, at 20 days (Red); and (h) primary and secondary feathers fully developed and bird capable of flight, and little residual down around the crown, at 23 days (Purple). Photos: C.N. Greenwell

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52 Australian Field Ornithology C.N. Greenwell et al.

feather-forming region was visible and was indicative of early pin development. The egg-tooth was barely visible, if at all, and the body remained covered in down. Chicks were relatively mobile but stayed close to the nest-site or took refuge near colony landmarks or within chick shelters selected by the adults. Adults often moved their brood to the periphery of the colony and established scrapes near features that increased the opportunity for shelter. This behaviour likely reduced detection by predators, competition with other terns in the colony, i.e. kleptoparasitism and the potential for alloparental care, and, potentially, ectoparasite loads (Greenwell et al. 2021). Some family units occupied these territories for up to 2–3 weeks until the juveniles fledged, although movement to alternative locations occurred.

At c. 8 days of age, feathers on the scapular, mantle and back tracts started to break from the pins (moult stage 2: see Lowe 1989), although chicks were still largely covered in down (Figure 1c). By 9–10 days of age, primary and secondary feathers started to break from the pins, rectrix pins first became evident, and a rufous collar started to develop (Figure 1d). Juveniles were highly mobile and, although they exhibited strong attachment to particular colony landmarks and territories, they often explored the surrounding environment up to several metres away. Juveniles were frequently left unattended for extended periods whilst the adults were foraging. On 24 January 2020, adults from several nests moved nine of the chicks ~30 m up the beach to a dune system where chicks took refuge in the surrounding vegetation. Adults returned to the original colony site with their chicks within hours, possibly because of the presence of a Black-shouldered Kite Elanus axillarus, which regularly hunted in the area, or interspecific aggression from nesting Bridled Terns Onychoprion anaethetus.

At c. 14 days of age, rufous feathers on the crown started to break through, although the head was still largely covered in down. Wing-coverts, scapular and mantle feathers were well developed, with rufous margins (Figure 1e). A distinct rufous crown was visible by c. 16 days, and by then feathers had started to replace down on the upper body, except for around the forehead, ear-coverts and nape. Primary and secondary flight-feathers were well developed, the tail (several centimetres long) and folded wings were almost equal in length, and dark lores started to develop (Figure 1e, f).

At c. 19–20 days of age, feathers on the lower and upper body completely replaced down, except for remnants around the nape and edge of the crown. Feathers on the body, crown, coverts, scapulars and flight-feathers were well developed, and the bill was about three-quarters of the length of the head. The feathers at the base of the bill, below the lores, had a rufous tone (Figure 1g). Juveniles remained on the outskirts of the colony and on the water-line and several birds were observed drinking and bathing in the shallows. High human foot-traffic on the beach probably largely restricted the movement of the young birds to the roped area of the colony. The juveniles continued to take refuge in chick shelters and among the surrounding vegetation during the heat of the day, particularly whilst adults were off foraging. Juveniles were capable of becoming airborne for several seconds, particularly during strong winds, but were not controlled in their flight (for detail see Greenwell et al. 2021).

At 22–23 days, primary and secondary feathers were fully developed and able to support independent flight. Little down remained around the crown (Figure 1h). Juveniles made short flights close to the colony (for detail on fledging see Greenwell et al. 2021) and rested on the outskirts of the colony and the wet shoreline. They were regularly observed drinking, bathing and picking up algal wrack and shells.

There was relatively little change in plumage between fledging and the time that juveniles left the colony site. All ten surviving banded juveniles left the colony site 4–8 days after fledging and were sighted on the Peel–Harvey Estuary, Mandurah. Not all individuals were observed during each survey on the estuary, which is unsurprising given the large area of the estuary, with numerous sandbars and islands available for roosting. In addition, some individuals might have been foraging during the surveys.

At 27–31 days of age, juveniles had a distinct rufous crown and collar, light-brown bill and legs, a prominent brownish-black semilunar band that extended from the eye to the nape, and the tail was shorter than the resting wing length (Figure 2a, c). Over time, the rufous crown moulted to black, interspersed with white speckling, and the semilunar band darkened (Figure 2b, d). By 65 days of age, the cap and semilunar head-band were black and the bill was longer. In addition, the resting wing length remained greater than the tail length and legs were dark brown. The chevron patterning to coverts on the wings, mantle, and back and scapulars was dark brown and these feathers lacked rufous margins (Figure 2e, g). By 84 days, feathers on the head cap and upper body started to moult and the chevron patterning on the coverts, scapulars and mantle feathers was reduced, resulting in a generally whiter appearance (Figure 2f, h).

No Fairy Terns were sighted around Creery or Boundary Islands after 22 April 2020 when beaches and sandbars were inundated during high tidal fluctuations for at least four consecutive days. It is probable that the Fairy Terns previously occupying the area moved out of the Peel–Harvey Estuary at this time because of a lack of exposed sandbars.

During surveys on the Peel–Harvey Estuary, adult Fairy Terns were observed provisioning banded juveniles—either by landing briefly on the water or by returning to sandflats with fish, which suggests that juveniles received supplementary food for at least 2 months post-fledging. On-water feeding of juveniles and mates is occasionally observed in this species (CNG pers. obs.), as has been recorded between adult and juvenile Caspian Terns Hydroprogne caspia (S. Stockwell pers. comm.), Roseate Terns Sterna dougallii (Watson & Hatch 1999) and Greater Crested Terns Thalasseus bergii (CNG pers. obs.). Presumably this behaviour functions to reduce the risk of kleptoparasitism (i.e. parasitism by theft, where one individual takes food caught or collected by another individual) and/or to reduce time and energy expenditure by negating the need to return to land for fish exchange to occur.

Although the extent and duration of post-fledging care in Fairy Terns remains uncertain, because of the difficulty in obtaining observations away from the breeding site, such behaviour has been recorded for various tern species globally, including Little Tern, Bridled Tern, Royal Tern

Juvenile Fairy Terns studied by novel banding and photography 53

(a)

(c)

(e)

(g)

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(f)

(h)

Figure 2. Juvenile Fairy Tern plumage during the post-fledging period, from 27 days through to 100 days of age. Individuals are identified by the colour of their leg-bands, as indicated. (a, c) At 31 (Pink) and 27 (White) days, respectively, juveniles had a distinct rufous crown and collar, light-brown bill and legs, and tail shorter than the resting wing length; (b, d) by 76 (Pink) and 84 (White) days, respectively, the former rufous crown, collar and covert margins now white, black cap interspersed with white speckling, bill longer, length of resting wing now greater than tail length, legs brownish, and dark semilunar band extends from eye to nape; (e, g) at 65 (Red) and 66 (Purple) days, respectively, chevron patterning on scapular, wing-coverts, mantle and back dark brown, and feathers lack rufous margins (compare with Figure 1e, g), and crown black speckled with white; (f, h) by 84 (Red) and 100 (Purple) days, respectively, feathers with chevron patterning starting to moult out, giving a whiter appearance, crown whiter and legs brownish. Note that (c) is a mirror image (flipped horizontally), for direct comparison with (d) and the band appears as if it is on the left leg. Photos: (a) & (g): C. Corker, (c): C.N. Greenwell, (b), (d)–(f) & (h): N. Goddard

54 Australian Field Ornithology C.N. Greenwell et al.

Thalasseus maximus and Greater Crested Tern, and may continue for ≥6 months (Escalante 1968; Burger 1980; Dunlop & Rippey 2007; Cabot & Nisbet 2013). Banded juvenile Fairy Terns are known to disperse many kilometres from their breeding sites in Western Australia (Storr & Johnstone 1988; Dunlop & Greenwell 2020), though no consistent observations have been made about the duration of parental care.

Temporary colour-marking

Curing time did not appear to affect the wear or durability of nail varnish on the leg-bands. However, band application was smoother where the varnish had been left to cure for >7 days although, for these bands, several millimetres of varnish was scraped clean on one side of the band opening when closed with the banding pliers (Figure 1e). For bands left to cure for <7 hours, the varnish remained slightly tacky, sand granules became embedded in the varnish of two of the colours, and pliers left indentations in the varnish.

All marked Fairy Terns could be identified based on the leg-band colour for the c. 30 days that the birds remained at the site and for several weeks post-fledging. On 30 March 2020, 80 days after banding, four juveniles were photographed on the sandbars off Boundary Island on the Peel–Harvey Estuary (Figure 3a–d). Although the varnish had started to chip away, a portion of it remained

intact, allowing for successful identification of individuals. However, after 95 days, no individuals could be identified by varnish colour alone and identification was only possible by photographic capture of individual band numbers.

It is unclear whether certain brands of varnish were more durable than others as not all colours could be compared at the same time period. However, based on the wear of four painted bands photographed on 30 March 2020, there did not appear to be much difference, with all varnishes appearing similarly chipped. Studies on varnish durability and band preparation could be undertaken in future to improve the longevity of paints if temporary colour-marking is required. Ideally, varnish should be left to dry for several days before band application. Overall, the temporary marking of ABBBS bands using nail varnish offered an effective short-term solution for identifying individuals in the field for 80 days after banding.

The information gained from this study is intended to be used for the basis of a field-friendly, bird-ageing guide, supporting efforts of other researchers, who have obtained empirical information on plumage development (but not necessarily on banded individuals: e.g. Department of Environment, Land, Water & Planning unpubl. data), and to enable the collection of standardised information on colony demographics, a key action identified under the Draft National Recovery Plan for the Australian Fairy Tern (Commonwealth of Australia 2019).

Figure 3. Wear of nail-varnish-painted Australian Bird & Bat Banding Scheme incoloy leg-bands on Fairy Terns 80–82 days after banding. Individuals are identified by the colour of their leg-bands, as indicated. Images also show variation of feather patterning of birds aged (a) 81 days (Dark Blue), (b) 81 days (Grey), (c) 84 days (Red) and (d) 84 days (White). Photos: N. Goddard

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Juvenile Fairy Terns studied by novel banding and photography 55

AcknowledgementsWestern Australian researchers acknowledge the traditional owners of the Whadjuk and Bindjareb country, upon whose lands we have had the great privilege of conducting this research. We thank the Parks and Wildlife Service staff for in-kind support and providing accommodation on Penguin Island during the study period. We thank Perth Wildlife Encounters for their generous in-kind support, ferrying researchers to and from Penguin Island during the breeding season. We sincerely thank Nic Dunlop for his guidance and ongoing support of Fairy Tern research and monitoring in Western Australia. We are grateful to Brett Newmarch, Merryn Pryor, Cherilyn Corker, Bob Pattison, Robert Wroth and Shelley Pearson for providing valuable recapture information on the juveniles banded as part of this research. The banding study was conducted with approval from the Australian Bird and Bat Banding Scheme. We thank Ron Johnstone and Richard Loyn, who provided constructive feedback to improve this manuscript. This research was conducted in accordance with Murdoch University Animal Ethics approval (Permit R3077/18).We acknowledge the work undertaken in Victoria, which has allowed for the comparison of data between states. We especially thank John Hutchison for his assistance, knowledge and invaluable photography skills, and ‘Skipper’ Peter Johnstone, who provided safe boat passage to survey sites. We sincerely thank the Department of Environment, Land, Water and Planning, Gippsland Lakes Co-ordinating Committee, Parks Victoria and BirdLife East Gippsland for their support of the small tern project. Victorian researchers acknowledge the traditional owners of the Gunai-Kurnai country, where the Gippsland Lakes Fairy Tern populations were studied.

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Received 12 September 2020, accepted 22 December 2020,published online 29 March 2021

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