Trip Report – Tutuila, American Samoa 20-23 May 2019

Prepared by André F. Raine

20th May – AR arrived at Pago Pago International Airport, Tutuila, at 21:20 and was met by Holly Freifeld. Drove to Moana o Sina Lodge and checked in.

21st May – meetings in the morning with NPS and DMWR staff. Then AR and HF drove with Mark MacDonald and Adam Miles (both of DMWR) around the east of the island, going as far as Tula, and also over Afono Pass to overlook Pola Island. Aim of the trip was to get an understanding of the terrain and scout out potential areas for burrow-nesting seabirds. In the evening AR, HF and Jennifer Higashino drove to a parking area on Afono Pass that abutted the western side of Rainmaker Mountain. Arrived at approx. 20:00 and immediately heard Tahiti Petrel calling from on top of Rainmaker. Stayed until approximately 20:25 and had petrels calling throughout. Multiple birds calling from the top of the mountain closest to the road and distant calls all along the mountain’s upper ridge line into the distance. A few birds calling on the west side of the road, though not clear if these were circling birds or ground callers. Very bright lights noted below the mountain from Pago Pago – particularly in the area of the tuna cannery. Drove on to the look-out at the beginning of Lower Sauma Ridge Trail overlooking Pola Island in the distance – didn’t hear any petrels calling from there. Did see a Barn Owl perched in a tree near the trail head.

22nd May – AR, HF and Tamafaiga Sagapolutele (NPS) hiked along Mount Alava trail up to the communication tower. Also hiked part way down several perpendicular ridges (Agapie Curve, Levaga ridge and the Levaga village trail) to assess suitability of deploying song meters in this area. White- tailed Tropicbird and White Tern seen during hike. Found two dead black rats on the trail, both looked like they had been depredated by Barn Owl. In the evening, went with Adam Miles to Olovalu Crater to look at fruit bat roost. No seabirds heard in this area while watching bat roost.

23rd May – AR, Loia Tagoai and TS (both of NPS) hiked up towards Mount Matafao which – being of a similar habitat to Rainmaker looked like it might be good for nocturnal seabirds. The trail was however very overgrown and blocked by multiple tree falls from Cyclone Gita and so progress was slow. After 4hrs, reached the saddle overlooking Mount Matafao peak, searched forested area for seabird sign (found none) and then turned back. Found dead White-tailed Tropicbird, presumably depredated but as it was an old carcass the predator could not be discerned. PM drove to multiple locations around Tau Mountain (habitat also looked good and identified in O’Connor & Rauzon (2004) as having had burrows located in 1986 by Engbring & Ramsey). No birds heard. Extremely bright lights were lighting up the mountain side from a nearby sports centre. Cats seen along road adjacent to mountain. AR flew back to HNL on 23:20 flight.

Next steps

Lots of Tahiti Petrel activity recorded on Rainmaker Mountain suggests that this habitat type is good for this species on Tutuila. Similar habitat is found on Mount Matafao and Mount Tao as well as a handful of other areas. Deploying song meters as high up these mountains as possible would help confirm whether or not birds are present there. Deploying song meters as high up on Rainmaker Mountain as possible and leaving them there all year would (i) allow for an annual acoustic pattern to be created for Tahiti Petrel on Tutuila and (ii) an assessment of whether any other seabird species (Herald Petrel, Tropical Shearwater, Polynesian Storm-petrel) are present.

While the intact native forests of the interior of Tutuila are not at all similar to the area on Rainmaker where Tahiti Petrels were heard on this trip, it appears very little is known about seabird breeding activity within these areas. Roving song meters could be deployed on a gradient on several of the long trails leading off the main Mount Alava Trail – both Agapie Curve and Levaga Ridge both looked ideal for this kind of assessment. Deploying song meters every 250m from the top of the Alava Trail down to sea level (or sea cliffs) would allow for a quick assessment of whether any seabirds are present in these forests. Lastly the ridge above Pola Island (and indeed Pola Island itself) would also be interesting to survey with song meters to assess presence/absence of burrow nesters (e.g. Tropical Shearwater).

Radar was also considered during the trip. While this is certainly a valuable tool for assessing fly-ways, as well as long term population trend monitoring, it would appear that song meters are a better option at present. This is because radar is expensive, requires significantly more training, and needs to be operated at multiple locations for an extended period of time by a trained operator. The presence of thousands of fruit bats will also potentially make isolating seabird tracks on the radar screen difficult (although not impossible). Song meters on the other hand are cheaper, can be deployed and left to collect data for long periods of time, and require less training to properly deploy and operate. Also, as this trip has shown, there are very discrete areas that should be initially surveyed based on observations from this trip, thus narrowing the search area down for nocturnal burrowing seabirds. If nothing is found using song meters, then a wider study using radar could be considered.

Suggest deploying roving song meters from mid Jan-mid Mar and moving them monthly to cover more ground. Suggest deploying static units on Rainmaker from Jan-Dec to obtain annual acoustic patterns for the target species.

Seabird threats

Multiple potential threats to nocturnal burrow-nesting seabirds were noted during the trip. The two most obvious were:

1. Introduced predators – rats were seen on multiple occasions during the visit and appeared to be both black and Polynesian rats. Cats were common around habitations abutting the mountains, as were large packs of dogs. Barn Owls were heard and seen (although this is apparently a native species?). All of these species are known predators of seabirds. 2. Light attraction - apparently fledglings Tahiti Petrels are regularly found (mainly during Sept- Oct) as fallout victims in the Pago Pago area (McDonald pers comm). Very bright lights were noted below Rainmaker Mountain, particularly around the tuna cannery, and lights at a newly built exercise facility were so bright they lit up the entire face of Mount Tao.

Rainmaker Mountain – Tahiti Petrel heard calling from the peak, and further back along the ridge line.

Rainmaker Mountain (as seen from Mount Alava Trail); note close proximity to Pago Pago (and thus artificial light sources) immediately below the mountain.

View of Pola Island from Lower Sauma Ridge Trail – the island and mainland adjacent to the island represent potential areas for song meter deployment.

View of forested ridges from Mount Alava Trail.

Forest interior on Agapie Curve, off Mount Alava. While very different from the top of Rainmaker, this would represent interesting habitat to survey for burrow nesting seabirds.

Dead black rat found on Mount Alava trail, indicating the presence of rats and possibly Barn Owl (injuries on body looked consistent with Barn Owl) within these potential seabird breeding areas.

Trail conditions on ridge line towards Mount Matafao.

Remains of White-tailed Tropicbird found on trail towards Mount Matafao

More open understory higher up trail to Mount Matafao.