1H - Drosophila Species Management YER 2014 CHAPTER 5: DROSOPHILA SPECIES MANAGEMENT 5.1 BACKGROUND Fourteen species of Hawaiian picture wing Drosophila flies are currently listed as threatened or endangered. Six of these are endemic to Oahu, and three – D. montgomeryi, D. obatai, and D. substenoptera – are currently known to occur on Army lands. OANRP work on Drosophila began in March 2013, and until recently has focused mainly on monitoring known populations and surveying for new ones. This report presents the first three-year plans for the two species currently under management, D. montgomeryi and D. substenoptera, drafted based on our survey results and in consultation with the weed control and restoration specialists. Results are also reported for D. obatai, which is not currently under management but will be formally included following consultation with USFWS. This is the first full year of Drosophila management for OANRP, and the first time systematic monitoring of Drosophila populations has been carried out on Oahu. Prior to this time, all surveys were done sporadically, and few sites were visited more often than quarterly. 5.2 SURVEY METHODS Many species of Hawaiian Drosophila, including the picture wing group to which all of the endangered species belong, are readily attracted to baits of fermented banana and mushrooms. Both baits are spread on a cellulose sponge which is hung from a tree in a cool, shaded, sheltered site, and checked for flies after about an hour. Depending on the quality of the site (number and size of host plants, and microclimate) and the density of baiting spots, surveys typically consist of setting out 16-32 sponges, in groups of four or eight with groups separated by 20-100 m. Baits are checked at least every hour, as flies do not necessarily stay at baits for long periods; number and species of all picture wings on each sponge are recorded at each check. The greatest activity is typically during the cooler hours before 10 AM and after 2 PM, but flies may appear at any time. Direct quantification of Drosophila populations is extremely tenuous, as populations may fluctuate not only seasonally but from day to day. However, repeated surveys may yield useful data on long-term trends. Abundance numbers are reported as the maximum number of individuals observed on a survey day (compiled by adding the maximum observed at each discrete group of bait sponges at any one time, assuming that the same individual flies may move between sponges within a group but are unlikely to be seen at two different sponge groups), since numbers fluctuate through the day. Known, significant populations of D. montgomeryi at Kaluaa MU and D. substenoptera at Palikea, where flies occur relatively consistently, were monitored monthly in order to determine approximate population trends through the year. Other known populations were visited periodically through the year. New populations of endangered Drosophila were searched for by looking in similar habitat both in areas suggested by other staff as having host plants, at historic collecting localities, and in new sites where surveys have been minimal. 5.3 RESULTS 5.3.1 Drosophila montgomeryi Drosophila montgomeryi is a small yellow-brown species which breeds in rotting bark of Urera kaalae and Urera glabra (opuhe). During the last reporting period (March – October 2013), it was found at three sites which we consider to be two population units (PUs; see section 5.4). Conducting additional surveys during a productive winter wet season in this reporting period has increased this to nine sites at four PUs, effectively covering nearly its entire historic range in the Waianae mountains (Figure 1). 2014 Makua and Oahu Implementation Plan Status Report 203 1H - Drosophila Species Management YER 2014 Chapter 5 Drosophila Figure 1. Distribution of Drosophila montgomeryi observations in 2014, with known Urera spp. sites and all survey points in the Waianae range. Kaluaa & Waieli MU Three sites in this MU – Puu Hapapa, North Kaluaa, and Central Kaluaa gulch 1 – have been monitored monthly since June 2013 (though not every site was visited each month) over a total of 32 survey days. Abundance of D. montgomeryi increased dramatically in the winter, with increasing rain and as treefalls from storms caused death or branch breakage of Urera near monitoring sites. Numbers were moderate to high at all sites between November 2013 and July 2014. However, month-to-month fluctuations were extremely high, particularly in North Kaluaa; these large swings were strongly correlated with those of some other species, including the common D. ambochila, D. crucigera, and D. inedita, but not D. punalua or the rare D. divaricata, suggesting that the effect was independent of at least host plant. There was also no obvious difference in weather or bait quality from high-abundance days that would explain the low numbers. A fourth site for D. montgomeryi in this PU, Moho Gulch, was discovered in March 2014. It has a small exclosure built for Urera kaalae, but the fence has been heavily damaged by rockslides and is not being maintained. At present there is only one living mature U. kaalae (outplanted) and one large U. glabra, with several smaller U. glabra (all wild). A single natural seedling of U. kaalae was also seen. Direct access is limited due to intensive use of South Range for live-fire training, though it may be reached via Puu Hapapa as well. 2014 Makua and Oahu Implementation Plan Status Report 204 1H - Drosophila Species Management YER 2014 Chapter 5 Drosophila Drosophila montgomeryi monitoring 35 30 25 20 Hapapa North 15 Central Palikea 10 5 0 May-13 Jul-13 Sep-13 Nov-13 Jan-14 Mar-14 May-14 Jul-14 Sep-14 Figure 2. Drosophila montgomeryi numbers during monthly monitoring at three sites in Kaluaa PU (Puu Hapapa, North Kaluaa, and Central Kaluaa) and Palikea. Y axis is the maximum number observed across the entire site on the survey day (see Survey Methods, section 5.2). Pualii This site was surveyed for the first time this year. At the time of the first visit, the last wild Urera kaalae tree in North Pualii Gulch had recently fallen and the decaying trunk was supporting a large number of D. montgomeryi. Flies were still present at a followup visit two months later, after the tree was fully rotted out and dried. Only seven U. kaalae (all outplanted), and no U. glabra, remain at the site; with no reproduction currently occurring among U. kaalae, it will not remain a viable population of D. montgomeryi without management intervention. Nevertheless, it is an area of high-quality native habitat, both in the immediate vicinity and further downslope in the gulch. Site Days Max No. Kaluaa - Central 8 23 Palikea Kaluaa - North 10 17 Despite continuous monitoring here since May 2013 (targeting D. Puu Hapapa 10 34 substenoptera, which is consistently found in the area), D. Moho Gulch 2 3 montgomeryi was not detected until May 2014. The numbers Pualii 2 6 were relatively low (one individual in May, and five in July), but Palikea 11 5 they occurred during a time when the species was on a seasonal Waianae 4 86 decline at other sites. The area where they were found is already Kawaiu 2 0 a target for weed management and restoration, and has high potential for management to benefit D. montgomeryi (see Makaha 5 0 Management Plan below). Urera kaalae is absent, but Urera Pahole 3 0 glabra has already begun to increase naturally as weed control has Palawai 1 0 reduced alien cover. Lihue 5 0 Table 1. Survey effort for D. Waianae Kai montgomeryi across all potential sites in During explorations for new sites, a large population of D. 2014 reporting year, in survey days. montgomeryi was discovered in the northeastern subgulches of 2014 Makua and Oahu Implementation Plan Status Report 205 1H - Drosophila Species Management YER 2014 Chapter 5 Drosophila Drosophila montgomeryi laying eggs in a rotting trunk of Urera kaalae, Pualii. Kumaipo stream, Waianae Valley. Three sites have been discovered so far, all at the base of Mt. Kaala and consisting of small patches (~0.5 ha) of diverse native forest constrained by alien-dominated vegetation above and below. Only Urera glabra is present, indicating that D. montgomeryi can thrive on it alone (U. kaalae was also found in nearby South Kumaipo Gulch as recently as 1995, but no longer occurs in the valley). All are located on or just below steep slopes that are vulnerable to landslides, which may preclude fencing as a matter of practicality. The middle gulch, where D. montgomeryi was found to be extraordinarily abundant during visits in January and February (Table 1) and is currently the only known site for the critically imperiled D. kinoole (see Other Species below), was impacted by boulders from ongoing severe erosion of the ridge to the north prior to a followup visit in May. Although originating about 200 meters away, a number of boulders rolled directly through the site and smashed several large Urera trees. During baiting at the time, many D. montgomeryi were observed resting on branches, though few were attracted to baits. The long-term impact on the population is uncertain; Urera glabra has a high capacity to regrow from damage such as this. Only three survey days have been spent in the valley to date, all focused in a relatively small area, so other sites may exist. Lihue The original rediscovery of D. montgomeryi was at Schofield West Range, South Haleauau Gulch near Puu Kalena in 2008. This site was revisited once in late 2013, but none were found. Access is difficult and it is probably still inhabited by the species, given the usual population fluctuations seen at other sites.