Journal of the Hawaii Audubon Society For the Protection of Hawaii’s Native Wildlife VOLUME 68, NUMBER‘EL 3 EPAIO APRIL 2008 What Threat Do Native Avian Predators Pose To Hawaiian Honeycreepers? Two Cases Of Predation By Pueo (Asio Flammeus sandwichensis) Hanna L. Mounce1 Habitat loss, disease and introduced predators are widely During the past two breeding seasons (2006 and 2007) in recognized for their negative effects on Hawaiian honeycreepers the Hanawï Natural Area Reserve (NAR), researchers with (Scott et al. 1986, Pratt 2005). Although it is often difficult to the Maui Forest Bird Recovery Project (MFBRP) documented assess the relative importance of each of these threats, predation Pueo depredating honeycreepers on two occasions. In the by non-native species is often cited as a key contributor to the early afternoon of 21 April 2006, while observing a Maui loss of endemic Hawaiian forest birds (Atkinson 1977; Scott Parrotbill (Pseudonestor xanthophrys) nest containing a single et al. 1986; Banko 1992). Overwhelming evidence indicates chick, a Pueo was observed soaring over the area. Later that that rats (Rattus sp.) are key predators of island birds (Atkinson day, presumably the same Pueo was observed approaching the 1985; King 1985; Thibault et al. 2002; Veitch & Clout 2002) nest tree. The brooding female immediately flew off the nest and the effect of invasive mammals on island populations and suggesting a behavioral response to the aerial predator and ecosystems is well documented (Coblentz 1990; Dowding & the owl quickly perched in the top of the nest tree. The nest Murphy 2001; Levy 2003; Nogales et al. 2004). In Hawai‘i was confirmed to be empty immediately after the owl’s visit, the black rat (R. rattus), the Norway rat (R. norvegicus), the suggesting that the owl had depredated the Parrotbill nestling. Polynesian rat (R. exulans), the small Indian mongoose This is the first observation of a Pueo taking a Maui Parrotbill. (Herpestes auropunctatus) and the feral cat (Felis catus) are On 8 May 2007, a Pueo was observed flying toward and eliciting well-established and predators of native Hawaiian birds (Ziegler loud alarm calls from at least two adult ‘Apapane (Himatione 2002). Conversely, there is relatively little information on the sanguinea). The two ‘Apapane dispersed and the owl returned frequency or details of predation events by native predators to a perch where it was observed consuming an ‘Apapane. It on native birds. For example, there is only one documented could not be determined whether the depredated ‘Apapane was observation of a Pueo, the Hawaiian Short-eared Owl (Asio a fledgling or a nestling but it appeared to be a young bird from flammeus sandwichensis), taking a native forest bird (i.e., Palila the plumage characteristics that were visible. (Loxioides bailleui), S. Fancy, National Biological Survey, pers. In both cases, the behavioral response of the native forest comm., from Mostello 1996). birds indicated that the Pueo was recognized as a predator. On Historically, Hawai‘i supported a number of avian predators two other occasions in Hanawï NAR, native honeycreepers and (Ziegler 2002) although only three exist today, two native and continued on page 20 one introduced: the Pueo, the ‘Io or Hawaiian Hawk (Buteo solitarius), and the Common Barn Owl (Tyto alba). The Hawaiian Hawk is the only remaining native Buteo and is restricted to the island of Hawai‘i. The Common Barn Owl was introduced in the 1950s to control rodent populations (Tomich 1962) but the history of the Pueo in Hawai‘i is not as clear. The Pueo is considered a native subspecies of the globally distributed Short- eared Owl although sub-fossils indicate that its arrival post- Hawaiian Short- dated that of humans (Olson & James 1982). During Polynesian eared Owl (Pueo, settlement, the creation of more open landscapes through Asio flammeus sandwichensis). This deforestation combined with the introduction of the Polynesian endemic race occurs rat likely promoted the species’ establishment (H. James, pers. on all main islands, comm.). Both owls are found on all the main Hawaiian Islands but is most common and on the island of Maui, the Pueo is the only extant native on Kaua‘i, Maui, and predator. Although, the competitive interactions of Pueo and Hawai‘i. It is listed as other introduced avian and mammalian predators have been endangered on O‘ahu examined (Mostello 1996), the role of Pueo in native Hawaiian by the State of Hawai‘i. ecosystems is poorly understood. Photo by Tom Dove. ‘ELEPAIO • 68:3 • APRIL 2008 19 continued from page 19 maximum of one young per year (Simon et al. 2000, MFBRP non-native passerines were observed mobbing a perched Pueo unpubl. data). Further, the Maui Parrotbill has very low nest and alarm calling loudly for up to 10 minutes until the Pueo flew success and is vulnerable to increases in nest predation. As part off, and on two further occasions a Pueo flying above the forest of our work, we control rats and small Indian mongoose, thus canopy was accompanied by alarm calls, though somewhat lowering the risk of nest predation. However, it is unknown if less raucous. In Kaua‘i forests, fledgling Puaiohi, the Small these activities (i.e., reduction of small mammal populations) Kaua‘i Thrush (Myadestes palmeri) also exhibit behaviors result in cat and owl populations switching to diets comprised that may reduce predation by avian predators (Snetsinger et al. of more birds. More research is necessary to determine the 1999). Given that historically a long-legged bird-eating Stilt- effect of removing small mammals on Pueo abundance, and owl (Grallistrix auceps), (Olson & James 1991; Ziegler 2002) the Pueo’s impact on honeycreeper nest success. did occur on Kaua‘i and Maui the observed predator evasion behaviors are not unexpected. Acknowledgements Short-eared Owls consume a variable diet. In Hawai‘i, pellet Our research is made possible through funding from the analyses indicate that mice, birds and rats, respectively are their State of Hawai‘i Division of Forestry and Wildlife, the U.S. Fish most common prey (Snetsinger et al. 1994; Mostello 1996), and and Wildlife Service, and through institutional support from large insects also are taken (Mostello 1996). Birds depredated the University of Hawai‘i, Pacific Cooperative Studies Unit. by Pueo have included passerines, seabirds and shorebirds Thanks to Sheila Conant for her helpful contributions and to (Pyle 1987; Snetsinger et al. 1994; Mostello 1996). Owls in Julia Garvin, Kirsty Swinnerton, Peter Sanzenbacher and David general respond to regional differences in prey abundance. For Leonard for their review and comments of the manuscript. Our example, owls in coastal regions depredate more birds than research is not possible without the dedication and hard work of those occupying interior regions (Holt 1993). The Pueo relies all past and present members of the MFBRP team. more heavily on birds and insects than its continental relatives (Snetsinger et al. 1994), likely because of the low rodent 1 Maui Forest Bird Recovery Project 2465 Olinda Road diversity of the Hawaiian Islands (Mostello 1996). Despite Makawao, HI 96768 this, the Pueo has not been considered a major threat to native forest birds as few honeycreepers have been identified in their Literature Cited pellets. For example, of 248 owl pellets examined by Snetsinger Atkinson, I. A. E. 1977. A reassessment of factors, particularly (1994) and Mostello (1996), only one ‘Apapane, two ‘Amakihi Rattus rattus L., that influenced the decline of endemic (Hemignathus virens) and five ‘I‘iwi (Vestiaria coccinea) were forest birds in the Hawaiian Islands. Pacific Science identified. However, Mostello (1996) determined that 15% of 31:109-130. the bird remains in Pueo pellets were juveniles, and could not Atkinson, I. A. E. 1985. The spread of commensal species of be identified to species. Undoubtedly a portion of these bones Rattus to oceanic islands and their effects on island were those of native birds, as Snetsinger et al. (2005) attributed avifaunas. ICBP Technical Publication 10:35-81. Banko, P. C. 1992. Constraints on productivity of wild Nene 10% of nest failures of the Puaiohi to Pueo. or Hawaiian Geese Branta sandvicensis. Wildfowl Observations indicate that Pueo are more common in 43:99-106. Hanawï NAR during the honeycreeper breeding seasons than Coblentz, B. E. 1990. Exotic organisms: a dilemma for during the rest of the year, and Pueo may be shifting habitat in conservation biology. Conservation Biology 4:261- response to an abundant and easily captured food source (see 265. Mostello 1996). If this is the case, they may be more of a threat to Dowding, J. E., and E. C. Murphy. 2001. The impact of predation native species than previously appreciated. The Maui Parrotbill by introduced mammals on endemic shorebirds in population is estimated at 500 individuals + 230 (Scott et al. New Zealand: a conservation perspective. Biological Conservation 99:47-64. 1986). Unlike other honeycreepers, Maui Parrotbill produce a continued on page 21 Board Roster: Committee Chairs: ‘Elepaio ISSN 0013-6069 John Harrison President Conservation: Norma Bustos Managing Editor: Lydi Morgan Wendy Johnson, First Vice President Education: Wendy Johnson Scientific Editor: Ron Walker Ron Walker, Second Vice President Elepaio: Ron Walker The ‘Elepaio is printed on recyled paper and published nine times per Liz Kumabe, Recording Secretary Field Trips: vacant year: February, March, April, May, June/July, August/September, Carol Bebb, Director Fundraising: vacant October, November, and December/January Phil Burner, Director Grants & Scholarships: Phil Bruner 850 Richards Street, Suite 505 Arlene Buchholz, Director Membership: vacant Honolulu, HI 96813 Norma Bustos, Director Program: Arlene Buchholz Phone/Fax: (808) 528-1432 Publications: Linda Paul E-mail: [email protected] Website: www.hawaiiaudubon.com Staff: Website: Lydi Morgan Lydi Morgan, Office Manager Pacific Fisheries Coalition (PFC) (a project of HAS) Linda Paul, Executive Director for Aquatics Tel: (808) 262-6859 Website: www.pacfish.org 20 ‘ELEPAIO • 68:3 • APRIL 2008 continued from page 20 Holt, D.