Palila Restoration

INTRODUCTION The palila (Loxioides bailleui) is an endangered Hawaiian honeycreeper endemic to the Big Island of Hawaii. The palila is a non-territorial, omnivorous passerine with a monogamous mating system. Annual population estimates (1980 to 1998) have fluctuated widely, with current estimates of 4811 ± 395 birds. The palila currently occupies approx. 5 percent of its historic range (Fig. 1). The extant population is located on the west slope of Mauna Kea volcano in a dry subalpine mixed mamane (Sophora chrysophylla) and naio (Myoporum sandwicense) forest. Palila depend on mamane trees for the majority of their dietary and nesting requirements. This mamane forest has become degraded due to browsing pressure by introduced herbivores. Restoration is required to speed the recovery of the population and return it to areas of its former range. Relocation efforts began in 1997 and continued in 1998, with a total of 53 birds moved to the north slope of Mauna Kea (approx. 18 km from the west slope core population). Research investigating roosting behaior of radio tagged palila was initiated during 1998 and continues in 1999.                                                      Figure 1: Historic and current ranges of palila on the Big Island of Hawaii.   The Palila

METHODS Tracking · 57 palila were radio-tagged during the roosting study. Roost locations were recorded for 29 birds. · Birds were tracked daily five days a week over the life of the transmitter battery (approx.8 weeks). We attempted to obtain two locations per bird per day. · All diurnal and roost locations were recorded with a GPS unit (plus,minus 10 meters) and plotted using Arcview 3.1. Roost locations · Roosts were located by tracking birds at dusk until they perched motionless for several minutes. · When birds were visible, we recorded height of roost perch, distance from top of canopy, location within canopy (center vs. edge), orientation (upslope vs. downslope) and presence of visible fecal accumulations. · Occasionally, roost trees were located after dark. In these cases, we were not able to visually confirm the bird's exact roost perch within the tree, so only tree species and weather were noted. · Behavior of the focal bird prior to roost and within the roost was recorded. Presence of roostmates also was noted when possible.

Analysis · In order to obtain independence between diurnal and roost locations, we removed all points before 0630 hours and all points within 30 minutes of a bird's earliest roost time. · Roost tree fidelity and a comparison of diurnal and roost locations were conducted for birds with greater than 5 roost nights (n=17). · Roost perch characteristics and tree species preference data were analyzed using all birds (n=29).

DIURNAL VERSUS ROOST LOCATIONS · We determined the center of diurnal and roost locations using harmonic means (Figs. 2a and 2b). · Distances moved between the center of diurnal and roost activity (determined by a straight line) did not differ for individuals on the north versus west slope (t = 0.74, df = 15, P = 0.47). · Mean distance moved between center of diurnal activity and center of roosting activity was 832 ± 307 meters (range = 38 to 4212 m).

RESULTS

Figure 2a: Locations of bird T2 38 on the west slope. Diurnal locations occurred primarily in the mamane dominant forest, while 27 of 28 roost locations occurred in the naio dominant forest.		Figure 2b: Locations of bird T3-02 on the north slope. Diurnal and roost locations both occurred in the mamane dominant forest. T3 02 roosted in the same mamane tree for 17 of 31 roost nights.

ROOST TREE FIDELITY · All birds (n=17) used multiple roost trees. · 94% of birds used each roost tree for at least two consecutive nights. · The maximum number of nights that birds roosted in the same tree averaged 17.93 nights (SE = 3.68, range 2 to 50 nights).

FECAL ACCUMULATIONS · Three of 10 (30%) birds killed on the north slope were found under roost trees used on multiple nights. Two birds were found dead beneath the tree where they were last seen the previous evening. · To investigate whether fecal material might serve as an olfactory cue for predators, we began noting the presence of fecal accumulation at roost perches. · We located roost perches in 47 different trees. On six trees, we found fecal accumulations on or below the roost perch. · Roost trees with visible fecal accumulations were used for an average of 8.6 nights (SE = 3.14, range 2-22 nights; n = 5 birds).

Mamane Tree	Naio Tree

TREE SPECIES PREFERENCE · Most individuals preferred to roost in one particular tree species (Fig. 3a). · Mamane was utilized less than 50 percent of the time on the west slope and 100 percent of the time on the north slope (Fig. 3b). · Although mamane was the only tree species used on the north slope, this may be due to the low density of naio trees in the area because birds that returned to the west slope reverted back to the pattern of roosting in both mamane and naio trees.

    

Figure 3a: Tree species preference of roosting palila. Individual preference is indicated by greater than 95 percent of locations in a single tree species. High mamane use on the north slope is likely to be an artifact of forest structure.	Figure 3b: Percent of roost locations in mamane trees on west and north slopes of Mauna Kea. West Return represents relocated birds that returned to the west slope.

ROOSTMATES · Ten of 29 birds (34.5percent) roosted with another palila on at least one occasion (three roosted with their pair bonded mate). · However, 89.5% of the time, palila roosted alone (n equal 313 roost nights).

ROOST PERCH CHARACTERISITICS · Height of the roost perch and orientation (upslope/downslope) did not differ for roosts in mamane and naio trees (Table 1). · However, in mamane, birds roosted closer to the top of the canopy and farther away from the central axis of the tree than birds roosting in naio trees.

Table 1

	MAMANE	NAIO	F VALUE*	P VALUE
Mean roost height (m)	3.95	4.05	3.109	0.08
Mean distance from top of tree (m)	0.83	1.16	15.538	0.001
Location within crown (percent birds in center)	50.6	88.2	11.339	0.001
Orientation (percent upslope)	64.9	65.2	2.065	0.16

*Multivariate General Linear Model; df equals 2,75

CONCLUSIONS · Roosting behavior is an important component of avian daily activity, comprising approximately one half of an individual's daily time budget. · Prior to the initiation of this study, researchers considered mamane to be the primary source for foraging, nesting and shelter. However, our results indicate that palila also use naio habitat for roosting. Thus naio plays a more important role in the habitat requirements of palila than previously thought. For example, the low density of naio trees on the north slope may be a contributing factor to why many birds return to the west slope following relocation. · Although palila use multiple roost sites, they change roost locations relatively infrequently. On the mainland, solitary roosting birds may frequently change roost sites to avoid predator detection due to fecal accumulation at the roost perch. Because palila evolved without mammalian predators, their fidelity to specific roost trees may make them more vulnerable to olfactory predators (feral cats, rats and mongoose) compared to mainland passerines. · A detailed understanding of roosting habitat requirements and roost behavior is critical for assessing habitat quality and predation risk for endangered avian species.

FUTURE DIRECTION · We currently are conducting a detailed investigation of roost tree characteristics and habitat requirements using modified B Bird protocols. · We are expanding spatial analysis of diurnal and roost activity centers to determine whether diurnal and nocturnal ranges are distinct. · We are continuing to study how roosting behavior influences nocturnal predation risk.

ACKNOWLEDGMENTS: We would like to thank the U.S. Army Garrison, Hawaii for funding the research. In addition, we would like to thank the United States Fish and Wildlife Service for their assistance, Division of Forestry and Wildlife for assistance and permission to work on Mauna Kea, The Peregrine Fund, and the many interns who aided with field work.