Breeding Biology of the Endangered Rota Bridled White-Eye

2004·3.8 MB·English

by  Frederick A Amidon

Wilson Bulletin 1 16(4):342-346, 2004
BREEDING BIOLOGY OE THE ENDANGERED ROTA
BRIDLED WHITE-EYE
FREDERICK A. AMIDONC^-' CAROLA A. HAAS,' AND JOHN M. MORTON^^
—
ABSTRACT. Little is known about the breeding biology of Bridled White-eyes (Zosterops conspicillatus),
especially the federally endangered Rota Bridled White-eye (Z. c. rotensis). Here, we report on the breeding
behavior, nest-site characteristics, and nest dimensions of Rota Bridled White-eyes. From 1997 to 1999, we
found 20 Rota Bridled White-eye nests in Elaeocarpiisjoga (35%), Hernandia lahyrinthica (30%), Merrillio-
dendron niegacarpiim (20%), and introduced Acacia confusa (15%) trees between 320 and 460 m in elevation.
Nests were 2.5-12.8 m above the ground (n = 18) in trees 3.3-14.6 m tall (n = 16). Clutch size ranged from
one to two eggs (n = 7) and the breeding season was from at least Decemberthrough August. Ne.stdimensions
(n = 4) were 36-44 X 57.7-60.8 mm (outer height X diameter) and 25-29 X 44.6-47.7 mm (cup depth X
diameter). Received / April 2004, accepted 4 October2004.
The Bridled White-eye {Zosterops conspi- brown treesnake {Boiga irregularis), however,
cillatus) is a small bird (—10 g) endemic to the Guam Bridled White-eye population rap-
the Mariana Islands in the tropical western Pa- idly declined and the subspecies is presumed
cific Ocean. Currently, the species is divided extinct (Wiles et al. 2003).
into three subspecies found on the islands of The first published record that detailed lo-
Guam (Z. c. conspicillatus)', Saipan, Tinian, cations of the Rota Bridled White-eye was of
and Aguiguan (Z. c. saypani)', and Rota (Z. c. four birds collected by Navy personnel at two
rotcnsis', hereafter referred to as Guam, Sai- low-elevation (0-150 m) areas (Songsong Vil-
pan, and Rota Bridled White-eyes, respective- lage and Malilok Point) in 1945 (Baker 1948).
ly; Stresemann 1931). Recent genetic work Baker (1948) considered the Rota Bridled
(Slikas et al. 2000) and observed differences White-eye “numerous,” though no surveys
in plumage, vocalizations, and behavior (Pratt were conducted and bird collection was pri-
et al. 1987, Collar et al. 1994), suggest that marily limited to low-elevation areas. By
the Rota Bridled White-eye may warrant spe-
1975, the Rota Bridled White-eye population
cies status.
was limited to high-elevation areas in the Sa-
The Saipan Bridled White-eye is abundant bana region, a plateau 450 m in elevation
and widespread on the islands of Saipan
dominating the topography ofthe western half
(2,221 birds per km^), Tinian (2,931 birds per
km^), and Aguiguan (1,930 birds per km^; of Rota (Pratt et al. 1979). In 1982, the first
Engbring et al. 1986). Historically, the Guam island-wide, avifaunal survey was completed
Bridled White-eye also was believed to be and the Rota Bridled White-eye population
abundant and widespread (Jenkins 1983), al- was estimated to be approximately 10,000
though no island-wide surveys were ever birds (183 birds per km^); it was primarily re-
completed. After the introduction of the stricted to high-elevation areas of the Sabana
region (Engbring et al. 1986). By 1996, the
' Dept, of Fisheries and Wildlife Sciences (0321), population was estimated to be approximately
Virginia Polytechnic Inst, and State Univ., Blacksburg, 1,000 birds and was further restricted to cliff-
VA 24061, USA. line forest in the Sabana region (Fancy and
^U.S. Fish andWildlife Service, Pacific IslandsFish Snetsinger 2001). The cause of this decline is
and Wildlife Office, PO. Box 8134, MOU-3, Dededo,
GU 96912, USA. uncertain; however, predation by the intro-
^Current address: U.S. Fish and Wildlife Service, duced Black Drongo {Dicrurus macrocercus)
Pacific Islands Fish and Wildlife Office, 300 Ala and habitat changes appear to be important
Moana Blvd., Box 50088, Honolulu, HI 96850, USA. factors (Craig and Taisacan 1994, Craig 1999,
^Current address: U.S. Fish and Wildlife Service, Amidon 2000, Fancy and Snetsinger 2001).
Kenai National Wildlife Refuge, P.O. Box 2139, Sol-
dotna, AK 99669, USA. Currently, the Rota Bridled White-eye is listed
“^Corresponding author; e-mail: fred_amidon@fws. as endangered under the Endangered Species
gov Act (U.S. Fish and Wildlife Service 2004) and
342
)
Amidon et al. • ROTA BRIDLED WHITE-EYE BREEDING BIOLOGY 343
critically endangered by the World Conser- ing, and feeding of nestlings and fledglings.
vation Union (2003). When nests were accessible, we attempted to
The paucity of life history information band nestlings with U.S. Geological Survey
about the Rota Bridled White-eye makes it aluminum bands and distinct combinations of
difficult to determine the specific cause ofde- color bands.
cline. Data on breeding biology are especially At all nests we measured diameter at breast
limited, as only brief descriptions of three height (dbh) ofthe nest tree, height ofthe nest
nests have been reported (Yarnashina 1932, in the tree, nest tree height, tree species (based
Pratt 1985, Lusk and Taisacan 1997). Data on on the taxonomic classification of Raulerson
incubation, nestling, and fledgling periods, as and Rhinehart 1991), distance from nest to
well as on parental care do not exist. Further, bole, and elevation. When nests were acces-
information on the breeding biology of Bri- sible, we also recorded nest dimensions and
dled White-eyes on Saipan and Guam also is nest material used. Eor nest dimensions, we
very limited. In this paper we report, often for recorded cup diameter and depth, and outside
the hrst time, information on nest-site char- nest diameter and height. Means are presented
acteristics, nest dimensions, and breeding be- ± SE.
havior of Rota Bridled White-eyes.
RESULTS
METHODS
We found 19 Rota Bridled White-eye nests
Observations of all nests were made on the during the 1998 (June to August) and 1999
island of Rota (14° 10' N, 145° 12' E), Com- (January to August) field seasons. An addi-
monwealth of the Northern Mariana Islands tional nest was found in December 1997 dur-
(CNMI). Rota is approximately 86 km^ and ing preliminary field work (S. M. Plentovich
has a maximum elevation of 490 m. The is- pers. comm.). Ten of the nests were active,
land is composed ofa series of upraised, coral and ofthese, seven produced one ortwo fledg-
limestone plateaus formed on an extinct vol- 2li)ngs. Of the three active nests that failed, one
canic peak. We conducted our field work pri- appeared to be depredated at the nestling
marily within the current range of the Rota stage, the 1997 nest was destroyed during Ty-
Bridled White-eye, from 300 to 450 m in el- phoon Paka in December 1997, and the third
evation in the Uyulan Hulo, Applatagua, Ein- was depredated or abandoned, possibly due to
ata, and Alesna regions from June to August observer disturbance. Ten nests were consid-
1998 and from January to August 1999. The ered inactive but were distinguishable from
climate in the CNMI is tropical, with mean other passerine nests, including those of the
temperatures of 24 to 32° C, high humidity, Micronesian Honeyeater (Myzofnela ruhni-
and average rainfall of 200 to 260 cm (Na- tra), based on nest structure, composition, and
tional Oceanic and Atmospheric Administra- placement within the nest tree and our obser-
tion 1998). vations of Rota Bridled White-eye activity at
We found nests by actively searching areas the nest site.
used by Rota Bridled While-eyes and by mon- We found active nests in December (/? =
itoring the movements of individuals carrying 1 , March (/? = 4), May (// = 2), July (// =
nesting material or food items. We monitored , and August (// = I ). Fledging dates of two
all active nests at least every 4 days, using nests indicate that breeding also occurs in
either a mirror on a telescoping pole or a spot- April and June. In addition, we ob.served what
ting scope. When possible, we recordetl clutch appeared to be two recently Hedged Rota Bri-
si/e, number of hatchlings and lletlged young, dled White-eyes (no eye-rings and a scruffy
and assessed reasons for nest or clutch failure. appearance) in late January.
1
Because Rota Bridled White-eyes are sexually Rota Bridled White-eye eggs were light
I monomorphic in plumage and none of the blue and unmarked: clutch si/e for seven nests
I adults at active nests was color-banded, sexes ranged from one to two eggs, and we docu-
I
could not be identified: however, we recorded mented the Hedging of two nestlings from one
i
observations of switching and simultaneous nest. Based on our observations at seven ac-
feeding by both adults to determine the in- tive nests, incubation and nestling periods ap-
volvement of both sexes in incubation, brood- peared to be at least 10 and as long as I2 days.
344 THE WILSON BULLETIN • Vol. 116, No. 4, December2004
During the incubation and nestling stages, we Pandanus spp. fibers. We also observed a
observed both adults incubating eggs and Rota Bridled White-eye recycling old nest
brooding nestlings, and both simultaneously material to build a new nest; we did not ob-
provisioning nestlings. We banded one nest- serve white-eyes reusing nests.
ling and documented a post-fledging parental
DISCUSSION
care period of at least 8 days. The banded
m
nestling was seen approximately 10 from Previously described nest-site characteris-
the nest with both adults and another young tics and nest dimensions (Yamashina 1932,
bird, possibly its nest mate, which had fledged Pratt 1985, Lusk and Taisacan 1997) are sim-
prior to banding. Both birds were observed ilar to what we found. Of the three nests pre-
actively begging (calling and quivering their viously reported, only two indicated the tree
wings) from both adults and did not appear to species in which the nests were found. One
be foraging, although they flew and hopped nest was in H. labyrinthica (Lusk and Taisa-
among the branches of trees. We also ob- can 1997) and the other was in Hernandia
served adult Rota Bridled White-eyes con- spp. (presumably H. labyrinthica', Pratt 1985).
structing and cleaning (eating fecal sacs) Both nests were also found in areas dominated
nests, but did not observe both adults simul- by H. labyrinthica/E. joga mixed forest at
taneously building nests or taking part in nest >240 m in elevation. In our study we ob-
sanitation. served the use ofthree additional tree species,
We found Rota Bridled White-eye nests at including one introduced species, A. confusa;
320-460 m in elevation in the native tree spe- we found 35% of our nests in two additional
cies Elaeocarpusjoga (n — 7), Hernandia la- forest types {M. megacarpum and A. confusa
byrinthica {n = 6), and Merrilliodendron me- forests). Lusk and Taisacan (1997) report that
gacarpum {n = 4), and in the introducedAca- the Rota Bridled White-eye breeding season
cia confusa (n = 3). Mean height of nests extends from at least March until June. Our
above ground (n = 18) was 8.3 m ± 0.7 observations indicate a breeding season from
(range; 2.5-12.8 m). Mean height ofnest trees at least December through August. However,
{n — 16) was 10.3 m ± 0.8 (range: 3.3-14.6 the species probably breeds year-round, as
m), and mean dbh of nest trees (n — 17) was was reported for the Guam Bridled White-eye
29.9 cm ± 40.2 (range: 2.3-60.2 cm). Mean (Marshall 1949, Jenkins 1983), because nest-
distance from tree bole to nest (n = 17) was ing was observed in both the wet and dry sea-
3.1 m ± 0.4 (range: 0.9-6.7 m). sons.
All Rota Bridled White-eye nests were cup- There is little published information on the
like and the nests found in E. joga, M. me- nests of Saipan and Guam Bridled White-
gacarpum, and A. confusa trees were all sus- eyes. Yamashina (1932) reported clutch size
mm
pended between branches and branchlets. Five (1-3 eggs), nest dimensions (40-55 outer
mm mm
of the six nests found in H. labyrinthica were nest height, 25-30 cup depth, 55-65
mm
suspended between branches and leafpetioles. outer diameter, and 40-45 cup diameter),
The remaining nest was suspended from Da- nest heights (2-4 m), and nest tree species
vallia solida ferns below a H. labyrinthica (Pithecellobium spp.) for three Saipan Bridled
branch. White-eye nests found on Tinian. Seale (1901)
We measured nest dimensions of four Rota reported nest dimensions (48 mm outerheight,
Bridled White-eye nests. Mean outer height 41 mm outer diameter, and 25 mm cup depth)
was 40.0 mm ± 1.0 (range: 36.0-44.0 mm) and nest tree species {Pithecellobium dulce)
and cup depth was 28.0 mm ± 1.0 (range: for one Guam Bridled White-eye nest. Jenkins
25.0-29.0 mm). Mean cup diameter was 45.9 (1983) reported on clutch size (2 eggs), nest
mm ± 0.7 (range: 44.6-47.7 mm) and outer dimensions (40-50 mm nest diameter and 70-
nest diameter was 59.0 mm ± 0.7 (range: 80 mm “deep”), nest height (2.4 m), and nest
57.7—60.8 mm). All nests appeared to be com- tree species {Leucaena leucocephala) for one
posed of rootlets, woven grass or Pandanus Guam Bridled White-eye nest. Hartert (1898)
spp. fibers, spider webs, light green moss, and reported on clutch size (2-3 eggs), nest width
a yellow, cottony material. The inner cup ap- (50-80 mm), and nest height (1-2 m) for
peared to be composed of woven grass or “several” Guam Bridled White-eye nests.
Amidon et al. • ROTA BRIDLED WHITE-EYE BREEDING BIOLOGY 345
Three active Saipan Bridled White-eye nests incubation, brooding, and feeding ofnestlings
m
were reported at 2.3-6 above ground in Ca- and fledglings. This parallels the behavior of
suarina equisetifolia and Phragmites karka many other white-eye species (Broekhuysen
(N. C. Johnson unpubl. data). and Winterbottom 1968, Ali and Ripley 1974,
Overall, the clutch size and nest dimensions Kikkawa and Wilson 1983, van Riper 2000).
we found for the Rota Bridled White-eye are In most species of white-eyes studied to date,
within the range ofthose reported for both the both sexes also participate in nest construction
Saipan and Guam Bridled White-eye. Height (but see Ali and Ripley 1974). Overall, the
above ground of Guam and Saipan Bridled breeding behavior of the Rota Bridled White-
White-eye nests is generally lower (<6 m) eye appears similar to that of other white-eye
than what we found for the Rota Bridled species.
White-eye. Differences may be due to the lim- We found Rota Bridled White-eye nests in
ited sample of Guam and Saipan Bridled H. labyrinthica/E. joga mixed forest, M, me-
White-eye nests. Interestingly, all of the iden- gacarpwn forest, and introduced A. confusa
tifiable plant species used as nest substrate by forest only at high elevations (>200 m). Each
Guam and Saipan Bridled White-eyes were
forest type comprised primarily tall trees (10
introduced to the Mariana Islands, whereas no m) that were large in diameter (>10 cm; Ami-
Rota Bridled White-eye nests were found in don 2000), and all forests were considered wet
any of these plant species. This apparent dif-
forests (Fosberg 1960, Falanruw et al. 1989).
ference in use of nest substrate is also likely Although apparently suitable low-elevation
due to the limited sample ofGuam and Saipan
white-eye habitat exists on Rota, white-eyes
BriNdoledinWfhoirtmea-teiyone noenstsi.ncubation or nestling are now restricted to mature forests at higher
elevations for reasons that are unclear.
and post-fledging parental care periods is We recommend additional research on the
available for Bridled White-eyes on Saipan,
breeding ecology of Rota Bridled White-eyes
Tinian, or Guam. Incubation and nestling pe-
riod data are known for Pale White-eye {Zos- and comparisons of their breeding ecology
terops pallidus), Silvereye (Z. lateralis), and with that of the Saipan Bridled White-eye.
Japanese White-eye (Z. japonicus). The Pale The information we obtained in our study was
(Broekhuysen and Winterbottom 1968) and limited; additional research may provide more
Japanese White-eyes (Isobe 1997) have 10- insight into—why the Rota Bridled White-eye
12 day incubation and 10-12 day nestling pe- is decli—ning and restricted to high-elevation
riods, but the Silvereye has incubation and habitats and provide valuable information to
nestling periods of 12-14 days each (Kikkawa help manage and recover this critically endan-
and Wilson 1983). The estimated duration of gered species.
post-fledging parental care is approximately 2
weeks for the Silvereye (Kikkawa and Wilson ACKNOWLEDGMENTS
1983) and 15-20 days for the Japanese White-
eye (van Riper 2000). Based on this infor- We would like to thank R. Dym/arov, M. Rogue.
I mation, the Rota Bridled White-eye’s period D. H Stauffer, and J. R. Walters for their assistance
I of post-fledging parental care may be subslan- throughout the study. We also thank S. Lawst>n and
!I tially longer than the 8 days we observed; SMa.ipVana,insS.tadM.foPrletnhteoirvicahssifsotranhceer ianssifsitnadnicneg onnestRsotoan,
more observations are needed. N. C. Johnson for the unpublished inlorniation on Sai-
Ij Kikkawa and Wilson ( 1983), report that the pan Bridled White-eye nests, and E. Taisacan for his
• eye-ring on recently Hedged Silvereye chicks hospitality and assistance. H. Higuchi also deserves
develops after a 1-week period. Van Riper special thanks for translating research papers on the
(2000) reports an eye-ring development period Japanese White-eye. f'inally, we would like to thank
i of 23 days for the .lapanese White-eye. Our J. A. Savidge, S. M. IMcntovich, anti an anonymous
, observations of one banded fledgling indicat- reviewer for hel[ilul comments on the manuscript. All
fuiuling lor this project was provided by the L.S. I'ish
ed that the eye-ring had not completely dc-
* veloped 8 days after fledging. OafnfdicWei,klMloitfieolSuclru\,iHcea,waPiaic.iliAcllIsrleasiuelasrclhiswhaasncdoWnidludcltiefde
Our observations of nest and fledgling at- untler F ederal Bird Marking and Salvage Permit 22.‘>70
tendance reveal that both sexes participate in and GNMl Pish aiul Game Permit PS 1447.
346 THE WILSON BULLETIN • Vol. !16, No. 4, December 2004
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