Corella, 2003, 27\4li 1o2-10s BOOBYNESTING ON RAINEISLAND, GREATBARRIER REEF P K. DYER Universityof the SunshineCoast, Sippy DownsDrive, Sippy Downs,Queensland 4556 Reeiwd:11February 2002 Collectingreliable field data on bregdingpopulations of boobyspecies on RaineIsland tor temporal comparison is challenging.This trial'saim was to establishbaseline data on nest censusestimates in December1998 to serveas ihJfoundationfor continuedmonitoring. Based On censuses, estimates of numbe.sof 3 700 Brown, 7OOMasked, and 330 Red-footedBooby nests were established. Egg predationby seagullsin December2000, however,prevented the first replicationof the studythus exposingthe limitationsol the method 'a INTRODUCTION 1993); and for the Red-footed Booby, range from few stragglers'in December l9l3 to 300 in February 1959 RaineIsland (144'01'E,11"37'S), a 28 hectarecoral cay (Warhaml96l). that consistsof a vegetatedridge sunounding a bare central few Australian studies detailing Red- depression,previously mined for phosphorous,is located Because therc are numbers or status approximately 100 kilometres ENE of Cape Grenville, footed or Masked Booby breeding (Marchant and Higgins 1990) this study attempted,in northernQueensland. The island supportsbreeding colonies data for continuing of three Booby species: Brown SuLaleucogaster', Masked December1998, to establishbaseline It was intendedto avoid Sukt doctylalrat and Red-footed Sula sula. breedingpopulation estimates. error due to absentbirds during the daytime, by estimating Brown Booby nestson Raine Island are distinguishable breedingpopulations based on nestcensus estlmates. 'loosely from those of the Masked Booby by the assembled'twigs gatheredin and around the nest, whereas METHODS Maked Booby nestshave a small collectionof pebblesor Milton el dl. (in Neil 1l dl. 2000 p.l3) stated that allhough the 'quadra! coral rubble in the centre with a similar collection search' for estimatesof seabird populations was more Practlcal 'line surrounding the outer perimeter of the nest (Marchant and when time was limited. there was less error in the transect'method in conjunction with line uansecl Shearwaler Higgins 1990).Although few MaskedBoobies nest in the This study was conducted data collection (see Dyer 2003). veg€tatedridges and on beaches,Warham (1961) suggests that guano mining, that denuded and extended the central To establish breeding estimates for the three Booby species, Boobies within ter north/south transects, made up of 4 depression,may haveinadvertently enhanced the preterred and their nest contents metre wide x 5 mctr€ long contiguous quadrats, were recorded Data habitatfor MaskedBoobies. collection was limited to a couple of hours in the moming and afternoon ro avoid the risk of heat stress for birds and researchersalike During The majority of the bare central depressionon Raine the day, because many birds are abseflt feeding or Ieave nesls when lsland is occupiedby Masked Boobies with Brown Boobies disturbed by researchers, the nest count was considered to indicate nestingaround the edges,extending into all areasof the breeding populations more reliably than bird counts. vegetatedridges. Red-footed Boobies roost and nest, about The ralio method for eslimating populations from stratified sample 'cases' a foot above ground, on matted vegetation or branchesof counts (Cochran l9?7, scc Dyer 2003) was used to eslimate all low shrubs.Except for Moulter Cay, Raine Island supports (i.e. nests with or wilhout birds, as well as birds without nests).In addition estimates for nests only, and birds only, were established for the only Red-footedBooby colony on the Great Barrier each of the three Booby species. Data were recorded according lo the Reef (Taplinand Blaber 1993). various habitats previously identified by Jeff Miller (J. C\nelius, pers. comm.) for coDtinuing bird studies (see Dyer 2003). In additior, The Raine lsland Brown Booby population has been 'in Pearson's Corelation Coefficient was used to eslablish any relationship recordedvariously as breeding small numbers'in July between sample areas and findings, and Chi-squared tesls were used to 'thousands 1843 (MacGillivray 1846 p. 1478) to all over test for any influence according to habita( type or transect location. 'guano theplace'in October l9l0 (MacGillivrayl9l8 p.l8l), and Stoddarl €l al- (1981) measured the density of birds in the between 8 000 and 16 000 (no dates provided) (Taplin and flats' using five sample areas. This was then extrapolated to estimale Blaber 1993). Without clarification of methods for the number of nests for Brown and Masked Boobies in lhe central according 1o Stoddart €r al., covered 40440 square estimatesor counts, little can be surmized conceming depression that, metres. This esdmate excluded absent feeding birds; those disturbed by population dynamics from the literature; however,Stoddart researchers;and birds nesting in the ridge areas.Although the sampling et al. (1981 pp. 23, 26) provided densitiesfor Brown mcthod was not replicated hcre, a similar mean density measure was (6.835/100mt,2'164 birds)and Masked(1.730/100 m'?, establishedand extrapolated for the ccntral depression, for comparative 'guano for the different 699 birds) Boobies in the whole of the flats' in purposes. Interpretation of comparisons should account research reportcd here was carried out population timing of data collection. The November1973. Reports of the MaskedBooby in the ea.ly morniflgs or late aftemooos belween 4 and 7 December rangefrom 400 to 500 in February1959 (Warham 1961) 1998 inclusive, whereas Sloddart, Gibbs, and Hopley's dala were to I 500-2 500 (no dates provided) (Taplin and Blaber collected at midday on 3 November 1973 (Stoddart er al. l98l). December,2003 P K. Dyet: Booby N€stingon Raine lsland, Great Barrier Reef RESULTS 5 460 (+ 97o se) cases altogether. The latter estimate allowed for absent birds and compared favourably with Brown Booby ( Entire Islond) total counts of Brown Boobies (by the author and others) The breeding stage for Brown Boobies ranged from using a quadrat method for counting, including visible empty nests, through adults incubating eggs and chicks but involving an unknown enor factor, of 2 073 mid accompaniedand unaccompanieddowny chicks, to almost afternoonon 28 November1998, and 1274 mid morning fledged chicks. This diversity complicatedanalyses so on 10 December 1998. The numbers of cases were censusesfor all cases (aggregating cases with birds and/ positively related to transect areas (Pearson'sCorrelation or nests), for cases involving nests without birds, and for Coefficient(df = 8): birds 0.0.914,p = 0.000;nests 0.872, birds without nests,were established. p = 0.001; all cases,0.926, p = 0.000). No significanr relationship was found between Brown Booby nests, In 31.9 per cent of cases,Brown Boobies were not Brown Boobies apart from nests, and habitat type (X, = obviously on or near a nest (Table l.l). Unaccompanied 1.529,df = 4, p = 0.Szt, n = 335) or transecrs(Ir= 6.551, chicksconstirured the majoriryof rhesecases 1i.e. 14.5 per df = 9, p = 0.684,n = 335). cenlof all casest.Empty neslsconstitured 39 per centof all cases(Table l.2). The remaining28.9 per cent of all Masked.Booby ( Entire Island) casesshowed signs of breeding.Of theseI5.4 per cent (of The breedingstage of all cases)represented birds still incubating one or two eggs the MaskedBooby was similar to that of the Brown Booby in (Table1.2). In additionto the habitatsanalysed, two chicks, that it encompassedthe full range from empty nests one nest,and one nest with an adult, a chick and an egg to almost fledged chicks. Masked Boobies were counted in (i.e. four casesin all) were presentin the vicinity of the those transectsthat traversedthe central depression.In 44.9 per transecttrajectories in the grassy verge that sunounded the cent of casesbirds were not vegetatedridge areas. obviously associatedwith nest (Table 2). Unlike Brown Boobies,lone MaskedBooby chicks were the minority in The censusfbr all habitatscombined resultedin estimates this category,constituting only 9 per cent of all cases.Lone of 3700 (1 (+ 77o se) nesrs, 1760 9o/ose) birds. and adults or pairs constituted the majority of cases not TABLE I.1 BrowDBoobies no! in nests,foufld in December1998, for habitatson RaineIsland: Central Dcpression; sourh section of the southernvegelated Ridgc (SsvR)r North Sectionof the Southemvegetated Ridse (NSVR): and NorlhemVeseralcd Rirtpe /NVRr Habitat Brown Booby Birds Depression NSVR NVR Nest No. % No. Vo Adult l4 4 1.2 4 1.2 l 0.3 23 Two adulls 6.9 I 0.3 0 0.0 0 0.0 l 0.3 2 0.6 Two adults and chick I 0.3 0 0.0 0 0.0 0 0.0 I Adult and chick 0.3 t2 3.6 l 0.3 4 t.2 3 0.9 Adult and juvenile 20 6.0 I {J 0.0 0 0.0 0 0.0 I 0.3 Chick 2',7 '7 8.2 1 0.3 2.1 13 3.9 48 14.5 T$o chicks I 0.3 0 0.0 0 0.0 0 0.0 I Juvenile 0.3 1 2.1 0 0.0 I 0.3 l Two juveniles 0.3 9 2.',7 0.0 0 0.0 I 0.3 0 0.0 I 0.3 Sub-total 64 r 9.3 6 t.8 17 5.1 19 5.'l 106 31.9 TABLE 1.2 BrownBooby n€sts found in December1998' for habiratson Rainelsland: cenFal Depression;south sectiooof rhesouthem vegeEled Ridge (ssvR): North Sectionof rhe Sourhem , VegeuredRrdge (NSVRt; ;nd NorthemVegetared Ridge iNVnl.- Habitar Brown Bobby Depression NVR SSVR TOTAL Nests No. E No. % No. No. Empty 65 19.6 l) 4.5 Adult 7.3 7.6 t29 39.0 6 L8 0 0.0 2 Adult and 0.6 3 0.9 u 3.3 chick l3 3.9 I 0.3 2 0.6 5 1.5 2l 6.3 Aduh, Chick and egg 4 t.2 I 0.3 I 0.3 0 0.0 6 Adult aod egg 28 NJ 1.8 I 0.3 3 0.9 3 0.9 Adult and two eBgs 8 2.4 35 10.6 0 0.0 0 0.0 I 0.3 Adult,egg and juvenite I 0.3 9 2.',7 0 0.0 0 0.0 0 0.0 Chick 4 1.2 I 0.3 0.0 0 0.0 7 2.1 l1 Egg i 0.3 0 0.0 0 0.0 0.0 I Two eggs 0 0.0 0 0.0 0 0.0 t 0.3 I 0.3 Sub-lotal 130 39.2 l8 5.4 32 9.',7 45 13.6 225 67.9 Toral1.2 and 1.2 r94 58.60 7.30 49 14.8 19.3 t00.0 P.K.