Breeding Biology of the Olive-Backed Oriole Oriolus Sagittatus on the Mid-North Coast of New South Wales

Australian Field Ornithology 2014, 31, 169–193

Breeding biology of the Olive-backed Oriole Oriolus sagittatus on the mid-north coast of New South Wales

Ashley J. Carlson

P.O. Box 4074, Forster NSW 2428, Australia Email: [email protected]

Summary. Although Olive-backed Orioles Oriolus sagittatus range widely through northern and eastern Australia, their breeding biology is poorly known. Data from 14 nests were recorded during three breeding seasons (in the period 2009–2012) on the mid-north coast of New South Wales. Nests were located in the outer foliage of four species of tree, between 1.7 and 9.8 m above the ground. Mean clutch-size was 2.3 eggs. Incubation was undertaken only by the female, and nest-attentiveness during incubation varied between 58 and 88%. The mean incubation period was 16.2 days, with hatching occurring synchronously in some nests and asynchronously in others. Similarly, brooding was also undertaken only by the female up to and including the sixth day after hatching, with nest-attentiveness during the nestling period ranging from 73% on the day of hatching to 15% on Day 6 post-hatching. The mean combined interval between feeding visits to the nest was 15.0 minutes, with a feeding visit rate of 4.0 h-1. Both males and females fed the nestlings although feeding effort by each varied considerably between individual nests. For nestlings fledging naturally, the mean nestling period was 15.0 days. Nest success was 80%, with an average 1.5 fledglings per nest. Once fledged, young Orioles remained within 70 m of the nest for up to 24 days and were fed at a rate of 3.3 visits h-1. Behaviour and vocalisations of the adults and young birds are also discussed. Data presented here fill a gap in the knowledge of this species within Australia, and are compared with available data for the only three species (out of a total of 33 species) within the Oriolidae family that have been studied in detail.

Introduction A review of the literature reveals that detailed studies on breeding biology have been undertaken for only three of the 33 species (Jønsson et al. 2010) of Old World orioles (Oriolidae), namely the Eurasian Golden Oriole Oriolus oriolus in Britain (Milwright 1998) and central Europe (see references cited by Milwright 1998), Black-naped Oriole O. chinensis in Taiwan (Chu 2007) and Australasian Figbird Sphecotheres vieilloti in Australia [Crouther & Crouther 1984; Turner 1995; Noske 1997; Birds Australia Nest Record Scheme (BA NRS)]. A major factor for this lack of study can be attributed to the location where most of these species reside, being equatorial Africa north to the Tropic of Cancer, India and South-East Asia through the many small islands of the Moluccas to New Guinea. Although Walther & Jones (2008) suggested that there is much uniformity within the family, Ghalambor & Martin (2001) concluded that Southern Hemisphere species tended to have higher adult survival and smaller clutch-sizes (which reduces risk to the adults), compared with their Northern Hemisphere congeners. Additionally, Martin (1996) found that European and North American passerines tended to have large clutches, short breeding seasons, low adult survival and short periods of parental care when compared with corvid species in Australia. Therefore, in this paper, 170 Australian Field Ornithology A.J. Carlson comparisons have been made between the Olive-backed Oriole O. sagittatus and the three previously studied species (Eurasian Golden Oriole, Black-naped Oriole and Australasian Figbird). In Australia, the distribution of the Olive-backed Oriole extends from the Kimberley region of northern Western Australia (WA), across the Top End of the Northern Territory (NT) to Cape York Peninsula in Queensland, then south to south-eastern South Australia, including the eastern edges of the western slopes of the Great Dividing Range and the eastern edges of the western plains (Barrett et al. 2003). Similar to seven other species within the family, Olive-backed Orioles are considered to be partly migratory (Loyn 1980; Marchant 1992; Newman 2007; Walther & Jones 2008; AJC pers. obs.). In New South Wales (NSW), eggs of Olive-backed Orioles have been located from September through to January (Higgins et al. 2006), indicating a long breeding season. Despite its widespread distribution and relative abundance, the breeding biology of this species is not well known (Higgins et al. 2006). Although Higgins et al. (2006) provided detailed information on the nest-site and nest-materials, eggs and clutch-size, there are no data on nest-attentiveness and incubation rhythm, and few detailed data on parental and brooding behaviour, feeding rates, development of nestlings and juveniles and vocalisations (at or near the nest, and by the juveniles). There are even fewer breeding data on the other Australian congener, the Yellow Oriole O. flavocinctus (Higgins et al. 2006). This paper describes the nest-site and interspecific associations, nest-building, eggs, clutch-size, incubation, brooding, nestling growth, fledgling behaviour, fledging success and vocalisations based on data from 14 nests located on the mid- north coast of NSW, during three breeding seasons, December 2009–January 2010, September 2010–January 2011 and October 2011–January 2012.

Study area and methods Observations of Olive-backed Oriole nests were made at five localities midway between Newcastle and Port Macquarie on the mid-north coast of NSW: Forster (32°12′S, 152°31′E), Green Point (32°15′S, 152°31′E), Pacific Palms (32°20′S, 152°31′E), Bungwahl (32°24′S, 152°28′E) and Cattai wetland (31°50′S, 152°38′E) (Figure 1). All nests were located within 10 km of the eastern coast of Australia, with an elevation of <10 m above mean sea-level. Individual nests were coded according to year, month and location, where F = Forster, G = Green Point, P = Pacific Palms, B = Bungwahl and C = Cattai wetland. The distance and direction to the meteorological site in Forster, site descriptions and nest codes are:

Forster (3.3 km NNW). The site consisted of two small swamp sclerophyll forest remnants separated by ~80 m, dominated by Swamp Mahogany Eucalyptus robusta and Broad- leaved Paperbark Melaleuca quinquenervia, but connected by a sclerophyll forest remnant of Red Mahogany Eucalyptus resinifera and Smooth-barked Apple Angophora costata to form a horseshoe shape around residential lots. Including several remnant trees within adjacent residential yards, the total vegetation area was ~1.4 ha. Additionally, there was a large tract of remnant sclerophyll forest (~60 ha) running parallel to (but 130 m distant beyond) a strip of residential housing. Nest codes for the Forster site are 0912F, 1009F, 1010F, 1011F and 1111F. Olive-backed Orioles breeding, mid-north coast, NSW 171

Figure 1. Locations of nests during the study of breeding Olive-backed Orioles on the mid-north coast of NSW. BOM = Bureau of Meteorology.

Green Point (7.5 km N). Nests were located along the edge of a large tract of Swamp Oak Casuarina glauca swamp forest backing onto residential housing, which forms part of the Booti Booti National Park, and also in a small reserve (0.12 ha) linking the forest with the residential street. The reserve was dominated by a stand of six large Broad-leaved Paperbarks and contained scattered Swamp Oaks. Nest codes for the Green Point site are 1010G, 1110G, 1111G and 1112G. Pacific Palms (17.5 km N). A small wedge-shaped Broad-leaved Paperbark–Swamp Oak forest remnant (1 ha) bounded by The Lakes Way, a major public road, the southern shore of Wallis Lake and the Pacific Palms Recreational Club. To the south is a large tract of undeveloped natural bushland and to the east is a parcel of Swamp Oak swamp forest (4.2 ha). Nest code for the Pacific Palms site is 1011P. Bungwahl (25.1 km N). A large tract of Swamp Mahogany–Broad-leaved Paperbark swamp sclerophyll forest bordering the southern shore of Smiths Lake and forming part of the Myall Lakes National Park. The nest was located in the lease area of the University of NSW field station. Nest code for the Bungwahl site is 1101B. Cattai wetland (40.3 km S). A large tract of forest of various vegetation types surrounding a modified wetland. The vegetation community at the nest-site is Broad-leaved Paperbark forest with Swamp Oak forest down-slope and mixed eucalypt sclerophyll forest up-slope. Nest code for the Cattai wetland site is 1112C; two old nests (10-C, 11-C) were also located and basic site data were recorded. Forster has a warm temperate climate with generally warm to very warm summers (January mean maximum 26.4°C) and mild to cool winters (July mean minimum 8.7°C). Mean annual rainfall (from 1896 to 2011) in Forster is 1220 mm, with spring and summer averages of 228 mm and 318 mm, respectively (Bureau of Meteorology 2012). Meteorological data from Forster are considered consistent for all nest locations in this study. Data recorded for nest-sites included height above ground level (to nearest 0.1 m) and orientation (based on eight cardinal directions) of the nest position from the tree-trunk, height of nest-tree (to nearest 1 m), distance from nest to end of branch on which it was placed (to nearest 0.1 m) and proximity to other nests (to nearest 5 m, up to 100 m). Internal and external dimensions of nests (to nearest 5 mm), maximum and minimum diameter of branches (to nearest 1 mm) at attachment of nest, and nest-material were recorded after each nest was abandoned. Length of a nest was measured in line with the leading branch 172 Australian Field Ornithology A.J. Carlson to which the nest was attached, and width was measured perpendicular to this. A mirror mounted on a pole was used for nest inspections. Eggs and nestlings from three nests (1010G, 1011P and 1110G) were individually weighed with spring balances (Pesola 60 g, Slater 200 g, Pesola 500 g) and measured with a steel ruler (graduated in mm) or electronic callipers. Measurements for nestlings were head–bill, wing- (from wrist to the tip of the longest pin or feather) and tail-lengths. Observations of nests were made from the ground at distances ranging between 13 and 15 m. An opened black umbrella in front of the observer provided screening of movements associated with note-taking during observations. Although in mostly clear view, activities undertaken by the birds were considered natural and not affected by the observer’s presence: within several minutes of disturbance (from nest inspections or accessing the observation position), the brooding female returned and settled on the nest. Nest-watches occurred during morning and afternoon sessions, and observations were recorded to the nearest 1 minute (nest 0912F) or 0.25 minute (nests 1009F, 1010F, 1010G, 1011F and 1011P). Generally, post-fledging events were recorded to the nearest 10 seconds, as visits were brief. Total observation times for nest-building, incubation, nestling and post- fledging periods were 9.4, 43.7, 97.7 and 30.6 h respectively. Nest-watches were generally made either daily or every second day. During laying, hatching and fledgling periods, two or three short visits were made daily. Time recorded as incubating or brooding by the female on the nest and absence from the nest are referred to as on- and off-bouts respectively. Nest-attentiveness refers to the percentage of time that the female spent on the nest. Observations of nests containing both nestlings and unhatched eggs have been included with nestling calculations. Consistent with Marchant (1980), the duration of the incubation period was calculated from the midpoint between the maximum interval (i.e. from the last observation before the clutch was completed to the first observation of all eggs hatched) and the minimum interval (i.e. from the first observation of the full clutch to the last observation of unhatched eggs) plus or minus half the range in hours between the difference of these intervals. The nestling period (hatching to fledging) was calculated in a similar way. Calculation of incubation and brooding bouts comprised full bouts only (i.e. partial bouts excluded), and the first or last bout was discounted from the analyses so that the number of on- and off-bouts was equal. Similarly, feeding rates were calculated for individual visits (visits by an adult where the apparent passage of food to a nestling occurred) with duration to the first and from the last visits excluded from analyses. Calculation of ‘nest approach’ was from the time the adult arrived in an adjoining tree to its arrival at the nest. No calculation of time at the nest was recorded where a female commenced brooding after feeding nestlings. All means are given ± standard deviation. For the analysis of the percentage of time spent incubating and brooding, replicates are observation periods. Observation periods in which there was at least one egg and one nestling have been excluded from the analysis, as was nest 1010F (nestling survived for only 2 days and an egg was present). The percentage of time for incubation is compared between nests with a one-factor Analysis of Variance (ANOVA). The effect of nestling age on brooding by the female was examined using a major effects Analysis of Covariance (ANCOVA) (StatSoft 1984–2012), with nestling age as a continuous variable and nest as a random effect. Hourly feed visit and faecal-sac removal rates were calculated per nest and per nestling for each observation period. The first observed feeding visit and the time before it and the time after the last feed visit for each period were excluded because of initial disturbance caused by the arrival of the observer. Rates per nestling are the rates per nest divided by the number of nestlings in the nest with a 95% Confidence Interval (CI) on the mean. Initial screening of rates suggested that the assumption of a normal distribution was reasonable, and screening of rates for each nest suggested no strong effect of nestling age. The factors Olive-backed Orioles breeding, mid-north coast, NSW 173 affecting rates were therefore investigated using ANCOVA, with time of day (morning/ afternoon) as a categorical fixed effect, age of nestlings as a continuous fixed effect, and nest as a random effect. To compare feeding rates by males and females, rates were calculated for each observation period as above but separately for each parent. Rates were compared with a repeated measures ANOVA with nest as a categorical variable. The effect of nestling age on faecal-sac removal rates was investigated using an ANCOVA with age of nestlings as a continuous fixed effect and nest as a random effect after initial graphical screening did not suggest any non-linearities in age effects.

Results Nest, nest-site and interspecific associations Nests were located in four species of tree: Broad-leaved Paperbark (71.4%, n = 10), twice in Blackwood Acacia melanoxylon and once each in Black Sheoak Allocasuarina littoralis and Swamp Oak, with a combined mean tree height of 15.5 ± 3.7 m (range 4.5–18 m, n = 14). Mean height of nest above the ground was 5.4 ± 2.3 m (range 1.7–9.8 m, n = 14) and the nest was positioned 0.6 ± 0.2 m (range 0.3–1.0 m, n = 12) from the end of the branch (Table 1). Orientation of the nest position from the tree-trunk varied from north-west clockwise to south, but the majority (64%, n = 9) were orientated to the north-west and north (Figure 2). Each nest was a suspended cup secured in a horizontal fork and attached along a minimum of two sides. In a few cases, an additional branch forked off and formed a third attachment site for the nest. Mean branch diameter at attachment of the nest was 6.0 ± 2.8 mm (range 2–13 mm, n = 44). When viewed from above, nests appeared either round or slightly oval in shape. Mean external dimensions were length 140 ± 12 mm (range 120–160 mm, n = 11), width 129 ± 11 mm (range 110–150 mm, n = 14) and depth 98 ± 11 mm (range 85–125 mm, n = 11) and mean internal dimensions were length 89 ± 7 mm (range 80–100 mm, n = 10), width 83 ± 4 mm (range 75–90 mm, n = 10) and depth 68 ± 11 mm (range 50–90 mm, n = 10). Nest dimensions are shown in Table 1.

Figure 2. Orientation of the nest (n = 14) position from the trunk of the nest-tree of Olive-backed Orioles breeding on the mid-north coast of NSW. 174 Australian Field Ornithology A.J. Carlson 4.5 11.0 17.0 17.0 14.0 16.0 16.0 16.0 16.0 18.0 18.0 18.0 18.0 18.0 Height of 15.5 ± 3.7 nest-tree (m) 1.0 0.7 0.7 0.5 0.5 0.3 0.4 0.4 0.4 0.6 0.9 0.6 0.6 ± 0.2 Distance of nest to end of nest-branch (m) 1.7 7.1 4.5 9.5 7.0 6.3 3.9 2.9 4.4 4.9 5.0 3.8 4.8 9.8 5.4 ± 2.3 Height of nest above ground (m) 3, 7 4, 7 5, 6 3, 6 3, 9 2, 9 2, 9 5, 11 2, 11 2, 13 6, 13 6.0 ± 2.8 Diameter of nest-branches (mm) Internal 95/75/60 95/85/70 85/85/65 85/80/75 85/85/50 80/85/70 90/85/60 90/80/70 80/90/90 100/80/65 89 ± 7 (L) 83 ± 4 (W) 68 ± 11 (D) Nest dimensions (L/W/D, mm) External 150/130/95 130/130/95 150/120/85 140/130/85 150/130/90 98 ± 11 (D) 130/145/125 140/110/100 140/150/100 130/120/100 120/120/100 160/130/100 140 ± 12 (L) 129 ± 11 (W) Nest parameters for Olive-backed Dimensions [external Orioles, mid-north coast, NSW: and internal length width (L), (W) and Table 1. Table depth (D)] of nest, diameter of branches to which nest is attached, height of nest above ground level, distance of nest to end of nest-branch, and height of nest-tree. The combined means are given ± standard deviation. See text for nest codes measurement dimensions. 0912F 1009F 1010F 1010G 1011F 1011P 1101B 1110G 1111F 1111G 1112G 1112C 10-C 11-C Mean Nest code Olive-backed Orioles breeding, mid-north coast, NSW 175

Table 2. Nests of other bird species located within 100 m of Olive-backed Oriole nests on the mid-north coast of NSW. The horizontal distances (m, measured to the nearest 5 m) between nests are given in the body of the table. See text for Olive-backed Oriole nest codes.

Species Olive-backed Oriole nest code

1009F 1010F 1010G 1011F 1011P 111oG 1111F 1112G

Spotted Dove 100 20 Streptopelia chinensis

Tawny Frogmouth 40 40 Podargus strigoides

Sacred Kingfisher 60 60 Todiramphus sanctus

Satin Bowerbird 20 Ptilonorhynchus violaceus

Little Wattlebird 15 20 Anthochaera chrysoptera

Red Wattlebird 15 15 Anthochaera carunculata

Noisy Friarbird 60 Philemon corniculatus

Striped Honeyeater 25 35 35 Plectorhyncha lanceolata

Black-faced Cuckoo-shrike 30 55 20 20 5 Coracina novaehollandiae

Australasian Figbird 70 35, 60a 3 × 20a 30, 40a Sphecotheres vieilloti

Olive-backed Oriole 85b 175b Oriolus sagittatus

Australian Magpie 35 Cracticus tibicen

Pied Currawong 60 Strepera graculina

Willie Wagtail 40 45 Rhipidura leucophrys

Torresian Crow 60 15 Corvus orru

Magpie-lark 45, 60 45 40 15 55 Grallina cyanoleuca

Common Myna 35 35 35 Sturnus tristis a Multiple Australasian Figbird nests were located within the vicinity of the Olive-backed Oriole nest. b Nest 1112G is a second nest by the pair from nest 1110G. Nest 1111G was built 85 m from nest 1110G, and nest 1112G was built 175 m from nest 1111G. Refer to results for full description. 176 Australian Field Ornithology A.J. Carlson

All nests were constructed predominantly of paperbark strips, with most nests adjacent to residential housing containing various amounts of the ornamental Spanish Moss Tillandsia usneoides. Other material used included Creeping Brookweed Samolus repens, vine tendrils, spider web and insect cocoon casings. Nests were lined with fine grass, Casuarina needles or Sea Rush Juncus kraussii, and all lining materials were <1 mm in diameter. Nesting attempts by 17 species of bird were recorded within 100 m of the Olive- backed Oriole nests. These species and the horizontal distances of their nests from the Olive-backed Oriole nests are summarised in Table 2. At Forster, Green Point and Cattai wetland, new nests were constructed in close proximity to that of the previous year/s. In September 2010 at Forster, a nest (1009F) was constructed 6.5 m from a nest-site used in December 2009 (0912F). This nest was abandoned, at completion of construction but prior to egg laying, and a second nest (1010F) was constructed 135 m away, from which the nestling was preyed upon. A third nest (1011F) was then constructed 8.5 m from nest 0912F or 3 m from nest 1009F. During November 2011, a nest (1111F) was located 19 m from the 1011F and 30 m from 0912F nest-sites. At Green Point, two pairs of Olive-backed Orioles nested in close proximity during 2011: the nest of the first pair, found in October (1110G), was positioned 60 m west of a 2010 nest-site (1010G). In November, the nest (1111G) of the second pair was found 25 m south- east of nest 1010G and 85 m from nest 1110G. The first pair constructed a second nest (1112G) 85 m north-west of their first nest (1110G) and 175 m from the nest (1111G) of the second pair. At Cattai wetland, two abandoned nests were located at 19 m (11-C) and 34 m (10-C) from the December 2011 nest (1112C). Nest 10-C was noted in early 2011 during a regular seasonal survey as recently abandoned, and nest 11-C, found during observations of nest 1112C, was also recently abandoned. Detailed observations of building were undertaken at two nests (1009F and 1011F) during morning (n = 3) and midday (n = 2) sessions lasting between 85 and 180 minutes and totalling 9.4 h (Table 3). Both nests were in the early stages of construction when found, and only the female was observed constructing the nest. Combined mean time between construction visits was 10.2 ± 11.9 minutes (range 1.8–67.3 min., n = 53) and the mean duration of construction visits (nest shaping) was 2.0 ± 2.0 minutes (range 0.3–13.0 min., n = 58).

Eggs, clutch-size and incubation Most eggs (n = 19) were fawnish white to mid fawn, with small to large brown to purplish or reddish-brown blotches (Figure 3a), but one egg in a clutch of three (nest 0912F) was whitish cream with a faint hint of pale-brown blotches, and one egg in a clutch of two (nest 1010F) was pinkish cream with small-to-medium brown blotches. Eggs were ovoid in shape, with a mean size of 32.2 × 22.7 mm (range 31.0–33.9 × 22.4–23.0 mm, n = 5). The weight of each egg (n = 5) from two clutches at commencement of incubation was 9.0 g, ~9.5% of the female’s body weight (94.4 g, n = 8: Higgins et al. 2006); just before hatching all eggs weighed 8.0 g each. Of nine clutches, six were of two and three were of three, giving a mean clutch-size of 2.3 ± 0.5 eggs. Olive-backed Orioles breeding, mid-north coast, NSW 177 Mean D between 12.1 ± 14.3 12.1 9.4 15.2 19.8 ± 12.2 19.8 23.0 ± 17.8 16.6 ± 16.2 ± ± Mean 8.8 12.4 10.2 ± 11.9 Egg adjustments 1.0–71.3 1.0–56.8 5.8–47.8 1.0–71.3 D between 15 31 43 89 No. No.

1.8–51.3 2.8–67.3 1.8–67.3 Mean D 9.1 ± 3.3 7.0 ± 3.3 5.9 ± 4.6 5.9 11.3 ± 7.3 11.3 7.7 ± 5.6 Intervals between contruction visits 33 20 53 No. 2.3–13.3 1.0–22.5 5.0–13.0 3.0–34.3 D of bout 1.0–34.3 7 17 10 36 70 No. 16 42 30 % T on T construction 537 70.0 64.0 Off-bouts 211.5 191.5

2.4 0.6 ± ± Mean 71 58 66 73 88 1.3 2.4 2.0 ± Nest- attentiveness (%) D Nest-construction visits 0.5–2.8 0.3–13.0 0.3–13.0 Mean D 12.9 ± 3.0 12.9 11.6 ± 11.2 11.6 27.4 ± 19.9 50.4 ± 31.6 50.4 21.1 ± 21.8 21 37 On-bouts 58 No. 5.5–67.5 8.0–16.0 0.5–52.8 D of bout 2.0–90.8 0.5–90.8 7 17 10 36 70 No. 1 4 5 No. T 90.0 1475 415.7 465.8 503.8

5 3 4 4 16 No. T 180 385 565 Observation sessions T 710 301 708 902 2621 Observation sessions Incubation by Olive-backed Orioles, mid-north coast, NSW. Means are given ± standard deviation; all times (T) and durations (D) Nest-constructionMeans are given ± standard deviation; all times by Olive-backed Orioles, mid-north coast, NSW. (T) and Table 3. durations (D) are measured in minutes. See text for nest codes. 4. Table are measured in minutes. See text for nest codes. Nest code 0912F 1010F 1010G 1011P Combined 1009F 1011F Nest code Combined 178 Australian Field Ornithology A.J. Carlson

Only females were observed to incubate. Detailed observations of incubation were undertaken at four nests (0912F, 1010F, 1010G and 1011P), totalling 43.7 h during both morning (n = 7) and afternoon (n = 9) sessions that lasted between 59 and 195 minutes. The mean duration of incubation on-bouts was 21.1 ± 21.8 minutes (range 0.5–90.8 min., n = 70) and the mean duration of off-bouts was 7.7 ± 5.6 minutes (range 1.0–34.3 min., n = 70) (Table 4). The percentage of time spent incubating during daylight hours varied significantly among nests (F3,12 = 12.2, P <0.001) with the nest mean being 71.4 ± 12.0%. On return to the nest, the eggs were not touched before the female started to incubate. The female rolled the eggs while sitting, at mean intervals of 16.6 ± 16.2 minutes (range 1.0–71.8 min., n = 89). Clutches hatched synchronously at three nests (<12 h apart: 3.8 h—two of two eggs, 11.2 h—two of three eggs, 9.3 h—two of two eggs) and asynchronously at three nests (>12h apart: 42.9 h—two of three eggs, 25.3 h—three of three eggs, 20.9 h—two of two eggs). A mean incubation period was calculated for five nests as 16.2 ± 0.5 days (range 15.3–16.6 days). Of the 21 eggs observed, 18 hatched (85.7%). For 10 eggs where times were recorded, half hatched before 0930 h, an additional two hatched between 0630 and 1230 h, two between 0630 and 1430 h, and one between 1230 and 1800 h. At nest 1010F, the female was observed departing from the nest at 0805 h with half an eggshell in her bill; she then flew out of sight.

Brooding As with incubation, brooding was only by the female. Detailed observations were undertaken at five nests (0912F, 1010F, 1010G, 1011F and 1011P: Table 5). Nestlings ≤6 days old were brooded during 15 of 17 observation periods totalling 43.3 h. The percentage of time spent brooding did not differ significantly between nests (F3,27 = 1.6, P = 0.20) but varied markedly with the nestlings’ age (F1,27 = 40.5, P <0.001, Figure 4). After regular brooding had ceased, the female brooded nestlings on several occasions, including one continuous 63-minute period, during moderate rainfall, up to and including the day of fledging. On one occasion, the male also crouched over the nestlings for ~2 minutes, during rain and while the female was foraging. These data were not included in the calculation of brooding statistics.

Feeding and feeding rates Most feeding visits involved single items of prey and only one nestling was fed per visit. The type of food delivery within the first few days after hatching could not be confirmed because of the depth of the nest and because adults often arrived at the nest with no visible prey sighted. Nestlings may have been fed by regurgitation, or small prey items may have been concealed in the bill of the adult. Occasionally, the adult arrived with a prey item and tried unsuccessfully to feed a nestling several times before re-orientating the item in the bill or feeding it to another nestling. On the day of hatching (Day 0), nestlings averaged 7.4 g (range 7.0–7.5 g, n = 4), but their weight increased rapidly (Figure 5) at least until 13 days post-hatching when Olive-backed Orioles breeding, mid-north coast, NSW 179

6 0 15 29 14 52 70 90 131 357 Total 7 5 5 9 35 U 21 17 21 43 95 4 I 7 9 56 36 46 42 62 28 148 3 0 1 66 7 33 C 10 22 40 2 56 33 66 52 1 2 S 6 13 22 No. of food items given to nestlings No. 1 71 79 58 70 5 4 L 13 30 52 a a

0 75 73 81 62 % brooding on day indicated (post-hatching)

Male 9 (17) 6 (43) 51 (57) 40 (57) 64 (49) D

170 (48) Mean 4.7 ± 2.6 10.1 ± 7.3 11.8± 14.9 11.8± 14.9 ± 12.3 30.4 ± 17.3 12.2 ± 13.0 Feeding effort: no. (and %) visits by 8 (57) 67 (51) 39 (43) 43 (83) 30 (43) Female 187 (52)

D a a 0.8–9.3 5.0–41.0 1.0–34.0 1.8–68.8 12.0–54.3 0.8–68.8 Off-bouts 0.46 0.64 0.54 per feed No. faecal No. sacs taken 7 0.63–0.52 8 0.58–0.90 15 18 22 70 No. a a 4.1 5.3 2.4 4.0 4.1–1.7 5.7–2.4 per hour No. feeds No. 70.8 213.0 104.0 223.0 243.0 853.8 Total T

mean D

11.4 ± 8.5 11.4 14.5 ± 9.8 14.5 ± 11.9 Interval D 25.4 ± 13.5 25.4 20.1 ± 23.5 20.1 15.0± 13.9 Mean 13.7 ± 9.7 13.7 14.1 ± 8.4 15.8 ± 9.9 15.8 15.7 ± 13.9 15.7 25.1 ± 16.9 25.1 15.6 ± 11.0 Feeding visits to nestlings 1.0–48.0 0.0–79.5 0.3–50.5 3.0–58.0 0.5–106.5 Interval D 0.0–106.5 1.0–37.5 1.8–45.8 0.8–31.0 6.0–57.0 0.8–32.3 D of bout 0.8–57.0 On-bouts 51 12 46 82 122 313 visits 7 8 15 18 22 70 No. No. of intervals No. between feeding 14 52 70 90 131 No. No. 357 125.3 176.0 237.3 246.5 309.8 Total T 1094.9 2 6 9 8

12 37 No. No. 3 2 4 4 4 17 sessions No. 360 Observation 1161 1557 1403 1380 5861 Total T 1 3 2 2 720 586 540 390 360 2/1 2596 Feeding of nestlings by Olive-backed Means are given ± standard deviation; all times (T) and Orioles, mid-north coast, NSW. Total T No. of No. Observation sessions Brooding by Olive-backed Means are given ± standard deviation; all times (T) and durations (D) Orioles, mid-north coast, NSW. nestlings

Table 5. are measured in minutes. See text for nest codes. Day 0 = day of hatching. 6. Table durations (D) are measured in minutes. See text for nest codes. Food items seen given to nestlings: L = lepidopteran S spiders, larvae, C = cicadas, I unidentified insects, and U items. Combined Nest code 0912F 1010F 1010G 1011F 1011P Combined Nest code 0912F 1010F 1010G 1011F 1011P Variation in rate between two nestlings present and one nestling nest (one fledged at 0912F, perished 1010G) Nest contained both nestlings and an unhatched egg (which subsequently hatched) during the observation period a a 180 Australian Field Ornithology A.J. Carlson

a c

Figure 3. Olive-backed Orioles breeding on the mid-north coast, NSW: (a) nest and eggs, Pacific Palms, (b) nestlings (4 days old), Pacific Palms, (c) fledgling (13 days old), Green Point. Photos: Ashley J. Carlson

20 % time brooding

0 4 8 12 16 Age of nestling(s) (days)

Figure 4. Percentage of time that Olive-backed Orioles spent brooding as a function of the age of their nestlings. Symbols represent nests as follows: = 0912F; = 1010F; = 1010G; ∆ = 1011F; = 1011P (see text). The fitted line is a 2-parameter negative exponential curve: % time brooding = 90.8 x e-0.32 days; r2 = 0.75 (r is coefficient of determination). Day 0 = day of hatching. Olive-backed Orioles breeding, mid-north coast, NSW 181

Table 7. Results of main-effects Analysis of Covariance of feeding visit rates by Olive- backed Orioles to nests containing nestlings, mid-north coast, NSW. F = ANCOVA test statistic, d. f. = degrees of freedom, P = probability.

Effect F d. f. P

A. Per nest Age of nestlings 2.44 1, 28 0.119 Time of day (morning/afternoon) 0.82 1, 28 0.421 Nest (random effect) 4.64 4, 28 0.003

B. Per nestling Age of nestlings 1.61 1, 28 0.214 Time of day (morning/afternoon) 0.93 1, 28 0.342 Nest (random effect) 1.79 4, 28 0.159 their mean weight was 66 g (range 62–71 g, n = 4) or ~70% of the adult weight (male 95.6 g, n = 19; female 94.4 g, n = 8: Higgins et al. 2006). Detailed observations of feeding were undertaken at five nests (0912F, 1010F, 1010G, 1011F and 1011P) during the morning (n = 19) and afternoon (n = 18), with observation sessions totalling 97.7 h and lasting between 70 and 210 minutes (Table 6). The combined mean feeding visit rate by both adults was 4.0 h-1 (range 1.7–5.7 h-1), with no significant difference between feeding visits during the morning or afternoon for all study nests considered for the full nestling period (t = 0.58, d. f. = 30, P = 0.57). The duration of the interval between feeding events varied from 0 (when both adults were present at the nest simultaneously) to 106.5 minutes, with a combined mean of 15.0 ± 13.9 minutes (n = 313). A full factorial model of feed visit rates per nest was not significant overall (P = 0.178) and yielded no significant effects or interactions (P >0.25). In contrast, a main-effects model was significant overall P( = 0.006, r2 = 0.46), indicating a significant effect of nest and a possible but weak negative effect of age of nestlings (Table 7A). Data suggested that the effect of nestling age was largely attributable to a single nest in which rates declined after being reduced from two to one nestling, and that differences between nests may be attributable to the number of nestlings in the nest. A main-effects model for feeding rates per nestling was not significant overall (P = 0.157) and yielded no significant effects (Table 7B), strongly supporting the suggestion that the main driver of feed visit rates is the number of nestlings in the nest. The mean feed visit rate per nestling was 2.2 ± 0.3 h-1. Males and females made roughly equal contributions (48–52%) to the provisioning of nestlings at each nest except nest 1010G, where 83% of feeding visits were by the female (Table 6, Figure 6). Using observation periods as replicates, there was no significant overall difference between males and females 182 Australian Field Ornithology A.J. Carlson

in nest feed visit rates (F1,30 = 1.3, P = 0.27), a strong effect of nest (F4,30 = 4.7, P = 0.004), but no significant interaction between nest and the feed visit rate

(F1,30 = 1.5, P = 0.22). Collection and consumption of faecal sacs was undertaken by both parents within 1 minute of a feeding visit at the nest. A faecal sac was removed on 57% of feeding visits to the nest. Only one faecal sac was removed per feeding visit, except once in a rapid sequence of two feedings by the male and female, in which the male was displaced by the arriving female, which then removed two sacs. Sac removal rates did not vary significantly with age of nestling (F1,25 = 0.6, P = 0.46) or between nests (F3,25 = 0.2, P = 0.92), and there was no significant interaction between nests and age of nestlings (F3,25 = 0.7, P = 0.56). Juveniles from three nests (0912F, 1010G and 1011F) were observed during morning (n = 8) and afternoon (n = 9) sessions totalling 30.6 h and lasting between 53 and 180 minutes (Table 8). Once fledging occurred, the combined mean feeding rate of adults to juveniles was 3.3 h-1 (range 2.8–3.7 h-1). Mean duration of the interval between feeding events was 18.5 ± 15.7 minutes (range 0.8–76.0 min., n = 70). Of the 357 feeding visits to nestlings observed at the five nests, food items were identified for 262 visits. Items delivered were: caterpillars (Lepidoptera) (n = 52), spiders (Arachnidae: n = 22), cicadas (Cicadidae: n = 40) and unidentified insects (n = 148) (Table 6). Similarly, for the 88 feeding events recorded during observation sessions of juvenile birds, 39 items were identified as follows: caterpillars (n = 3), spiders (n = 5), cicadas (n = 17), unidentified insects (n = 13) and a single red berry. Numerous wingless or partially winged cicadas were delivered, suggesting that these had been beaten in preparation for ingestion. Additionally, several large spiders were observed to be beaten up to a dozen times, with re-orientation in the bill between each beat. Similarly, a hairy caterpillar was beaten and/or dragged across the rough bark of a Swamp Mahogany before delivery to the nest.

Development of young and fledging behaviour At hatching, nestlings were largely naked, with yellowish-pink translucent skin, except for yellowish-orange down on the crown, and along the spinal (from mantle to the upper rump), femoral and humeral feather-tracts (Figure 3b). At fledging, down was still present on the crown and spinal tract (Figure 3c) and remained visible on the crown up to and including 4 days later. Eyes appeared as thin slits at 5 days post-hatching, and fully opened at 9 days (Front cover). The bill colour at hatching was pink, but by fledging had graded from pinkish-ivory at the tip through to pale brown at the base with creamy-white rictal flanges. The growth of the head–bill length is depicted in Figure 7. The trailing edge of the wings began darkening within 2 days of hatching, with remige pins emerging on Day 4 (Figure 3b) and feathers visible 4 days later. Growth of the outer wing fitted a polynomial function (Figure 8). Body and tail (rectrix) feather-tracts were in pin 6 days post-hatching, with body feathers emerging 2 days and rectrices 3 days later. Growth of the tail fitted an exponential function (Figure 9). At fledging, feathers where present on the crown, dorsally from Olive-backed Orioles breeding, mid-north coast, NSW 183

80 70 60 50

40 30 20 Weight (g) 20 10

0 2 4 6 8 10 12 14 Age post-hatching (days)

Figure 5. Growth of Olive-backed Oriole nestlings, mid-north coast, NSW: weight. Day 0 = day of hatching.

Nest visits per hour Male 0 Female

0912F 1010F 1010G 1011F 1011P Nest code

Figure 6. Modelled feed visit rates by male and female at five Olive-backed Oriole nests on the mid-north coast of NSW (mean ± 95% Confidence Interval). Nest 1010G had only one nestling during all observation periods. See text for nest codes.

50 45 40 35 30 25 20 15 10

Head–bill length (mm) 5 0 2 4 6 8 10 12 14

Age post-hatching (days)

Figure 7. Growth of Olive-backed Oriole nestlings, mid-north coast, NSW: head–bill length. Day 0 = day of hatching. 184 Australian Field Ornithology A.J. Carlson

12 52 24 88 Total Mean D 1.0 ± 1.5 1.0 1.9 ± 2.3 1.9 0.7 ± 0.3 0.7 1.4 ± 2.0 7 6 U 36 49 Male D I 1 4 8 13 0.5–1.3 0.3–11.0 0.3–10.0 0.3–11.0 1 1 B 9 55 49 113 visits No. of No. 1 5 C 11 17

1 1 3 S 5 D at the nest D at the No. of food items given to juveniles No. 1 2 L 3 Mean D 1.6 ± 1.7 1.6 1.6 ± 3.3 1.6 3.8 ± 4.1 3.8 2.6 ± 3.4

D Female 3.7 2.8 2.8 3.3 0.3–8.5 0.5–15.8 0.5–18.8 0.3–18.8 Feeds/h 32 22 46 100 visits No. of No.

mean Interval D 16.4 ± 13.7 16.4 21.5 ± 16.0 21.5 21.3 ± 22.2 21.3 18.5 ± 15.7 Mean D 3.2 ± 2.3 3.2 1.0 ± 0.8 1.0 0.8 ± 0.8 0.8 2.2 ± 2.1 1.0–76.0 D 1.8–69.8 0.8–53.3 0.8–76.0 Interval D Feeding visits to juveniles Male 0.3–4.8 0.3–2.0 0.8–10.5 0.3–10.5 41 19 10 4 70 47 35 86 No. of No. No. of No. intervals approaches between visits 12 52 24 88 Mean D 1.8 ± 2.5 1.8 ± 2.1 2.6 No. visits No. 0.5 ± 0.4 0.5 1.7 ± 2.1 D approaching the nest the D approaching . . D 2 4 11 17 No 0.3–2.3 0.3–14.8 0.5–10.0 0.3–14.8 Female 33 28 40 280 480 101 1075 1835 No. of No. Total T Observation session approaches Feeding of juveniles Means are given ± standard deviation; all times (T) and by Olive-backed Orioles, mid-north coast, NSW. Duration of activities female and male Olive-backed Orioles approaching at the nest while nestlings were present, mid-north

Table 8. Table durations (D) are measured in minutes. See text for nest codes. Food items seen given to juveniles: L = lepidopteran S = spiders, larvae, C = cicadas, B berry, I unidentified insects, and U items. 9. Table coast, NSW. Means are given ± standard deviation; durations (D) measured in minutes. See text for nest codes. Nest code Nest code 0912F 1010G 1011F Combined 1010G 1011F 1011P Combined Olive-backed Orioles breeding, mid-north coast, NSW 185

90 80 70 60 50 40 30 20 Wing-length (mm) 10 0 2 4 6 8 10 12 14 Age post-hatching (days) Figure 8. Growth of Olive-backed Oriole nestlings, mid-north coast, NSW: wing- length. Day 0 = day of hatching.

5 Tail-length (mm)

0 2 4 6 8 10 12 14 Age post-hatching (days) Figure 9. Growth of Olive-backed Oriole nestlings, mid-north coast, NSW: tail-length. Day 0 = day of hatching. the mantle to the rump (Figure 3c) and ventrally between the breast/upper belly and vent. Feathers were emerging on the outside edges of the chin, thighs and tail while the flank, nape, neck and throat areas all remained bare. Feather cover of these areas was noted 9 days later or 24 days post-hatching. Also, underwing- coverts were not visible during preening by a juvenile up to 8 days after fledging. Nestling periods were calculated for 12 nestlings from six nests, although five of these nestlings were from three nests (1010G, 1011P and 1110G) for which detailed data on nestlings were obtained. Handling these nestlings to obtain detailed data resulted in their fledging 1.6 days earlier (13.4 ± 0.4 days; range 12.4–14.0 days, n = 5), on average, than those that were not disturbed. The mean nestling period for the undisturbed nestlings was 15.0 ± 0.4 days (range 14.2–15.8 days, n = 7). Most (natural) fledging occurred during the early morning (up to 0930 h), but one nestling fledged between 1200 and 1400 h. Mean nest productivity was 1.5 fledglings. At fledging, flight was generally poor, but the juveniles managed, through a series of hops along branches and short fluttering flights (<5 m), to move vertically through to the canopy. During one morning observation session, a 1-day-old 186 Australian Field Ornithology A.J. Carlson juvenile was located within 1 m of the ground but within 1 h had managed to attain a height of 7 m. Generally, 6 days post-fledging, fluttering flights by juveniles were up to 20 m in distance, and by ~14 days post-fledging, flight resembled that of adults, including brief wing closures in mid flight. Juveniles were observed within the natal area (<70 m from the nest) for up to 19 days (nest 0912F), 21 days (nest 1011F) or 24 days (nest 1110G) after fledging. Two juveniles were found accompanying an adult 185 m from their putative nest (1111F) 43 days after fledging. Other juveniles were located 235 m and 170 m from their putative nests (1011F and 0912F, respectively) 45 and 46 days after fledging, respectively. Juveniles from different nests were seen being fed a caterpillar and a cicada at 43 and 45 days post-fledging, respectively, by a presumed parent. A juvenile that fledged from nest 0912F was observed attempting to forage independently 46 days after fledging, in the presence of an adult, when it landed in the top of a 3-m-high Sandpaper Fig Ficus fraseri and failed to detach a fruit from the stalk after twisting it. Another juvenile (49 days post-fledging) flew from the mid canopy down to within 0.5 m of the ground and removed and ate several fruits from a Snake Vine Stephania japonica growing amongst Common Bracken Pteridium esculentum. One fruit was wiped across a branch numerous times, to break off the stalk before being consumed.

Parental behaviour An adult Olive-backed Oriole was mostly present within 25 m of the nest during both the incubation and nestling stages. During incubation, the female rarely left the nest to forage before the male arrived in an adjoining tree, although the male may have been present or arrived unnoticed. With nestlings present, the adults mostly arrived in the mid-to-upper canopy of an adjacent tree, within 25 m, before descending to the nest to either feed the young or for the female to brood. Generally, at the presence of the second adult, the first adult vacated the area. Once at the nest, feeding and collection of a faecal sac were completed quickly, after which the adult either remained at the nest for a further period of time or departed to one of the adjacent trees. Detailed observations of nest approach and time at the nest by the adults were undertaken at nests 1010G, 1011F and 1011P during the nestling stage (Table 9). Some of the longer durations of approach included instances involving disturbance by other birds (see Table 10) and, in several cases, the female waiting for the male to approach, feed and vacate the nest vicinity. Combined mean duration approaching the nest was 1.7 ± 2.1 minutes (range 0.3–14.8 min., n = 101) for females and 2.2 ± 2.1 minutes (range 0.3–10.5 min., n = 86) for males. Combined durations at the nest were 2.6 ± 3.4 minutes (range 0.3–18.8 min., n = 100) for females and 1.4 ± 2.0 minutes (range 0.3–11.0 min., n = 113) for males.

Vocalisations The most common vocalisation of Olive-backed Orioles is the melodious oree-oree- ole (Bryant 1928, 1945) or or-ee-ee, or-ee-ee (Leach 1928) call, herein referred to Olive-backed Orioles breeding, mid-north coast, NSW 187

Table 10. Bird species recorded showing aggression towards (T) or receiving aggression from (F) breeding Olive-backed Orioles within 20 m of the nest (n) or juvenile (j), mid-north coast, NSW. See text for nest codes.

Species Olive-backed Oriole nest code

0912F 1009F 1010F 1010G 1011F 1011P 1110G 1112C

White-faced Heron F(j) Egretta novaehollandiae

Brown Goshawk F(j) Accipiter fasciatus

Australian King-Parrot F(n) Alisterus scapularis

Laughing Kookaburra F(n) F(n) Dacelo novaeguineae

Sacred Kingfisher F(n) F(j) Todiramphus sanctus T(n) T(n)

Satin Bowerbird F(n) F(n) F(n) Ptilonorhynchus violaceus

Noisy Miner F(j) Manorina melanocephala

Little Wattlebird F(n) F(n) F(n) F(n) Anthochaera chrysoptera T(j)

Red Wattlebird F(n) F(n) F(j) T(n) Anthochaera carunculata T(n)

Black-faced Cuckoo-shrike T(n) T(n) Coracina novaehollandiae

Australasian Figbird F(n) F(n) F(n) Sphecotheres vieilloti

Olive-backed Oriole F(n) Oriolus sagittatus

Grey Butcherbird T(n) Cracticus torquatus

Pied Currawong F(n) F(n) Strepera graculina 188 Australian Field Ornithology A.J. Carlson as the ‘oriole roll’. The general vicinity of nests can be located by the presence of the male vocalising the oriole roll within 50 m of a nest. During the present study, the female was not observed to use the oriole roll. Brooding females were quite vocal on the nest, with two dominant calls, draah or draah drit, used either singly or repeatedly. These calls seemed to serve as a contact call to the male, and were often associated with the imminent departure by the female from the nest. An additional vocalisation, sounding like peet, by the female began once nestlings were present in the nest. While perched in an ‘observation’ tree, the female periodically gave single peet calls at intervals ranging between 5 and 60 seconds. Upon sighting the male on his return from foraging, the peet calls became louder and were repeated more rapidly. As the female arrived back in the surrounding trees from foraging, she also uttered the peet call. On one occasion, when the male at nest 0912F failed to feed the nestlings after three attempts, the female (also perched on the nest-rim) made soft chatter, with bill opening and closing rapidly, after which the male passed the food to her. A short growling grating noise was also heard on four occasions just after both the female (n = 3) or male (n = 1) fed nestlings. A scolding oork oork orka kaoork was often used by both the male and female when swooping on either myself or the mirror during nest inspections or nestling measurements. The first audible noises from the nestlings were heard 7 days (nest 1011F: three nestlings), 8 days (nest 1011P: two nestlings) and 10 days [nests 0912F (two nestlings) and 1010G (one nestling)] post-hatching; these developed into a buzzing git, git, git, … during feeding. Recently fledged juveniles were often located by their occasional squeaky draah drit or a cheep resembling the sound of a squeaky plastic toy being squeezed. These calls generally ceased within 2 days of fledging, but some juveniles continued the buzzing git call during feeding visits up to and including 3 days after fledging. On 23 January 2010, a juvenile (36 or 37 days post-hatching) from nest 0912F made a call similar to that of the adult oriole roll.

Discussion Before this study, no data on nest-attentiveness and incubation rhythm of the Olive-backed Oriole had been published, and only few detailed data on parental behaviour, including brooding behaviour and feeding rates, nestling and juvenile development and vocalisations (at and near the nest and by juveniles) were summarised by Higgins et al. (2006). Here I present data to address these deficiencies for breeding Olive-backed Orioles. As there are even fewer data for this species’ single Australian congener, the Yellow Oriole, comparisons in this paper have been limited to two well-studied species in the Northern Hemisphere, the Eurasian Golden Oriole and Black-naped Oriole. Some additional comparisons have been made with the closely related and similar-sized Australasian Figbird. Sexing adult Olive-backed Orioles in the field is generally difficult. Variations between the sexes in the nominate subspecies (O. s. sagittatus: eastern coast of Australia) are less than those for the two northern subspecies (O. s. affinis: WA Olive-backed Orioles breeding, mid-north coast, NSW 189 and NT; and O. s. grisescens: Cape York) (Schodde & Mason 1999; Higgins et al. 2006). In the present study, subtle variations in crown and throat colour and streaking intensity could be observed when adults were near a nest, but streaking intensity also varied between adults at different nests. During the first and second observation periods at the first nest (0912F), it became apparent that vocalisations by the female provided an additional identification trait. This vocalisation was consistent at all nests observed. All of the nests in the present study were positioned adjacent to small clearings between trees. Marchant (1992, p. 40) also noted that ‘Nests [of Olive-backed Orioles] were suspended at the ends of branches that spread out into small clearings, …’. This position provided clear access for returning adults to alight from adjacent trees (in most cases, from the upper canopy) to the nest. Additionally, adults appeared to undertake sentinel duties, and a position adjacent to a small clearing allowed good views of the nest. Chu (2007, p. 13) stated that male Black- naped Orioles ‘… would guard upon trees near the nest …’ whereas females usually remained close to the nest after feeding if not brooding. Theories on nest concealment versus visibility have been tested by various researchers (e.g. McLean et al. 1986; Götmark et al. 1995; Cresswell 1997; Ford 1999), with Andersson & Wiklund (1978), McLean et al. (1986), and Götmark et al. (1995) suggesting that more aggressive species tend to construct nests in more conspicuous locations. During this study, breeding Olive-backed Orioles showed aggression towards 14 bird species within 20 m of either the nest or a juvenile (Table 10). Both Chu (2007) and Milwright (1998) recorded three avian predators each in their respective studies of Black-naped and Eurasian Golden Orioles. A success rate of 1.5 fledglings per nest in this study is lower than that recorded near Beaufort, Victoria (2.75: BA NRS cited in Higgins et al. 2006) for Olive- backed Orioles, but is similar to the success rate recorded for the Eurasian Golden Oriole in eastern Britain (1.4: Milwright 1998), lower than for the Eurasian Golden Oriole in Russia (2.5: cited in Milwright 1998), but higher than for the Black-naped Oriole in Taiwan (0.2: Chu 2007). Milwright (1998) and Chu (2007) noted poor weather, predation (including humans) and disturbance as the dominant factors in nest failure for Eurasian Golden and Black-naped Orioles respectively. One Olive-backed Oriole nest during the present study was abandoned prior to eggs being laid following constant investigation by a Little Wattlebird Anthochaera chrysoptera, and a second nest had a nestling preyed upon, resulting in an 80% nest success rate. However, the combined success rate for 85 Olive-backed Oriole nests in the BA NRS was only 57.6% (Higgins et al. 2006). For the Eurasian Golden Oriole (Milwright 1998), bad weather and predation each caused ~30%, and disturbance by human activity (tree-felling in the vicinity) caused 9% of nest failures. Nest failure in the Black-naped Oriole varied between the two sites studied by Chu (2007). Reasons for failure were: typhoon (25%), ‘fake’ nest and human disturbance (22% each), and poaching (20%); although poaching was recorded at only one study site, it accounted for 55% of all nest failures. Although avian predation was recorded by Chu (2007), these acts alone did not result in a failed nest. Nest success rates for Eurasian Golden and Black-naped Orioles were 67% and 21.5% respectively (Milwright 1998; Chu 2007). Throughout eastern 190 Australian Field Ornithology A.J. Carlson

Australia, avian predators are generally considered to have the most impact on the success of passerines that build cup-shaped nests (Major et al. 1996). A mean clutch-size of 2.3 eggs for the Olive-backed Oriole is less than recorded in the BA NRS (2.8 ± 0.4 eggs, n = 26: see Higgins et al. 2006). Storr (1984) recorded a similar mean for nine clutches in Queensland (2.4 ± 0.5 eggs), and in the Kimberley, WA, he located six clutches of two eggs (Storr 1980). For Eurasian Golden Orioles in eastern Britain, Milwright (1998) calculated a mean clutch-size of 3.5 ± 0.6 eggs, which is lower than for the same species in continental Europe (Czechoslovakia, Germany and Switzerland) (3.8: see Milwright 1998). Given the variability between nests, the mean incubation on- and off-bouts recorded during this study (21.1 ± 21.8 min. and 7.7 ± 5.6 min., respectively) were similar to those calculated by Chu (2007) for the Black-naped Oriole [18.4 ± 12.6 min. (range 3.5–87 min.) and 9.8 ± 9.2 min. (range 1–52 min.), respectively]. The nest (1011P) for which elevated nest-attentiveness (88%) was recorded during incubation was located within 5 m of the edge of Wallis Lake and at a height of <2 m above the water’s surface. Although not measured, mean ambient air temperature at this site may have been lower, because of the cooling effect of this large waterbody. Higher brooding attentiveness was also recorded at this nest on Days 4 and 6 post-hatching. The mean incubation period of 16.2 ± 0.5 days calculated in the present study is shorter than the 17 days (n = 2) and ‘approximate’ 18.2 days (n = 1) determined for this species by Crouch (1970: cited in Higgins et al. 2006) and Marchant (1980, p. 32), respectively. For the Eurasian Golden Oriole in eastern Britain, Milwright (1998) deduced an incubation period of 18–19 days in comparison with the same species in continental Europe (16–17 days: see references cited by Milwright 1998). Incubation by only female Olive-backed Orioles is consistent with both the Black-naped Oriole (Chu 2007) and Eurasian Golden Oriole (Milwright 1998). However, incubation and brooding is undertaken by both male and female Australasian Figbirds (Turner 1995; AJC pers. obs.). During this study, combined male Olive-backed Oriole feeding effort (48%) was less than that for the Black-naped Oriole (58%: Chu 2007). However, as shown in Table 6, male feeding effort in the Olive-backed Oriole was consistent between four of five nests (0912F, 1010F, 1011F and 1011P). If only these four nests are considered, median male feeding effort increases to 53%. Observations by Bryant (1939, p. 416; 1945, p. 174) concur with the discrepancy of male feeding effort during this study, being that ‘The male, …, fed the young less frequently’ and ‘With some [Olive-backed] Oriole pairs, the male shares in feeding the young, but with others the hen appears to carry out all such duties’, respectively. As all other nests studied in detail during this study involved multiple nestlings, analysis could not be undertaken between feeding effort by males at nests with a single nestling. The greater feeding effort by male Black-naped Orioles may relate to the female of this species spending more time on the nest protecting young nestlings from potential predation (Chu 2007). Additionally, male Black-naped Orioles were observed passing food items to the female on the nest, which she then either fed to a nestling or consumed herself (Chu 2007). During the present study, male Olive-backed Orioles were also observed passing a food item to the female on the nest, which Olive-backed Orioles breeding, mid-north coast, NSW 191 she then fed to a nestling, but this occurred only when both unhatched eggs and nestlings were present in the nest. Adult Olive-backed Orioles are omnivores, consuming primarily arthropods and fruit, but also seeds, nectar and nestlings (Higgins et al. 2006). However, during this study, all items identified were arthropods except for a single red berry that was fed to a young juvenile. Adult Black-naped Orioles also consume a wide variety of items during the breeding season, with fruit comprising an average 17% of this total, although the percentage of fruit fed to nestlings varied between the two study sites from 2% to 16% (Chu 2007). Woodall (1980) recorded 6 feeding visits h–1, to a nest with three young Australasian Figbirds; multiple fruits were fed to nestlings on each visit, averaging 24.9 fruits h–1. This feeding rate is slightly higher than that recorded during the present study for a nest with three Olive- backed Oriole nestlings (5.3 feed visits h–1),and may reflect the lower nutritional value of fruit to young Australasian Figbirds, though with a trade-off of being able to deliver multiple fruits in one visit. The 15.0 day mean nestling period calculated here for the Olive-backed Oriole is the same as the lower of Crouch’s (1970: cited in Higgins et al. 2006) two recorded durations of 15 and 17 days. Two further records of the nestling period are outside this time-frame: Bryant’s (1945, p. 174) statement of ‘The young birds remain in the nest for nearly three weeks …’ and Marchant’s (1980, p. 32) ‘doubtful’ duration of 12 days (n = 1). This nestling period is also slightly less than that recorded for the Black-naped Oriole (16 days: Chu 2007) and at the upper limit for the Eurasian Golden Oriole [13.8 ± 0.75 days (range 13–15 days): Milwright 1998]. Juvenile Olive-backed Orioles remained in the natal area (<70 m from the nest) for up to 24 days in the present study. Milwright (1998) provided a range of 10–14 days for juvenile Eurasian Golden Orioles staying in the natal area. Fledgling Black-naped Orioles from a first brood remained near the nest of a second attempt and were fed by the male, and juveniles from any second broods remained with the adults until they dispersed to wintering quarters (Chu 2007). The most widely recognised vocalisation of the Olive-backed Oriole is the oriole roll. Crouch (1970, cited in Higgins et al. 2006) noted that this species called loudly and almost continuously when first claiming a territory but that the calling rate declined as nesting progressed. He also noted that the call of the female was similar to that of the male, but shorter and uttered less often, which was not witnessed during all observation sessions in the present study. During nesting, however, various other calls were made by both adults and young in the present study. The draah and draah drit vocalisations made by the female while incubating is in contrast with Bryant’s (1945, p. 172) observation that ‘… the female settles down to brood [sic] and thereupon practically ceases to call.’. Peet calls were predominantly made by the female on her or the male’s approach to the nest. These calls alerted the observer to the arrival of an adult, and helped confirm the sex of the adult. Similarly, Bryant (1945, p. 173) noted ‘… a purring succession of squeaks that advises the young of the approach of the adults with food.’ The draah or draah drit call was also consistent with another pair of Olive-backed Orioles feeding a juvenile with berries of Climbing Guinea Flower Hibbertia scandens at 192 Australian Field Ornithology A.J. Carlson

Kattang National Park (31°38′S, 152°50′E) on 20 February 2010 (AJC pers. obs.). Different scolding vocalisations combined with aggressive swoops were noted by Leach (1928, p. 99) as ‘utter angry cries’, Bryant (1939, p. 416) as ‘noisy in their attacks’, and Crouch (1970, cited in Higgins et al. 2006, p. 372) as ‘loud brrr’ during disturbance about the nest. Therefore, it can be concluded that the suggestion by Walther & Jones (2008) that there is much uniformity within the Oriolidae family does not necessarily hold true for breeding Olive-backed Orioles. A detailed study of the breeding biology of the Yellow Oriole would be beneficial in clarifying the discrepancy between the Australasian species and their Northern Hemisphere congeners.

Acknowledgements I would like to thank the following people for help in various ways in the preparation of this manuscript: Donald Franklin for resource material, advice on drafts and compilation of statistical analysis; both Sarah Guppy and Walter Boles for resource material; Peter Higgins for advice on an early draft; Win Filewood for resource material, the location of nests 1011P and 1101B and measuring equipment; Rudy and Rebecca Jacobs for measuring equipment; Mathew Bell for help in identifying floral species; and John Hughes and Philippa Jones for observations at nest 1010G during hatching. Referees and editors provided comments to improve the manuscript and encouragement to undertake further statistical analysis of the data.

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Received 27 April 2012