AUSTRALIAN 152 BIRD WATCHER AUSTRALIAN BIRD WATCHER 1995, 16, 152-160 Roosting Patterns of the Laughing Kookaburra Dacelo novaeguineae by K. A. WOOD, 7 Eastern Avenue, Mangerton, N.S.W . 2500 Summary At Wollongong, New .SOuth Wales, a suburban roost of Laughing Kookaburras Dacelo novaeguineae was visited in four sampling periods, each of 47-65 nights, between October 1991 and September 1993. The roost-site was defined by 24 branches, 23 of which were in a row of five adjacent Spotted Gums Eucalyptus maculata. Some birds (maximum 9) were present on 178 of214 inspections (83%). There was an overall tendency for all Kookaburras at the roost to perch on the same branch, touching one another and facing the same direction. Roost-splitting on different branches occurred in two of the sampling periods and subsequently the number of birds in the group probably decreased. Data obtained on roost-splitting were incomplete because individual birds were not marked and only one roost-site was studied, but it is possible that this behaviour could indicate an unstable dominance hierarchy and may precede dispersal of some birds to other groups. Introduction Laughing Kookaburras Dacelo novaeguineae live in permanent territories as either mated pairs or family groups consisting of a mated pair and up to six auxiliary members (Parry 1973). These auxiliaries or helpers are the progeny of the breeding pair; they remain with their parents for several years and help incubate the eggs, brood and feed young of subsequent breeding seasons and defend the group territory. Within the family, the breeding male is dominant over all auxiliaries of the same sex and older male auxiliaries dominate younger males (Parry 1973). A similar dominance hierarchy exists among females. Eggs are laid in September or October. Between July and September, inter-group conflicts are most common as territory boundaries are adjusted in preparation for breeding. Some auxiliaries disperse from their natal territory at this time and become dominant breeding partners in other groups. In a two-year study near Melbourne, Parry (1970) found that family members roosted together in two or three regularly used trees throughout the year. In Sydney, Hindwood (1947) reported that five Kookaburras roosted on the same branch consistently from June to early October 1945. In the following weeks, he observed one bird incubating eggs and noted that the number of birds remaining on the usual roost branch was variable. Hindwood later concluded that the family group had split, leaving only the breeding pair and one helper to care for the young. In Tasmania, Prestedge (1993) reported six Kookaburras roosting together (touching) with four juveniles in the centre of the perched group and the parent birds bracketing them on opposite sides. Conversely, Shields (1994) saw a group of seven at a roost near Singleton, N.S.W., with the adult pair side by side on a eucalypt branch and the three helpers '10 metres away on a lower branch, close to two fledglings (still showing down)'. Mangerton is a 55-year-old suburb in Wollongong, N.S.W., with a mosaic of tree­ lined streets and natural public reserves. Kookaburras are common, perhaps because the landscape is dominated by 20-30 m eucalypts (see Blakers et al. 1984). Recent observations of four roosts near my residence revealed that the number of birds roosting at night was highly variable. Subsequently, I selected one particular roost and visited it as often as possible during four discrete periods between October 1991 and September 1993. The aim of the study was to determine (1) the fidelity of Kookaburras in the group to the particular roost, (2) whether a tree or branch or clump of trees was used and (3) whether sleeping birds clustered together or perched apart. I hoped to assess the stability of the dominance hierarchy within the group by regularly observing the spatial arrangement of roosting birds. VOL. 16 (4) DECEMBER 1995 Roosting of Laughing Kookaburra 153 m g b p h ( d a e J f 12- rn l (Sth) MANGERTON ROAD (Nth) Figure 1. Spotted Gum roost trees and roost branches 'a' to 'x' used by Laughing Kookaburras during four sampling periods between October 1991 and September 1993. Roost-site and methods The roost-site was a row of mature Spotted Gums Eucalyptus maculata growing in the front garden of a residential allotment (Figure 1). These trees were 23-27 m high [diameter at breast height (dbh) 22-54 em] with the crown foliage starting about 10 m above the ground. They were planted in a straight line so close to one another (spacing mostly about I. 6 m) that their foliage overlapped laterally. Based on numerous daytime searches for white faecal droppings on the ground and searches for roosting birds at night, I feel confident that no other trees within a radius of about 50 m were used as roosts. Counts of faecal dropping spots before and after the study revealed that a roosting Kookaburra defecates about 16 times a night (range 10-20, n=7). Unlike other workers, I was unable to find regurgitated pellets on the ground below any roost (see Eastman 1970). The site was visited mostly at night between 2000 h and 2200 h during four sampling periods as follows: ( 1) 52 of 69 nights between 3 October 1991 and 10 December 1991, (2) 50 of 51 nights between 14 May 1992 and 3 July 1992, (3) all47 nights between 30 October 1992 and 15 December 1992, and (4) all65 nights between 12 July 1993 and 14 September 1993. A further 55 night inspections were made mainly between these sampling periods to monitor changes in the roosting pattern. Observations were from a distance of 20-25 m with a hand-held spotlight and binoculars. On each AUSTRALIAN 154 WOOD BIRD WATCHER v1s1t, I recorded the branches on which the ~ ~ N Kookaburras were perched, the approximate ~ compass directions that they faced and the estimated ~ spacings between adjacent birds. On seven =4> afternoons, I also looked for birds arriving at the ..... roost-site from before sunset until after dark . ! "" ..... .s Civil twilight (sun 6 o below the horizon) is ::; ..... marked by the onset of street-lighting. ,gi .f!l"' Results 4> During the afternoon watches, all -~ ~ "' '"' N Kookaburras that were seen arrived and -a ~ \0 eventually settled in one of the trees ... ..... ~ depicted in Figure 1. Fourteen birds (70%) rl1= "' <:3< arrived during civil twilight, three arrived g before sunset (earliest 17 minutes before) ..... '"Q ~ and another three arrived just after civil = twilight (latest four minutes after). A wide ..... C) N g::"' variety of contact calls was given when Kookaburras arrived and when they moved ..... r- s:: about selecting a branch on which to fmally =~ ~ "''"' E settle. Most contact calls were given within ~ "tis:: a few seconds of landing on a branch but '"Q 4> ~- I was unable to determine whether the bird :g Cl:i which had just landed, or one of the others, 4> -'< made these utterances. The laughter song ..... 4> 4> -~ was heard three times: on 23 October 1991 ,-... :c ..... ....... N by four birds four minutes after civil 4> E-o"' twilight, on 4 October 1992 by three birds ~ 0"1 (i; 16 minutes after sunset and on 12 September 1993 by two birds 13 minutes ~ ~ ~ $ after sunset. No additional Kookaburras :~ ~ arrived after these laughter songs were 0 "" given. :=- ""-, 00 ~ A total of 24 roost branches was used, 4> .:"' lr) of which 23 were in five adjacent trees Col "' -.:t (Figure 1, Table 1). In each sampling = ..... period, the birds showed a distinct ,Q"' ~ -.:t - preference for roosting on one particular -"' 8 " branch. They used the 'e', 'd', 'r' and 's' - branches on 45, 41 , 36 and 23 nights "' -t:) respectively in periods 1, 2, 3 and 4 (Table ,Q-= 1). All branches used were between 15 and ...: <:I 8"' 24m high (83% between 15 and 20m). ~ Only three branches ('q', 'r' and 's') were - of dead timber. The preferred position on -="' live branches was on the central third, ~ where they were approximately horizontal toll ·a ..... N N ~ with estimated diameters from 25 to 50 0"1 0\ 0\ 0\ ...0 mm. On three occasions when winds were u .Q u <!.l,-.. s:: :::~--. strong (gusting at )25 knots), birds roosted ;.:::"\:j"" ....,o Clr- Clllr)fr- .! oN' ,'-0 - ' lr) ' lr) •-.:t lower than those of the ~ - g ..; II ~II ..; II .QII on branches were z= <55~ OS :::;s OS .....:::1 '-'= preceding night when winds VOL. 16 (4) DECEMBER 1995 Roosting of Laughing Kookaburra 155 Oct.- Dec. 1991 May - Jul.1992 40.----------------------, 40.-----------------------, n=52 n=50 Q) (.) c :;~ 20 20 8 0 0 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 Oct.- Dec_ 1992 Jul- Sep. 1993 40 40.-------------~--------~ n=47 n= 65 c Q) (.) 20 20 Q; c._ 0 0+---~~-Y-~--,-,-,-.---~ 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 Number of roosting birds · Figure 2. Frequency of occurrence of various total nwnbers of Kookaburras at the roost­ site during four sampling periods between October 1991 and September 1993. moderate. On 12 September 1993, I watched two birds from the time they finally settled for the night in very light drizzle (1757 h) until they were asleep in light rain at 1827 h (civil twilight ended at 1806 h). The angle of their sleeping posture noticeably changed as the rain gradually became heavier, and they adopted a much more 'vertical' posture while perched in steady rain at 1827 h than during light drizzle at 1757 h. Before this study, the roosting positions of Kookaburras at the three other known roosts were 12 m above ground in a 20 m Blackbutt E.