VOL. 15 (2) JUNE 1993 49 AUSTRALIAN BIRD WATCHER 1993, 15, 49-59 Seasonal Variation in the Distribution of the Noisy Friarbird Philemon comiculatus and the Red Wattlebird Anthochaera carunculata in Eastern New South Wales by A.S.J. SAUNDERS, 8 Polworth Close, Elderslie, N.S.W. 2570 Summary Seasonal variations in the distribution of the Noisy Friarbird and the Red Wattlebird are compared with respect to habitat, altitude and latitude in eastern New South Wales, from data collected from March 1982 to November 1991. The habitats most frequently used by both species were open forest and woodland, with Noisy Friarbirds recorded more frequently in open forest and Red Wattlebirds recorded more frequently in woodland. There is some segregation by altitude and latitude. Noisy Friarbirds are generally absent on the Divide and low in numbers on the southern New South Wales coast during winter, when Red Wattlebirds can be found. This pattern for Noisy Friarbirds suggests that in these two areas they are summer breeding migrants. The pattern for Red Wattlebirds is not clear and it is likely that this species is more nomadic. The occurrence of Red Wattlebirds in lower numbers and their arrival just after the departure of Noisy Friarbirds from many localities suggest that the Noisy Friarbird is the more dominant species in most localities. In some localities where both are resident, they are segregated by altitude, with Red Wattlebirds being restricted to the higher altitudes. These two honeyeaters were not observed together very often. Aggression between them has been observed, and they have also have been observed foraging together without aggression at abundant nectar sources. Introduction Competition can take place when two species exploit common resources which are in short supply, or when they exclude each other from resources even when they are not in short supply (Birch 1957 cited by Ford 1979). Competition between two species can be measured by the degree of overlap in utilised resources or niche overlap (Krebs 1978). However, this may only be true when the utilised resources are in short supply (Pianka 1976, Ford 1979) . Also, if resources are only temporarily abundant and relatively unpredictable in space and time a high niche overlap may occur and interspecific competition may be indistinguishable from intraspecific competition, e.g. territoriality (Cody 1974). Caution should be exercised in assessing the degree of competition from niche overlap, but in a comparison of two or more species, an examination of similarity is inevitable and this leads to measures of niche overlap. Measures of niche overlap between the Noisy Friarbird Philemon corniculatus and the Red Wattlebird Anthochaera carunculata are high (e.g. Ford et al. 1986). They have a large area of sympatry in New South Wales (Figure 1) and are the twb largest honeyeaters in this state. Bill length, body length and mass for the Noisy Friarbird are 39 mm, 360 mm and 107 g respectively and for the Red Wattlebird 25 mm, 360 mm and 125 g respectively (Ford et al. 1986, Longmore 1991). They are principally nectar feeders, taking nectar mainly from eucalypt blossom., but they also consume insects, particularly in summer (Ford et al. 1986; ASJS pers. obs.). Their preferred habitats are open eucalypt forests and eucalypt woodland (Pizzey & Doyle 1980, Blakers et al. 1984, Simpson & Day 1984, Longmore 1991). These similarities in size, foraging and habitats suggest that competition may occur. This is supported by frequent observations of aggression between the two species (Ford et al. 1986; ASJS pers. obs.). Where interspecific competition moulds a species' niche, the competing species are frequently different along another resource dimension (Ford & Paton 1976). High niche overlap can exist between two species, but they may reduce competition through temporal segregation, in other words by using the resources in AUSTRALIAN 50 SAUNDERS BIRD WATCHER Figure 1. Distribution of the Noisy Friarbird and ~ Noisy Friarbird the Red Wattlebird (after Blakers et al. ~ Red Wanlebird \j 1984). an area at different times in a diurnal or annual cyclic manner (Cody 1974). The seasonal distributions of the Noisy Friarbird and the Red Wattlebird in New South Wales are not well understood and may be very complex. They are often described as being 'migratory or nomadic' (Longmore 1991). I suggest that local and seasonal resource abundance and competition when resources are scarce affect the seasonal distribution of these two species. In this paper the following questions were asked of the data: 1. What are the more frequently used habitats for each species? 2. Is there a significant difference in habitat use between the two species? 3. Is there seasonal variation in habitats where each species was encountered? 4. Is there seasonal variation in altitudinal distribution for each species between the Great Divide and the coastal plain? 5. Is there seasonal variation in latitudinal distribution north and south of latitude 33 as · for each species within the coastal plain? 6. Do 'actual counts' show similar trends to 'percentage of visits where a species was recorded', and hence is the latter a valid method for evaluating the distribution of a species? 7. Is there a relationship between resource abundance and interspecific interactions? Methods Data on each species were collected opportunistically from March 1982 to November 1991 inclusive. A species was recorded for each locality visited if it was positively identified by sight or call. The habitat of each locality was described according to the structural form of the vegetation (Specht et al. 1974). Date, time of day and weather conditions were also recorded. Counts for both species were done at Wallacia (33°52 'S, 150°37 'E), altitude 200m, for the years 1990 and 1991 using a fixed-width transect method. Three areas each of 3 ha were surveyed once a month, birds were counted for 20 minutes in each area, and all counts began at 2 ± 0.5 hours after sunrise. Conditions for each transect count were calm and sunny. The total area surveyed was 9 ha and the duration of the total count was I hour. Counts are expressed as no. of birds/9 ha/hour. The natural habitats where each species were recorded have been divided into closed fore:;t, open forest, woodland and mallee/heath (Specht et al. 1974) and all these habitats were dominated by eucalypts. Localities were also separated into the Great Divide and the coastal plain. The coastal plain is defined as the area generally below 100m a.s.l. extending from the sea to the nearest elevated land, and the Great Divide includes all adjacent plateaus and mountains to the west of the coastal plain. Data for localities west of the Great Divide were few for both species and so these data are not considered in this paper. The coastal plain is divided into two regions, north of 33 °S and south of 33 °S. As most of the observations were recorded as presence or absence, the data are expressed as percentage of monthly visits where each species was recorded. As visits were infrequent for many of the months, it was necessary to group data into seasons for analysis. As localities were not visited equally and visits were not divided equally over all seasons of the year, observed and expected frequencies are compared using a Contingency Chi-squared test C?e). VOL. 15 (2) Noisy Friarbird and Red Wattlebird, JUNE 1993 Seasonal Variation in N.S.W. 51 100 90 m=Noisy Friarbird 80 ~ = Red Wattlebird !!! 70 u; > 60 0 :g. 50 c"' fl 40 ~ 30 20 10 C. F. 0. F. W. M.+ H. (n = 49) (n = 270) (n = 102) (n = 33) Figure 2. Percentage of visits to various habitats where Noisy Friarbirds and Red Wattlebirds were recorded. (C.F. = Closed Forest, O.F. = Open Forest, W = Woodland, M + H = Mallee/Heath, n = number of visits to each habitat). Results Frequencies in each habitat The percentage of visits where each species was recorded, in the four vegetation groups, is shown in Figure 2. Open forest and woodland show a higher percentage of records/visits than other habitats for both species. The Noisy Friarbird appears to have nearly equal frequencies for both of these vegetation types, however the preference for open forest was more significant in the analysis, i.e. observed frequencies were higher than expected frequencies for open forest when compared with the frequencies for woodland. Observed frequencies for closed forest were lower than expected, and zero for mallee/heath (X2 = 38.50, d.f. = 3, P(O.Ol). For the Red Wattlebird in woodland, the observed frequencies were significantly higher than the expected frequencies and Figure 2 shows that the highest percentage of records/visits occurs for this habitat. Observed frequencies in closed forests and mallee/heath were lower than expected and were about equal to expected frequencies for open forest (X2 = 13.36, d.f. = 3, P(O.Ol). Differences in habitat use between species When the numbers of records for each habitat were compared between species, a significant difference was found with the mallee/heath habitat. The Noisy Friarbird was not recorded in mallee/heath and the Red Wattlebird was recorded on 4 out of 33 visits to this habitat. For closed forest there was little difference between observed and expected frequencies. Observed frequencies were higher than expected frequences in open forest for the Noisy Friarbird and higher in woodland for the Red Wattlebird (X 2 =8.29, d. f. =3, P(0.05). AUSTRALIAN 52 SAUNDERS BIRD WATCHER Noisy Friarbird Closed Forest (n = 49) Red Wattlebird 100 100 80 80 60 60 % % 40 40 20 20 10 12 10 17 Sum. Aut. Win. Spr. Sum. Aut. Win. Spr. Open Forest (n =270) 100 100 80 80 60 ~ 60 % ~ :'1 ::::-: % 40 40 20 « :-: 20 1~ ~5 ·~ ~~ Sum.