Do Pallid Cuckoo in southern Tasmania regulate the numbers of Black-headed Honeyeaters, a preferred host species? Mike Newman 72 Axiom Way, Acton Park 7170 [email protected] Abstract preferred host in my study area, using the results of six Birdata surveys in an area of south-east Tasmania were years of Birdata monitoring using standardised survey used to assess the status of the Pallid Cuckoo, Heteroscenes methods. Pallid Cuckoos prefer open-cupped nests, pallidus, and the Black-headed Honeyeater, Melithreptus often parasitising honeyeaters: Black-headed and affinis, a preferred host, between 2014 and 2019. Pallid Strong-billed Honeyeaters, M. validirostris, are known Cuckoos were abundant in lightly developed areas of hosts in Tasmania (Higgins 1999). However, the latter dry woodland and avoided areas dominated by Noisy species is absent from the South Arm peninsula. Miner, Manorina melanocephala. The breeding season Home ranges for Pallid Cuckoos appear to vary population of territorial males at the location of highest between regions. In a previous paper (Newman 2019), I occupancy was estimated to be 3.4/km2 between 2014 speculated that the breeding season home ranges might and 2017, before falling to 1.7/km2 in 2018 and 2019. be larger in the Hunter, possibly of square kilometre Both Pallid Cuckoos and Black-headed Honeyeaters magnitude, than in south-east Tasmania. In contrast, decreased during the six-year period. These decreases Kennerley et al. (2019) suggested that, in near coastal may have been caused by drought. However, it is also south-east Queensland, the breeding season home range possible that continual parasitism by Pallid Cuckoos of female Pallid Cuckoos might be as small 3–5 ha with resulted in decreased breeding success for the honey- males having territories of at least 25 ha. This paper eaters, ultimately resulting in part of the Pallid Cuckoo seeks reasons for the discrepancies in these estimates of population deserting their territories in 2018 and 2019. Cuckoo home ranges. Additionally, it places on record Some new aspects of the breeding season behaviour novel observations of new courtship display by a pair of of Pallid Cuckoos are presented, including a raptor-like Pallid Cuckoos. courtship display. Methods Introduc.on Observations of Pallid Cuckoo and Black-headed Honey- Kennerley et al. (2019) have highlighted the lack of eater were made while conducting Birdata surveys in information concerning the natural history of the Pallid south-east Tasmania in an area extending approxi- Cuckoo, a brood parasite, and the need for increased mately 25 km south from Stringybark Gully in the research into its breeding behaviour. Meehan Range to the end of the South Arm peninsula Because one female cuckoo can affect many host (figure 1, page 00). breeding attempts, cuckoos clearly have the potential to The results presented below (pages 00–00) are based impact adversely the breeding productivity of host predominantly on standard Birdata 2-ha surveys, which species, at least locally (Newton 2013). For instance, in record all birds seen and heard within a 2-ha area an extreme case (Bayliss 1988), one female Common during a period of 20 minutes. These surveys provide Cuckoo, Cuculus canorus, parasitised in one season the more reliable information for determining temporal nests of 24 different female Reed Warblers, Acrocephalus trends than Birdata 500-m and 5-km area searches scirpaceus, one twice. To investigate this possibility, I because the area and duration of the survey are fixed. examined the relationship between the occurrence of The results of the less standardised 500-m were used to Pallid Cuckoos and Black-headed Honeyeaters, the corroborate the results of the 2-ha surveys. Article In Press, Tasmanian Bird Report 41 (2021), final pagination to be advised 1 Figure 1: Distribu(on of 2 ha survey sites in study area in south-east Tasmania near Hobart. Article In Press, Tasmanian Bird Report 41 (2021), final pagination to be advised 2 Surveys were conducted in the morning, mostly Cohen 1986). between one and three hours after sunrise, when the Territory sizes were calculated based on the birds were active. Although other observers contributed assumption that 2-ha records of Pallid Cuckoos relate to to the dataset, all of the surveys at the 20 most inten- an area of 5 ha because of the difficulty of estimating sively surveyed sites were made by the author, thus the position of calling birds in relation to the notional providing a consistent approach. boundaries of the 2-ha survey site. It is also assumed The initial analysis considered all available Birdata 2- that the detection rate of male cuckoos will be very high ha survey data for the period 1/7/2014 to 1/3/2020. because they call extremely frequently early in the With one exception, all the Pallid Cuckoo records in the morning when the surveys were conducted (Keast study area (including those by other observers) occurred 1985). The estimated population densities and territory in the months September to January, with the earliest sizes in this report are proportional to the assumed area arrival on 2 September. Consequently, annual breeding in which cuckoos were detected (5 ha) and the detection season occurrence was assessed for those months in rate (100%). order to minimise any bias associated with variations in survey effort in other months. Breeding seasons are Results identified by the year in which the cuckoos arrived (e.g. For both the Pallid Cuckoo and Black-headed 2014 refers to the 2014–15 breeding season). Honeyeater, the breeding season statistics from 2-ha and A subset of 20 survey sites, involving three locations 500-m Birdata surveys for the six-year period 2014–19 within the study area (figure 1), were monitored once in are summarised in table 1 (page 00). The Black-headed most months over six successive breeding seasons Honeyeater was the only brood host identified during between 2014 and 2019 (i.e. c.30 breeding season the study (three instances). surveys per site). The results from these sites provide There were 161 breeding-season records (September– much of the analysis presented below. These sites were December) of Pallid Cuckoo in 933 Birdata 2-ha grouped as follows: surveys: a reporting rate (RR) of 17.3%. Pallid Cuckoo 1. Meehan (42.840°S, 147.401°E) — six sites in dry occurred at 25 of the 50 sites at which surveys were sclerophyll woodland located on 3.5 km of track in conducted. However, some of the sites received the vicinity of Belbins Creek, including one site on insufficient survey effort to conclude that the species was the escarpment above Stringybark Gully within the absent. There was evidence of a 53% decrease in Meehan Range. annual RR over the six years. However, this decrease 2. Acton (42.855°S, 147.487°E) — two sites on the may have been exaggerated by increased survey effort in Tangara Trail surrounded by small acreage the latter years of this study at sites that were less properties with some retained native vegetation. suitable to Pallid Cuckoo. Consequently, it was decided 3. South Arm (43.006°S, 147.479°E) — 12 sites on the that the detailed temporal analysis presented here would South Arm peninsula, mainly in dry woodland with only consider the 20 survey sites that had been surveyed limited understorey vegetation. Most of the sites consistently at three locations where Pallid Cuckoo were located in roadside vegetation along a 100 m occurred regularly (South Arm, Acton and Meehan) high ridge extending 14 km north from the southern and where surveys had been conducted in all six end of Gellibrand Drive to another ridge on Dixon breeding seasons. At Acton the sites were surveyed more Point Road. The woodland is more continuous than frequently in some years. There were 633 surveys at at the Acton sites. these three locations (i.e. 69% of all 2-ha surveys for the An additional two sites at Acton, in a more extensively area shown in figure 1). cleared area edging open paddocks, were surveyed The Birdata 500-m surveys (343 surveys at 33 sites) intensively by the author for four years. increased the spatial sampling of the study area and The 2-ha survey sites at Meehan, Acton and South provided an independent measure to the 2-ha surveys. Arm were located 500 m or more apart. This is a Pallid Cuckoo were recorded at 42% of these sites. The standard Birdata protocol designed to prevent birds results were superficially similar with evidence of a 20% being recorded at more than one site on the same day. decrease in breeding season RR towards the end of the Newman (2018) provides habitat descriptions for six years. However, this decrease was not statistically survey sites typical of the three locations. significant (χ² = 1.38, p = 0.24). A detailed analysis of Reporting rate (RR), the ratio of the number of the 500-m survey results was not conducted because records to the number of surveys expressed as a percent there were fewer observations and the results would value, was used to assess variations in the annual have been less reliable. Only three sites were surveyed breeding season and monthly occurrence. monthly in all six years. The Chi-square test χ2 was used to determine the Comparison of locations statistical significance of differences in RRs between The 2-ha survey RRs for the Pallid Cuckoo and Black- several periods of pooled years (e.g. 2014–17) using headed Honeyeater are compared for the three Yates’ correction for 1 degree of freedom (Fowler and locations in the figure 2 scatter diagram (page 00). Article In Press, Tasmanian Bird Report 41 (2021), final pagination to be advised 3 Table 1: Breeding season sta(s(cs for the Pallid Cuckoo and Black-headed Honeyeater in an area in south-east Tasmania near Hobart for the period 2014–19.