Stilt 69-70 (2016): 7-19 Red-necked Stint and Curlew Sandpiper in South-East Tasmania RED-NECKED STINT AND CURLEW SANDPIPER IN SOUTH-EAST TASMANIA: PART 1 RED-NECKED STINT - POPULATION TRENDS AND JUVENILE RECRUITMENT MIKE NEWMAN1 AND ERIC J. WOEHLER2 172 Axiom Way, Acton Park, Tasmania 7170 [email protected] 2BirdLife Tasmania, GPO Box 68 Hobart, Tasmania 7001 [email protected] Red-necked Stint Calidris ruficollis numbers in south-east Tasmania have fluctuated by an order of magnitude during the last 50 years. Current numbers (2010 - 2015) of between 500 and 1000 are at the lower end of the range, which peaked at nearly 4000 between 1981 and 1983. Superimposed on an overall long-term decrease are medium-term fluctuations in the size of summer populations. These fluctuations are similar to those reported in Victoria on the Australian mainland, but the magnitudes of the long-term changes in Tasmania are greater and slightly lagged in time relative to Victoria. The results of banding studies in south-east Tasmania and Victoria provide valuable insights into the overwintering (non-breeding season) behaviour of Red-necked Stints in Australia. In both Tasmania and Victoria, adult birds usually return to the same location each year after breeding in the northern hemisphere. Juveniles do not migrate to breed in the northern hemisphere until at least 18 months of age, although some juveniles undertake a partial movement northward in the Austral winter. Consequently, winter count numbers in Tasmania underestimate annual juvenile recruitment. In Victoria, juvenile proportions of Red-necked Stint in summer cannon net catches have been used to indicate recruitment rates, with annual variations attributed to changes in Arctic breeding success. Similar annual variations are apparent in the proportions of juvenile Red-necked Stint in south-east Tasmanian summer populations, based on the winter / summer count proportions. Between 1980 and 2005, the magnitudes of these metrics were similar during periods when the summer population was increasing, but the Tasmanian proportions were much lower when the populations were decreasing. The results are consistent with a demographic model involving high levels of juvenile recruitment into the south-east Tasmanian population when Red-necked Stint populations are at high levels during summer on the Australian mainland and the juveniles are forced farther south to Tasmania to find foraging opportunities. Short term fluctuations reflect variations in Arctic breeding success, but are variably attenuated by the extent to which juveniles find foraging opportunities at more northern latitudes. Since 2010, south-east Tasmanian results are inconsistent with the previous long-term trends suggesting fundamental change(s) to one or more of the factors affecting the balance between recruitment and mortality may have occurred. INTRODUCTION counts are recorded in the Tasmanian Bird Report (most recently Woehler et al. 2014 and Woehler and Drake Shorebird populations in the Hobart area of south-east 2015). Overviews and syntheses have been published at Tasmania were surveyed from July 1964 to December various times (e.g. Newman and Fletcher 1981; Moverly 1968 by Thomas (1968, 1970). He highlighted that 1995). The summer and winter counts of 2014 marked south-east Tasmania was an ideal location to study the the 50-year milestone since Thomas’ initial surveys. This dynamics of annual variations in trans-equatorial migrant remarkable long-term data set comprises 46 summer and shorebird populations. Its location at the end of the 40 winter population counts, with monthly counts in flyway removed the complication of the presence of eight years. passage birds experienced at most other sites in An intensive campaign of shorebird banding was Australia. Monthly survey totals provided the size of conducted between 1978 and 1985 in south-east peak summer populations, and the numbers of birds Tasmania with regular catches of the two most numerous remaining through the Tasmanian and southern species, Red-necked Stint Calidris ruficollis and Curlew Australian winter are considered to be juveniles (Rogers Sandpiper C. ferruginea (summarised in Barter 1984; and Gosbell 2006). Harris 1983, 1984). In 1973, the Bird Observers’ Association of Tasmania This paper (part 1) details the long-term fluctuations (BOAT, now BirdLife Tasmania) commenced annual in the population of Red-necked Stints in south-east summer population counts (SWCs), which were Tasmania, and focuses on the relationship between the supplemented by annual winter counts (WWCs) that trends in juvenile recruitment rates and summer commenced in 1980; both summer and winter counts population sizes. Subsequent papers will (a) examine have continued to the present, generating the longest time how the balance between mortality and juvenile series data for migratory shorebirds in Australia. The recruitment determines fluctuations in the summer 7 Stilt 69-70 (2016): 7-19 Red-necked Stint and Curlew Sandpiper in South-East Tasmania population size, and (b) undertake comparisons with consistency of shorebird numbers in Thomas’ monthly analyses of Curlew Sandpiper counts. Our ultimate aim is counts, and his interpretations and conclusions with to assess whether the south-eastern Tasmanian data respect to fidelity of birds to sites and limited movement support the hypothesis that trends at the extremities of between the sites he counted were subsequently the flyway in locations like south-east Tasmania provide supported by the BOAT banding data (Harris 1983, a litmus test for, and a mechanistic understanding for 1984). processes impacting elsewhere in the flyway, for Although Thomas’ work involved a single observer example, as suggested previously in relation to the whose counts were not synchronised, it was possible to Eastern Curlew Numenius madagascariensis by Close eliminate double counting by comparing site and total and Newman (1984), and Reid and Park (2003). population trends over a period of months (MN is in possession of Thomas’ original records and analyses). METHODS However, although banding studies indicated that most local movement was between and amongst the sites During the 51-year (1965 – 2015, inclusive) period, counted by Thomas, there was occasional movement south-east Tasmanian shorebird monitoring has between these areas and Marion Bay. From 1981 summer predominantly involved annual summer and winter population counts described below included Marion Bay, counts. However, as discussed below there were two but not Bruny Island, which was more remote and periods when monthly counts were conducted. Minor supported fewer birds. differences in method of counting and data evaluation SWCs were conducted in late February because over the 50-year period are presented, and are discussed Thomas’ studies had indicated that some species in relation to the accuracy of population estimates. commenced their northern migration in early March. Count Protocols and Effort Thomas and Dartnell (1970) showed the pre-migratory Thomas initiated the Hobart area studies in July 1964, build-up of fat by Red-necked Stint occurred in March, conducting monthly counts until December 1968. His providing further justification for the selection of studies provided five summer population estimates (i.e. February as the appropriate time to conduct SWCs. A 1965 to 1969; summers defined by calendar years i.e. team of experienced observers conducted synchronised 1969 SWC refers to the Austral summer of 1968/69). He counts of all migrant and resident shorebird numbers at identified and surveyed most of the areas holding high tide roosts on a day that was selected with high tide significant numbers of migratory shorebirds in south-east occurring near noon. In 1980, a corresponding set of Tasmania, and demonstrated through monthly counts that annual WWCs was initiated, conducted in July before the there was only limited movement between and amongst first of the northern hemisphere migrants had returned. the different feeding areas, which he termed resorts Separate teams counted each of the sites identified by (subsequently referred to as sites). He did not survey Thomas and where possible led by the same person who areas at Marion Bay and Bruny Island that hold relatively became expert with behaviour of shorebirds at the small populations of migratory shorebirds. The assigned site. Figure 1. Map of south-east Tasmania showing shorebird roost sites monitored since 1964: Barilla Bay (A), Pitt Water/Orielton Lagoon (B), Lauderdale (C), Clear Lagoon (D), Pipeclay Lagoon (E), South Arm Neck (F), Calverts Lagoon (G) and Marion Bay (H). Inset: map of Australia showing the location of the study site in southeast Tasmania and the location of Victoria. North is to the top of the page. 8 Stilt 69-70 (2016): 7-19 Red-necked Stint and Curlew Sandpiper in South-East Tasmania Subsequently, the Australian Wader Study Group mortality and the recruitment of juvenile birds, which can (AWSG) implemented a national Population Monitoring be calculated using equation 1. Program (PMP) in the early 1980s and the south-east Ni = Ci - Ci-1 .S (1) Tasmanian counts were incorporated into that scheme Where Ni is the number of juveniles in year i, Ci and Ci-1 with SWCs in January or February and WWCs in June or are the number of Red-necked Stint of all ages in the July (Gosbell and Clemens 2006). SWC in the ith year and the preceding year (i-1), and S is The team involved in the initial south-east Tasmanian the annual survival rate, which is assumed to be age wader counts formed the Tasmanian Shorebird Study independent. Group, which increased the frequency of surveys to In applying this model to the population in south-east monthly between 1980 and 1985, generating data directly Tasmania, we have assumed that the same annual comparable to that of Thomas. In periods when monthly survival rate applies to all ages of birds, and that there is counts were conducted, the February and June counts no emigration to, or immigration from other populations. were used for that year’s SWC and WWC totals (i.e.