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Annual Report: Migratory Shorebird Monitoring – Understanding Ecological Impact
 

Choi C-Y, Moffitt DJ, Fuller RA, Skilleter G, Rogers D, Coleman J & Klaassen M (2016) Annual Report: Migratory Shorebird Monitoring – Understanding Ecological Impact (CA130019). Report produced for the Ecosystem Research and Monitoring Program Advisory Panel as part of GPC’s Ecosystem Research and Monitoring Program. 49 pp.

EXECUTIVE SUMMARY

We have completed all field work, lab work is nearing completion, and we are on track to complete the project successfully. This 2016 annual report constitutes a progress update, and provides a preliminary view of some of the key discoveries that are already apparent from the data. It does not repeat material given in the 2015 annual report, and does not yet include the full analysis that will form the backbone of the final report in January 2017 (see timeline in Section 4). Progress against each of the eight project aims is as follows:

Aim A1: Map tidal flat distribution and exposure

100% complete. There is a minimum of 216km2 of exposed intertidal substrate in the ERMP Survey Area when the tide is in the bottom 10% of its range.

However, there is enormous temporal and spatial variation in tidal flat exposure. Across the whole ERMP Survey Area, about half of the full extent of intertidal substrate is exposed at half-tide. Yet in key shorebird foraging areas, characterised by large contiguous tidal flats, exposure of most of the potential foraging habitat is very brief, with only 10–25% of the intertidal habitat exposed at half-tide. Moreover, several weeks or months can elapse between exposure periods of the intertidal substrate in the lower levels of the tidal range.

We will integrate our quantitative data on exposure patterns with the benthic sampling data to derive carrying capacity estimates.

Aim A2: Measure benthic prey availability

90% complete. We collected 1560 benthic samples from six major tidal flats from the Fitzroy Delta to Rodds Bay to measure spatial and temporal variation in benthic prey availability. All of the samples have been processed and sieved in the laboratory, and we have started counting and measuring the animals. Once this final stage of the lab work is complete, we will be in a position to report on benthic prey availability.

Aim A3: Estimate how many birds the area can support

80% complete. The method for calculating carrying capacity is fully developed, and data enabling the calculation will be available by the end of August 2016. Analysis of the pilot benthic sampling data suggested rather high capacity to support migratory shorebirds, but we need to finalise these estimates based on the full benthic sampling program, and including what we now know about patterns of tidal flat exposure, which might mean that some of the richest foraging areas are only infrequently exposed by the tide, and somewhat variable across the season.

Aim A4: Identify priority areas for management

60% complete. We have mapped tidal flats, and we have roost site data available from previous surveys as well as our own counts. Once the carrying capacity estimates are available in September 2016 we will be able to identify priority tidal flats that have the potential to support large numbers of birds.

Aim B1: Describe the patterns of flow of birds into the study area, in relation to impacts

80% complete. We have modelled the migratory movements of birds through the ERMP Survey Area, by developing a method to infer total population size calibrated against historical data available from sites across eastern Australia.

Aim B2: Discover how birds move around the study area

75% complete. We radio tracked 35 birds of four species using hand-held, aircraft-borne and automated receiver systems, and supplemented this with 319 re-sightings of 86 birds marked locally by us, and 61 birds marked elsewhere. We observed marked birds from other states in Australia, as well as Alaska, Russia, Japan, China, and New Zealand.

Although highly site faithful for most of the time, our individually-marked birds made three distinct kinds of movements: (i) local commuting flights of up to 10km between alternative feeding and roosting locations, strongly associated with tidal patterns; (ii) exploratory movements of up to 40km between regions of the ERMP Survey Area, and; (iii) migratory transitions through the Survey Area. High site fidelity was evident within and between non-breeding seasons.

Aim B3: Determine how many birds currently use the study area

85% complete. The final step is to analyse our count for the northward migration phenology in the same way, and we will be able to provide a complete estimate of the size of the migratory shorebird population for each species using the study area, both while on migration, and during the non-breeding season.

Aim B4: Identify size of management units

50% complete. Preliminary analysis of the tracking and re-sightings data suggest that development impacts in the ERMP Survey Area extend well beyond a pinpoint location; most shorebird species appear to be moving among a portfolio of roosting and foraging areas within a c. 10km radius, and some species only transited the study area and spent their non-breeding season further south.

Diurnal and nocturnal movement patterns were strikingly different, such that birds may be depending on more than one roost site even during the course of a single 24-hour period. This suggest that studies, such as on the impact of light spill, must focus on nocturnal roosting and foraging sites, and not necessarily those places where birds are present during the day. Longer exploratory movements did occur, but were rarer. This suggests that impact assessments must look beyond the immediately impacted area to assess possible effects on shorebirds.

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