Shorebird counts

What are shorebirds?

Shorebirds, (waders, gulls and terns) are birds principally found along the shores of beaches, estuaries, rock platforms and wetlands. They belong to families of plover, sandpiper, godwit, curlew, oystercatcher, gull, tern and related forms that are part of the order Charadriiformes. Most of these birds can be found along shorelines, especially during migration, but they are also found at inland wetlands, grasslands, mangroves, saltmarshes, coastal wetlands and rocky reefs.

Pied Oystercatcher

Pied Oystercatcher

Eastern Curlew

Eastern Curlew

Common Greenshank

Common Greenshank

Pacific Golden Plover

Pacific Golden Plover

Immature Kelp Gull

Immature Kelp Gull

White-winged Black Tern

White-winged Black Tern

Photo 1. Examples of shorebirds

Australia has at least 109 species of shorebird [1, Table 1], while recent estimates of total Australian populations are 1.1 million for resident species and 2 million for migratory species [2]. Most migratory species visit Australia during the austral summer (October to March) from the northern hemisphere (Russia, China, Mongolia, Japan, North America), and at least two species migrate to Australia during the austral winter (March to September) from New Zealand. The main trans-equatorial migration pathway is known as the East Asian - Australasian Flyway.

Figure showing the East Asian - Australasian flyways

Figure 1. The East Asian - Australasian Flyway with sites of significance marked. Source: Australasian Wader Studies Group

The presence of large numbers of shorebirds in an estuary is sometimes considered indicative of an areas biological productivity and health and many shorebird enthusiasts spend time each year counting or estimating numbers at selected sites throughout continental Australia, New Zealand and the East Asian flyway. Such population estimates are useful in detecting long-term changes in shorebird populations. Changes in shorebird populations are an indicator for State of the Environment reporting (e.g. indicator 1.3 in the Estuaries and the Sea volume).

However before you can start estimating shorebird numbers, it is necessary to learn how to identify differences between the many species that superficially appear similar and have different breeding and non-breeding plumage. There are now many books able to assist those drawn to the challenge of shorebird identification. Recent Australian field guides [3, 4, 31] will assist, but the two most important works are Shorebirds of the World [5] which is a comprehensive study with detailed plates of illustrations and species descriptions, and Shorebirds of Australia [6] which has excellent photos of the species in different plumages and a good introduction and text on behaviour and habitat. There are several WEB-sites that can also provide useful visual aids for shorebird identification and information (see Useful Internet Links section).

Visual comparative guide to common Australian shorebirds.

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What causes shorebird populations to change?

Shorebird abundance (and species composition) naturally fluctuates due to seasonal and environmental events. Most migratory species return to their breeding grounds during their respective breeding season. The exceptions are juvenile birds which generally stay in Australia for their first two to three years. Additionally, resident Australian species may move between inland and coastal locations due to drought and/or seasonal behavioural mechanisms [2, 6]. Unpredictable environmental events associated with climatic variability (drought, flood, cyclone, ENSO events) can affect shorebird distribution in Australia [7, 8, 9] and in their breeding grounds [10]. Additionally, hunting of shorebirds has been a common practice in many parts of Asia and eastern Russia [11, 12].

Within Australia, human pressure on shorebird habitats can result in the alteration of the quantity and quality of critical habitat [13, 14]. Some specific threats to shorebirds include:

  • coastal development and marine services (harbours, marinas, ports, oil terminals), which may cause a reduction in feeding and roosting habitat [18, 19],
  • coastal tourism can disturb shorebird roosts and nesting sites, e.g. by off-road vehicle traffic and trampling [14, 18],
  • Tidal barrages can change the tidal range of an estuary and the availability and type of feeding habitat [19],
  • Introduced pets such as dogs, cats, foxes and rats may prey on nesting shorebirds [18, 20],
  • discarded fishing gear and other rubbish (e.g. plastic rings, cigarette butts and other debris) can be ingested by birds or otherwise interfere with feeding and roosting behaviours [13, 18],
  • The removal of shellfish from intertidal rocky shore can reduce the amount of food available for shorebirds and alter foraging behaviour [19, 21],
  • global warming may have an effect on relative sea level rise and effectively increase or decrease of prey and hence the amount of food available for birds [15, 19],
  • Pollution of coastal wetland areas by excessive nutrients, heavy metals and other toxicants can have a direct impact on intertidal invertebrates (crustaceans, polychaetes, molluscs), fisheries and shorebird health,
  • See also the specific threats to mangroves, saltmarshes and coastal wetlands in the linked fact sheets.

Because shorebirds concentrate in certain areas during migration, loss or degradation of key sites could devastate populations [2].

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Significance of shorebirds

Shorebirds are highly specialised predators, adapted to exploit specialised niches that their invertebrate and piscivorous prey inhabit. Shorebirds are intrinsic indicators of estuarine biodiversity, helping to maintain trophic equilibrium in a complex environment. Each species of shorebird found in a given estuary has evolved to exploit a selected number of prey organisms, and a number of species with different bill lengths and leg lengths can forage over the same area of an estuary foraging at different depths for different prey. There is even sexual dimorphism in many species such as oystercatchers, curlews and godwits, where the length or shape of the bill is different between sexes [28]. This adaptation facilitates subtle differences in foraging depths or facilitating different feeding techniques thereby maximizing food procurement over a given foraging space [21, 22, 23].

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Considerations for measurement and interpretation

Existing information

As mentioned above, shorebird counts are irregularly conducted at a number of known important sites around Australia. These counts are primarily conducted by members of the Australasian Wader Studies Group (AWSG), though there are a number of sites which are surveyed by other research groups and individuals [e.g. 25, 26, 27]. Within most Australian States and Territories there are groups that organise regional shorebird surveys, often in association with AWSG. Examples are Queensland Wader Study Group (QWSG) and Victorian Wader Study Group (VWSG). Organisations and email addresses can be found here.

Many results from these surveys are published in the AWSGs newsletter The Tattler and journal The Stilt.

How to count shorebirds?

Depending on the size of the estuary to be surveyed there are three principal methods of counting;

  • Land-based assessment - roosting and/or feeding sites accessible by vehicle and foot
  • Water-based assessment - roosting and/or feeding sites accessible by boat
  • Aerial-based assessment - remote and very large sites (e.g. Great Sandy Strait, Qld)

A useful guide to assessment protocols used in North America can be found here, while an Australian example exists for northern NSW coastal surveys [30]. A useful text on bird census techniques is that of Bibby [32].

With all three methods, a basic set of equipment is required;

  • Knowledge of the estuary, access points, potential feeding and roosting sites - primarily derived from local topographic maps, published information, local relevant government departments, local councils, regional birdwatching groups, local knowledge,
  • Field guides [3, 4, 5, 31] to assist in the identification of shorebirds,
  • A note pad and pen, GPS (global positioning system) if available,
  • A pair of binoculars, ideally 8x30 to 10x50 in size (smaller or larger binoculars are inappropriate for bird watching),
  • A spotting scope (small tripod-mounted telescope), ideally x20 to x60 in size.

Photo of binoculars and spotting scope, essentials in shorebird assessment

Photo2. binoculars and spotting scope, essentials in shorebird assessment.

Counting shorebirds is accomplished by either directly counting individuals of each species present at a roost site or through a feeding area or estimating if numbers are in the thousands. With a bit of experience individually assessing numbers of birds up to a few thousand is not difficult, however when flocks exceed several thousand, estimating is a faster and often more appropriate method. To do this, either using binoculars or spotting scope, pan across the area occupied by the birds. Often, the birds are equally spread. Starting at say the left hand side of the flock, count how many are in on field of view, then move the view to the right and assess if a similar number are in that view. Continue moving to the right and determine how many views the whole flock use, then multiply the first assessment by the total number of views. For example, suppose you find a flock of Bar-tailed Godwits spread over a roost site of 150m. You position your binocular view at the left hand side of the flock and count 120 birds in the first view. You then pan to the right and find that 10 fields of view account for the majority of the flock and that the density of birds in each of the ten views is similar (naturally some views will have higher and lower density). The whole flock can be assessed as 120 birds multiplied by 10 views equalling approximately 1200 godwits. Again, experience at trying this method will increase your ability to use it. The more times you use this method the better you will become at using it. For best results, always try and have the birds you're assessing with the sun either behind you or to the side. It's always difficult if your looking into the sun due to glare off the water and mud. To gauge how your experience is growing, always use and compare direct counting and the assessment method where practicable.

Many shorebird observers prefer to count birds at high tide roosts. This is simply because a number of species often congregate in a few discrete locations along or adjacent to the estuary as described in the critical habitat section. It can be logistically more efficient to estimate estuary populations using this strategy, especially if a boat is unavailable to explore the estuary at low tide. As the tide begins to ebb, shorebirds disperse from roost sites to their preferred foraging habitat and this can greatly increase the amount of time and effort required to assess the population. Similarly, unless a team of investigators is used at low tide to simultaneously assess foraging sites, overestimates may occur due to birds moving from one feeding ground to another. Nevertheless, in order to understand how shorebirds are utilising a given estuary, some evaluation of the relative foraging value of a feeding ground needs to be incorporated in the estuary assessment.

Most shorebirds forage primarily during low tide and the majority of shorebirds will forage at night as well as during the day, thereby maximising their food intake potential each day.

For Australian estuaries the best guides to which species are likely to be encountered in different geographic locations (and their relative abundance) is found in two sources [2, 29]. It should be noted that experience has shown the best times to evaluate an estuary is between November and March (summer) and June to August (winter), for summer and winter populations respectively. Additionally, shorebird populations are notorious for varying between years and even within seasons when environmental conditions change [8, 25]. Indeed for reasonable estimates of shorebird populations from any estuary, counts should be conducted at least twice during summer and winter for several years, so that natural variation can be accounted for and used to predict potential future trends [8, 21, 22].

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Initiatives

All migratory shorebird species are protected under national legislation and there have been several initiatives to address the various pressures on bird populations [1]: For example:

The following links provide other sources of information:

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Critical habitat

Shorebirds use a wide variety of habitat ranging from open grasslands, freshwater wetlands, estuarine wetlands, intertidal zones of beaches, rocky shores and off-shore reefs and even marine environments [2,5,6]. Within estuarine environments, two functional-habitat types are of critical importance; roosting sites and feeding sites.

Foraging sites

Shorebirds forage during low tide in intertidal sand and mud flats, rock shelfs, oyster leases, saltmarsh and mangroves [8]. The location of foraging sites within an estuary varies with the foraging requirements of each species present. Generally, shorebirds distribute themselves across the tidal flats as the tide begins to ebb. Each species forages uniquely, depending on a combination of bill-length, leg-length, vertical prey distribution within the substrate, tidal exposure and spatial distribution of preferred prey within the estuary. Time is another important factor, with birds often moving up an estuary as the tide progresses towards low tide, thus exposing more up-stream foraging habitat. The distribution of prey species, generally intertidal invertebrates, crustaceans and small fishes, is a function of variables such as substrate particle size and composition (sandy to muddy to gravely to pebbly), vertical stratification of the substrate, nutrient and oxygen availability, predator density, tidal exposure and seasonal reproduction [8, 16, 17, 23, 24].

Roosting sites

When the tide is high, most shorebirds habitually congregate together in mixed-species groups and roost at regular locations within and adjacent to the estuary. Roosting sites can vary from estuary to estuary though they usually conform to a simple set of rules. The key criteria for a roost site is to be slightly elevated from its surrounds with 360 degree vision, primarily for predator evasion and warning of human encroachment. During periods of foul weather, this habit can change and shorebirds may roost in depressions, behind low shrubs, behind sandy hummocks and even in four-wheel drive track depressions.

Principal roost sites include exposed sands at the estuary mouth and on adjacent beaches, saltmarshes that are only marginally submerged during high tide, grassy areas adjacent to the estuary, nearby freshwater wetlands, claypans and occasionally rock groynes and exposed reefs.

More information on biota removal/disturbance.

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References

  1. Christidis, L. and Boles, W.E. 1994. The Taxonomy and Species of Birds of Australia and Its Territories. Royal Australian Ornithologists Union, Monograph No. 2, Melbourne.
  2. Watkins, D. 1993. A National Plan for Shorebird Conservation in Australia. Report No. 90. Royal Australian Ornithologists Union, Melbourne.
  3. Pizzey, G. M. and Knight, F. 1997. Field Guide to the Birds of Australia. Harper Collins Publishers, Sydney.
  4. Morcombe, M. 2000. Field Guide to Australian Birds Steve Parish Publishing. Archerfield, Queensland.
  5. Hayman, P.J., Marshal, P.J. and Prater, T. 1986. Shorebirds: an identification guide to the waders of the world. Croome Helm, Beckenham, UK.
  6. Pringle, J.D. 1987. The Shorebirds of Australia. Angus and Robertson Publishers, North Ryde.
  7. Norman, F.I. and Nicholls, N. 1991. The Southern Oscillation Index and variations in waterfowl abundance in southeastern Australia. Australian Journal of Ecology 16, 485-490.
  8. Chafer, C.J. 1998. The Effects of Temporal Geomorphological Processes on Shorebird Populations at Shoalhaven Heads, NSW. MSc(Hons) Thesis, School of Geosciences, University of Wollongong.
  9. Jessop, R. and Collins, P. 2002. The effects of cyclonic weather conditions on the bird life around Broome, Western Australia. The Stilt 36, 16-19
  10. Hotker, H.., Lebedeva, E., Tomkovich, P.S., Gromadzka, J., Davidson, N.C., Evans, J., Stroud, D.A and West, R.B. (editors) 1998. Migration and International Conservation of Waders: Research and Conservation on North Asian, African and European Flyways. International Wader Studies 10. 1-500.
  11. Ming, M., Jianjian, L., Chengjia, T., Pingyue, S. and Wei, H. 1998. The contribution of shorebirds to the catches of hunters in the Shanghai area, China during 1997-1998. The Stilt 33, 32-36.
  12. Gerasimov, Y.N. and Gerasimov, N.N. 2002. Whimbrel Numenius phaeopus on Kamchatka, Russia. The Stilt 41, 48-54.
  13. Burger, J. 1981. The effects of human activity on birds at a coastal bay. Biological Conservation 21, 231-241.
  14. Kingsfprd, R.T. 1990. The effects of human activities on shorebirds, seabirds and waterbirds of Comerong Island at the mouth of the Shoalhaven River. Wetlands (Australia) 9, 7-12.
  15. Galbraith, H., Jones, R., Park, R., Clough, J., Herrod-Julius, S., Harrington, B. and Page, G. 2002. Global climate change and sea level rise: potential losses of intertidal habitat for shorebirds. Waterbirds 25, 173-183.
  16. Grant, J. 1984. Sediment mircotopography and shorebird foraging. Marine Ecology Progress Series 19, 293-296.
  17. Quammen, M.L. 1984. Predation by shorebirds, fish and crabs on invertebrates in intertidal mudflats: an experimental test. Ecology 65, 529-537.
  18. Australian State of the Environment Committee. 2001. Coasts and Oceans: State of the environment report 2001. CSIRO Publishing, Collingwood. http://www.ea.gov.au/2001/coasts/pubs/coasts.pdf
  19. Institute for Freshwater Ecology, Centre for Ecology and Hydrology, Dorset.
    20. 20. Morrison, M. 1986. Bird populations as indicators of environmental change. Current Ornithology 3, 485-490.
  20. Chafer, C.J. 1994. Prey-specific foraging techniques of the Sooty Oystercatcher Haematopus fuliginosus.25, 23-32
  21. Kaljeta, B. & Hockey, P. A. R. 1994. Distribution of shorebirds at the Berg River estuary, South Africa, in relation to foraging mode, food supply and environment features. Ibis, 136, 233-239.
  22. Piersma, T., De Goeij, P. & Tulp, I. 1993. An evaluation of intertidal feeding habitats from a shorebird perspective: towards a relevant comparison between temperate and tropical mudflats. Netherlands Journal of Sea Research 31, 503-512.
  23. Yates, M.G., Goss-Custard, J.D., McGrorty, S., Lakhani, K.H., Dit Durell, S.E.A., Clarke, R.T. Rispin, W.E., Moy, I., Yates, T., Plant, R.A. and Frost, A.J. 1993. Sediment characteristics, invertebrate densities and wader densities on the inner banks of the Wash. Journal of Applied Ecology 30, 599-614.
  24. Chafer, C.J. 1991. Waterbird Dynamic of Lake Illawarra and its peripheral wetlands. Australian Birds 25, 29-59.
  25. Driscoll, P. 1993. Survey of waders in the Great Sandy Strait, south-eastern Queensland, Australia. The Stilt 22, 24-36.
  26. Wilson, J.R. 2001. Wader surveys in the Coorong, South Australia. The Stilt 40, 38-54
  27. Lauro, B. and Nol, E. 1995. Feeding behaviour, prey selection and bill size of Pied and Sooty Oystercatchers in Australia. Wilson Bulletin 107, 629-640.
  28. Marchant, S. and Higgins, P.J. (eds). Handbook of Australian New Zealand and Antarctic Birds Vols 3 and 4. Oxford University Press, Melbourne.
  29. New South Wales National Parks and Wildlife Service 1995. Vertebrates of North-eastern New South Wales. NSW NPWS Hurstville (300pp).
  30. Simpson, K. and Day, N. 1986. Field Guide to the Birds of Australia. Viking Penguin Books Australia, Ringwood, Victoria.
  31. Bibby, C. J., Burgess, N. D. and Hill, D.A.. 1992. Bird census techniques. Academic Press, London. 257 pp.

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Useful internet links

  1. www.speedlink.com.au/users/cchafer/bird_doc/book/book9/book9.html shorebirds of the southern NSW area
  2. www.awabakal-e.schools.nsw.edu.au/shorebirds/ general shorebird pictures and text for schools
  3. pw1.netcom.com/~djhoff/sbimage.html shorebird images
  4. www.abc.net.au/wing/htmlv/interface.htm interactive site to follow the migration route of Eastern Curlew from Australia to Russia
  5. www.abc.net.au/wing/community/fromthewet-03-03.htm latest news on shorebird movements
  6. www.anu.edu.au/BoZo/jennions/publications/PatAnimBehav98.pdf an interesting paper on temporal predator-prey interaction
  7. www.tasweb.com.au/awsg/index.htm home page for the Australasian Wader Study Group
  8. www.arcticbirds.ru/ information on the breeding season success of migratory shorebirds in the Russian Arctic breeding grounds 1998-2002.
  9. www.idrisi.clarku.edu/10applic/idr96cd/scheiff/Idrisicd.htm modelling the spatial distribution of shorebirds in an estuary
  10. www.im.nbs.gov/iss/iss.html international shorebird survey protocols
  11. srmwww.gov.bc.ca/risc/pubs/tebiodiv/shorebirds/index.htm#preface details of shorebird assessment techniques used in North America
  12. www.tasweb.com.au/awsg/flyways.htm information on East Asian - Australian Flyway
  13. web.uct.ac.za/depts/stats/adu/wsg/rpw78.html Recent publications on shorebirds in the scientific literature

Author

Chris Chafer, Water Science and Research Sydney Catchment Authority.

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