Introduction

The data

This overview is generated using the data from the VWSG, updated 18-8-2018. For species where sufficient data is available, minimal age overviews and variations in juvenile percentages over the years are being calculated and provided. The data does not include ABBBS recoveries and leg-flag sightings. Some noteworthy data characteristics:

  • it includes all birds originally banded as adults, immatures or juveniles by the VWSG in South Eastern Australia and notably Victoria (for approximate area covered by these activities see map below).

  • it contains data where a year (season) runs from August 1- July 31 the next year.

  • it presents conservative age overviews (e.g. a bird aged 2+ upon banding was assumed to be 2 years of age).

  • the data has been rather conservatively filtered for obvious errors in observations.


Age overviews per species

The following statistics are being presented:

recaptured: is the total number of individuals for which recaptures exist. The data presented are the last known recaptures of banded individuals (all intermediate recaptures have been filtered out). banded: is the total number of individuals that have been banded.

Things to consider when viewing these data:

  1. we only conservatively estimate the age of the birds, where 0 means that the bird was recaptured as 0 years old. So, the bird was both banded and recaptured within its first year of life. Similar to how you age people; mind you that these birds were never seen again, since we only used the last known recapture of each individual.

  2. we do not really measure maximum age (only the age at which a bird was recaptured for the last time).

  3. since recently marked birds are also included that likely haven’t seen the end of their life yet, younger birds are overrepresented.

  4. assuming high site-fidelity of birds, the method will see younger birds overrepresented if incidental catching sites are included; only consistent regular catching gives unbiased results.




Juvenile percentages per species

Juvenile percentages can provide good insights in annual reproductive success and variations therein over the years. The juvenile percentages are calculated using data from all cannon-net catches (since other techniques may be skewed towards juvenile birds), with the exception of winter catches in migratory waders (which typically contain juvenile birds only). What we consider “winter” and “summer” catches may vary from species to species. The dates used take account of when it is judged that all adults and all juvenile birds have arrived in the non-breeding areas which we sample and also the date up to which we believe no adult birds have yet departed for their breeding grounds. These dates are mostly the dates which have been used in recent years for those species which are annually monitored and reported on in Arctic Birds, Stilt and the VWSG Bulletin. For other species then the recommended dates have been derived from our knowledge of the timing of movements of adults/juveniles into and out of the non-breeding flocks.

These dates may differ for some species from those used historically for preparing juvenile data. You may well find therefore that in these species the figures you will derive are not exactly the same as the figures published previously. An example to illustrate this relates to Turnstone and Sanderling. Initially cut-off dates of March 1 were used. Our more detailed knowledge of departure dates for adults on northward migration has enabled us to extend the sampling period by having termination dates in early April for these two species, giving a whole month of extra data collection opportunities.

Seasonal averages (i.e. years starting 1 August) are presented for selected species (i.e. species where enough representative data is available) with 95% binomial confidence intervals. For species where we have >1000 birds caught, we also conduct a logistic regression to study trends in juvenile percentages over time.




Species overviews

The age overiew and juvenile percentages are shown in alphabetical order as listed below. The further reading link directs to the species’ BirdLife Australia webpage for more information on e.g. its identification, distribution, behaviour and conservation status.

Number Species
1 Banded Stilt Further reading
2 Bar-tailed Godwit Further reading
3 Caspian Tern Further reading
4 Common Greenshank Further reading
5 Common Tern Further reading
6 Crested Tern Further reading
7 Curlew Sandpiper Further reading
8 Double-banded Plover Further reading
9 Eastern Curlew Further reading
10 Great Knot Further reading
11 Greater Sand Plover Further reading
12 Grey-tailed Tattler Further reading
13 Grey Plover Further reading
14 Gull-billed Tern Further reading
15 Hooded Plover Further reading
16 Latham’s Snipe Further reading
17 Lesser Sand Plover Further reading
18 Little Tern Further reading
19 Masked Lapwing Further reading
20 Pacific Golden Plover Further reading
21 Pied Oystercatcher Further reading
22 Red-capped Plover Further reading
23 Red-kneed Dotterel Further reading
24 Red-necked Avocet Further reading
25 Red-necked Stint Further reading
26 Red Knot Further reading
27 Ruddy Turnstone Further reading
28 Sanderling Further reading
29 Sharp-tailed Sandpiper Further reading
30 Silver Gull Further reading
31 Sooty Oystercatcher Further reading
32 Terek Sandpiper Further reading
33 Whimbrel Further reading
34 Whiskered Tern Further reading