Bird of the Week: White-fronted Tern

Betka Beach April 2021

I chose this bird as a result of having recently seen one (illustrated above) at Betka Beach.  Since I had also seen one at Betka and near the Mouth in May 2019 I believed them to be quite common in the area.  The next image shows the Mouth bird, highlighting some salient features:

Bastion Beach May 2019

The green arrow indicates it has longer legs than the Corgi  (thanks Wendy) Arctic Tern.  The red arrow shows the black carpal bar and the blue indicates scalloping (ruling out Common Tern).

In terms of plumages the plate by Jeff Davies in "The Australian bird guide" Menkhorst et al is an excellent reference.  I thank Jeff for permission to use this scan here - I hope I haven't lost too much quality in the process.

The records in eBird show 'common' not to be the case with only 10 Mallacoota District records since 2013 (or in fact since 2016).  Extending the scope to East Gippsland only generates another 9 records since 2014 (plus 1 record for August 2013).  Birdata has 26 records for East Gippsland, of which 10 are for 2011 or earlier.

But despite this relative rarity I will persevere with the species since it gives an opportunity to illustrate a number of interesting points.  A first point is that with a relatively uncommon species combining eBird and Birdata records gives a more useful pool of information to work with.  (I don't believe that any of the records are duplicated in the sense of an observation being copied in both datasets.  It is of course likely that different surveys have included the same bird, but that level of duplication is evident within the two data sets anyway.)

The following chart shows the total records (combining Birdata and eBird) for East Gippsland since 2016.

Although I have a record for 2021 I haven't included it above since the season of sightings only really starts in May, as illustrated in the following chart for East Gippsland combining eBird and Birdata records.  (Note that this month chart includes Birdata records prior to 2016 and eBird records for August 2013 and  April 2021)

The seasonal pattern is the second interesting point in that the species breeds in New Zealand and some migrate to Australian in Winter.  The first map shows the eBird gridcells for November to March ...

.. and the second from May to September.

Other terns in this size range (notably Arctic and Common Terns) migrate North-South.  There are a few other bird species which move East West across the ditch.  The commonest example of this is the Double-banded Plover, common on our sandbars from April to September.  Other species I have noticed with the East-West pattern are Hutton's and Fluttering Shearwaters: perhaps there are others, which have not drawn themselves to my attention.

My third interesting feature is the relative sizes of Tern species.  When I saw the bird photographed as the header it was very clear that it was a lot smaller than the horde of Crested Terns around it.  (It was very similar in size to the Arctic Tern about 5 m away, but the White-fronted had legs 😁.) This next chart uses the weight ranges in the Australian Bird Guide to illustrate how the Terns fall into size ranges - Whiskered Tern sort-of bridges the small-medium boundary but looks small in the flesh.

The next image shows the White-fronted Tern compared with Crested Tern and Silver Gulls.

Betka Beach May 2019

After 2 weeks trying to relocate the White-fronted Tern - with them being reported several times by other observers - I finally managed to track one down at the mouth, looking from Captain Stephenson's Point.  It positioned itself nicely with Crested Terns and a Little Tern for comparison.

So my starting point with tern ID now is to check the size relative to something else nearby (if possible).  Caspian Tern is easy: huge (and with a red traffic light stuck on the front of its head);  Crested and and Gull-billed are large and bill colour sorts them out,  That leaves the medium and little groups: its beyond my pay scale to advise on how to split them within the two groups.  Take

• photographs (as many as possible); and 
• good field notes focusing on leg length and colour shape of the head, bill colour, and extent of mottling on the wing feathers 

 which should enable the species to be sorted by reference to reference works and helpful experts.