Mallacoota bird records

I recently compiled a list of all species (and other taxa) reported to eBird.  After sharing with the Mallacoota Birds Facebook Group I was asked a question about when those records started, and said I would investigate.  This more or less coincided with a discussion with Frances about which was the commonest bird in the Mallacoota area.  So I have done a trivia-trawl on my database to see what interesting facts emerge.

I'll start with the two questions I have been asked.

Timing of records

The first line of discovery was to look at the number of checklists over time.  The history of eBird is on wikipedia - basically launched in 2002 in the US and became worldwide in 2010 - but this doesn't mention that people with the necessary records could enter historic sightings.  It took a while to become established but really took off when the mobile version was launched in 2015.  (As an aside, finding that information was an interesting byway to this project.)  A first graph shows the number of eBird records for Mallacoota by decade.

 Of the 54,000 records, 6000 relate to periods before eBird was launched: probably most of these were lodged through an Australian app Eremaea Birds.

The second graph focuses on the last decade (with a prorata estimate for 2019).  The rate of growth continues.  (Truth in advertising: some of this growth may reflect the fact that we now spend about 75% of the year in Mallacoota, rather than about 10%. )

Which species is the commonest?

A simple answer is to count the number of records for each species.  Doing that the top 10 are:

COMMON NAME Count Superb Fairywren 1537 Grey Fantail 1319 Silver Gull 1250 Rainbow Lorikeet 1233 Welcome Swallow 1229 Red Wattlebird 1172 New Holland Honeyeater 1140 Wonga Pigeon 1086 Eastern Yellow Robin 1075 Brown Thornbill 1044

Another way of looking at "commonness" is the total number of birds reported.  Again the top 10: .

COMMON NAME	Sum
Silver Gull	20735
Crested Tern	13643
Chestnut Teal	7368
Yellow-faced Honeyeater	6905
Australian Wood Duck	6104
Welcome Swallow	5741
Australian Pelican	5505
Rainbow Lorikeet	5284
Short-tailed Shearwater	5161
Little Black Cormorant	4668

A small difficulty arises with summing the counts as some observers only report presence (ie report 'x')  rather than counting (or estimating) numbers.  We aren't talking rocket science here, so can safely assume the x's are similar in distribution to the reported values.  

The differences between the two measures seem to be due to species with restricted habitats (and thus not covered by some checklists) occurring in large flocks within that habitat.  For example Crested Terns only appear in lists including beaches and/or jetties but are often in groups of 50+ birds when they are reported.  Chestnut Teal are typically only reported at sites with open water but are often in flocks of >20 birds.

It would be possible to build up an index of attributes of reports but that might need to include adjustments for such things as the "obviousness" of the species.  For example a small brown skulker may get under-reported while a larger lurid bird (eg King Parrot) is rarely overlooked.  At present I can't work how to do that objectively.  Taking the average rank of the count and sum for each species gives a 'Top 20' list as follows:

Silver Gull

Welcome Swallow

Rainbow Lorikeet

Superb Fairywren

Yellow-faced Honeyeater

Red Wattlebird

Australian Pelican

New Holland Honeyeater

Great Cormorant

Bell Miner

Chestnut Teal

Grey Fantail

Silvereye

Little Wattlebird

Brown Thornbill

Crested Tern

Australian Wood Duck

Wonga Pigeon

Australian Magpie

Little Black Cormorant

There are several species I'd consider as very common not included on that list, but I will merely say "Isn't Mallacoota an excellent birding area" and pass on to other topics.

Seasonal pattern

Its well known that the ongoing population of the area is about 1000 rising to several times that in Summer.  So it could be expected that an increased number of observers will interact with the presence of migrants to give increased numbers of reports in the warmer months.  The next few paragraphs and - I am sorry to say - graphs look more at how the number of observers and/or observations vary through the year.  (I have excluded my own observations from this as my status as a very frequent visitor/resident might bias the results.)

As a general note I have used a financial year for these charts since that seems a better split for things to do with nature (the breeding season is August to about February so that keeps the events in one place).

This graph is pretty crowded but shows the expected seasonal pattern with a peak in January - most likely early January - after Christmas itself.  The number of lists per observer does not have such a good fit to trend, especially the high value for June.  Perhaps only dedicated birders come in that chilly month?

 I then had a look at the effort data included in eBird: some historic records don't have that so have been excluded.  To avoid clutter I have blanked out the original data and just shown the trendlines below.   Looking at the number of hours per observer (summed over all visits by the observer in the month) shows that birders effort seems to peak a little before the Christmas break: perhaps avoiding the midday heat?  The total number of hours shows much the same pattern as total number of observers and thus peaks in January.

Although not strictly a seasonal matter I will note in passing that eBird has reports from 295 observers: not a bad contribution to the local economy.

Odds and ends

Currawongs and Magpies

I was intrigued when scanning the information about number of records that Pied Currawongs were slightly more frequently reported than Australian Magpies.  Looking at the number of birds reported per observation  shows more Currawong records with no number given or just one bird.  I suspect this reflects Currawongs' noisier behaviour so that observers know the species is around, whereas except in breeding season Magpies are much quieter.

Big numbers

As with any citizen science undertaking when the data is peered at in detail some oddities can be found.

In this case there were two estimates of huge numbers (4,000 and 3,500) of Black Swans.  This is not impossible, but highly unlikely so I have raised a query with eBird asking them to check with the observers if possible.  The response from eBird was that they believed this possible.  I have since spoken with a very experienced birder from Bairnsdale who said that flocks of swans of that size or bigger are not unusual on the Gippsland Lakes - but the birders likely to monitor those flocks do not use eBird.

There are few records of Rock Dove,  However one of them  shows 200 birds.  I note that Mallacoota is a popular site for releasing pigeons for a race and would bet that this was a flock heading for home rather than being birds living in the area.

On the other hand  there are a few large flocks of Short-tailed Shearwaters with the biggest being 3,000 birds.  I have seen one huge flock close inshore that I estimated at a conservative 1,000 birds and quite easily believe that an observer with a good telescope could see many more than that if the weather conditions and supply of food was appropriate.

In late Summer flocks of White-throated Needletails travel along storm fronts.  These flocks can be well over 1,000 birds further North so several reports of 100-300 birds are believable.  The fact that most of the large flocks have flocks sizes ending with 1 or 2 '0's indicates people have estimated, rather than tried to count a highly mobile flock travelling at 100kph!

Conclusion

This is just a quick dabble into some things that interested me.  I'll continue to do so and issue further reports in the future!