The Falco Fingerprint - Working backwards from first summers to move forwards with juveniles

Falco fingerprints are something I have been looking at ever since illustrating and observing raptors and there is a lot that can be said about them.

It all began when looking at recently fledged juvenile Kestrels (falco tinnunculus) and juvenile Kestrels migrating through the Straits of  Messina.

In this post I'm not talking about the wing formula but the patterning on the feather themselves.

I noticed juvenile male kestrels had a unique ventral fingerprint compared to that of juvenile females. I concluded that each primary (digit) had a individuality all of its own and even simple groups of feathers, such as the inner primaries can show a lot about the sex of a juvenile bird when observing raptors against sky.

I intend to post some of my findings in later posts relating to sexing juvenile kestrels but for now I wish to talk about a 1st summer female Red-footed Falcon (falco vespertinus) whose unique fingerprint highlighted quite a nice little migratory path!

For the past 6 months I have been studying the 1st generation remiges and rectrices of  Red foots along with other feather tracts to try and get to know this species a little better. To do this I headed straight to 1st summer birds!

The beauty of 1st summer birds in its second calendar year is the fact that they have completed the majority of their post juvenile body moult and therefore become instantly assignable to a sex. This is fantastic for a raptor watcher because instead of questioning the sex of the bird according to its remiges you instantly have the closure to start studying the feather patterning with certainty i.e. the falco fingerprint. You can therefore begin to study whether particular feather patterns are more commonly found in males or in females.

Although this might not seem like it has any value given the sex of a 2cy bird is already apparent from it post juvenile appearance, it helps to start to piece together pointers that could enable the sexing of juvenile birds and i would like to think flybys during autumn migration. Something that is usually only obtainable in the hand through bio-metrics or assessing sexual dimorphism, which is usually hard to observe in the field unless multiple birds are observed together.

This is VERY MUCH a work in progress but at present there appears to be a higher proportion of segmentation in the white areas in the proximal 3rd of juvenile female red-footed Falcon primaries compared to juvenile males, that seem to show more conjoined segments that span the majority of the 10 primary tips throughout the wing. These are early studies and females most certainly do show conjoined segments also but they appear more infrequently than in males. I need to do a lot more further research but i think this is a starting point along with some other ideas I have. The inner secondaries also seem like and interesting area to study given juv/2cy males look to show a wider dark trailing edge to the secondaries resulting from what appears to be reduced white segments at the basal end of the inner secondaries compared to females. Work in progress!

Red-footed Falcon primaries provided by Croatian Feather Atlas - I have attached the above image to try to convey what I mean. In this photo i'm not trying to highlight the birds sex simply what I'm looking at when studying feather patterns and the bird fingerprints. Very early days but males have a tendency to show a greater majority of conjoined markings on the proximal 3rd of the feathers throughout the 10 primaries.


What is certain is each 1st generation primary has a unique feather pattern and every individual seems to have a unique fingerprint.

The bird below is a 1st summer female (2nd calendar year) that was part of a healthy influx of red foots that arrived on Britain's shore during late may.

She was one of 4 birds that migrated south past Spurn Bird Obs on the 28-05-17 and was nicely photographed as she tanked south by the LUCKY observers.

I unfortunately missed that incredible day but spent ages gawping at Tim Jones's and Jake Gearty's pics on the spurn website and studied each of the birds closely. About three weeks later whilst doing my daily sift through the latest Uk raptor pics I came across a fine photo taken by Mark Wright of a 1st summer female hawking around Morden Bog in Dorset. Her fingerprint rung a bell and i knew i needed to compare the pics of the two females side by side

Sure enough she looked like the same bird. I have drawn pointers on the pic to show my thoughts and have listed some points below the comparison piece to further my workings.

  • Tail shape very much the same - arising from newly moulted 2nd generation rectrices that portrude from abraded 1st generation feathers. clearly a greater number moulted on one side giving the a-symmetric tail shape
  • very diagnostic carpal patch of left wing showing a very white leaf shaped area housing two prominent dark spots that can be seen in both pics
  • the proximal pattern of the white segmentation in the primary tips (fingerprint) of  P9, P8 and P7  matches in shape. Note the inner web of p8 seems to be cloaking P7 on the spurn bird which throws the shape of the fingerprint a little.

Obviously without colour rings or a sat tag I can never be 100% but pretty positive this is her. In just under three weeks she had migrated around 220 miles to Morden Bog.

I personally reckon the majority of these overshooting red foots take a simlar root and slowly meander south-south west before hitting the south coast before working out east across the channel. This looks to be reinforced by the late June sightings of birds in the south and south east of the country, excluding the the long staying lingerers that arrived in May and found a prey rich site allowing them to summer and moult through into their 2nd generation attire.

I feel there is a lot of exciting work to be done here and hope to share some findings as and when I have a few more thoughts regarding sexing juvenile red foots!

Cheers for your time and eyes to the skies!