Black Brant Hybrids

in Norfolk

by James McCallum

(all photos by Martin Garner)

Adult Black Brant X Dark-bellied Brent, Holkham, February 2013

Some of my earliest memories of growing up on the north Norfolk coast are of flocks of Brent Geese and their lovely muttering calls. In my early teens I developed a stronger interest in the local bird life and a closer look at the Brent flocks occasionally revealed the presence of a few Pale-bellied Brents and, more rarely, a Black Brant. Such occurrences set the scene for the following two decades – although in some winters, small influxes of Pale-bellied Brents occurred and occasionally two or three Black Brants graced the local flocks.

In January 2001 I was watching a flock of Brents at Burnham Deepdale when, suddenly, a rather well-marked Black Brant walked into my telescope view. This well-built bird frequently adopted a very upright stance and regularly made threat postures aimed towards other geese that ventured too close. I was confident that it was a gander and it wasn’t too long before it became apparent that it was paired to a Dark-bellied Brent Goose. This was the first occasion that I could recall seeing a vagrant Black Brant that had formed a pair bond with a Dark-bellied Brent and my interest turned to surprise when the pair came towards the edge of the flock to reveal four hybrid goslings in tow!

This was the first time that a mixed pairing had been recorded in Norfolk and, prior to this, there had only ever been one other documented British record -a mixed pair with six hybrid young was found by Barry Collins at Thorney Island, West Sussex in the early winter months of 1989 (two of these original hybrids returning during the following three winters). The same observer also found a second adult Brant (another gander, but this one was without a mate) in the same area between October 1991 and March 1992, accompanied by four juveniles that resembled berniclas (the other adult may have died on migration or on the breeding grounds, or the Brant may even have adopted the family).

In subsequent winters after 2001, two more mixed pairings with hybrid young appeared in Norfolk, both in the Wells and Holkham area. They could often be encountered, with ease, on the Pitch & Putt course near Wells Beach Road or in the fields adjacent to Lady Anne’s Drive at Holkham. These Norfolk hybrid youngsters have shown high survival rates and, in common with many of the Brent flocks, are largely site-faithful.  At least seven birds have returned as adult hybrids and currently, in the winter of 2012-’13, at least four are to be found in north Norfolk – one at Burnham Overy and three in the Wells/Holkham area (with one or two of these also appearing at Cley during a period of cold weather in January).

Picking out a potential Black Brant as it walks into view amongst a flock of Dark-bellied Brents is both instantaneous and exciting – working out whether it is a pure Brant or a hybrid may take a little longer but, so long as the views and light are good, it should prove possible. The returning birds have provided an excellent opportunity for observers to familiarise themselves with the appearance of adult hybrids of known parentage. Interestingly these hybrids have (so far!) all shared a remarkably consistent appearance.

Plumage

Pure Black Brants show distinct brown hues on their body feathers. The tone can vary in its darkness but the brown hue is always present – I tend to liken the colour to ‘plain chocolate’ or ‘tar brown’ whereas others describe the brown colour as having ‘tobacco’ hues. The pale flank patch usually has a striking chalky-whiteness which contrasts greatly with the rest of the dark brown body feathers. Hybrids, at first glance, can closely resemble a Black Brant, but more prolonged study will reveal some subtle differences in plumage hues that hint at the Dark-bellied influence -the body feathers have distinct grey hues and the flank patch often appears slightly ‘dirty’, caused by a pale buff-grey wash.

These plumages hues can, however, be influenced by light. Bright but overcast days are particularly good for assessing the subtle plumage hues of Brent Geese.  Full sun can sometimes ‘burn out’ some of these subtleties. On very dull, overcast days assessing the plumage colours can prove problematic. Hybrids can look quite dark and, at times, the grey hues of the body feathers frustratingly difficult to see. During these lighting conditions it is worth concentrating on the back feathers that catch the light e.g. the mantle and upper scapulars. As the bird turns, these highlighted areas will often be the first to show the telltale grey hues of a hybrid. As ever prolonged observation will often provide a more accurate picture of true colour and tone. (It may be worth noting that on very dull days most pure Black Brants appear very ‘black and white’, they often appear as if the contrast level has been turned up! On such days there is very little or no distinct division between the breast and belly and this dark feathering can make the flank patch and collar especially white and dazzling.)

Neck Collars

The neck collar detail of the returning adult hybrids has varied between individuals.  When viewed from the side most birds have a large, striking Black Brant-like collar but on the majority of birds the collar is broken at the front, particularly on the upper edge (see illustration). NB when relaxed or feeding it can be difficult to correctly interpret the detail of the collar at the front, some individuals can appear to have a broad unbroken neck collar at the front and it is only when a bird is alert that the true shape of the collar can be seen.

Neck collars of known hybrid adults – B&C are most frequent whereas A is more unusual (2 individuals). James McCallum.

 

To date, the plumage colour hues of all of the known hybrids in Norfolk have been consistent. This has suggested that colour hue is probably more helpful than the presence of neck collar that meets at the front when identifying a hybrid.

The following photos, taken in Feb 2013, are of two adult hybrids that continue to return each winter to the Wells and Holkham area.

Hybrid One

This eye-catching individual readily stands out from the accompanying Dark-bellied Brents. At first glance it does look very like a Black Brant. The presence of grey hues in the body plumage and the ‘dirty’ wash to the rear flank-patch are indications of a hybrid.

In duller light the plumage can appear more contrasting and, frustratingly, the body plumage can sometimes appear to have brown hues. During such conditions this individual can appear extremely Black Brant-like, however,  a greyish ‘bloom’ can often be visible on areas of the mantle and upper scapulars that catch the light as the bird turns.

In better light the grey hues and buffy/grey washed rear flanks area much more evident making it easier to identify this bird as a hybrid.  When seen well, the neck collar of this individual is obviously broken at the front. (See Fig ‘C’ in the illustration of neck collar patterns)

Hybrid Two

This bird has a striking collar. (The collar usually appears unbroken but, at very close range, it has tiny dark flecks eating into the upper edge, immediately below the bill.)

In spite of the bold neck collar this bird is easier to identify as a hybrid due to the paler greyer hues of the body plumage and the obvious buffy/grey wash to the flank patch.

In brighter light the Dark-bellied Brent influence is clear to be seen. In the winter of 2012-13 this bird returned paired to a Dark-bellied Brent, with a gosling in tow. The bird’s behaviour showed it to be a gander and it would readily threaten any of goose that wandered too close to his mate and young.

Hybrid gander paired with Dark-bellied Brent and gosling. This family has spent most of the winter at Lady Anne’s Drive, Holkham. The Brent flock with which they associate often fed close to the road allowing close views and the opportunity to obtain excellent photographs. The resulting images may well represent the first documentation of definite F2 hybrid.

In terms of plumage the 1^st winter F2 gosling shows strong similarities to that of a Dark-bellied Brent. The neck collar is perhaps more striking than an average 1^st winter Dark-bellied but it is not exceptional.

Living in the heart of a traditional wintering ground of Dark-bellied Brent Geese it has been possible to get to know many of the local flocks and to watch them in a variety of weather and lighting conditions. This privileged situation has proved invaluable for regularly sharing observations and thoughts with other local observers, notably Andrew Bloomfield, Mark Golley and Richard Millington.

Further thoughts – Vagrant Black Brants in Norfolk can vary in the darkness of their body feathers, not all are distinctly ‘black and white’ and it is not uncommon to see a distinct division between the brown body feathers and the blackish neck, (as discussed above, light conditions will, of course, have a great influence). The presence of a neck collar unbroken at the front is often a requirement of an ‘acceptable’ pure Black Brant. It is now clear that an unbroken collar doesn’t exclude a hybrid Black Brant X Dark-bellied Brent.  The question that has to be asked is – how variable are the neck collars on pure Black Brants, particularly during the winter months?  (I have seen a Black Brant in Alaska in early summer with a neck collar that only met at the front on the lower edge). I guess that the answer can only come from those with experience of Black Brants within their native range.

James McCallum

Many thanks to Mark Golley for reading through the first draft and commenting on the text.