Amir Ben Dov (Israel)
Chris Gibbins (Scotland)
Hannu Koskinen (Finland)
Mars Muusse (the Netherlands)
2cy heuglini: May
General description of 2cy heuglini in spring
The variation in moult strategies within the LBBG-complex is nearly larger than the inter-specific variation in moult strategies between most other European large gull-taxa.
To a certain extent this has been caused by intra-specific differences in the geographical position of the winter-quarters. Concerning first summer LBBGs, several authors highlighted the different moult strategies between fuscus / heuglini and their western relatives graellsii / intermedius in recent publications.
But what exactly is the moult strategy for heuglini?
On the basis of concise descriptions and photographs of a hundred representative individuals, we would like to give an impression of our observations made over the last few years.
In analogy to western taxa, we recognize three types of 1st-summer LBBGs, which occur in Finland in April and May. Birds with intermediate characteristics are certainly not rare, but at least a considerable part is distinguishable. Anyhow, we would like to stress that our classification has mainly been based on the differences in plumage patterning or moult strategy on the winter grounds.
We have no data set of ringed 2cy heuglini, but a considerable part of the 2cy birds is very reminiscent of western taxon graellsii; especially the vanguard of 2cy heuglini arriving in April in N Europe. Still, despite the similarity, it is believed we are dealing with true 2cy heuglini; example birds can be found HERE, HERE, HERE & HERE. In what respect do these bird look like the English same-aged graellsii?
Normally, the 2nd generation scapulars and mantle feathers have a pale or greyish base with an onvious pattern, either brown anchors or broad barring (HERE, HERE, HERE). The wing-coverts are usually completely juvenile or juvenile with only a small number of 2nd generation coverts (HERE, HERE, HERE). The tail is largely black-brown (HERE, HERE, HERE) and nearly always juvenile (or at most a 2nd generation R1). The under-parts and head are patterned with bold markings on a dirty base (HERE). The bill is mostly blackish, with only a slightly paler base. Legs are pink.
First type birds thus have had a very limited post-juvenile moult at the wintering grounds and will show a complete moult strategy identical to the western relatives in summer. This type has not moulted flight feathers on the wintering grounds (HERE, HERE, HERE). Active primary-moult in the inner primaries appear in the last week of May in the vanguard of birds in Finland. The relative number of 2cy heuglini that start the complete moult rapidly growns in the first 10 days of June. This is four weeks later than typical English and Dutch graellsii we scored in NW France and the Netherlands and scored by Peter Stewart in the UK (PDF). By July all birds (including 2nd & 3rd type birds) are in active primary moult, with the inner primaries already replaced (but our sample size for 2cy heuglini in July is still small).
Graellsii has the remaining juvenile primaries in spring usually in bad condition, caused by heavy bleaching and wear. That is unlike heuglini, as 2cy heuglini in spring often show surprisingly neat primaries and even the fringes of wing-coverts may be crisp.
Variation in the first type
First type heuglini has a similarity to graellsii in blochy under-parts, very limited / no moult in wing-coverts, tertials, secondaries; and anchor-shaped patterns on 2nd gen scapulars (HERE). However, individual birds may differ at points, e.g. THIS bird, which is typical 1st type in scapular pattern and showing no moult in coverts or flight-feathers. However, the under-parts are immaculate white, not blotchy and such birds may stand out in a group of western graellsii. Thus, when you click on the example birds linked above, you may find some birds not completely matching the definition for 1st type, still they are classified in this category.
We believe 'core-representatives' of the 2nd type (and the 3rd type as well) are different from 'core-first types' regarding their moult strategy and pattern on wing-coverts and scapulars. The basis for this difference is not known, and could be related to population differences. Still, 2nd type birds do show up in Finland in April - July regularly, and they differ from typical English graellsii; though may recall some intermedius LBBG, which also may show an advanced post-juvenile moult in late winter.
The wing-covert moult on the wintering grounds has been extensive in 2nd type birds (HERE, HERE, HERE). Typical birds of the 2nd type have all wing-coverts, but also all tertials renewed, and resting birds appear in complete 2nd gen plumage, except for the primaries (HERE).
Some 2nd type birds are slightly retarded, their wing-covert moult has been suspended prior to migration, leaving a generation contrast between the inner and outer coverts (HERE, HERE). This especially applies to the greater coverts, which often show a mix of replaced 2nd generation inner coverts and retained juvenile outer greater coverts.
All tertials and median coverts have been renewed, even in retarded 2nd type heuglini. The moult-stage of lesser coverts is more advanced than in the greater coverts, but especially 'upper' lesser coverts are less advanced than the tertials and median coverts, and the carpal edge may contain juvenile feathers until the last stage of moult.
Regarding the under-wing coverts and axillaries; it is often very difficult to obtain good views to determine the generation. In advanced individuals, these under-wing coverts are already partially or completely renewed and often nearly all-white, like the underparts (HERE). It might turn out that the moult of under-wing coverts and coverts show similarity in moult strategy.
Second type heuglini has a number of moulted tail-feathers in the winter-quarters (HERE, HERE, HERE, HERE). The extent is variable and subsequently we find large variation in May and June. Typical individuals show a complete 2nd generation tail, while retraded birds return with a clearly suspended rectrices moult-stage (HERE, HERE). In the winter-quarters, many individuals do not proceed the moult of the rectrices in a descendant sequence ('centrifugal moult as in the complete moult of large white-headed gull taxa'), since migrating birds in spring really show every conceivable moult-stage (e.g. R5-6 2nd generation, while R1-4 are still juvenile, etc).
Some birds do not show fully-grown rectrices, but it is at least not usual to find a tail in active moult by April-June. Apart from the obvious fresh white tips, the pattern of the 2nd generation rectrices is mostly juvenile-like, but the darker parts are pure black and the pattern is more vermiculated at the base of the feathers. The extent of black on the 2nd generation feathers is very variable, even within a single bird. This may be a hormone related issue, with feathers looking more 'adult-like' when replaced in a period bright and saturated colours are essential for mating (when in adult plumage). Birds with for example a partially white R2, a nearly complete black R3 and with a R4 showing much white, are common. A small minority shows only very little black on the 2nd generation tail-feathers, hence looking very 3rd gen-like.
The renewed upper-tail coverts are completely white or with some sparse barring on a white base.
Typical 2nd type heuglini have a variable number of secondaries replaced (HERE). The variation of loci where feathers have been replaced seems endless. However, the common strategy involves the inner secondaries, adjacent to the tertials. But variation is large, and it may be argued that the moult in a 'jumping' (random) order is a common strategy as well (HERE, HERE, HERE).
If primaries are included, we classify almost birds as belonging to 3rd type birds. So, by definition, 2n type birds have all primaries still juvenile. This is a clear dividing line, but a bit problematic in heuglini. From graellsii & intermedius observations we derived a line from greallsii-like moulting birds (no wing-coverts, no flight feathers) to advanced intermedius birds showing a new tail and the most advanced birds even showing new secondaries. For heuglini moult strategies may be more complicated, as we have scored birds which had 'average' wing-covert moult combined with replaced primaries. We even have observations of birds with 2nd generation P10, while all other primaries are still juvenile, as is S1 (HERE).
The onset of the primary moult in 2nd and 3rd type 2cy heuglini in early summer is on average slightly later (1-2 weeks) than in typical 1st type birds. Additionally, the individual variation is more pronounced, with e.g. in the 3rd week of June, birds with only P1-2 missing and birds which already shed P6. In comparison with first type birds, differences in timing of primary moult is probably not significant.
An interesting phenomenon we encountered, was the remarkably good condition of the remaining juvenile primaries in some birds. In a few cases we experienced real difficulties in determining the generation of the primaries.
Variation in the second type
In short we will discuss the general variation of the 2nd type and its difference from the 1st and 3rd type.
Compared to the first type, we already stated that both second and third type usually return to the breeding grounds (northern feeding grounds) with many renewed wing-coverts, tertials and regularly rectrices (HERE).
In comparison with the 3rd type the only dividing feature between the two is 'primary moult on the winter grounds'. For instance compare these two birds: HERE & HERE. Very similar birds in upper-parts and bare part coloration and very advanced looking. One bird with old juvenile primaries (type 2) and one with replaced outer primariesd (type 3 bird). For both categories you may find birds with the under-parts more or less patterned, especially on the flanks and hind-neck. The 2nd generation upper-parts and wing-coverts often show limited patterns, so often just a simple dark shaft streak on a pale silvery grey base. The tertials show contrastingly bold blackish centre and a broad white tip.
The upper-parts seem to be moulted in an earlier stage than the wing-coverts, resulting in a 'wear contrast' between fresher coverts/ tertials against heavier worn scapulars and mantle feathers.
The 3rd type of 2cy heuglini has a major difference to same aged intermedius, which still proofs to be very robust: replaced primaries in first winter, moulted prior to turning up in N Europe.
Third type heuglini are defined by us as birds which included primaries in the first moult cyclus (should it be called 'post-juvenile' moult?) on the wintering grounds. In this respects it is similar to nominate fuscus, as we have never accounted western 2cy graellsii or intermedius returning with 2nd gen primaries from the wintering grounds. The extent of the primary moult in 3rd typre heuglini is variable (some birds replace all primaries: HERE), and even the sequence is not prefixed (HERE).
Including primaries in the first moult cycle is normally only reserved for the most advanced 2cy heuglini in spring, i.e. birds that replaced rectrices and most (or all) of the secondaries as well (HERE).
We have not found any 2cy heuglini yet, that had moulted primaries, without replacing secondaries and rectrices (HERE). Typical 3rd type birds have a large number of secondaries replaced and the complete tail.
Except for these three recognizable types, individuals with serious characteristics of fuscus or with serious characteristics of intermedius turn up in Finland every spring and early summer. There have been ring reading of birds from these populations, so a minor possible problem may arise and birds may be identified wrong.
The exact moult serquences in 2cy heuglini in late winter are not documented yet. But we do have more data from western LBBG. The most common post-juvenile moult strategy in graellsii and intermedius LBBG is:
- start wing scapular moult. This may even start in autumn of 1cy. Especially for graellsii LBBG this is also the final extent of this post-juvenile moult. Hence, many 2cy graellsii return with 2nd gen scapular region, but coverts, tertials and flight-feathers remain juvenile.
- many LBBG include a limited number of wing-coverts in the post-juvenile moult. This is similar to michahellis YLG in extent and loci involved. Typically, it includes upper tertials, inner greater coverts, most of the median and lower lesser coverts and randomly some lesser coverts.
the third category holds birds with the complete wing-covert panel replaced for 2nd generation. When the tail is shown in preening, there often appear to be a variable number of replaced tail-feathers as well. From ring recoveries, we understand these birds normally are intermedius LBBG. Such bird have the post-juvenile moult late in winter, but is much more extensive.
- the last category comprises of most advanced western
LBBG. These birds have a variable number of replaced secondaries (sometimes all secondaries 2nd generation). If 2cy western LBBG have replaced secondaries, then the prior steps were taken as well (scapulars replaced, wing-coverts replaced, tail-feathers replaced).
From these categories, we conclude that the moult startegy follows a more or less prefixed stramine, with the moult loci stimulated in a fixed order throughout the post-juvenile moult process. This is true in general; it is not very difficult to find birds that differ from this outlined principle.
The 2cy birds we see in Finland may have replaced primaries on the wintering grounds, and are therefore categorized in 'type 3'. This primary moult is often arrested (apparently there was no time to include all primaries in the process) prior to migration to N Europe again.
The moult loci that were stimulated in the primaries differ individually. Commonly, the inner primaries are involved, but loci may also lie further outwards, as several birds illustrate (HERE, HERE). We even have observed a bird with all primaries juvenile, except P10 in both wings (HERE).
The complete moult in western LBBGs has the standard sequence starting from primary P1, the innermost primary. The moult wave enrolls outwards. Apparently, this is often not the sequence in 2cy heuglini.
|Heuglini 2cy, May 29 2009, Tampere, Finland. Picture: Markku Kangasniemi.