Sunday, November 12, 2017

Black Wheatear

Passions of mine include Wheatears (Oeneanthe, a genus in the family Muscicapidae) and one of particular interest is the elegant, comic and enigmatic Black Wheatear. Here in my mountains I can connect with these friends at any time I want, through the depths of winter through to high summer. Nothing is more relaxing and holds my fascination more than observing males demonstrate strength and attraction to watching females. The males decorate nesting places with stone platforms, individual stones can weigh up to 22gms and the older the male, the heavier these stones can be. It appears these demonstrations of strength cement bonds between pairs and also advertise the superiority of some older males.

Largely resident in my area (Serrania de Ronda), with only some altitudinal dispersal noted, my Black Wheatears pair for life. The pair will defend their territories against interlopers and this more often than not involves younger birds seeking to usurp the resident pair. However, there appears to be a certain amount of tolerance displayed towards neighbouring pairs and an overlapping of territories, perhaps a recognised buffer zone between territories. Monogamy too seems to be social rather than sexual, permissiveness being observed by both male and females.

--> One of these days I hope to find time to detail my studies of this fascinating bird and share my intimate knowledge of their behaviour. Whilst my knowledge is local and confined to my local mountains, perhaps such an article might interest people and be of some value. In the meantime, see below, I have given a brief summary and by no means complete account of Black Wheatear in my area.




Study Area


With Ronda being the centre point, the study area takes in most of Parques Natural Grazalema and Sierra de las Nieves. Additional principle mountain ranges are also included. The study area chosen, see accompanying map and grid, has been determined by suitable and likely habitat for all three species of summer resident Oenanthe. The area has, to some degree, been increased to account for the more isolated populations of the localised Oenanthe leucura. Otherwise the area covered is limited by the physical possibilities to adequately trek any larger an area in the time available. As the study progresses, boundaries may change, especially if certain areas are virtually void of any Oenanthe species and other areas bordering the study area contain worthwhile numbers of principle study species. Initially the area is to be divided into populations West, Central and Eastern. Some conjecture in determining these divisions arises, but until experience teaches otherwise, then a choice had to be made as a starting point.

Typical Black Wheatear territory/habitat

Objects of The Project/Study
By the capture of adult birds for ringing and also the ringing of pullus, the main objects are to establish site fidelity of adult birds and dispersal or fidelity of young returning adult birds. In the case of Oenanthe leucura the additional objects are for monitoring any post juvenile dispersal and population exchanges between various isolated breeding areas. Of course in addition to the main objects of the study, the equally important objectives will be to establish population densities and provide a basis for monitoring future population dynamics within the area. It should prove very compatible to ring secondary study species belonging to the same family group, as these are likely to be discovered breeding within the same principle study area and habitats. Again, population densities alone should provide critical information for future reference and comparison.

Methodology

For the purposes of the project’s objectives it is essential to use, in addition to standard rings, colour rings for the principle species of this study. The use of colour rings, coded for different areas within the study area, will give visual aid to monitoring site fidelity and population movements.

It is envisaged, that two colours per area are used, one for adult birds and another for pullus (essential for establishing whether juvenile displacement occurs). In all cases only one colour ring would be fitted to a single bird. In all six colours for rings will be needed, three sub-regional population studies with two colours for each area ( 1 = Adults 2 = Pullus). Each and every discovered breeding bird of all three Oenanthe species will be ringed where possible. The use of baited (mealworm) spring traps will be used for adult birds. Nestlings, where safely accessible, will be ringed at the nest. All captured breeding adult birds will be ringed, aged, overall wing measurement taken and then released. Because of the sensitivity of ringing breeding adult birds at the nesting area, then birds need to be released within the minimum time necessary. The use of colour rings would appear the only sensible way to monitor site fidelity and juvenile displacement/dispersal. Where population densities require (single pairs or small to large colonies), then individual sites will be named within any one grid reference. Each grid will be scaled into quarter sections i.e. A1, A2 northern half and A3, A4 southern half and visited, dependant on suitable habitat, during March through to the end of August. Each suitable quartered grid section will be visited at least once per month.

Initial reservations and conclusions

Without doubt the size of area within the chosen boundaries is and will remain a mammoth undertaking, not to mention physically demanding for a solitary study. With time the area requiring coverage will be less due to the absence, in certain areas, of the principle study species. Access to certain areas within the boundaries may be restricted and sometimes prohibited by landowners, which could in theory devalue the project to a degree. The zoning of the area into three parts may have to be reviewed with experience of any biased findings i.e. small distances involved for displaced first year breeding adults. However, this may be recognised and compensated for by the fragmentation of the main grids into four sections and retrapping previously ringed individuals.

It cannot be in doubt, that a study of this nature will enhance knowledge of local requirements for the three main study species. Also and as an offshoot from this main study, other species will be recorded and impressions given to overall population densities for several species. If past experience is any guide, then a few and maybe pleasant surprises could be expected. In one such experience, Oenanthe oenanthe within an area of moorland (Bodmin Moor UK) was given a population of no more than 50/60 pairs maximum. Upon species-specific study and ringing, this 10 x 10 square kilometre Moor was discovered to contain 450 + pairs! The figure was later supported by UK Nature Conservation Council funded Tetrad Study.

The Study Area is vast and fragmented in places

 
Collalba Negra                  Black Wheatear                                             Oenanthe leucura

Field Characters:

General. Largest of the breeding Oenanthe in Europe. Unmistakable black plumage with white rump, under tail coverts and tail. Tail broadly tipped black forming typical ‘T’ shape characteristic of Oenanthe occurring in Europe (O.hispanica not so pronounced). In flight appears heavy with typically shallow rapid wing beats, reminiscent of Stonechat S.torquata. Strong flight only observed whilst in pursuit of or chased by other territorial members of Turdidae i.e. Blue Rock Thrush, or when being chased by predator. Favours rocky and mountainous areas. Takes readily to tall scrub or tree as song or lookout post.

Adult Male    : 2nd winter males black body feathers. Wing coverts black, primaries and secondaries black with very slight rich deep brown fringing to leading edges, becoming darker with age. Upper and lower tail coverts white, central tail feathers 2/3rds black, outer tail feathers white with outer 3rd black, the black forming a typical ‘T’ shape for Oenanthe sp., but even more pronounced than O. oenanthe. 1st winter and summer males are typically brown/black body feathers and rich dark brown wing feathers (lesser coverts and some medium coverts are black), deep brown outer edges tail outer tail feathers and to 2/3rds of central tail feathers.


 
Adult Female     : 2nd winter females deep brown/black body feathers. Wing coverts typically the darker than colour of body feathers. Primaries and secondaries dark brown, not black. Under and upper tail coverts cream to white, central tail feathers 2/3rds deep brown, outer tail feathers white/cream with outer 3rd deep brown, pattern as male. 1st winter and summer females are typically lighter brown, almost juvenile rust coloured on head and mantle.



Juvenile              : Until post-juvenile moult, body feathering is rust brown, contrasting with  wing coverts and flight feathers, which are brown. Rust coloured fringing to body feathers abrade and slowly reveal basal brown ground colour to plumage.

Habitat. Mountain and hillside slopes, generally rocky outcrops and scree, but typically with an area of over/grazed pasture or bare area. Tolerant of sparse tree or scrub cover. Altitude of territories wide ranging i.e. 400m up to 1800m. Broader range of habitats frequented by juveniles and some adults in winter i.e. dried riverbeds, river valleys.

Distribution. Very common, where habitat is suitable, across the whole range of the study area. Becomes more widespread in autumn and early winter as juveniles disperse from breeding areas. Very few adults appear to vacate breeding territories in early winter, but those that do are normally returned by December to early January.

Population. Minimum 400 pairs with likely maximum 500 pairs. Occupation of small niche habitats contained and surrounded by highly adverse habitats i.e. woodland, suggests healthy populations in residence at all suitable and primary sites.


Map 1. Black Wheatear . Collalba Negra . Oenanthe leucura – Study Area Distribution & Population Density Map



Movements. Although some adults do move from breeding areas in late autumn and early winter see under distribution, the ever presence of adults at most known territories, indicate movement is largely confined to juvenile dispersal, with most adults remaining site faithful during winter to extended breeding territories. Birds are commonly seen at lower altitudes (river valleys etc.) during winter and around human habitation i.e. village fringes, even the centre of Ronda! No observations have been made of flocking or mass movements. Up to 8 individuals seen together and commonly 4 to 5 during postnatal period, these being family parties. Juveniles tend to leave natal site around October, with individuals returning during January to February, only to be displaced by resident adults. Occupation of niche habitats surrounded by inappropriate habitats i.e. Woodland, suggests wide ranging dispersal of juveniles displaced and forced into secondary sites.

Stone Platform constructed by the male at the nest entrance

Social Pattern & Behaviour. Appears site faithful throughout the year, with natal territory extending during autumn and winter (in some cases overlapping with adjacent and occupied territories). Normally the same pair remain together during winter, although occupying the same territory, the male and female range separately during the day, but have been observed roosting together. Both male and female appear tolerant of other Black Wheatears throughout the seasons, but use posture threats to protect their territory during early spring, very rarely have I observed actual threat and pursuit by either sex of encroaching adults occupying adjacent territories. Juveniles are tolerated up until September/October, when the male will pursue and harry until the juvenile departs, remarkably, the occupying pair appear more tolerant of juveniles entering occupied territory during February and March, when the pair are preparing the nest and the male is busy carrying small stones into the crevice containing the nest! The male will pursue and threaten all other Turdidae species when courtship begins in January, in particular, the male will endlessly harry and pursue Blue Rock Thrush which sing in their territory. Apart from Blackbird, other Turdidae are normally wary of defending male Black Wheatears, only rarely have I seen Blue Rock Thrush threaten and chase Black Wheatears and then it has usually been the female who has been pursued. The male, although appearing to remain faithful to his mate throughout the year, will display and court neighbouring females and at times pursue them until their mate appears. At all times of the year there appears to be a recognition and tolerance shown towards other Black Wheatears occupying adjacent territories, with birds often observed perching closely together with no more of a threat than tail flicking (tail flicking/fanning is common among all Oenanthe sp. in Europe).

Note: The above is a summary only and a part of an ongoing and incomplete survey. 

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