How to differentiate the sex and age of Great Bustard

 

We are working in census and dated of the population of Great Bustard in Extremadura. This census help us to start new projects of conservation for this specie. The first thing that we have to know is to differentiate the sex and the age:

ADULT BIRDS (not born during the year)

Birds generally larger, less stylized, less long-legged, with the background color on the back and that more yellowish reddish brown wing coverts. The tail feathers (tail feathers) have only one subterminal black band.
• Male: birds silhouette robust, more corpulent, thick neck and long, sturdy legs. white band along the bottom marked edge of the wing (wing supracobertoras), with the presence of “neckline” on the back, going towards the back. large tertiary, with black barreado parallel and uniform, lined with white.
• Females: smaller birds, silhouette much slimmer, shorter legs, thin neck and head and beak proportionally longer than in males, compared to the thickness of the neck. white band along the much less conspicuous lower edge of the wing (wing supracobertoras). No “neckline”. Tertiary and smaller design with a black stains less “orderly”.

JUVENILE BIRDS

In general, youngs of both sexes, plus a smaller size have
one aspect zancudo or leggy, with a hood or brown pileus (beware !, this hood can keep up the 2nd or 3rd calendar year). Rectrices have two subterminal black bars.
The behavior also helps differentiate adult birds juveniles since the first show a much less fearful than adult females behavior: while they watch, often eat chickens confident.
• Males: females distinguishable from juvenile to show a marked along the edge of the folded wing, corresponding to the alar supracobertoras white band. Along with this white band, usually show a black bottom, smaller, but also quite evident, corresponding to the flight feathers. Have a greater length of the tibia and the talus, giving a more zancudo look and lanky juvenile females (in the absence of female juveniles that allow comparison, is indicative overall structure and silhouette of mother with male juvenile, the latter having proportionately longer legs).
They have tertiary “male type”, large and evenly barreadas.
• Females: they are like adult females, but smaller, with proportionately longer than they feet, but less than male juveniles, neck proportionally shorter than their mothers, lighter plumage, lighter and neck grayer, and design general less marked plumage. white band of the narrow and irregular wing supracobertoras.

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1.- 1&2 Adult Male (Spring); 3&4 Adult Female (Spring); 5 Adult Male (not reproductive); 6 Adult Female (not reproductive); 7 Juvenile Male (summer); 8 Juvenile Male.

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