SEEN - SE European Bird Migration Network
Fat determination
Fig 1. Fat scores

Fig. 2. Technique of the fat scoring. A - blowing to the belly, B - blowing to the furcular depression

(after Busse 1983 and Kaiser 1993, combined)
Determination of fat goes through three levels (Fig. 1):

Level I - belly
Level II - furculum
Level III - pectoral muscles

Key to fat determination:

I
  1. Belly is without visible fat or with reddish traces only - II A
  2. Belly with infused bands of fat (intestinum is visible) - T2
  3. Belly has a fused cover of fat; intestinum is not but the liver is visible - T3
  4. Belly is completely covered with fat, a very narrow band of the liver may be visible but, if this is so, the roll of fat is just above it - II B
II A
  1. Air -sack is visible within furculum (some fat may occur) - TO
  2. All the interior of furculum is covered with fat - T1
II B
  1. Fat in furculum flat or concave - T4
  2. Fat in furculum forms a convex cushion - III
III
  1. Sides of pectoral muscles without stripes of fat - T5
  2. Sides of pectoral muscles with stripes of fat - T6
  3. Pectoral muscles partly covered with fat - T7
  4. Pectoral muscles completely covered with fat - T8
Note: In some species loss of fat does not follow exactly the same sequence in which it was attained, this results in problem with fat determination in some specimens. Anyhow, always follow exactly the key, as specific differences are covered by species-specific validation of the scale.

Technique
  1. Lay the bird on its back on the palm (Fig. 2); the neck should be between the second and third fingers of the hand; the second and the third fingers of the second hand should gently part the bird's legs; the proper position of bird is very important.
  2. Blow the belly (Fig. 2A) with a continuous stream of air and choose one of four possibilities under section I of the key; if the second or third subsection is chosen you have determined the fatness as T2 or T3 respectively.
  3. If II A or II B are chosen, you must direct your blowing to the furculum (Fig. 2B) and choose one of the two subsections under II A (fatness TO or T1) or II B (fatness T4 or higher - III).
  4. If your choice is III, look at pectoral muscles and choose fatness T5 - T8.
The most common mistakes
Mistakes are usually made when someone has a tendency to "liberal" interpretation of rules, e.g. when the bird has a thick cover of yellow fat on the belly but part of the intestinum visible; this should be T2 but is classified as T3 because it "looked like a fatty bird". Some mistakes are possible when the bird is not properly handled when the furculum contents are evaluated.
Note that the fatness of an individual bird properly determined twice at the same time may be different. This is because in border cases different tension of the bird's belly muscles at the moment of blowing may expose (or not expose) the intestinum or the liver from under the fat layer. Difference in determination cannot, however, exceed one degree of fatness.
Created by Pronetix 2006