Moerdijk Field Research 2005-2006

(last update: 14 August 2010)

P10 and P9 Primary Patterns

Regarding the methods for P10 and P9 primary patterns classification: Following Goethe’s classification, we used six classes to characterise these feathers.
I: No mirror.
II: Mirror on one web.
III: Full sub-terminal black band, mirror on both webs.
IV: Sub-terminal black present, but band broken.
V: No sub-terminal black, mirror completely merged with tip.
VI: ‘Thayeri’ pattern, medial band not reaching the feather-edge of the inner web.
For more details, see plate 1 and Goethe (1961).

..I	II	III
IV	V	VI

In Herring Gull, the most frequent pattern in both sexes was a broken sub-terminal band on P10 (figure 2 and plate 1). The distribution of the P10 patterns did not differ significantly between sexes (Mann-Whitney U = 8441, Z = -1.593, P = 0.111, male n = 147, female n = 127).

Exactly half (50%) of the trapped Herring Gulls showed a complete sub-terminal band and a mirror covering both webs on P9. Again, there was no difference between the sexes in the distribution of P9 patterns (Mann-Whitney U = 9216, Z = -0.094, P = 0.925, male n = 146, female n = 127).

Twenty breeding birds were trapped in both 2005 and 2006. Of these retraps, 16 birds remained in the same P10 pattern category, one bird showed less black (m51) and one bird showed more black (m6P) in 2006. For P9, 12 birds remained in the same category, four birds showed less black (m2T, m4J, m46, mVE) and one bird showed more black (m51). Nog checken wat de Kalev Rattiste over larus canus vond

Three sub-adult birds (black on the primary coverts) showed no mirror on P10. When all sub-adult birds are excluded from the sample, the difference between sexes remains non-significant (P10: Mann-Whitney U = 7523, Z = -0.837, P = 0.403, male n = 129, female n = 123. P9: Mann-Whitney U = 7598, Z = -0.533, P = 0.594, male n = 128, female n = 123).

The vast majority (80%) of Lesser Black-backed Gull showed a complete sub-terminal black band across P10, with the mirror covering both the inner and outer web of the feather. For P9, there was no real dominant pattern (Figure 2). There is no significant difference between sexes for either the P10 or P9 patterns (P10: Mann-Whitney U = 106954, Z = -0.314, P = 0.754, male n = 433, female n = 498. P9: Mann-Whitney U = 103740, Z = -0.962, P = 0.336, male n = 433, female n = 496).

Forty-three Lesser Black-backed Gulls were caught in both 2005 and 2006. For P10, 35 birds remained in the same category, 3 birds showed less black and 1 bird (oNL) showed more black in 2006. Regarding P9 pattern, 32 retrapped birds remained in the same category, and 7 birds showed less black when retrapped in 2006.

Three sub-adult birds (with extensive black on the primary coverts) showed no mirror on P10. When all sub-adult birds (4cy and 5cy birds) are excluded, the difference between sexes remains non-significant (P10: Mann-Whitney U = 102672, Z = -0.015, P = 0.988, male n = 415, female n = 495. P9: Mann-Whitney U = 97749, Z = -1.309, P = 0.191, male n = 416, female n = 493).

Neither Herring nor Lesser Black-backed Gulls showed marked differences between the sexes in the sharpness of the division between the grey inner and black outer webs of P10. In Herring Gull about 56% shows a diffuse gradient on the underside of P10. In Lesser Black-backed Gull, 58% shows such a pattern on P10. This is in line with the findings of Barth (1975).

Figure 2: distribution of P10 and P9 patterns in Herring & Lesser Black-backed Gulls breeding at Moerdijk in 2005 & 2006.

Click HERE for larger pies / figure 2.

Read further on RESULTS: 5. P5 PRIMARY PATTERNS >