yellow on the forehead of white-eyes, and I have seen similar patches on 
individual sunbirds, but I had never before seen so consistent a feature 
on a whole flock of birds over several days, nor had I seen purple 
discolouration. 
Derek Harvey, IOC Clinic, PO Box 19751, Sana' a, Republic of Yemen 
A change in the nut-cracking 
technique used by Hooded Crows in 
Kibbutz Netzer Sereni, Israel 
Henk K Mienis 
Pecans Can/a illinoensis are popular nut trees in agricultural settlements 
all over Israel. The nuts are also popular with birds, in particular the 
Syrian Woodpecker Dendrocopos syriacus, the Jay Garrulus glandarius 
atricapillus and the Hooded Crow Corvus corone, which are considered 
agricultural pests in commercial plantations. 
Until about 10 years ago, the Hooded Crows in Netzer Sereni used only 
one technique for opening the nuts. They pulled the nuts from their husks 
with their bill and carried them to a flat, hard surface. There they grasped 
the nuts with their feet and started to break them open by pecking at 
them. 
In 1984, we noticed that one particular crow opened the nuts by dropping 
them from a height of 10-15 m on to a tennis court. After a while, other 
crows followed its example, so that by the end of the season approximately 
20% of the crows used this new technique. 
The following year almost half the Hooded Crows employed the nut- 
dropping technique, and in 1986 the figure rose to almost 80%. 
This winter (1992-1993), the grasping-pecking technique is, however, 
again very popular (about 60%). This is probably because this year's nuts 
have an extremely thin shell, which is easily smashed by one or two 
blows with the bill. The balance appears to be between the energy saving 
benefit of dropping nuts and increased piracy with this technique, with 
thickness of the shells being a deciding factor. 
Henk K Mienis, Zoological Museum Dept. Evolution, Systematics & Ecology, 
Berman Building, Hebrew University, 91904 Jerusalem, Israel 
29 
