348 l\Ir. Svvynnerton on Mixed Bird-parties. 



tliis district as compared with the neiglibourliood of Salis- 

 bury) — also possess this habit .... appears to me to indicate 

 that it is due in part to mere social instinct. '' 



Sociableness, drawing the stray birds encountered into 

 the passing throng, as Bates suggested, may account for the 

 inclusion of purely frugivorous birds in these parties (if 

 indeed they were not the nucleus round which the throng 

 first formed), but neither this nor mutual protection nor 

 protection by the Drongos now seems to me to be the sole 

 objects of these mixed parties. I have during the past few 

 years given much time to accompanying and closely watch- 

 ing such parties, and I have been led to believe, in common 

 doubtless with numerous other observers, that their main 

 function is co-operative hunting. They are probably drives. 



The following is an instance from my journal in Gaza- 

 land : — 



"April 18, 1911. Entering the forest, I found myself in 

 the thick' of a large ' Drongo^s hunting-party.' The birds 

 had been quite uudisturl)ed by my arrival and I was able to 

 see within a few feet of myself a good deal of what was 

 going on. The party was doing its work in nearly as close 

 formation as I have seen, and from the ground to a height of 

 50 feet or more all was bustle and excitement. The twigs 

 were everywhere vibrating and the foliage rustling with the 

 movements of birds, scraps of bark and dry leaves were 

 everywhere falling, and every now and then I was fortunate 

 enough to witness an obvious attack on some flying or falling 

 insect, often invisible to myself. 



" The Bristle-necked Bulbuls {Phy/hstrephus capensis), a 

 large party of them, worked, as usual, below. They carefully 

 searched, not only the ground, knocking the dry leaves from 

 side to side with their bills, but also the branches and foliage 

 of the large shrubs forming the undergrowth. Amongst 

 them I once for a minute or two caught a glimpse of a small 

 family party of our common forest Er'ithacus. 



" Next above came the Barratt's Bulbuls (P.flavistriatus), a 

 very large and scattered party or parties comprising probably 

 not fewer than forty or fifty individuals in all. This party 



