Macrobenthos 



317 



1000 



2000 - 



1000 - 



(SJullSe^ ^3jJun l8^ua,l8Jun l2Sep^ 

 1975 1976 1977 



FIGURE 7-10. Abundance of 

 individual cohorts o/Chirono- 

 mus pilicornis in Pond J from 

 1975 through 1977. Mean num- 

 ber of larvae per m^ ±1 S.E. is 

 shown for two dates in each 

 year. Cohorts are named for 

 the year in which they were 

 recruited. 



there was undoubtedly a great deal of mortality in the very small first 

 instars before they appeared in our pond-center samples. 



Birds ate both larval and adult chironomids, as confirmed by the 

 stomach contents of red phalarope (Phalaropus fulicarms), andby the study 

 of Holmes and Pitelka (1968) in the pond area. Bierle examined a number 

 of phalaropes in 1972, and found that 20% had eaten only immature 

 stages. Another 30% had eaten adults as well as the pupae and larvae. 

 Other bird species are also feeding their young during this period of most 

 intense chironomid emergence in early July. It would therefore be 

 reasonable to expect predation by birds to have some effect on 

 chironomids but this does not seem to be the case. Quantification of bird- 

 hours per pond in 1973 indicated that birds spent relatively little time 

 feeding on any one pond (D. Schamel personal communication). Given 

 that there are a hundred or more square meters in each pond and that each 



