Table 2. — Approximate number of nests of great blue herons and American egrets in heronries in the Illinois Ris'cr valley. 1958- 

 1964, based on counts made from a circling light aircraft. 



V 1958 1962 1964 



Location of Great Blue American Great Blue American Great Blue American 



Nesting Colony Heron Egret Heron Egret Heron Egret 



LakeDepue 250 250 250 300 75 120 



Wise's Lake 60 



Pekin Lake 125 125 280 iM) 60 75 



Clear Lake 110 100 110 



Ingram Lake 250 



Meredosia Bay 90 500 1 50 



Total 775 375 J, 140 640 385 305 



on October 5. From 1959 to 1965 veiy small numbers 

 of cormorants, usually fewer than 200, have been ob- 

 served at any one time in the autumn. On October 18. 

 1965, only 22 cormorants were observed on an aerial in- 

 ventory of water birds in the Illinois River valley. This 

 was the largest number seen in 1965. 



We do not know the cause of this decrease in num- 

 bers of cormorants migrating through the Illinois River 

 valley, but somewhere along the line a great change in 

 their environment must have occurred. 



Herons and Egrets 



There is a subjective feeling that the great blue heron 

 (Ardea herodias) exists on the Illinois River in diminish- 

 ing numbers, and it appears fairly certain that although 

 the numbers of American egrets [Casmcrodius albus) in- 

 creased until 1962 there has been a decline since then. 

 Our data, however, cover such a short span of time that 

 they do not present a strong basis for evaluating long- 

 term population trends (Table 2). Nesting populations 

 of these two species have fluctuated considerably from 

 19.58 to 1964. 



Counts of great blue heron and American egret nests 

 were made at several heroniies along the Illinois Ri\er 

 in June, 1939. A direct comparison of these nest conc<'n- 

 trations with those of more recent times is not possible, 

 for several of them have been vacated and new ones 

 created. However, the nest data suggest that the num- 

 bers of great blue herons ha\c declined and that the 

 numbers of American egrets have increased. Only 17 

 egret nests were found in four heronries in 1939, while 

 305 were located in three of the lieronries in 1964. 



CONCLUSION 



An attempt has been made in the preceding pages to 

 make comparisons which relate measurable changes in 

 fish and wildlife populations of the Illinois River and 

 its bottomland lakes to human activity during the past 

 ihrec-tiuarters of a century. Even though a tremendous 



amount of biological data is available for the river, there 

 are still many areas where we know very little concerning 

 the organisms which li\ e in or have lived in this habitat. 



Some things become apparent from this study. Noth- 

 ing in our physical environment ever remains static: 

 change is the rule. But in this period in historv" when 

 people are gaining more and more mastery over their 

 environment, they have bent their intelligence toward 

 making unusual changes that may benefit them temjx>- 

 rarily but may be deleterious when a longer period is 

 considered. 



It is unrealistic to delay doing things which benefit 

 people until we know all of the possible side effects which 

 may go along with these actions. If we were to do this 

 there would never be any progress. But when such side 

 effects become apparent and are not good, and there are 

 ways of circumventing them, we do not use our intel- 

 ligence if we fail to make corrections. 



It is difficult to believe that so much has happened 

 to the Illinois River and its floodplain since Kofoid pub- 

 lished his comprehensive work in 1903. Starting with 

 the diversion of Lake Michigan waters into the river in 

 1900. the ecology of this stream has been changed dras- 

 tically several times. This diversion added to the fish 

 liabitat in the lower stretches and remo\ed it completely 

 in the upper river. Drainage enterprises removed half of 

 the floodplain that the river once used and eliminated 

 fish and waterfowl habitat. Navigation dams created 

 new water areas while destrcning important waterfowl 

 marshes. Domestic pollution has fluctuated up and down 

 as new sewage treatment plants have been activated and 

 then found to be inadecjuate as the rising tide of human 

 population in the basin caught up with them. Chemicals 

 ha\e been released into the waters from developing in- 

 dustries on the river's banks and in the watershed. 



Although these actions have caused conditions to fluc- 

 tuate widely, the net result has been an ever-diminishing 

 biological resource as the aquatic habitat and its inhabi- 



22 



