 Another letter , dated June 21 , 1990 , was sent by FWS to USACE , reporting that at least eight interior least terns , an endangered species , had been found on a small island in the Arkansas River approximately 2 @,@ 000 feet ( 610 m ) south of the site of the proposed turnpike bridge . Although the bridge was not yet under construction at the time , the anticipated eighteen @-@ month period of bridge construction had the possibility of interfering with the terns ' nesting period , which runs from mid @-@ May to mid @-@ August . FWS was also in favor of requiring OTA to prepare a full EIS , a process that could have taken up to three years . 
