chisq.test(c(90,30))

E.i = (total birds caught during study)/(total hours of effort)*(hours of effort at site i)

#observations
obs1 <- 128; obs2 <- 141
obs.tot <- obs1+obs2

#sampling effort ("net hours")
nethours1 <- 287; nethours2 <- 157
nethours.tot <- nethours1+nethours2

#expected counts based on effort
expect1 <- obs.tot/nethours.tot*nethours1
expect2 <- obs.tot/nethours.tot*nethours2

#ch2 test statistics:
ch2 <- sum(c(((expect1-obs1)^2)/expect1, ((expect2-obs2)^2)/expect2))

#p value
pchisq(ch2,1,lower.tail = FALSE)