by Robert McFarlane, Houston Bird Survey Coordinator

In Part One we constructed a Cumulative Species Curve using data submitted by Garrett Stewart from 12 surveys conducted at his residence in Kingwood. He detected 91 percent of the 22 total species observed by his fourth survey (the red line of the graph).

Now we consider three additional June survey sites. Jim Sigmund submitted 10 surveys from his residence in the Tomball area, charted as the pink line. He observed a total of 20 species but only 13 (65%) by the fourth survey, and 15 (75%) by the fifth. He did not record 90 percent of the species until his eighth survey.

In contrast, we have surveys submitted by Greg Mason for two sites inside of Loop 610. The two curves are strikingly similar, beginning with 25 and 26 species in the first survey and terminating with 35 species in the eighth and final survey. One survey site is his residential block, adjacent to some water sources, thus adding water birds to the mix (green line of chart). The other site (blue line) is the Memorial Park jogging trail, more than three miles in length, encompassing forest and a golf course with water features. The residential area surveys tallied 32 (91%) by the fourth survey; the park area had 30 species (86%) by the fourth and 31 (89%) by the fifth survey.

From this comparison we learn two things: (1) larger areas and water features will add species to your list, and (2) it may take more than four surveys to get a reasonable estimate of the total species present at a survey site.