Bob and Mark plotted the locations of Hermit Thrush nests on…

Bob and Mark plotted the locations of Hermit Thrush nests on their study area on the Chippewa National Forest.  Bob plotted [HT1] nests and Mark plotted [HT2] nests.  When they compared data, they both observed only [HT3] nests in the same study area. What is the estimate for the population size of Hermit Thrush nests?   (Round your estimate to the nearest whole Hermit Thrush nest; enter only a number)