Fig. 2. Apparent nitrogen retention increased significantly with nitrogen intake in both species. Minimal nitrogen requirements (MNR) and total endogenous nitrogen losses (TENL) were determined using the x and y intercepts of the least-squares linear regression, respectively. Yellow-vented bulbuls: y=0.78x-5.4, r²=0.99, F_1,8=797, P<0.0001; y=0.86x-3.4, r²=0.99, F_1,8=7208, P<0.0001, first and third day, respectively. Tristram's grackle: y=0.8x-19.8, r²=0.98, F_1,6=277.6, P<0.0001; y=0.8x-11, r²=0.97, F_1,6=231.2, P<0.0001, first and third day, respectively. TENL in both species decreased significantly between the first and third day of experiment. In yellow-vented bulbuls, but not in Tristram's grackles, MNR also decreased on the third day. MNR and TENL values are presented in Table 2. Open squares and solid lines represent measurements on day 1 and closed squares and broken lines represent measurements on day 3.