During a study of fawn mortality of sympatric white-tailed (Odocoileus virginianus) and mule deer (O. hemionus eremicus) in west-central Texas from 2004 to 2006, we made observations that should help deer researchers increase their efficiency of capture of fawns, obtain better estimates of ages of fawns, and obtain more reliable estimates of fawn survival. We experimented with vaginal-implant transmitter designs and found that larger holding wings and antennas protruding <1 cm past the vulva resulted in more successful drops at birth sites. White-tailed fawns moved farther from birth sites than mule deer fawns of similar ages (P = 0.027). Our model predicted that white-tailed and mule deer fawns moved an average of 100 m away from birth sites after 12.5 and 17.5 h postpartum, respectively; outliers may be expected. Compared to previously published models estimating ages of captive fawns from new hoof growth, our model predicted that free-ranging fawns were generally 1.5 weeks older. As others have suggested, abandonment induced by marking was rare, and we suggest methods for monitoring does and fawns that could minimize such occurrences. Behavioral and morphological models that we describe may be species-, site-, and time-specific, and biologists should use caution when extrapolating inferences from captive animal–derived models to free-ranging populations.