2. It actually seems kind of strange to me that Sam was the one to notice the birds thing the first time around. Teal'c has extensive off world experience and is known to be SG-1's best wild lands tracker. Maybe Sam got sent to some woodlands survival boot camp, but it's not something people generally notice right off unless they grew up rurally or got special training. By later seasons, both Teal'c and Sam (and Daniel) should be noticing it right away.

3. But Daniel knows Earth's military mindset—Teal'c's an alien, Vala's an alien. Daniel is an American and was already a military consultant, so "trustworthy."