Are conifers poisonous to birds

Some types are. Yews, for example, are very toxic. Even a small bite can be fatal. Other types have toxic effects, too, but what happens depends on the size of the bird and how much is eaten. Many pines can produce digestive upset in small amounts. The amount that might make a Cockatiel sick could kill a finch or canary. If you know the specific species of conifer, I can give you more detailed information. The following site has more information on toxic plants:

http://www.peteducation.com/article.cfm?c=15+1912&aid=2236