2nd year fall/winter: Start looking looking around and investigating your options.
2nd year spring through 3rd year fall: Apply for programs. (Most programs are “first come, first serve” and encourage you to apply 1 to 2 years before your desired start date.)
Note: Zoo/wildlife externships accept applications very early. If you’re interested in another field, most people finalize externships throughout their 3rd year.
Familiarize yourself with the UCD externship restrictions. Approved externships are located under on Viper under “Students > Externship Database > Search”. Know how many weeks your curriculum choice will allow. If you are only taking one stream, then you generally have 12 weeks. If you are planning on taking a second stream section during your 4th year, you have less (generally around 4-8wks). Make sure your externships are within the approved dates.
Contact the appropriate person for your desired externship. Clarify expectations, length of duration, housing, etc.