APA (7th ed.) Citation

Petersen, P. C. a., (curator), I. S. U. S. C. a. U. A., Halmi, N. S., & Koenig, D. (1977). Peter C. Petersen letter to Nicholas S. Halmi regarding bird sightings, January 3, 1977.

Chicago Style (17th ed.) Citation

Petersen, Peter C.et al, Iowa State University. Special Collections and University Archives (curator), Nicholas S. Halmi, and Darwin Koenig. Peter C. Petersen Letter to Nicholas S. Halmi Regarding Bird Sightings, January 3, 1977. 1977.

MLA (9th ed.) Citation

Petersen, Peter C.et al, et al. Peter C. Petersen Letter to Nicholas S. Halmi Regarding Bird Sightings, January 3, 1977. 1977.