APA (7th ed.) Citation

Petersen, P. C. a., (curator), I. S. U. S. C. a. U. A., & Halmi, N. S. (1979). Peter C. Petersen letter to Nicholas S. Halmi regarding winter bird sightings, February 10, 1979.

Chicago Style (17th ed.) Citation

Petersen, Peter C.et al, Iowa State University. Special Collections and University Archives (curator), and Nicholas S. Halmi. Peter C. Petersen Letter to Nicholas S. Halmi Regarding Winter Bird Sightings, February 10, 1979. 1979.

MLA (9th ed.) Citation

Petersen, Peter C.et al, et al. Peter C. Petersen Letter to Nicholas S. Halmi Regarding Winter Bird Sightings, February 10, 1979. 1979.