Keller LF., van Noordwijk AJ. (1993). A method to isolate environmental effects on nestling growth, illustrated with examples from the great tit (Parus major). Functional Ecology, 7(4):493-502. DOI: 10.2307/2390037
Hellriegel B., Leugger U., Keller LF., Zandt H. (1993). Education and science for maintaining biodiversity. Biodiversity Letters, 1(5):131-133. JSTOR: Journal Article