Lorenz took a large clutch of goose eggs and kept them until they were about to hatch.
Found that geese follow the first moving object they see, during a 12-17 hour critical period after hatching.
He took half of the eggs and placed them under a goose mother, while the other half he kept beside himself for several hours.
When the geese hatched, Lorenz imitated a mother duck's quacking sounds, upon which the young birds regarded him as their mother and followed him accordingly.
The other group of chicks followed the goose mother.
If no attachment has developed within 32 hours then its unlikely any attachment will occur ever.
This process is known as imprinting, and suggests that attachment is innate and programmed genetically.
Imprinting has consequences for short term survival and in the longer term forming internal templates for later relationships.
Imprinting occurs without any feeding taking place.
Evaluation
One issue of Lorenz' study is that it lacks generalisability to humans; mammalian attachment systems are different from that in birds. For example, mammalian mothers show more emotional attachment to young than the birds do.
It supports the view that having a biological basis for an attachment is adaptive as it promotes survival.