The egg collection
The egg collection consists of ca 28,000 clutches. Most clutches are of Palearctic birds but the collection has no geographic limits and species from the entire World are represented.
In the 1960's it was discovered that the eggshell of some raptor species, e.g. the Peregrine Falco peregrinus, was exceptionally thin and many eggs chruched under the weight of the incubating bird. By measuring the thickness of eggs in the collection of the Swedish Museum of Natural History and other museums, it was proven that modern eggs were considerably thinner than before.
It later became evident this was an effect of the accumulation of DDT in top-predators. In this case, the old collections served to judge what shell thickness is "normal" in these birds which made it obvious that something was terribly wrong in nature.