Not all isolated populations will show evidence of genetic drift. Genetic homogeneity can be attributed to one of two explanations, both of which indicate that natal philopatry is not absolute within a species. Firstly, a lack of divergence may be due to founder effects, which explains how individuals that start new populations carry the genes of their source population. If only a short (in evolutionary timescales) period of time has passed, insufficient divergence may have occurred. For example, study of mitochondrial DNA microsatellites found no significant difference between colonies of black-browed albatross ("T. melanophrys") on the Falkland Islands and Campbell Island, despite the sites being thousands of kilometres apart. Observational evidence of white-capped albatross ("T. steadi") making attempts to build nests on a south Atlantic Island, where the species had never been previously recorded, demonstrate that range extension by roaming sub-adult birds is possible. Secondly, there may be sufficient gene exchange as to prevent divergence. For example, isolated (yet geographically close) populations of the Buller’s albatross ("T. bulleri bulleri") have been shown to be genetically similar. This evidence has only recently, for the first time, been supported by mark-recapture data, which showed one bird marked on one of the two breeding islands was nesting on the other island.