This is probably a paper of interest for all those surprised or otherwise intrigued by the gene flow now detected between H. neanderthalensis and H. sapiens.
Melanie L. Lancaster et al. Two behavioural traits promote fine-scale species segregation and moderate hybridisation in a recovering sympatric fur seal population. BMC Evolutionary Biology 2010. Open access.
The two fur seal species share the same reproductive spot at Macquarie island in New Zealand (and two other sites) and they do engage in fact in rather high interbreeding. However the two species remain neatly separated because of habitat preferences (colder/warmer waters, pebble/boulder beaches) and maybe also proposed fitness costs for the hybrid offspring.