Norwegian authorities on Thursday reported more than a dozen unexplained reindeer deaths in the Svalbard archipelago in the Arctic, considered "highly unusual" for the summer season. "It is very unusual for females of breeding age and adult males to die during the summer. The Norwegian Institute for Nature Research (NINA) told AFP it had "no clear indication nor any specific hypothesis" to explain the unusual summer deaths. Svalbard, roughly twice the size of Belgium, has a population of around 22,000 reindeer -- about seven times more than the number of people. They are significantly smaller in size than the mainland reindeer.