Daily Invader

Chesapeake Bay Mammals 

Sika Deer (Cervus Nippon)


Have you spotted a Sika Deer (Cervus Nippon) lately?

Fawns have spots to keep them from being spotted, but Sika Deer are one of the few deer species to keep their spots into adulthood. Sika Deer are native to Japan, Eastern China, Korea, and southeastern Siberia. They are rare in most of their native range except for Japan, but have been widely introduced in Europe, Australia, New Zealand, South Africa and the United States. In the United States they are established in Maryland, Virginia, Texas, Oklahoma, and Wisconsin. The first introduction in the Chesapeake region was the release of 4 or 5 deer on James Island in Dorchester County MD in 1916. Over time, the offspring of these few deer spread all along the eastern shore of Dorchester County, Somerset, and Wicomico Counties. Today one of the most popular places to see these introduced spotted deer is Assateague Island. In 1923, seven deer were released on the island and by the late 1960s the population exceeded 1,000. Today the population is controlled by hunting. They are terrestrial, but do much of their feeding in marshes and swamps, where excess browsing can promote erosion. Complete Record  


Assateague Island Ponies (Equus caballus)


Assateague Island ponies (Equus caballus) have been trotting the island since the late 1700's.



Visitors of Assateague Island have many stories to tell about the small, wild ponies that live among the sand-dunes and saltmarshes. There are two herds on the island that are managed in different ways by the two Federal agencies, the National Park Service and the United States Fish and Wildlife Service. On the Maryland side of the island ponies roam free and are controlled with a contraceptive vaccine but on the Virginia side they are confined to fenced areas and are controlled by annual roundups. Herds of ponies have been on the island since the beginning in the 1700s and were likely released by farmers who had surplus animals, but shipwrecks are another possible source. The island ponies’ small size may result from the source stock, natural selection, and/or the limited diet on the island. Complete Record  


House Mouse (Mus musculus)


The House Mouse (Mus musculus) is at home both indoors and out.  




For as long as there have been boats the House Mouse has been a stowaway. Over the years they have become established throughout the world, especially indoors like houses, cabins, and abandoned buildings, but they are also found in the wild. With such a long history of spread it’s hard to know for certain where they originated, but they are probably native to central Asia and Mediterranean. It’s likely the mice arrived in the Chesapeake with the first European settlements. William H. Fisher, writing in 1895, mentioned that one was caught in Baltimore in 1881 but other reports suggest they were here during the time of the American Revolution in the 1770s, when the Redcoats had to rely on grain shipped from England. Aside from the more common indoor locations, mice also occur on shorelines and marshes throughout the Chesapeake Bay region, but have been best studied on the Atlantic barrier islands (Assateague-Hog Islands), where they occurred in all habitats, including dunes and salt marshes. Mice have been seen living in the floating nests of waterfowl in marshes. Complete Record 


Nutria (Myocastor coypus)


Nutria (Myocastor coypus) were imported for their fur starting in 1899.



Nutria fur coats are fetching high prices throughout the US, an economic attraction that spurred the import of Nutria to the US from their native South America (Argentina, Uruguay, Paraguay, and southern Brazil) starting in 1899. In places like Louisiana, wild populations were started with releases from fur farms, but some were deliberately released into marshes to control aquatic vegetation. In fact, the first nutria brought into Maryland came to the Fur Animal Field Station at Blackwater National Wildlife Refuge in 1939, where they were kept in outdoor enclosures in the marshes. By 1979 they were well established along the Eastern Shore of Maryland and Virginia with isolated occurrences along the Potomac River and Patuxent Rivers. Today there is a limited market for the fur, and major control efforts are underway to eliminate Nutria and protect marsh grasses in areas like Blackwater National Wildlife Refuge. Complete Record


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