An Endangered Salamander in Mexico: The Toluca Axolotl or Michoacán Stream Salamander

As if a morning in Mexico gazing at a wildlife spectacular—one of the sites where Monarch butterflies gather in their millions from all over North America east of the Rockies to overwinter—was not enough, a short distance away from the entrance to the Monarch Reserve at Sierra Chincua and at an altitude at just over 10,500 feet (3220 metres) was another gem. A slowly-moving shallow stream across a cow field has a population of the endangered Michoacan Stream Salamander, and a number were out and about and feeding while we were there at the end of January.

We could see the salamanders moving about on the bottom of the slightly cloudy stream and had I not picked up the wrong-sized polarising filter for the camera lens when packing I would have better photographs and video to show. We were able to see them feeding on small invertebrates in the water and of blowing water from their lips to stir up the sand and reveal hidden prey.

Ambystoma rivulare, the Michoacán Stream Salamander or Toluca Axolotl

These salamanders are said to be like their close relation the Axolotl (Ambystoma mexicanum) in being neotenic but also capable of metamorphosis and breeding as transformed adults.

The evolution and taxonomy of salamanders from the Trans-Mexican Volcanic Belt is complex. It does not help when two species are sometimes known by the same common name, as in this case. However, it is clear from distribution maps and publications from Mexico on the fauna of the Monarch reserve that the species here is the Michoacán Stream Salamander, Ambystoma rivulare, which in Mexico is also being called the Mountain Stream Salamander. The distribution of A. rivulare in fact straddles the state border between Michoacán and Mexico (the latter a state within the country of Mexico).

Range of Ambystoma rivulare (from IUCN Red List) with the site we visited shown by the red dot

Ambystoma rivulare seems to have acquired another common name amongst Mexican scientists. The authors of a number of research paper call it the Toluca Axolotl, Toluca being the nearest city (and capital of the State of Mexico) to the sites where it can be found.

Confusion can arise because another species is also known as the Michoacán Stream Salamander. Thus two species with that same common name are listed in the IUCN Red List. The other species is Ambystoma ordinarium. However, that one is found further west than A. rivulare according to the distribution maps in the IUCN Red List.

The population of A. rivulare is reckoned to have decreased in recent years, particularly since non-native trout have been introduced to the streams for anglers.

None of the distances between the distributions of Ambystoma species in the Volcanic Belt is very great. Thus the ranges of the Axolotl (Ambystoma mexicanum), A. rivulare and A. ordinarium all occur within 100 miles, illustrating the adaptive radiation that has occurred in this volcanic region of central Mexico, producing what seems to be more than 10 species, each confined to a relatively small area.

The term ‘mountain stream’ suggests to me fast-moving water tumbling over rocks, quite unlike the habitat of A. rivulare that we were in, a stream across a flat field at high altitude. The only way to describe it was that it reminded me of the stream in which we used to catch Common Newts in the lowlands of the East Midlands 70 years ago.

Google Earth view of the site. The stream enters the pasture from the pine forest (top left)

Along with the Monarchs and a good lunch we had what can only be described as a grand day out—tempered only by the dreadful dinner later.