The Oregon spotted frog is Canada’s most endangered amphibian, with fewer than 300 breeding individuals in the wild. Without intervention, it will almost certainly disappear. The recovery plan for Oregon spotted frog calls for conservation breeding, headstarting and release to re-establish viable populations in at least six sites. Wildlife Preservation Canada began coordinating these efforts in 2010, adding a conservation breeding program to the headstarting work taking place at the Greater Vancouver Zoo. Andrea Gielens, Lead Biologist, gives us an update on headstarting work at the Zoo.
Each year with the projects we run we hit some specific milestones. For frogs one of our most significant achievements of the summer is seeing our first froglets.
Up until this point our goal has been to grow healthy tadpoles as fast as we can. Each tadpole needs to reach a minimum size before metamorphosis will be triggered. For the Oregon spotted frog that length is about 2 inches from nose to tail. Once this size is reached back legs form, followed by front legs and tail absorption. It is critical that the tadpoles are both large enough and morph quickly enough that they do not run out of energy during the metamorphosis. If a tadpole is under-nourished or the weather changes and metamorphosis slows down the individual might not have enough energy to complete the transition. Once the tail begins to be absorbed the tadpole can no longer eat, as its mouth and digestive tract are part way between vegetarian and carnivore, meaning no food sources are appropriate. If something goes wrong during these stages the tadpole will not survive metamorphosis.
If everything goes well the resulting frog is much smaller than people often expect. The froglet is only about the size of the main body of the tadpole, excluding tail. At this point the froglets are eating insects, mainly the crickets we feed them but also naturally occurring mosquitoes, mayflies and beetles that get into their outdoor enclosures. Because tadpoles reach metamorphosing size and produce a frog that is only so big, we are back at square one with the smallest frogs possible and are under the pressure to get them to eat and grow as much as possible before release in September!