Please excuse us, we have been a “tad” preoccupied over here at the Greater Vancouver Zoo!
Our captive breeding population of Oregon spotted frogs have been busy, and we have the tadpoles to show for it…1,858 to be exact! Our females started producing egg masses in early March and continued to do so until early April. Oregon spotted frog egg masses are quite dense and gelatinous, with the individual eggs easily visible.
Remember, frogs rely on external fertilization by the males after the females expel the egg mass! Unfortunately, not all egg masses get fertilized in a captive breeding setting and this is an issue that is a focus of ongoing research for our team.
For the masses that were fertilized, we could visually confirm this within a few days, as we would see elongation and differentiation within the eggs. Over the next few days, we watched as these blobs of future tadpole underwent a transformation, all within the jelly of their individual eggs. Eventually, the tadpoles emerge from their jelly and consume it as an important food source.
In addition to the egg masses produced by our captive population, we also had four masses brought in from the wild to be cared for. These eggs originated from a new population that we have been starting with released animals from our breeding program. This was very exciting for us because up to this point we had not seen any signs of breeding in this new wetland population, which we have been adding individuals to for several years! It has been very encouraging to know that our efforts to protect and stock this wild population have not been in vain!
In late April, approximatley 1,400 of our freshly hatched tadpoles were released to further supplement this population. At the zoo we have retained 766 individuals whom we will care for until after they have undergone metamorphosis, at which point they will be released as juvenile frogs into the same wetland.
The tadpoles that remain in our care at the zoo will continue to undergo rapid growth for the next few months. Tadpoles are herbivorous and feed on pond scum and algae in the wild. Our captive population is treated to a daily greens super-food smoothie consisting of boiled lettuce, spirulina, alfalfa and stinging nettle. Yum!
Later in the summer, after their limbs have developed, the tadpoles (called metamorphose or the super cute “froglette” at this point) will cease to eat for about a week. During this time, their gut undergoes a huge rearrangement to that of a carnivore. In order to survive, a process called apoptosis occurs, in which they absorb their tail in order to obtain nutrients. From this point on, their diet consists solely of crickets and what ever other creepy-crawly’s they can find in their tubs.
The frogs will remain with us until the end of the summer until the bitter-sweet day we put them back where they belong: in the wild.