Timetable of Animal Events at the Main Vernal Pool at the Santa Rosa Plateau

See Introduction To The Pool Critters to know which creatures are discussed below.

My Detailed Observations of Pool Critters from 1996 to 2001 showed that animal events at the Main Vernal Pool at the Santa Rosa Plateau follow a regular schedule that depends only on the date of first filling of the Pool. Observations from 2003 to 2006 confirmed that timetable with only slight variation. Hence the following timetable can be used in future years to predict when these events will occur, as long as the pool does not dry up before a given event.

If the pool dries up and then refills, the situation gets more complicated, and there may be a mix of ages in the pool simultaneously. For example, in early 2006, the initial pool was only one inch deep, and almost completely dried up before eventually refilling to a depth of 11 inches. Nearly all the fairy shrimp died before they could mature; a small number survived in puddles and ended up maturing in the refilled pool. When the pool reformed, a new crop of fairy shrimp was not produced. However, a second crop of all other critters occurred, resulting in a mix of some critters developing on the schedule from the first filling, and others developing on the schedule from the second filling.

For pools that do not dry up and then refill, the only dates affected by specific conditions in any given year are ones that would have occurred after the pool dries up. The fairy shrimp die if the pool dries up before they mature. However, if the pool doesn't last as long as needed for typical tadpole maturation, tadpoles are usually able to speed up their maturation to match when the pool dries up. The warmer water of a shallower pool drives this faster maturation.

The timetable for plant events at the Pool depends entirely on when the Pool dries up, which depends on future rain after the date of first filling.

The date of first filling is Day 1 in the following timetable. To adapt the timetable to any given year, simply replace the Day Number with the appropriate date.

Day #Event
1Date of pool formation, no matter what the depth is at formation.
4Largest fairy shrimp now 1/10 inch long; earliest date at which the fairy shrimp can be seen and identified as fairy shrimp
10Largest fairy shrimp now 1/5 inch long
15Largest fairy shrimp now 2/5 inch long; Daphnea, aka water fleas, aka "gray shrimp", first visible.
20Largest fairy shrimp now 1/2 inch long; a few percent are sexually mature, with visible eggs in their egg sac for female, visible gonads for males; Cyclops, "red shrimp", first visible.
25Largest fairy shrimp now 3/4 inch long; first tadpoles visible, now ~1/10 inch long
27Most fairy shrimp now sexually mature
30Largest fairy shrimp now full-grown, 1 inch long
40Largest fairy shrimp species dead; largest remaining fairy shrimp species now 1/2 inch long; tadpoles now ~1/4 inch long
50All fairy shrimp dead; tadpoles now ~1/2 inch long; two-striped garter snakes now visit regularly for tadpole lunches
~70Tadpoles begin to develop rear legs
~80Tadpoles leave the Pool, with baby frogs and toads everywhere on land.

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Copyright © 2008 by Tom Chester.
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Comments and feedback: Tom Chester
Updated 14 January 2008.