June 28, 2018: The Birds of Summer;
and Nature’s clever schedule for survival.
By Robert Alvo.
Last time I promised to tell you about how the frogs and birds are doing in June and to continue with some surprise topics. Many of our birds have nests as I write (June 9) and will continue to be on nests this month.
In July, young will abound — many early nesters already have young now. Recently-fledged young in the city are particularly vulnerable to prowling cats, who take them for fun and leave them as dead gifts for their owners. Too bad that city cats have no predators, but they should really all be kept indoors for their own good, not to mention for the good of our birds and small mammals.
In August, many young birds will be difficult to distinguish from their parents because the former have become adult-sized while the latter may have started to moult their feathers. Of course, all these generalizations about timing are contingent on the bird species in question. For example, many Common Loon chicks will still be stuck on the lake on which they hatched in September or even October, whereas most other migrant species will have departed south.
Meanwhile, in the amphibian world, the early-breeding and mid-season breeding frogs have stopped singing, and their ponds will start drying up. Now it’s time for the late breeders: Green Frog, and Bullfrog. Rather than being in a big rush to occupy their temporary ponds upon ice-out in spring so as to complete their reproduction cycle before their fishless ponds dry up, the late breeding strategy is to use deeper waters like marshes and lakes, which have fish, and lay many eggs in a surface film to take advantage of the warmest water layer. The thousands of eggs cannot all be eaten by fish in the short 2-3 days before hatching, and because the roughly half-metre thick winter ice does not extend to the bottom, the tadpoles can overwinter in the water under the ice — for 1-3 winters.
Were these late species to lay their eggs in surface films in early spring, all the eggs would freeze during a night with sub-zero air temperature. That’s why early spring breeders lay their eggs below the water surface and/or in egg masses that, even if the top eggs in the mass lie at the water surface, the lower ones will not freeze. These eggs, such as in Spotted Salamanders, can take up to six weeks to hatch in the frigid water.
Nature is so smart with its strategies, and not just breeding ones. Strategies exist for all aspects of life in all organisms. Biologists study feeding strategies, migrating strategies, predator-avoidance strategies, etc. It’s Nature that crafts them over evolutionary time, leaving it up to humans to study and name them. What are your strategies.
Photo Caption: Green Frog image provided by the author.
Photo Caption: Image on the left: Wood Frog egg mass: “Wood Frogs are early spring breeders, laying their eggs in masses that, if it freezes, only the top eggs in the mass will die.”
Image on the right: Green Frog surface film: “Green Frogs breed in late spring/early summer. The eggs are laid in a surface film to take advantage of the highest pond water temperature, and thus a short incubation period.”