Survival by the Numbers
“I just saw a big snapping turtle pull another baby mallard underwater on the pond in my backyard!”
These were the first desperate words I heard after answering the phone at the nature center I worked at for many years.
Without pausing for a breath the distraught caller went on, “Oh what can I do?! There were originally 9 ducklings in the bunch and it seems that every few days another one disappears. And now another one is killed! Only three remaining!”
I paused before responding. I knew she was looking for sympathy and a solution to put a halt to the murders, but I was going to try a different route.
“As hard as that is to watch,” I told her, “you are lucky to witness a predator catch its prey. And did you say there are three left?”
She exhaled a sad, drawn out “Yes.”
“Wow,” I exclaimed, “that’s terrific!” There was silence on the other end but I could almost hear the puzzled look of horror.
I continued, “Let’s assume the three remaining continue to mature and live for a year. One will replace its mother and one will replace its father and that means there is one extra, a fifty percent increase in the family population.” I was on a roll. “That’s fantastic! To experience a fifty percent growth rate is very rare.”
I gave her room to respond. And after a moment I heard a softer toned, “Really?”
“Absolutely. Most baby animals are born to be food. Like it or not the future of predators depends on the death of their prey.”
Another pause before she responded, “So if I heard you correctly, if the remaining three ducklings survive that will be unusual and considered a success for the population of mallards?”
“Yes.”
“Well thanks for your information. But I still don’t like to watch baby ducks die.”
It is a common survival strategy for a particular species to have large numbers of offspring. Generally the greater number of eggs or young indicate their vulnerability to high losses through predation, bad weather, food shortages and so on.
A wild female monarch butterfly will lay 100 to 300 eggs in her life with a survival rate of 2-10% living to maturity. For the sake of example, let’s say the monarch that is flitting around laying her eggs here and there on the milkweed leaves lays a total of 100 eggs. (Incidentally, everyone should have a milkweed patch.) That means we can expect anywhere from 2 to 10 mature butterflies will survive to maturity from her output of 100 eggs.
Consider a bluegill sunfish. In the Upper Midwest a mature female might lay 6,000 – 18,000 eggs in one or more nests. Sometimes none of those eggs survive but usually enough reach breeding age. This allows more human kid-predators a chance to learn the joys of watching the jiggle of a bobber and catching fish.
Humans, those irascible critters that continue to foul their own nests by denigrating the very natural systems that assure their survival, do not bear large litters. However, like other animals that bear one to three young, such as deer, bear, whales, eagles and albatrosses, the chances of their young reaching maturity is much higher. With few young to care for, more attention and resources can be offered for their survival.
Last week, while hunting wild turkeys, I stepped quietly into the woods to begin calling. I paused and in that moment of stillness, a hen turkey exploded only a few feet from me.
My stopping had flushed her off her nest. In her haste she had kicked one of the eggs out of the nest so I leaned down and tucked it among the others. I counted 15 eggs. I have never seen a turkey nest with this many eggs; though they average a dozen eggs per clutch.
Now some of you might gasp because I touched the egg. As youngsters many of us learned “Never touch a birds egg or it might abandon the nest.” While that is good advice, it has nothing to do with your scent on the egg. Birds are not going to abandon if you touch the egg, but some birds, such as loons might abandon their nest just because the nesting site has been disturbed.
Quietly, I left the nest site. In a few minutes I heard an out-of-sight hen giving an alarm call. I suspect this was the mother of the eggs that I had just left.
And like a snapping turtle, I moved with stealth looking for the father of some of those eggs.