Who Really Killed Cock Robin?
Facts in Chapter 1: Cock Robin
p. 3: Tony wrote in his journal on April 29: "A male robin arrived from the south in the maple tree across the street just after sunup...He hasn't sung yet, so I don't know if he is on his way to Canada or is home." On April 30 he added, "The male·sang the territorial song of the robin who is home from the south."
Tony observed the robin in the maple tree just after sunup and assumed the robin had just arrived, because so many songbirds migrate by night. But robins usually migrate during daytime. His robin might have arrived somewhere in the neighborhood the day before and waited to come out in the open until he'd had a little time to check conditions. Tony realized that robins usually wait to sing until they arrive on a territory that they wish to claim for themselves, so if the male wasn't singing, he may well have been a migrant still moving farther north. When the robin did sing the next day, Tony was sure he was on territory. He supported that conclusion with further evidence: robins in other yards in the neighborhood were also suddenly singing.
p. 8: Mayor Joe ... said that Mrs. Robin had brought mud from the marsh and worked it into the grass like a potter strengthening a bowl."
This is a good description of how and why a female robin works mud into her nest.
p. 9: Tony tells the Mayor, "A robin decorates her nest the day before she lays an egg. It takes her about four or five days to build her nest, one day to put in the lining of rootlets, and one day to decorate. Then, if it doesn't rain and soften the mud, she will lay the next day."
Robins don't actually decorate their nests. When the Mayor described the female robin carrying in a piece of bright yellow cloth, it was probably intended as part of the soft lining rather than a "decoration." She does usually lay the day after she's finished the nest unless it rains.
p. 10: Male robins never announce eggs, nor do females.
Males don't specifically "announce" eggs, but do continue to sing at a high rate from the time courtship begins until the first egg hatches.
p. 11: Songbirds lay one egg a day until their clutch is complete. Four or five is a clutch for a robin. Then the female starts to incubate so that they all hatch at once.
True.
p. 12: The female would now brood the eggs, and that this interlude was known as the incubation period. Both birds would change their behavior during this time.
The female is the one whose behavior changes most during incubation. Males only rarely bring food to the females.
p. 12: The Mayor says, "Now she is standing up and leaning down to·count her eggs. She is touching each one and moving them. " p. 13: Tony realizes that Mrs. Robin was not counting her eggs the other day, but turning them so that the embryos would not stick to the shells.
Tony understands this, and the Mayor clearly does not.
p. 13: Rarely does a male robin sit in the open and sing when his mate is incubating. He's very quiet so as not to attract predators.
The male does not sing near his mate and the nest, but he continues to sing at the peak rate until the eggs hatch.
p. 15: Tony guesses the length of incubation period as "Twelve to thirteen days, but since there was a frost the night before Mrs. Robin started incubating, I'd say thirteen for her."
This is a good guess. No scientist could be more certain.
p. 18: Cock robin was sitting on his toolshed all puffed up and looking like a proud papa. To Tony that meant he was sick.
Journey North's science writer Laura Erickson has taken care of many sick birds that people thought were fine because they were puffed up. One of the first signs of sickness can be that a bird has trouble regulating its body temperature, and that means it must "puff up" its feathers to thicken its insulation. Tony knows about this.
p. 19: DDT is a hydrocarbon. It takes it two hundred thousand years, or a geological age, to break down into safe elements. Because it is hard to destroy, it gets passed from plant to worm to fish, chicken, and man.
DDT is certainly a very stable hydrocarbon, and it does get passed down from the soil into worms and insects, and from the water into insects and small fish, into larger animals who store the DDT in their fatty tissue for a long period of time. The half-life in most animals (the amount of time it takes for an animal to break down half the DDT in its fat) is about 8 years. In the soil and water, current studies indicate that it probably takes between 2 and 15 years for DDT to break down into non-toxic chemicals. Using DDT has been prohibited in the US and Canada for over two decades, and during that time much of the DDT has disappeared from the environment. Some remains, however, and some continues to enter from water and animals that travel here.
p. 20: Mrs. Robin never stayed away from the eggs longer than ten to fifteen minutes. CR calls Mrs. Robin from her eggs when she needed to eat. She had dined until CR had felt if was time for her to return. He had then sung a song that sent her home.
As usual, the Mayor mixes up actual observations with inaccurate conclusions. Mrs. Robin knows when she's hungry, and doesn't need Cock Robin to tell her when to start and stop--he's simply singing as usual. During incubation in normal spring conditions, female robins are normally on the eggs 75 - 80% of the time during daylight hours. They incubate only 65 - 70% of the time in June and July, when the air can keep the eggs much warmer.
p. 22: He hasn't flown once, just twitches... When a bird fluffs up as much as that, he's sick. So poorly coordinated he was flopping. He's sick, and he's trying to get away from the marsh hawk.
Sick birds are much more vulnerable to predators because they lose coordination and alertness.
p. 23: The marsh hawk is important to the ecology. He takes the sick animals and leaves the well.
Marsh Hawks (now called Northern Harriers) actually take as many animals as they can, and if they could have their choice, would always want healthy prey because then they wouldn't be as likely to get sick from the animals they eat. But it's very hard to catch alert, healthy animals, so they are far more likely to take a sick robin than they are a healthy one. They are essential to keeping snakes, mice, and a lot of other species at healthy population levels.
p. 24: Robins do not feed their hatchlings earthworms but the larvae of the cabbage looper.
For the first four days, robins feed their hatchlings regurgitated food, which certainly includes larvae of the cabbage looper but also a wide variety of other insects, earthworms, and berries. Robins do not depend on cabbage loopers.
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