Birds in June

(Robin's nest in a Syringa.  Why are the eggs of the American robin blue?)

I spent an hour this morning appraising the avian situation in my forest.  Male singing has changed over the past month in an interesting way.  Species that were quite vocal earlier in May are now fairly quiet, but others are singing constantly.  Dark-eyed juncos, chipping sparrows, song sparrows, black-capped chickadees, wood thrushes, all the woodpeckers, white-breasted nuthatches, eastern phoebes, American robins, gray catbirds, and blue-headed vireos are relatively inconspicuous now.  I assume that the frequency of bird song is correlated to the stage of the nesting cycle.  Males sing to keep other males at arm’s length and to attract females.  When the male or female (usually the female) is incubating eggs or tending nestlings, males tend to be quieter.  I am sure this is to avoid attracting predators to their territory, where the nest is located.

But other species are quite vocal.  Ovenbirds, red-eyed vireos, great-crested flycatchers, eastern wood pewees, and veerys are still waking me up early in the morning.  Because they returned from migration later than the group of silent species, some of whom are year-round residents, these late arrivals may be further behind in their nesting chronology.  If they are mated, then they must be at an earlier stage of the nesting cycle.

Some of this can be documented.  The phoebe nest hatched five nestlings about three weeks ago, and they are now working on their second brood of the season.  By the way, I covered this bird in a blog several weeks ago.  It turns out that this pair nested on a window ledge on the back of my house rather than on the light fixture on the front.  The chickadees that I described last week are now incubating eggs.  And I found a nest yesterday of an American robin in a Syringa shrub next to the house with four eggs.

But let’s review songbird nesting chronology a bit.  Males establish territories, sing, and, if fortunate, acquire a mate.  One or both adults build a nest, which is distinctive to that species (i.e., mud, moss, grass stems, twigs).  Bird nests are truly marvels of the animal world.  How birds actually build these structures amazes me constantly.  During this stage, they copulate, which is done by the male hovering in flight above the female; their cloacas touch, sperm is transferred, and voila. When the nest is complete, the female will start laying eggs.  Egg-laying occurs early in the morning, and the female lays only one egg per day.  Even the famous while leghorn chicken, which has been bred to do nothing but produce and lay eggs, can only lay one egg per day.

Clutch size varies from about 3-6 in temperate species, but the number is relatively fixed within a species.  One of the parents, usually the female, then begins incubating the clutch after the next-to-last, or penultimate, egg is laid.  Eggs do not begin developing until the heat from the female’s body is applied during incubation.  The last egg laid, which occurs one day after incubation starts, will hatch about 24 hours after the rest of the clutch; this “runt” of the litter is often the one not to survive because it is always one day smaller than its siblings.  Incubation takes about 10-14 days, depending on species, and then the real work begins.

One or both parents must then find food, and I mean a lot of food, to feed the hungry nestlings.  These morsels usually consist of insects or other invertebrates, which are high in protein.  Nestlings fledge from the nest after 10-12 days.  For large birds like hawks, incubation and the nestling period are about three times as long as for small songbirds.  If you have never found a nest of a small bird and followed it, you should do so.  The rate at which nestlings grow is truly astounding.  You can see the difference in size and feather development every 24 hours.  But here is a puzzle.  Those nestlings have to defecate several times per day, and yet you will see no feces in the nest.  Where is it?

Will you cause the adults to abandon the nest if you find it and check on it up close once or twice a day?  It depends.  If the adults are only at the nest-building stage, they may abandon that effort and relocate because they “think” a predator has found the nest.  Why continue if something is going to eat your eggs?  But once they have reached incubation stage, they will usually not abandon the nest.  Too much time and energy have now gone into that nest to just walk away.  So find an active nest, observe it until the babies fledge, and report to us here.  There are worse family activities in which you could be involved.

Once the young have fledged, many males will begin singing all over again in the hopes of attracting a new female who wants to nest.  And on it goes, throughout the ages—the stuff of which poems are made.

Gulliver, the red-eyed vireo

(Red-eyed vireo)

One morning in June a few years ago, I went out onto the deck to have my morning coffee. I heard a loud begging squawk of a bird, which was quite persistent and lasted all morning.  Finally, my young son and I went into the yard to investigate.  Bingo!  There on the ground was a young nestling bird, which I determined was a red-eyed vireo (Vireo olivaceus).  About 25 feet above the location of the baby vireo, I could see a nest on a limb of a red maple tree; obviously, the bird had fallen from the nest, which was too high for me to reach.  I always hate these decisions, but the choice was clear: either try to raise the baby by hand-feeding it, or let it die.  Lazy DrTom probably would have let nature take its course, but my empathetic 12-year old son would have none of that.  He was such a cry-baby.

We put the bird in an old bird cage that we had from our daughter's zebra finch days, and then the work began.  The bird was hungry even now, so we started the laborious process of collecting crickets and other insects from the yard, and feeding them to the open mouth of this insectivorous species.  Nestling birds can eat a tremendous amount.  How adult birds can locate and collect enough insects to feed 4-5 ravenous babies has always amazed me.  They eat so much and grow so fast that you can literally see the increase in their body size within a 24-hour period.

The vireo, which we named Gulliver, begged and ate, and we hunted and searched.  This was really getting old. Insects were getting more difficult to find for some reason, even when I used a sweep net.  So I did what most red-blooded Americans do to solve their problems--I went shopping.  I bought mealworms at the local pet store.  This solution was a little expensive, but mealworms are a nice, plump juicy meal, and Gulliver loved them.  So far, so good.  We even took Gulliver on a little trip with us to Hershey Park.  When we got to the park on a really hot afternoon, we left Gulliver in his cage in the car while we reconnoitered a bit.  We returned to the car only about 20 minutes later to find the bird lying on the bottom of the cage, with bird guano all over the car seats.  The poor thing had gone apoplectic before passing out from the heat.  Of course, our son was hysterical (cry baby), so we rushed to our motel room, and hustled the patient into the air-conditioned room.  After applying drops of water to his bill for several minutes, Gulliver lapped up the life-saving liquid and made a remarkable recovery.  Whew!

We returned home that day and decided that it was time for Gulliver to try his wings.  He was now about 12 days old, the time at which he would normally fledge from his nest anyway, so I banded the bird with an aluminum leg band, and set him free.  We didn't know what to expect.  Would he zoom off, never to be seen again, or what.  Quite the contrary.  Because we were his sole source for a well-balanced meal, he was not about to leave the cafeteria.  He stayed very close to the house for several weeks, mostly on the deck railing.  Whenever any of us went outside or came home from work, he immediately flew to us, landed on our shoulder, and begged incessantly.  As the summer continued, he spent more and more time in the forest next to our yard, but I could call him to the deck to feed him.  He was adult size by now and eating quite a bit, so I decided to adopt an economy of scale and order a box of 2,000 crickets from Rainbow Mealworms of California.  On the very day the crickets arrived, Gulliver apparently moved into migration mode and was gone.  Red-eyed vireos spend the winter in South America, so I figured his ancient instincts had kicked in or he had been picked off by a predator during the night, leaving us with beaucoup crickets and no mouth in which to insert them.

Throughout that winter we often discussed our experience with Gulliver, this interesting little bird that had befriended us.  Had he made it to Argentina?  Did he even know that he was a red-eyed vireo?  Had his instincts developed normally so that he could function as he should?  Our answer came the following spring.  I was standing on the deck one May morning, when a red-eyed vireo landed on the railing for only 1-2 seconds, and then returned to the woods.  Vireos are common in our woodlot, but they never land on our deck.  In addition, I saw the unmistakable glint of a shiny metal band on one leg of the bird.  Gulliver had survived his first migration and returned to the location of his birth.

We never saw Gulliver again after that brief encounter that May morning.  It was almost as if he was signaling to us that he had made it, and to say thanks, and now I'm an adult, and I'm nearby.  I usually hate that anthropomorphic stuff (i.e., making it sound like animals have human emotions), but even DrTom is allowed to slip once in a while.