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.

Homage to Amelanchier

(A flowering Juneberry in May at DrTom's.)

One of the required trees to learn in my field biology course was a relatively insignificant species (from a timber perspective) called Juneberry, or shadbush, or serviceberry. It has several common names, but I am referring to the genus Amelanchier. The common species in our area is Amelanchier laevis, or smooth Juneberry. This shrub or small tree is in the rose family, and rarely gets more than 10 meters high. It flowers in May when the American shad (a fish) used to run up the eastern rivers, and it bears ripe fruit in June (thus, Juneberry).

The tree was always difficult for students to identify in autumn when it contained neither flowers nor fruits, so I made a big deal of how much I loved this tree. During the semester, I often heard students say in discussing the trees they were required to know from their list, “you know the one, Gavin’s favorite tree.” I thought that by exaggerating my love for this species that they would more easily remember what I wanted them to know. But I really do love this species; it is one of my favorite trees in the eastern deciduous forest. But why?

First of all, everything about Amelanchier is attractive. The gray bark with weaves of green running through it, the finely serrated leaves, the abundant white blossoms, and the purple fruits that resemble blueberries offer much. But many open-grown specimens have a growth form that reminds me of a small tree you might see in a Japanese garden, almost like a giant bonsai tree. Based on my observations, they are slow growing, adding only a few centimeters of new growth per year. Although I have never worked the wood, it is supposedly hard and durable and was used in former times as tool handles.

Second, starting about mid-June, the fruits ripen and the show begins. So, my evening ritual (you know, scotch, cigar, binoculars, and folding chair) is often spent sitting several meters away from my favorite Juneberry. Every fruit-eating bird in the area is attracted to this offering, which, of course, is how the tree disperses its seeds. Birds swallow the fruits while they are in the tree and defecate the seeds elsewhere several minutes later. American robins, gray catbirds, veerys, and cedar waxwings are the most common visitors on my property. Lat year on June 14 the fruits were not yet ripe, but the waxwings started feeding on those fruits a couple of days before. (Are those seeds ready to be dispersed yet? Are they yet viable?) This is really curious to me and it deserves further investigation. In a few days, the branches of the tree will be moving constantly with the shifting of bird bodies intent in harvesting as much as they can as rapidly as possible.

The most interesting visitor is the yellow-bellied sapsucker, the fruit-eating woodpecker with a sweet tooth. Remember that this is the species that drills small holes in a neat horizontal line in certain species of trees (like red maples), and then visits these holes later to lick up the sweet sap that oozes from them; it may also feed on insects that are attracted to the sap. For several years, I have had a pair of sapsuckers that visit my Juneberry trees as long as there is ripe fruit available.

Gray squirrels and eastern chipmunks also love these fruits and, although I have yet to witness this, I am betting that deer mice in the genus Peromyscus climb these trees at night to eat the fruits. George Petrides writes that foxes, skunks, raccoons, and black bears also relish Juneberry fruits. They are also quite edible by humans.

I have described my hobby of thinning my woodlot for various purposes. One of the objectives has been to release this sun-loving tree to fuller sunlight along my driveway so that it flowers more profusely. There are now 14-15 specimens lining my long driveway, which provide a beautiful show of flowers in May. I usually proclaim that spring has really arrived when Juneberry is in flower. Oh, I did not mention this, but an old etymology of the third common name, serviceberry, is consistent with my proclamation of spring arrival. Pioneers are said to have used the flowering of Juneberry to know that the ground had thawed sufficiently to bury those who had died during the winter—funeral services could be held at that time.

My enthusiasm for Amelanchier has not changed over the years. About all that has changed is what used to be called “Gavin’s favorite tree” is now referred to as “DrTom’s favorite tree.” Same tree, different name.