If there were sycamores, then another mystery needs solving

If it turns out that sycamores once stood in a half-circle around the Pulitzer Fountain at Fifth Ave. and 59th St, just as E.B. White says in his 1929 poem, what might have caused them to be replaced? Here are several reader responses:

Margot Roby Treybig sent a link to a website that included the following info:

Potential Problems - American Sycamore is very prone to annual infections of anthracnose, a fungus that destroys the new growth in spring. This causes dieback of the emergent leaves and stem, and subsequently the lateral buds break (either at the base of the new growth, or from previous year's branchlets) and form a whorled pattern of new stems, which resemble witches' broom growth. This secondary growth occurs in late spring and usually becomes the growth of the season, as drier weather does not encourage new fungal growth.

Other diseases and pests may occur on American Sycamore, but the most serious problem after anthracnose is usually hollow trunks, which eventually make the tree subject to storm damage, and of course getting too big for its space in urban areas. In both cases, the tree may need to be removed.

Diane D'Arcy wrote:

[Sycamores] would not be very tolerant of the conditions in NYC. Even here in Northern Virginia they do not do well in the more urban, exposed locations.

But another mystery will remain:

Let's say that our diligent research unearths the fact that indeed, the present-day Lindens at the Pulitzer Fountain were preceded by Sycamores. The next question would be: Did grackles and starlings by the thousands roost in those Sycamores too? While much has changed about New York City in the years since 1929, we know from old Central Park bird records that huge flocks of Grackles did, indeed, congregate in the park at certain times of year. Did they spend their nights at the fountain?

Though E.B. White's poem does use a word evocative of birds --"twitter" --in his winter dream of a future spring, I am again ready to hazard a guess about whether the sycamores that [may have]once surrounded the Pulitzer Fountain were night roosts. My guess is No, the sycamores of yore were not used as night roosts for grackles and starlings as the Lindens are today.

What do communally roosting birds like robins or grackles require for their roosting trees? Above all, it seems to me, they need thick cover that will allow them to melt into obscurity even on moonlit nights. The Linden is a tree that provides an almost impenetrable cover. With a super-strong flashlight I have peered into a Linden where I know more than a hundred robins are roosting. [See previous website reports about roosting robins].I have trouble finding even one. Meanwhile, sycamores are far more sparcely leaved, or is it leafed. I believe that a roosting bird would be easily spotted in a sycamore or in any other member of the planetree family.

But all this is guesswork. I hope I'll come up with some concrete answers soon.