Scarlet Tanagers, Cherry Trees, and Greater Functions Within An Ecosystem

Scarlet Tanagers, Cherry Trees, and Greater Functions Within An Ecosystem

by By Jan D. Axtell

There are very few birds in our northern forest as striking as the Scarlet tanager (Piranga olivacea). The male’s deep, bright red plumage and contrasting oil slick black wings and tail are unmistakable when seen high up amongst the deciduous canopy.

As of late we have had the fortuitous appearance of the Scarlett tanager in the forested hedge row bordering the southern boundary of the garden. This strip of woods connects the continuous forests on the east and west margins of the Lodge’s grounds, and it is not uncommon to see birds more closely associated with the interior of the forest moving up and down its length. It is of little wonder in that there are many mature cherry trees that make up the hedgerow’s species composition.

When these trees produce fruit –some years are more prodigious than others - the hedgerow becomes a mecca for all manner of birds. This year appears to be a pretty heavy crop and since the cherry’s fruit has begun to ripen I have seen both the male, female, and juvenile tanagers high in the canopy feeding over the last few days on numerous occasions.

I walk that hedgerow almost every day conducting tours and until the cherries started to ripen I had not seen a scarlet tanager there. I’d like to think I wouldn’t miss such a striking bird singing and nesting in a place with such an open view throughout the breeding season. So I am left to deduce that it is the largess of ripening fruit hanging from the trees bows that has attracted the tanager’s presence.

This is not an uncommon relationship or function within an ecosystem. Examples are everywhere in the forest. All animals select, relatively speaking, habitat to exploit for their own survival whether it be for protection, breeding, or feeding. Black bears will migrate out of their established home ranges to feed on distant beech ridges and gorge themselves on the nuts in the fall. Large Lake and Rainbow trout will move out of the deep water refuges to feed on the massive Hexagenia limbata mayfly that hatches in such prodigious numbers they can be seen on radar. Moose actually move higher up into our mountains during the winter – despite increased snow depth - to be more proximally located near large stands of Balsam fir, their preferred winter browse, in the Montane Spruce/Fir forest that dominates our landscape above 2500’ here in elevation in the Green Mountains. All animals, in their own way, seek out optimal patches of habitat to feed in; like our garden hedgerow.

It is interesting to think that the Scarlet Tanager’s recent arrival in the Garden hedgerow is interlinked with the greater process of habitat selection and optimal forage theory. The hedgerow has lots of fruit in it this year, and that abundance of food attracts new birds. They will feed there until it is no longer energetically beneficial. I wonder how long that will take? It is obvious that the time:energy ratio is tipped in the favor of the tanagers now (i.e. they are spending lots of time there because it is profitable from an energy intake stand point). Their presence is evidence of that. At what point does the ratio tip the other way? What happens in years when there is less fruit, or more? They are interesting questions to chew on – no pun intended.

Perhaps one day the visiting Scarlet Tanagers feeding on the abundant cherries will become the food for our resident Cooper’s Hawk hunting birds on the hedgerow because there are a lot of other birds feeding there. They are quite adept at exploiting the unwary and uninitiated. Sometimes being scarlet red can be a disadvantage in that one is easily seen. It’s not that farfetched an idea in that Cooper’s hawks already are known for hunting other birds at residential bird feeders. Why not natural food plots that attract large numbers of feeding birds?

I delight in the fact that this is all taking place a couple hundred meters away from the Lodge. Sometimes I find myself spontaneously laughing. To think that these intra-ecosystem functions are happening right here makes me wonder what else is going on that I might be missing. It keeps me racing up Trapp Hill Rd., with the kind of enthusiasm reserved for children at play, every morning to observe and document the great spectacle of life- and its trials and tribulations -in our Northern forest plays out on a day to day basis.