Spotlight on unusual Myrtle Warbler - American visitor that has made itself comfortable in an Ayrshire garden

 

Illustration from The Warblers of North America (1917) by Frank Chapman

One of the star birds of 2024 so far has undoubtedly been the Myrtle Warbler, a first winter male, that has been a long-staying resident in the garden of  Jimmy Crawford, a birder, in Kilwinning, Ayrshire. It is understood to be the first and only American warbler to have been recorded in Ayrshire. Jimmy has kindly been letting fellow-birders into his home to view the bird. In gratitude, some have contributed, via JustGiving, to North Ayrshire Cancer Care which has been treating his mother-in-law. Meanwhile, a scan through records of the species has revealed an article on its diet - Food of  the Myrtle Warbler (1901) written by Clarence Weed and Ned Dearborn.  Below is an extract.

It is only within a comparatively few years that the service rendered to agriculture by birds has been appreciated. 

It is becoming, however, to be more and more believed that the birds as a class are set over against the insects as a class to maintain a balance which shall prevent the latter from destroying plant life, both wild and cultivated. 

But the economic status of each species of bird has to be determined with precision before we can say that that particular species deserves protection and encouragement. 

Of all the members of the warbler tribe that are found in southern New Hampshire, either as summer residents or passing migrants, probably none excels the Myrtle or Yellow-rump Warbler  in abundance.

They are especially noticeable because, unlike most warblers, they  largely neglect the woods in favour of orchards and scrubby pastures.

They are hardy birds, wintering regularly as far north as Cape Cod.

Aududon says: "This species feeds on insects, is an expert fly catcher and a great devourer of caterpillars.

"During the winter, however, its principal food consists of berries of various kinds, especially those of the myrtle and pokeweed.

"They also feed on the seeds of various grasses."

"Nuttall’s account is in the same tenor. 

"Writing from Massachusetts, he says: 'Passing parties continue with us in gardens and woods till almost the close of November, feeding now almost exclusively on the myrtle-wax berry Myricacerifera as well as on those of the Virginia junipers.'

"This bird is called the Myrtle Warbler because of its fondness for the berries of the bayberry or waxberry myrtle, a small bush common along the Atlantic coast. 

"To determine the food value of these berries, Prof F. W. Morse kindly made an analysis of them which he reports as follows: 'The berries were extracted with hot alcohol and yielded a waxy matter.

"'After this treatment, there was left on the seeds a loose coating which could easily be rubbed off, leaving the smooth, hard seeds in about the state in which they are excreted by birds. 

"'This coating was removed by rubbing the seeds with a stiff brush over a fine- meshed sieve.

'"The waxy extract was greenish in colour and contained 1.06 per cent, protein. 

"'The loose coating was brown  and contained 13.2 per cent, protein.

"'Summing up, the total matter separated from the seeds amounted to 30.5 per cent of the whole of which over one half was wax.

"'The protein formed 5.7 per cent of the total matter removed or 1.75 per cent of the original seed.'"

* The article by Weed and Dearborn goes on to carry more detailed analysis of the stomachs of  Myrtle Warblers, revealing the presence not just of berries but also of caterpillars, spiders, flies, gnats, aphids and various other insects.