[cobirds] Blackburnian Warbler feeding activity, Fort Collins (Larimer) 5/11/2022

First off, thanks to John Bruening for a call this morning about a Blackburnian Warbler at Spring Creek Park in Fort Collins.

A lot of folks were able to watch this beautiful bird working hard to feed itself in a large American Hackberry tree.  Here is what I think was going on.  Its main food today was a very tiny insect (3-4mm) called the Hackberry Blistergall Psyllid (Pachypsylla celtidisvesicula).  The pics below show a close-up of an adult and five adults on new hackberry leaves.

   

I've promoted the value of hackberry gall-making psyllids to migrating birds, especially neotropicals, for years.  We have two main species that makes galls on hackberry leaves.  One, the hackberry nipplegall psyllid, makes galls that are big green volcano-like bumps.  The blistergall psyllid makes little flat patches or "blisters" that are usually purple.

The adult psyllids overwinter in the bark and emerge in spring to lay eggs on swelling hackberry leaf buds.  The eggs look like white pearls (several in the pic below).

   

If the stars align and peak psyllid emergence from the bark coincides with songbird migration in spring, like is happening this spring, hackberries get a lot of attention from little birds.  That was the case today at Spring Creek Park where adult psyllids were milling about in the air, crawling on the bark, buds and new leaves.  And fast-twitch birds of at least several types (Black-capped Chickadee, Pine Siskin, Red-breasted Nuthatch, Orange-crowned Warbler, Yellow Warbler and the Blackburnian) were scoring several times a minute.  A Rose-breasted Grosbeak female was also present but I think it was eating buds/fresh leaves.

Psyllids that live thru spring bird migration usually fulfill their evolutionary mission, mate, lay eggs on about-to-burst buds, then die.  Nymphs which hatch from the eggs tunnel inside the upper and lower layers of the leaf and spend the summer feeding on the inside walls of the chamber (gall) their presence caused the plant to form around them.  They emerge in the fall in search of overwintering sites in the bark.  During the few days they are out and about in fall (usually late September or early October), they again attract the attention of southbound migrants.

It's all very fun to watch, especially when one of the coolest birds on the Planet is involved.

  

Dave Leatherman

Fort Collins