In my yard about a mile east of the CSU campus in Fort Collins (Larimer), I had both a Swainson's Thrush and a young male Rose-breasted Grosbeak today. Evidence that birds are still on the move.
A major activity that Norm Lewis alluded to in Lakewood the other day that I am also seeing in Fort Collins is feeding of birds of several species on the larvae of the Elm Leafmining Sawfly (Kaliofenusa ulmi). Sawflies are actually non-stinging wasps. The adults of the Elm Leafmining Sawfly are blue-black and about the size of a house fly, maybe a tad slimmer. They were commonly seen on the leaves of elm a few weeks to a month ago. They lay eggs on the expanded elm leaves and their larvae tunnel between the upper and lower layers, eventually forming a big brown blotch called a "mine". When the larvae are done feeding and as big as they'll get, they chew out of the mines and drop to the ground for pupation in the soil. Those that are successful in completing their development will emerge next late spring as blue-black adults. At this time of year, zillions of larvae drop from heavily infested elms and are a major source of food for House Sparrows, American Robins, Common Grackles, European Starlings, and probably many other species. The characteristic feeding pattern involves running around plucking at the ground like a chicken. The larvae are but a few millimeters long and pale yellow. You can't see them unless you lie on your stomach on a sidewalk or grass-free patch of earth under an elm to the point of drawing extreme suspicion from your relatives and neighbors.
I suspect both the Hermit Thrush and the Rose-breasted Grosbeak were eating these today, the thrush going after larvae on the ground, the grosbeak munching mined areas of leaves that still had larvae within them.
Dave Leatherman
Fort Collins
A major activity that Norm Lewis alluded to in Lakewood the other day that I am also seeing in Fort Collins is feeding of birds of several species on the larvae of the Elm Leafmining Sawfly (Kaliofenusa ulmi). Sawflies are actually non-stinging wasps. The adults of the Elm Leafmining Sawfly are blue-black and about the size of a house fly, maybe a tad slimmer. They were commonly seen on the leaves of elm a few weeks to a month ago. They lay eggs on the expanded elm leaves and their larvae tunnel between the upper and lower layers, eventually forming a big brown blotch called a "mine". When the larvae are done feeding and as big as they'll get, they chew out of the mines and drop to the ground for pupation in the soil. Those that are successful in completing their development will emerge next late spring as blue-black adults. At this time of year, zillions of larvae drop from heavily infested elms and are a major source of food for House Sparrows, American Robins, Common Grackles, European Starlings, and probably many other species. The characteristic feeding pattern involves running around plucking at the ground like a chicken. The larvae are but a few millimeters long and pale yellow. You can't see them unless you lie on your stomach on a sidewalk or grass-free patch of earth under an elm to the point of drawing extreme suspicion from your relatives and neighbors.
I suspect both the Hermit Thrush and the Rose-breasted Grosbeak were eating these today, the thrush going after larvae on the ground, the grosbeak munching mined areas of leaves that still had larvae within them.
Dave Leatherman
Fort Collins
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