All Worked Up: Notes on Yellow Warbler Parental Behavior


This adult male Yellow Warbler, photographed at Detroit Lake hear Detroit, Oregon on 7 July 2012, rarely stopped moving as it flew from perch to perch scolding our presence.

If you spend a day in the field at this time of year, it's a virtual certainty that you will draw the ire of adult birds that are protecting newly-fledged offspring. Highly-dependent young of many species are fresh out of the nest. Although there may be no youngsters in sight, the incessant sharp chips, physical distraction displays, and the generally agitated movements of their parents inform us of what lies hidden away in the vegetation.

During a day birding on the mid-level slopes of Oregon's Cascade Range on 7 July 2012, Shawneen Finnegan and I came upon many family groups and were scolded by a host of species. These included Spotted Sandpiper, White-headed Woodpecker, Mountain Chickadee, Common Yellowthroat, MacGillivray's Warbler, Yellow Warbler, and surely others that I'm forgetting. 

Our most interesting encounter occurred along the shores of Detroit Lake in eastern Marion County. We pulled over near the lake edge to look over some waterbirds and almost immediately an adult male Yellow Warbler unleashed a tongue-lashing of sharp chip notes from the strip of low vegetation between the road and the lake edge. An adult female was also in the tangle of vegetation, but her actions lacked the agitation shown by the male.

Given the male's behavior, we assumed that it had nearby young, and after several moments Shawneen spotted a somewhat teed-up fledgling. It was all bill and gape, tail-less, and possessed stubby little wings barely capable of flight. It remained essentially motionless as the adult male interspersed feeding visits to the youngster with scolding chips directed at us. Shawneen saw the adult male feed this juvenile several times, but neither of us saw the female give it food. We observed both adults making brief flights to a nearby stand of cottonwoods, with the female making most of those trips, so we presumed that they were feeding other nestlings that had yet to fledge.


Here's the cause for all the excitement. This days-old juvenile (above and below) was likely less than 24 hours out of the nest, as it could barely fly. During the couple minutes we watched, it never left its perch on this blackberry and only shifted its position once or twice when the adult male brought it food.


In this instance, I was most intrigued by the behavior of the female, as she seemed to take far less interest in–or, was at least less agitated by–our presence than the male. Although she remained in the immediate vicinity of the juvenile most of the time, she continued feeding and did not go to feed it. On a couple of occasions she disappeared deep into the brush for more than a minute at a time.


We found it interesting that this female went about gathering food and often disappeared into the deep brush instead of being overtly agitated by our presence. In the image below she is emerging from one of her forays. Note the indistinct narrow chestnut streaking on the sides of her upper breast.


At one point she came very near our parked truck, so I walked behind the truck and used it as a blind. As I watched from about 12 feet away she fluttered her wings in a manner somewhat similar to the way many juvenile passerines flutter their wings when begging for food. I wondered if this might be some sort of feigned injury distraction display, which are known in this species (pers. comm. George Lozano Ph.d), but she continued to gather food and again burrowed deep into the dense vegetation. 

While it's always informative and exciting to watch this type of behavior and to see newly-hatched birds, it is best to make such observations as brief as possible and then move on. Gathering enough food to keep hungry offspring fed is very demanding on the adults. While outside distractions are inevitable, prolonged interruptions of their normal routine can have negative impacts. We watched these birds for just a few minutes. We were unable to determine if there were other hatchlings hidden in the brush, as we heard no begging calls and did not see any juveniles other than the one in the photo above. The fledgling that we saw may well have been the only one that had left the nest.


This youngster looks like a Spadebill! Great shots!


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