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Dead Redpolls

by
Jim Goltz

      As most of the readers of NatureNB know, I work as a veterinary pathologist and thus might be expected to speculate on the possible causes of mortality in redpolls at two feeders in the Moncton area. Speculation is an academic exercise. A thorough necropsy examination is needed to be absolutely certain as to the cause of death. There are three veterinary diagnostic laboratories that do necropsies in the Maritime Provinces: the Provincial Veterinary Laboratory in Fredericton, the Animal Pathology Laboratory in Truro and the Atlantic Veterinary College in Charlottetown. Unfortunately, all of these laboratories must charge fees for necropsy service, so if you're contemplating submitting specimens for necropsy it's best to phone ahead to find out the rates and to obtain advice on specimen submission.

      One of the more likely causes of death in small finches found dead on feeders is a bacterial infection. To illustrate this, here's a short case study: About two weeks ago, some friends in Fredericton found a juvenile redpoll that could not fly very well. They captured it and placed it in a cage with a perch, lots of appropriate food and water, and kept it in a warm room free from drafts. The bird seemed to be eating well, and was quite lively. One wing seemed to be drooping slightly but I could not palpate any fracture. I took the bird home with me and it seemed fine the next morning. However, it was dead by the evening. The bird died as a result of an overwhelming infection (i.e., septicemia) with an unusual strain of E. coli that had some characteristics suggestive of Salmonella.

      From time to time, outbreaks of Salmonella occur in finches frequenting bird feeders. The affected birds are often just found dead. Necropsy examination may reveal an inflammation of the crop (the dilated part of the esophagus), intestine and/or liver. Salmonella and other bacterial infections may be acquired from other infected birds that share the feeder, from other birds or mammals to which the birds may have been exposed, or from contaminated feed. Since Salmonella and many other bacterial infections are shed in the feces, it's best to keep your feeders as clean as possible.

      In my experience, starvation and trauma (including predation) are the most common causes of death in all species of wildlife. Far more birds and other wildlife species starve to death than we can ever imagine. As for trauma, birds commonly meet their demise by flying into windows or cars, or falling prey to free-roaming cats. Several years ago, a friend gave me two small birds (a chickadee and a finch) that had been found dead at a feeder. Both had lacerations to the head that were undoubted caused by the penetration of a larger bird's beak. These lacerations were almost completely undetectable on external examination. Blue Jays were high on the list of likely suspects.

      Toxic substances must also be considered as a possible cause of mortality in wild birds. Persons who are putting out substances for rodent control purposes should be careful not to place them in areas where non-target species of wildlife, including songbirds, may fall victim to them.

      These are some of the more common causes of death in wild birds but I continue to be surprised at the range of possibilities.