This morning was sunny at least, but the temperature was barely 40 and the wind was blowing cold out of the NW when I went to the grid, filled with apprehension over what might be waiting there. That I only found one dead Tree Swallow was somewhat of a surprise, but every death here is saddening, and brings a feeling of defeat. This is why I had hoped for success with the feeder experiments.
I couldn’t determine the sex of the dead swallow in Box 4. It didn’t show a female’s brood patch or a male’s cloacal protruberance – too early in the season. It had no brown feathers above its bill, which a few females show. Its legs and feet were sound, so I don’t believe it was the injured swallow from Box 3, mentioned in an earlier post. But there was little doubt in my mind as to cause of death. It had almost certainly starved, a victim of the unholy combination of cold, wind and rain over several days’ time that is so dangerous for aerial insectivores like swallows, martins and swifts. A quick examination was revealing. Parting the feathers of the swallow’s breast I uncovered the keel of the swallow’s sternum sticking out like a knife. What was left of the Pectoralis majors, the normally large and powerful muscles so essential for pulling wings down during flight, were shrunken to the point that had this bird been alive I doubt it could have flown.
A weight check supported starvation as the probable cause of death. Tree Swallows in decent condition weigh 20 grams, plus or minus a gram or two. But this unfortunate swallow was down to only 10.2 grams when it died, having metabolized half its body’s soft tissue mass trying to survive.
Sadly, many other people in the northeast will be discovering dead swallows, martins and bluebirds today and in the next few days, because if the weather folks are correct the cold spell we’re under is going to linger. Here at Salmon Creek we’re looking at highs in the 40′s and 50′s for the next week, no higher. The swallows really need a recovery day or two, and soon.
For more on Tree Swallow mortality see: http://www.treeswallowprojects.com/cmortaly.html.