Keep those hummingbird feeders up until they might freeze

Hi Doug,

We have enjoyed watching the ruby-throated hummingbirds at the feeder on our deck, and their acrobatic displays in the air as they chase one another. We know that chirping can be a territorial behavior of males to ward off a competitor, but we have an individual that chirps between sips at the feeder when there are no others in sight. Any idea why?  We will keep our feeder up (and sugar water frequently changed) until October. When do hummers typically head to South America?

Michelle Gregoire and Bill Karl, Westbrook

As Michelle and Bill mention, ruby-throated hummingbird vocalizations are mostly just short calls given during territorial or agonistic encounters (social interactions that include threats, aggression, and submission in members of the same species). Even the song of our eastern hummingbird is hardly more than a few complex squeaks and squeals to our ears, but probably contains a lot of information to the attentive female. Biologists have identified at least six different types of notes made by ruby-throated hummingbirds. One is mentioned as given only
by the victor of an agonistic encounter near a feeder. So perhaps the noise you are hearing is the proud exclamation of the still victorious hummer, or maybe it’s just a hummingbird burp!

By the time most people are reading this, many of our hummingbirds will have left Maine and be well on their way to wintering grounds between Mexico and Costa Rica. That is a remarkable journey to be traveling over 3,000 miles on just a few grams of fat. While most ruby-throated hummingbirds will leave by the end of September, I always recommend people keep their hummingbird feeders up as late as possible. Lingering migrants will appreciate the easy meal and we also see western hummingbirds, like rufous or calliope hummingbirds, who occasionally show up in the east, typically in October and November. So keep those feeders up until the day before they would freeze and drop me an email if you have a hummingbird visitor after the first week of October.

Many possible causes for small, dead mammals

Hi Doug,

Here is a somewhat weird question: In the past several weeks I have been increasingly curious and puzzled to find several dead shrews, voles, meadow/woodland mice and moles lying on the ground in our yard or on the seldom-used driveway. There is no evidence of injury on these critters (no missing heads, etc.). There are no cats in the vicinity, and although we have a resident barred owl family, I wouldn’t think they would be leaving whole critters behind. We use no ‘cides of any kind here. Should I submit the next critters I find for some kind of testing, or do I simply need a better education in rodent life history?

Jan Getgood

Encountering a deceased animal (or any wildlife) can be a jarring experience, but for the more curious naturalists among us, it is a mystery to be solved. Grab your deerstalker cap and calabash pipe for this one, we’ve got a lot to discuss in the case of the furry cadaverous encounters!

It isn’t all that uncommon to encounter a deceased small mammal while walking through their habitat. At least a few times each year I encounter a short-tailed shrew or star-nosed mole along a clear path, typically through a meadow or on the edge of a marsh. These critters are fairly abundant, low on the food chain, and generally have very high reproduction rates, so it is almost surprising that we don’t encounter more, but I’m sure most homeowners are glad we don’t. We can consider a few reasons why we’ve got a dead mammal in front of us.

First, predators. The paths and clearings – like yards and driveways – that we make can create unfavorable crossings for prey and make them more vulnerable to predators. Perhaps the mammal was recently killed and your presence caused the predator to abandon the prey. I’ll always remember finding a meadow jumping mouse in the trails at Gilsland Farm while leading a bird walk. Hunched over the lifeless mouse in the middle of the trail, we were examining its kangaroo-like hind feet when a short-tailed weasel (aka ermine) poked its head from the grass. Weasels are pretty focused hunters and not likely to ditch that meal, unlike a fox which would be more frightened by approaching humans. As soon as we backed off, the weasel came in, grabbed the mouse and bounded off. (It needs to be mentioned that there is insanely high predation of small mammals by one non-native species: an estimated 12.3 billion small mammals are killed by cats that are allowed outside by their owners.)

Second: natural causes. Death by predator typically leaves prey with visible wounds, but in this case, if there are no apparent injuries, it could be natural. Spontaneous death is a pretty rare phenomenon in general, but may be the case in some species. Remember the life histories of these small mammals, which we could summarize as “live fast, reproduce aplenty.” One study on short-tailed shrew longevity highlights that shrews often only live a couple of years, and tooth wear is a good indicator of age. By two years of age, shrews are nearly toothless, which for an animal that needs to consume 200% to 300% of its body weight per day, would be very disadvantageous and possibly deadly. I’m not recommending you check the teeth of dead shrews you find; just know that is what I’ll be doing.

One last cause of death that we should talk about, because it is arguably the most anthropogenic, so we can and should stop it, is the use of poisons for animal controls. In Jan’s case, no pesticides or poisons are present, but these animals could be coming from nearby areas where they are in use. Some of the most common products trick the animal into consuming zinc phosphide, which stomach acids convert to phosphine, a toxic gas. The phosphine passes into and kills the body’s cells in a slow and inhumane way. Another unfortunately common product for small mammal control is the use of anticoagulants (often Bromadiolone) which over the course of several days will reduce the body’s vitamin K (needed to clot blood) and cause them to bleed to death.

These are apparently favored by consumers because of their “hands-off” approach, meaning you probably won’t have to deal with the deceased animal, but that sets up our biggest problem: the animal and the poisons in its body are now out in the food system. These small mammals support the upper levels of the food chain and they can pass along those poisons even postmortem. Now we see rare predators, from elusive mammals to endangered birds, dying from indirect poisoning. Perhaps there is a time and a place for the use of rodenticides (read Rat Island by William Stolzenburg for proper examples), but I don’t think anyone with small mammals around the house should be introducing such deadly chemicals into the environment. If you have a problem, snap traps are targeted and fast solutions.

To wrap this up with a happier fun fact, you may have noticed I tried to not refer to all of these small mammals as rodents. This is because animals like moles and shrews are in the order eulipotyphla, not rodentia with mice, rats, squirrels, etc. Despite their similarities, they probably haven’t shared a common ancestor since the Cretaceous period.

Have you got a nature question of your own? Email questions to ask@maineaudubon.org and visit maineaudubon.org to learn more about virtual and backyard birding, online classes, and other programs about Maine wildlife and habitat.