The Question: From time-to-time, birds fly into our picture windows and die. On two occasions, once last summer and then again just two days ago, a squirrel or a chipmunk retrieved the carcass and proceeded to devour it. This seems to be unusual behavior, and I wonder what triggers it, or if it happens more often than I am aware? Submitted by: A. C., Georgia, USA

The Short Answer: Like most people, I once thought of rodents as seed eating herbivores, but it turns out that many, if not most, rodents are really omnivores that will eat insects or meat whenever they can get it. Gray squirrels (Sciurus carolinensis) and eastern chipmunks (Tamias striatus) are known nest raiders that will eat eggs or chicks. They also occasionally kill and eat adult birds. And gray squirrels are commonly seen eating road kills. So the answer to your question is that this carnivorous scavenging by a gray squirrel and a chipmunk is not unusual behavior at all. Great photos, by the way!

More Information: Scientific reports of predation by rodents list gray squirrels as eating other gray squirrels and birds.  The list of observed prey for chipmunks also includes birds, as well as other chipmunks, voles, snakes, frogs and salamanders.  Surprisingly, even small mice are significant predators of birds, mostly eggs and chicks, but they occasionally kill adult birds as well.

Given that squirrels and chipmunks are such frequent nest raiders, you might think that adult birds would defend their nests against them, but adult birds often simply abandon a nest if a squirrel comes near. This may be because, as mentioned above, squirrels are capable of killing adult birds. Under such circumstances, it might make sense for adult birds to simply give up and save their own lives in the hopes of nesting again in the future – especially under conditions where if the adult bird is killed while defending the nest, the chicks aren’t likely to survive anyway.

So, now you are going to have to view squirrels a little differently. And those cute little chipmunks are actually pretty good hunters. In fact, one study showed animal matter in the stomachs of 75% of chipmunks examined.

And all of this gives a new perspective to the Rodents of Unusual Size (ROUSes) that feature prominently in the satirical fairy tale movie, The Princess Bride. Turns out they are just imitating their relatives of usual size.

Sources:

CALLAHAN. (1993). Squirrels as predators. The Great Basin naturalist, 53(2), 137-144.

LANDRY, SO. (1970). Rodentia as omnivores. The quarterly review of biology, 45(4), 351-&.

Bradley, JE, & Marzluff, JM. (2003). Rodents as nest predators: Influences on predatory behavior and consequences to nesting birds. Auk, The, 120(4), 1180-1187.

Pietz, PJ, & Granfors, DA. (2005). Parental nest defense on videotape: More reality than “myth”. Auk, The, 122(2), 701-705.

Lima, S L. (2009). Predators and the breeding bird: Behavioral and reproductive flexibility under the risk of predation. Biological reviews, 84(3), 485-513.

Tom | Animals, Questions and Answers, Uncategorized | 08 4th, 2011 | 2 Comments »

The Question: On a recent mid-July trip to the Trinity Alps in Northern California we saw many of these 2′-4′ tall plants, most just starting to show emerging flower heads. I thought they were so common that ID would be a cinch, but no such luck. Any help would be greatly appreciated! Submitted by: Marianne, California, USA

The Short Answer: According to several helpful people at www.gardenweb.com’s
Name That Flower forum, this is probably corn lily (Veratrum californicum), also known as false hellebore. “True” hellebores are Eurasian plants in the genus Helleborus. What connects the two is that plants in both Veratrum and Helloborus are toxic, and are often eaten by livestock with disastrous results.

Veratrum californicum is found throughout the western United States, and I was able to find specific references to it in the Trinity Alps, so this seems like a pretty likely identification. To verify that it is the californicum species of Veratrum, a responder on Gardenweb.com suggests: “If the original questioner has a picture of an open blossom, there should be a green mark in the shape of a ‘y’ at the base of each petal.”

Thanks to carol23, mytime, and bboy on Gardenweb.com for their help with identification.

More Information: Veratrum californicum is famous in the scientific world for the specific poisonous effect it has on sheep. All parts of the plant are poisonous, and according to the United States Department of Agriculture (http://www.ars.usda.gov/Services/docs.htm?docid=9992), symptoms include excessive salivation with frothing; irregular gait; vomiting; fast, irregular heartbeat; slow, shallow breathing, coma and convulsions. What triggered the interest of developmental scientists, however, is that lambs born to ewes that eat the plant often have major developmental abnormalities, including misshapen heads and a single eye. This disorder is called “cyclopia” after the one-eyed Cyclops of Greek mythology. Cyclopamine, the specific compound in corn lily that causes the abnormalities, does so by interfering with the action of the “sonic hedgehog” gene, which is crucial in embryonic development (see below for an explanation of the sonic hedgehog name). Studying the effect of cyclopamine on embryonic development helped lead to a much better understanding of how genes direct development. Also, the sonic hedgehog gene normally shuts off after fetal development, and the out of control cell growth of cancer can result when it is turned back on incorrectly. Because cyclopamine can disrupt the sonic hedgehog gene, it is sometimes used as a chemotherapy drug.

So while you definitely don’t want to snack on corn lily the next time you are hiking in the Trinity Alps, you can look on it with a different view, knowing its toxicity has led to increases in our knowledge about embryonic development and cancer.

Why Sonic Hedgehog: Newly discovered genes are generally numbered these days, but in the early days of gene discovery, they were often given descriptive names. “Hedgehog” describes an abnormality where the embryo is covered with small projections that make it look something like the spiny animal. When the mutated gene that causes this abnormality was named, the sonic part was apparently added as a joke to reflect the video game Sonic the Hedgehog, which was popular at about the time the gene was discovered.

The Trinity Alps: The Trinity Alps Wilderness Area is located in northern California and is known for its beautiful alpine views.

Tom | Plants, Questions and Answers, Uncategorized | 08 3rd, 2011 | 1 Comment »

The Question: There are six gorgeous monarch caterpillars on a milkweed plant in our front yard. The only problem is, the plant is next to a high traffic public sidewalk. Once the chrysalis is formed, can we move each one to a safer location in our back yard? Does it matter where the butterfly emerges, i.e. does it have to be on milkweed plant? Submitted by: Mike, Minnesota, USA

The Short Answer: I was delayed in responding to Mike’s question, so this answer is too late to help him, I’m sure, but for the sake of other readers who might wonder the same thing about moving the chrysalis of a monarch butterfly (Danaus plexippus) or other butterfly, the answer is that you generally can carefully move butterfly chrysalises to another location in your yard or even indoors. As long as you don’t change the temperature of the chrysalises drastically, by, for example, moving them from a shady spot to a sunny one, they should do okay.

Monika Maeckle, who writes for
The Texas Butterfly Ranch Blog offers this advice: “You can simply take a piece of the plant and tape or pin it elsewhere. Stick it in a vase, or figure out some way to keep it upright. What’s important is that the chrysalises are hanging as vertically as possible. When monarchs and other butterflies emerge, they need the assistance of gravity to help them develop properly. Their wings are soft and still forming for about an hour after they eclose and gravity helps them develop fully. Good luck!”

More Information: Monika was inspired by this question to write an article on The Texas Butterfly Ranch Blog about this issue. You can read it at:

http://texasbutterflyranch.wordpress.com/2011/07/31/butterfly-faq-is-relocating-a-monarch-chrysalis-ok-yes-and-heres-tips-on-how-to-handle-them-with-care/

Surprising Information: 

I was surprised to learn that Monarch butterflies, which I always thought were limited to North America, turn up all over the world – pretty much anywhere you find the milkweed species on which their caterpillars feed.  The 140 or so species of milkweeds (genus Asclepias) themselves are primarily North American species, but there are species native to Africa, and milkweeds have been spread around the world as garden flowers, and have become invasive species in some places.  Wherever there are milkweeds, monarchs eventually show up.  This may be because they arrive as eggs on transplanted ornamental milkweeds, or it may be that migrating monarchs that get blown off course by storms end up surviving and multiplying where there are already milkweeds.  There are now populations of monarchs in South America, New Zealand, Australia and even Hawaii, for example.

What surprises me about this is that Monarchs have a famously elaborate migration pattern in North America (for more info, click here and here).  I would think that would make it more difficult for the species to become established on another continent where patterns of climate and geography are completely different.  But monarchs in places like Australia have developed new migration patterns there.  And usually, as in North America, monarchs in other parts of the globe also congregate in large numbers in specific areas during the winter (click here for more info).  The striking coloration, amazing migratory patterns and dramatic concentrations of monarchs in winter have made it one of the most well-known butterflies in the world.

Tom | Animals, Questions and Answers, Uncategorized | 07 31st, 2011 | 2 Comments »

The Question: Recently, I saw a butterfly holding on to another butterfly beneath him. It caught my eye when the two began to spiral downward into a field of grass. The “carrier” was able to ascend again and flew off holding the butterfly that appeared to be one of his own kind. Do you know why the “carrier” was doing this? Submitted by: Judy, USA

The Short Answer: The butterflies were mating. Here’s a short video clip showing monarch butterflies doing exactly what you describe.

http://www.youtube.com/watch?v=_Dx09DIRkIE

Warning, this one is a little dizzying: http://www.youtube.com/watch?v=Z-kFgUVhK4I

According to Martin Olofsson, who studies butterfly behavior at Stockholm University in Sweden, when two mating butterflies are disturbed while copulating, they may try to fly away together, with one member of the couple as the carrier and the other going along limply as the carried. Interestingly, within a species, it is always the same sex that carries. In one species it’s males, in another it’s the females.

More Information: The data, Olofsson says, suggest that this behavior is about escaping from predators and not about “mate-guarding.” Mate-guarding is a collection of behaviors common in many animals, where males will guard their mate to prevent other males from fertilizing her eggs. In birds, fish and mammals this might involve chasing other males away from a territory. In insects, mate-guarding often involves staying physically attached to a female long enough for sperm to find their way to the female’s eggs, or for the female to stop being receptive.

It’s possible that in some species at least, the butterfly behavior of flying off with a mate may be a male’s attempt to hide the mated female from other males.  Olofsson, points out, however, that females carry the males in some butterflies, so that makes male mate-guarding unlikely as a general explanation for this behavior.  It might, however, be an added benefit, at least in those species where males do the carrying.

Thank you to:  Martin Olofsson for his generous help.

Tom | Animals, Questions and Answers, Uncategorized | 07 27th, 2011 | Click to Leave a Comment »

The Question: On Martha’s Vineyard, I found this spider. It’s bright green, with what looks like a florescent face painted on its body. Is it poisonous? Submitted by: Virginia, Massachusetts, USA

The Short Answer: This is Araneus cingulatus, one of many types of orb-web spiders. These are the spiders that build the classic dew bejeweled webs that appear overnight.  You can see additional pictures of  Araneus cingulatus at www.bugguide.net.  Though it’s probably true that all spiders have venom that incapacitates their insect prey, most are not dangerous — as long as you don’t have six legs.  Araneus cingulatus is not known to have a dangerous bite.

There is not a lot of information on the behavior of this particular species, which doesn’t have a common name, but the genus Araneus is a large one with many similar orb-spinning members. Females are larger than males, and often exhibit the mate-eating behavior many people associate with spiders. Typical Araneus species are about 1-2.5 cm (1/4-1 inch) with males 1/4-1/3 the size of females. As this lovely green spotted Araneus cingulatus Virginia found on Martha’s Vineyard shows, Araneus spiders are often beautifully decorated. Here’s a gallery of a few other striking Araneus species:

Thanks to Lady Arachnophile, one of the staff members at www.spideridentification.org, who identified your spider for me.

More Information: As so often happens, when I started reading in preparation for answering this question, I came across something very interesting that I did not know. It turns out that most orb-spider webs are not quite round. I never noticed this before, but if look closely at these two webs, you’ll see that the center spot, where the spider sits waiting for insects to become trapped, is slightly above center. You might think this is just random variation, but scientists who have studied this question find that it’s not. Most of these spiders build webs that are pretty consistently asymmetrical – slightly longer on the down side than the up side. And if you observe the spiders sitting in the middle of these webs, you’ll find that most often, they are pointed head down, towards the longer part of the web.

Why would that be so?

There are at least a couple of possible answers. It might be that it relates to the way spiders build their webs. Maybe it’s easier to build downhill than uphill. Another hypothesis, which seems to be gaining the most support from mathematical models and experimental manipulations of spider behavior, is that it’s about how spiders capture prey. It turns out that just as for people, spiders can run faster downhill than uphill. So they build their webs with a slight downhill bias, which probably equalizes the time it takes to cover the whole web. They probably face in that direction because with the web being slightly larger in that direction, the odds of catching a bug are slightly larger in the downhill direction. And they want to get there quickly before the insect escapes.

The final answers on this question aren’t in yet, but it seems likely to be one of those examples where natural selection has fine-tuned an animal’s behavior to a remarkable degree.

As I said, I never noticed this before, but I’m going to have to watch for it the next time I see a nice orb-web.

Sources:

Zschokke, S, & Nakata, K. (2010). Spider orientation and hub position in orb webs. Naturwissenschaften, 97(1), 43-52.

Coslovsky, M, & Zschokke, S. (2009). Asymmetry in orb-webs: An adaptation to web building costs? Journal of insect behavior, 22(1), 29-38.

Maciejewski, Wes. (2010). An analysis of the orientation of an orb-web spider. Journal of theoretical biology, 265(4), 604-608.

Tom | Animals, Questions and Answers, Uncategorized | 07 24th, 2011 | Click to Leave a Comment »