Archive for July, 2014

In the last week, I have been seeing some impressively large insects right around our place in West Sacramento. The first was a few days ago, when I was out walking around our little condo complex with my wife and daughter enjoying the evening air and each others company. I looked up at one of our walls and saw a huge insect walking along the wall. It was about 2.5 inches long, bright green, and its body looked very leaf-like. I thought it was a katydid of some kind, but having never actually seen a katydid before, I was not confident. Well, I looked it up, and sure enough, it was a California Angle-wing Katydid (Microcentrum californicum). My first!

Copywrite Natalie McNear

California Angle-wing Katydid (Copywrite Natalie McNear)

It turns out that there are six species of angle-wing katydids in North America. The California Angle-wing is the smallest of the six and is only found in California and Arizona. Adult katydids appear in late summer and fall and are mostly active at night. They are attracted to lights, but not strongly, so you are unlikely to find lots of these insects gathered together. The males attract females by rubbing their front and hind wings together (not a wing on their leg as is often thought). Once the female is close, she will respond with calls of her own and the two individuals will close in on each other through this back and forth conversation. Both sexes perceive sound through small slits in their front legs. I am very much looking forward to spending some time outside and listening for these stradulation calls. I may try to get some recorded. If so, I will attempt to post the recordings here.

The second large insect encounter happened yesterday. Again, my wife, daughter, and I were out walking the grounds when a really big, black wasp flew past me. It was at least an inch long, and was cruising back and forth across the lawn just above grass height. It was completely black. Its body was black and shiny metallic, and its wings were a smoky black as well. After looking this one up, I found that it was a female Great Black Wasp (Sphex pensylvanicus), and no I am not making that name up. This is only the second Sphex wasp I have ever seen!

Great Black Wasp (Copywrite Paul A. Scharf)

Great Black Wasp (Copywrite Paul A. Scharf)

Sphex wasps are diggers. The females dig underground burrows in which they lay their eggs and then go out and hunt for insects for their young to feed on when they hatch. The Great Black Wasp has a very precise way of paralyzing their prey with exactly three stings; one to the neck and two to the thorax. This paralyzes their prey without killing it so that it stays fresh longer for the young wasps. Interestingly, their preferred prey are Orthopteran insects (such as grasshoppers and katydids)! Great Black Wasps are found across most of the continental USA and into parts of northern Mexico. As an interesting side note, the Great Black Wasp was the subject of the first insect article written by a native of the new world (John Bartram of Pennsylvania) to be presented at the Royal Society in 1749.

So cool to see and learn about these impressive animals!

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A few days ago, I found myself in Blackwood Canyon on the west coast of Lake Tahoe. It is a beautiful spot where Evening Grosbeaks have been reported regularly over the last couple of weeks. The day was lovely, and the birding was terrific with lots of classic mountain birds all around. Warbling Vireos and Hermit Warblers were foraging in the poplars that grow along side the stream that runs down the middle of the canyon. MacGillivray’s and Wilson’s Warblers were leading young birds around through the willows. Spotted Sandpipers were walking and bobbing their tails as they foraged along the rocky stream edges. Female Mallards lead broods of ducklings from pool to pool.

I did find a flock of Evening Grosbeaks, though they were not particularly cooperative in terms of my research plans. However, while I did not get the experimental trials I had hoped for accomplished, I did see something new and cool. I was stopped along the side of a road at around 9:30am beside a small group of spruce tree when I heard an Evening Grosbeak giving really loud flight calls. They were actually kind of spectacularly loud! As I watched, I saw the grosbeak, a male, flying from tree top to tree top and continuing to give these high amplitude calls. After standing below him recording for a few minutes, I figured out why he was behaving this way. There was an adult Red-tailed Hawk perched in the top of one of the spruce trees and the grosbeak was mobbing it. Now, Evening Grosbeaks are known to use their flight calls to coordinate the movement of a flock and they are also used by birds to locate other individuals over long distances. Further, they may possibly play a role in mate choice decisions and in population identification. However, to the best of my knowledge, this is the first time flight call have been observed being used in a predator harassment context! After a few more minutes, the Red-tailed Hawk flew off. The Evening Grosbeak, having succeeded in annoying the predator into leaving, quieted down and then departed on his own business.

This was yet another reminder that calls can have many different functions even when it is basically the same call, and even when that call is has a fairly simple structure. What subtle differences communicate different information to a receiver? Was the volume of these calls an important component of harassing a predator? Are there other differences (speed of delivery, frequency range, something else) between flight calls that are used in different contexts? I have this one recording, and so will certainly examine it to see if there is anything that jumps out at me, but with only the one occurrence, it will be hard to identify smaller differences, even though such small differences may be quite important to the birds involved. This also served as a reminder that exciting things can happen, but you have to spend time out with your study subjects to see them!

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