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10 July 2011 @ 07:23 pm
A Dashing Discovery  
After a relatively uneventful outing on Saturday I decided to head out to the east end on Sunday. I hadn't been to Petrie Island in a few months, and as it's one of the best spots for dragonflies along the Ottawa River I thought I would check it out see what was around. Petrie Island is also home to the Hackberry Emperor, a beautiful butterfly which depends on Hackberry trees as its larval foodplant. Petrie Island is the only place in the Ottawa area with a mature stand of Hackberry trees, and as such it is the only place in Ottawa where the Hackberry Emperor is found. I wasn't sure whether this butterfly would be flying yet, but thought it would be worth checking.

I arrived shortly before 8:00. I stopped along the causeway to see if any marsh birds were present. I didn't see or hear any rails, but a Black Tern did fly over the marsh, heading west. A couple of swallows were hunting for insects; while most of these appeared to be Tree Swallows, I did count two Barn Swallows. A Green Heron also flew over. Further along the road, at the entrance to the Basswood Trail, I noticed a few large dragonflies perching in the vegetation in the warm sunlight. One was a male Common Pondhawk; the other was a female. On closer inspection I realized the female was eating another female pondhawk!

Common Pondhawks

I crossed the road and began exploring the marshy area near the entrance to the Sunrise Trail. I'd had Slaty Skimmers and two different spreadwing species here before, and was hoping to find some more. Though I had no luck with the Slaty Skimmers, I came across several metallic green spreadwings. The first two I caught were females, and difficult to identify. The third one was a male, and the shape of its claspers was distinctive: the two lower claspers were longer than the top ones, meaning it could only be an Elegant Spreadwing. Petrie Island is the only place I've seen these lovely damselflies.

Elegant Spreadwing

I also noticed a couple of moths in the area, and this lovely Four-lined Plant Bug. Ever since I'd seen one in my garden two summers ago I'd been hoping for a chance to get some better photographs of this species. Notice the giant shadow cast by the low-lying sun.

Four-lined plant bug

I followed the Sunrise Trail to the beach, then cut across the island to the Turtle Trail, encountering a Brown Creeper, a single Veery, several Warbling and Red-eyed Vireos, a Northern Flicker, and a couple of Eastern Wood-Pewees and Great Crested Flycatchers on the way. I came across a few more Elegant Spreadwings, none of which wanted to sit out in the open for a photograph, and this lovely lady beetle nectaring on some Swamp Milkweed.

Spotted Lady Beetle on Swamp Milkweed

Further along the trail where it becomes the William Holland Trail I encountered my first Slaty Skimmers. These beautiful dark blue dragons like to perch in the vegetation above the water and will frequently dart out to chase other insects or even other Slaty Skimmers.

Slaty Skimmer

When I first saw this black and yellow skimmer sitting in a small shrub, I thought it was a clubtail because of its colouration. However, clubtails have widely separated eyes while this fellow does not. I began to suspect it was a newly emerged Slaty Skimmer based on the shiny wings and the fact that it was a large dragonfly, similar in size to the Slaty. The dark wingtips confirmed my tentative ID.

Slaty Skimmer (teneral)

Then I found a smaller dragonfly sitting among the vegetation which puzzled me. It had a black abdomen with yellow dashes down the length of it, and my first thought was that it was an immature whiteface (genus Leucorrhinia). However, the thorax had black and yellow stripes, too, which immature whitefaces do not. I attempted to take a picture of the mystery dragonfly, but it flew off before I could focus my camera. I later found a second one which allowed me to take some very close macro images.

Mystery Dragonfly

I also noticed something else: the dashes along the abdomen were paired. This again ruled out the whitefaces, though the structure was certainly suggestive of the skimmer family, despite the obelisk position it was resting in. I would have to check my field guide once I got home, though for the moment I had no clue as to what it was.

Further along the Bill Holland Trail I came across a small skipper flying along the vegetation. I was able to identify it at home as a Crossline Skipper, though the only decent photo I took doesn't show the distinctive pattern on the underside.

Crossline Skipper

I came to the large wooden structure at the end of the trail. Just beyond that the sandy spit comes to an abrupt end, entirely surrounded by water. This is a wonderful spot for dragonflies, but before I got the chance to examine them a small, brownish butterfly buzzed around my head and landed on my shirt! I was trying to decide how best to take a picture when it darted off, circled around, and landed on me two more times! I got a long enough look at it to identify it as a Hackberry Emperor, a species known to attack people and land on them. Unfortunately I didn't see where he went, so I wasn't able to get any photos.

I did get several photos of the dragonflies in the area. These are a few of my favourites:

Common Pondhawk

Slaty Skimmer on Flowering Rush

Common Pondhawk

I didn't stay too long as it was getting hot. On the way back to the parking lot I encountered a singing House Wren. Petrie Island is a great place to find these cute, energetic birds.

House Wren

By the time I left Petrie Island it was after 12:00 and getting crowded. Still, I stopped by the causeway one last time to check for marsh birds. I heard some type of rail squeaking in the cattails, but it wouldn't come out into the open. I found some Flowering Rush in bloom, however, so I took a few pictures.

Flowering Rush

Then a small, dark butterfly zipped by and landed in the reeds. It looked bluish, with small dark circles on the forewing, and at first I thought it was a Silvery Blue. However, the Silvery Blue flight season was over. I took a few pictures and later identified it as an Acadian Hairstreak. This was a terrific find, as hairstreaks are difficult to find and even harder to photograph!

Acadian Hairstreak

I saw an Eyed Brown flutter by as well.

Eyed Brown

After that I went home to see if I could identify my mystery dragonfly. While browsing the skimmers, I found it: a female Blue Dasher! There she was, all black with yellowish stripes just like in my photographs. I was stunned, for this species has only been recorded in the OFNC study area only once before, last summer at the Baxter Conservation Area. Christine Hanrahan photographed a male, the first known record for Ottawa although it is more common south of the study area. I studied all the other photos I had taken, and found to my surprise that one of the blue “Common Pondhawks” I had photographed was a male Blue Dasher. This meant at least three individuals were present at Petrie Island, a rather significant discovery. That made me wonder how many more males had I missed, thinking they were Common Pondhawks instead.

Blue Dasher

Thrilled with this discovery, I resolved to go back the following day and conduct a count to see how many Blue Dashers were present. Seeing one individual is one thing - Christine's dragonfly could have been a stray which had flown up the Rideau River - but finding several individuals was quite another. If a small population did exist at Petrie Island, perhaps they would breed here and establish a colony. I couldn't wait to find out!