2012: The Season of the Migrant

By any measure, the butterfly season of 2012 was spectacular and one that Ottawa area butterfly enthusiasts won't soon forget.

Things got off to an early start in March with the emergence of the overwintering Anglewings and Tortoiseshells. Several observers sighted Mourning Cloaks as early as St. Patrick's Day, and by the end of the month, all the local hibernating species had been reported in varying numbers ( including the Satyr Comma which I observed in Gatineau Park ). The migrating Question Marks did not begin to arrive until April 16, which coincided with the deluge of Red Admirals that swept through the province.

Though we had warning of what was headed our way, it was still a bit of a shock when it hit. We'd seen a sizable influx of Red Admirals in 2010, but it was eclipsed by the invasion of 2012. Millions streamed through the province in mid to late April, garnering considerable media coverage. Even urbanites who normally pay little heed to these ephemeral creatures took notice. Most of the other migrants that comprised this first wave - American Ladies, Question Marks, and the odd Buckeye - were familiar enough, but the numbers were unprecedented. Ross Layberry ( co-author of the Butterflies of Canada ), quipped that he was seeing more Question Marks in an afternoon than might be seen over the course of an entire season in a "normal" year. In Southern Ontario, butterfly watchers were reporting rarities like the Pipevine Swallowtail, Dainty Sulphur and White-M Hairstreak.

The Mourning Cloak, not normally thought of as migratory in these parts, also seemed to have come north in large numbers. This wave was foreshadowed by reports that numbers of Mourning Cloaks had been found washed up on the Lake Erie shoreline with other migrants. We subsequently observed larger, darker versions of this familiar butterfly moving through the area long after the local Mourning Cloaks had emerged from hibernation. In addition to being distinct in appearance, these interlopers were often observed "on the move", behaving like the other migrant species that had passed through the area earlier in the season.

It was also a good spring for our resident butterflies, with several rarities putting in appearances. The Bog Elfin seemed to buck the trend of early emergences. It was reported during its normal flight season by several observers at a known site near Newington. The isolated colony of Juniper Hairstreaks in the far West end of Gatineau Park appears to be holding its own. I photographed 2 individuals there during two separate visits. There were no confirmed reports of Early Hairstreaks from the Quebec side of the river, but there were a number of reports from various locations around Eastern Ontario. I had one near Achray in Algonquin Park, which is likely one of the northernmost reports ever in Ontario.

But it wasn't all good news for Ottawa butterflies. There have been no reports of Mottled Duskywings from either of the two known colonies in the area - the Burnt Lands near Almonte and the Constance Bay Sandhills - for several years now. The decline of the Mottled Duskywing remains a bit of a mystery since New Jersey Tea ( its larval food plant ) can still be found in both these locations and the habitats seem healthy enough.

Later in the summer, butterfly numbers were much lower, largely due to drought conditions across the region. With wild nectar sources in short supply, ornamental flowerbeds provided welcome way stations to any butterflies arriving here, and late August saw the appearance of another visitor from the South. Prompted by reports of yet another migrant incursion in Southern Ontario, I paid a visit to the flowerbeds at the Central Experimental farm on August 15. There, I found several Fiery Skippers taking advantage of the floral buffet. The Fiery Skipper had previously been reported in Ottawa only once before in 2002, at this same location. Over the course of the next month or so, a number of local butterfliers took advantage of the opportunity to see this southern wayfarer without having to leave the city.

While these transitory migrants grabbed the headlines, a pair of butterflies that have been extending their range northward generated a buzz in the Ottawa butterfly community. The one is huge and showy, the other is small and inconspicuous, and we’re wondering if they will be hardy enough to become permanent residents here.

Although the Giant Swallowtail has been sighted in Ottawa in the past, this was the first year where it appeared here in numbers. I had my first ever Ottawa area sighting in Gatineau Park on July 21, followed by several sightings near Britannia on the Ottawa River shoreline. More significantly, this year also saw the first reports of Giant Swallowtail larvae feeding on local vegetation (Prickly Ash). Fittingly, local naturalist Steve Wendt of North Gower made the initial observation. He also has the honour of having the first documented sighting of an adult Giant Swallowtail in the Ottawa area back in 1992. Though the Giant Swallowtails appear to have established a bridgehead here, their pupae may not be able to survive an Ottawa winter. We should know shortly, but it’s probably been a hard first winter for them.

A less spectacular, but in some ways more interesting case is that of the Wild Indigo Duskywing. According to The Butterflies of Canada, the caterpillars of this small, gray/brown butterfly feed on plants in the Indigo family. These plants are rare in this province, and confined to the extreme southwest. In an unusual case where wildlife actually benefitted from the actions of humans, this butterfly adopted crown vetch, an introduced plant species, as an alternative larval food plant. Liberated from the restricted range of its traditional food sources, the Wild Indigo Duskywing is steadily expanding its range. With no shortage of crown vetch in Ontario, experts thought that it would only be a matter of time before the Wild Indigo Duskywing reached Ottawa. On Sept. 3, I spotted and photographed a fresh female Duskywing in the flowerbeds at the Central Experimental Farm. It appeared a bit too large to be a Columbine Duskywing, and it was a bit late in the season for the summer generation of that species. It was relatively docile, as though it had recently emerged from its pupa. I was able to hold a penny next to it for scale in a photograph and subsequent measurements put the wingspan in the range of the Wild Indigo. My online report caused considerable excitement among the local butterfly enthusiasts, along with some skepticism. Local expert Peter Hall ( co-author of the Butterflies of Canada ), went to see for himself a few days later, and observed what might have been the same individual in the very same flowerbeds. He also discovered what appears to be an ornamental species of indigo growing there, which may explain the presence of this Duskywing some distance from the nearest patch of Crown Vetch. Around the same time, another local naturalist, Arnet Sheppard, independently found what appears to be a colony of Wild Indigo Duskywings near an area of the Ottawa transit-way that features large swaths of Crown Vetch. Are they newly arrived, or was this colony established some time ago?

It will be interesting to see how these recent arrivals fare following a “normal” Ottawa winter, as opposed to the milder winters we’ve been having for several years. Hopefully, this winter’s heavy snowfalls will help restore habitats damaged by last summer’s drought.

2012's migration madness was the result of a “perfect storm” of favourable conditions for butterflies in the US. It doesn’t appear that we’ll have a repeat in 2013, so perhaps this will be a season to focus on our resident species. With a somewhat late spring, most species should be appearing closer to their traditional emergence dates. The winter’s ice and snow did significant damage to trees in some areas ( especially Gatineau Park ), so the hibernating Anglewings and Tortoiseshells should have plenty of sap to sip. As of April 1, there have already been a few reports of Mourning Cloaks in the Ottawa region.

Copyright © 2013 Rick Cavasin. All rights reserved.