When Cortes Currents asked the Friends of Cortes Island (FOCI) who to interview for more in depth coverage of ‘species at risk,’ they responded ‘Jenna Cragg’ from BC’s Ministry of Environment. That was last January, which shows how busy she is. Sabina Leader Mense described Cragg as one of FOCI’s key ‘go to’ species at risk biologists, who provides the facts that FOCI brings into the community.
In the emails we exchanged prior to this interview, Cragg specifically mentioned five species: the Marbled Murrelet, Great Blue Heron, Double Crested Cormorant, Pelagic Cormorant and Western Screech Owl.
Cragg came into contact with FOCI when living on Cortes during 2010. She was doing field work and met Sabina Leader Mense while helping a grad student collect some tree core samples from a heron colony on her property.
“Since then I’ve kept in touch and they’ve invited me to come and give some presentations to the community about species at risk. I’ve helped train some of the members to do Marbled Murrelet surveys of nesting habitat and dawn surveys to find where the birds nest. More recently, I worked with Helen Hall at FOCI to develop a Screech Owl project proposal that was funded by Environment Canada,” Cragg explained.
She researched Marbled Murrelets for 20 years and is the lead or co-author of at least six research papers about them.
Cragg was one of the co-authors of a 2016 study of the murrelet’s movements in the Cortes/Quadra area, Clayoquot Sound and the Douglas Channel.
“We were based on Cortes, but found that there was a really specific spot off Mink Island in Desolation Sound where it’s easy to catch birds. It wasn’t very easy to find them anywhere else,” she explained.
They went out at night to sneak up on the birds and flashed a spotlight in their eyes. The murrelets were scooped up in nets, while they were still blinded by the light. They were then tagged, so that their movements could be tracked by satellites, and released.
Up until then, murrelets were believed to remain close to their nests.
“We found that these birds seem to be moving north at some point in the summer, probably to take advantage of better foraging opportunities,” said Cragg.
Two of the birds in their study flew to Southeast Alaska.
“Marbled Murrelets dive to eat fish like Sand lance, Herring, Anchovies – basically small fish that are called forage fish as well as some krill and Euphausids,” explained Cragg. “Sand lance are thought to be probably the most important prey species. They are a fish that likes to burrow in a very specific type of sand, and there’s a lot of that good sand around Cortes and Savary Islands.”
They nest in old trees with big branches.
Cragg said a number of these nests have been found on Sonora Island, the Redonda Islands and neighbouring Mainland coast.
Cortes Currents’ next question pertained to the decreasing number of Western Screech Owl sightings.
Cragg said scientists are not sure why this has happened:
“It’s thought to be a combination of urbanization, logging of their nest trees and the abundance of bard owls, which are a species that has invaded the coastal habitat of Western Screech Owls over the last 30 or 40 years. They’ve become a lot more abundant in the last 20 years on Vancouver Island.”
While there has been some direct observations of Bard Owls preying upon Screech Owls, the latter may also be less vocal when the two are in close proximity because they don’t want to be heard by a predator.
Cragg said the population of the third species, Great Blue Herons, was in decline, but may have stabilized of late.
“Eagle predation has affected a lot of seabirds, including herons. We think that eagle predation causes smaller colonies of herons to move around quite frequently, especially in the northern part of their range of the Salish Sea. Basically north of Nanaimo, we’re seeing smaller colony sizes that tend to move around more frequently and they have kind of a pattern of boom and bust reproduction where some years they produce a lot of fledglings and other years they get wiped out by eagle attack,” she said.
There are large colonies of herons to the south in Tsawassan, Beacon Hill Park and Cowichan Bay.
“We think that in some of these large colonies, there’s potentially a resident eagle that defends its territory so that the birds nesting within the resident eagle territory are protected from other birds that would potentially attack the colony. They call it the mafia effect,” she explained.
The two species of cormorants in the Salish Sea (Double Crested and Pelagic) also suffered from eagle predation, but the numbers of nests appear to have been relatively stable over the last five to 10 years. 2019 was the last year in which they obtained a good count from colonies.
“In that year we did see a little uptick in the number of Double Crested Cormorant nests that were counted. We think that this could be potentially a result of birds moving north into the Salish Sea from some of the large colonies in Oregon state that failed. The largest colony in western North America was in the mouth of the Columbia River and that colony failed for the first time, I think it was in 2017 or 2018. Since that time, birds have been dispersing to other colonies, so they might be moving north into the Salish Sea.”
Scientists have also noted that whereas cormorants used to nest on small islands, now colonies concentrate on cliffs where they are less vulnerable to attacks.
The cormorants on Mitlenatch Island are an exception to this trend, but observers say the colony failed in 2021 because of eagle predation.
“It’s sad to see that, but it’ll be interesting to see if that happens again this year,” said Cragg.
She added, “I just wanted to thank the Mitlenatch Island Stewardship Team for all their work that they’re doing monitoring the colonies of double Crested and pelagic cormorants on Mitlenatch Island, because it’s been really valuable for us in terms of tracking populations in the Salish Sea.”
Jenna Cragg started a new job with the Ministry of Land, Water and Resource Stewardship this year and is now working on a province wide scale scale.
There is more in the podcast.
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