Another Ontario Species at Risk – a barn swallow – provides a fly-by feeding to its fledgling at the Carden release site

A lot has happened in Carden, Ontario with the Eastern Loggerhead Shrike Program since my last blog post. Wild eastern loggerhead shrike monitoring has continued and become more complicated with breeding pairs and fledglings leaving their original nesting territory. Conservation rearing is in full swing with six clutches of juveniles arriving to the prepared field aviaries to acclimatize themselves to our site and prove that they are capable hunters prior to soft release. In addition to these two busy tasks, I spent the second week of July back in Bruce and Grey Counties looking for shrikes. This would have been impossible to schedule without our new captive husbandry technician, Samantha, a pre-vet undergrad at the University of Guelph.

Other fledglings on our release site – newly hatched killdeer

Almost as soon as we fell into a rhythm with wild monitoring the situation changed. Fledglings have become more independent and family groups have begun hunting together throughout a much larger territory, requiring a lot more time and effort to locate and identify them. Many known breeding pairs moved to new areas to make a second nesting attempt or changed mates to attempt another nest, or have simply gone their separate ways. Each time a shrike is spotted, an attempt is made to determine if they are banded and if so, what their colour band combination is so that they can be identified. This enables us to determine their age, release or capture location, and when they were last spotted. Not very many wild-bred birds have been banded in recent years, so determining whether an unbanded bird is an adult or juvenile can be quite challenging now that many fledglings are fully grown with the same markings as adults. In lucky lighting with a well-trained eye, you can often distinguish a slight difference in colouration between juveniles and adults. Some juveniles have subtly striped feathers on their crown or wings, but the best differentiating factor is the quality of the primary wing and tail feathers. This is best observed when preening, so it is fortunate that shrikes spend several hours doing this each day.

There are no visible molt limits here, but this preening fledgling loggerhead shrike’s growing primary feathers (the longest wing and tail feathers) are notably shorter than an adult.

The feathers of freshly hatched, first year birds must grow very quickly so that they may leave the nest as soon as possible to decrease their risk of predation. Because of this, they are not able to expend as much energy and nutrients on the quality of their feathers as adults. This makes their primary feathers slightly more dull and brown-tinged than the pitch black, glossy feathers of a mature adult. The difference between brownish-black and true-black is quite small, but often visible with a good scope and enough experience. The most effective way to learn to differentiate between these subtle colour and quality differences is to observe a preening second-year bird because loggerhead shrikes molt approximately half of their feathers between their hatch year and second year (first breeding season). This delineation between first and second year feathers is called a molt limit and sometimes it is possible to determine the approximate age of wild, unbanded birds as second year or after second year (two or more breeding seasons).

The molt limits on this young osprey are more obvious than those on a shrike, but illustrate the principle more clearly.

I was hoping to use these aging techniques on unbanded birds in Grey and Bruce counties, as there were two sightings reported by members of the public in June. Unfortunately, after a week of thorough surveying I was unable to locate any shrikes. The locations where they were reportedly sighted were not appropriate breeding habitat, so it is likely that the individuals spotted were just vagrants passing through the area in search of better territories. I was able to find a few patches of high quality habitat in Grey-Bruce, but less than I had hoped. This is likely due to a change in ranching practices from free-range cattle grazing, which creates excellent shrike habitat, to cutting hay or growing feed crops for livestock kept in barns. Even though it was a bit frustrating to spend the week searching for shrikes and coming up empty handed, I updated our records of potential habitats so that surveys may be more successful in the future.

This pasture in Bruce County could be excellent loggerhead shrike habitat. It contains Hawthorn bushes for nesting and impaling large prey, short grass for easier prey capture thanks to grazing cattle, and even has overhead powerlines – a favourite hunting perch for shrikes.

For now, I’m back in Carden to have more shrikes in the hand during banding… they’re worth two in the bush, anyways. I’ll post more about juvenile banding and release shortly.

– Alisa Samuelson, LoyaltyOne Young Conservation Leader for 2017