(Submitted by Susan Church)
The open grasslands and aspen stands at Glenbow Ranch Provincial Park (GRPP) provide ideal habitat for the cerulean-colored thrush Mountain Bluebirds (Sialia currucoides) and Tree Swallows (Tachycineta bicolor). Harbingers of spring, these birds return to GRPP as early as mid March and into late April.
Both of these bird species are secondary cavity nesters. And, they are attracted to the nest boxes which are built especially for them. The boxes have an entry hole of exactly 40mm – any smaller and the male Mountain Bluebird cannot squeeze in; any larger, and predating and non -native Starlings and House Sparrows can enter and eat the eggs. Historically, these two predatory birds dealt a blow to native cavity nesters.
There are several nest boxes throughout GRPP; installed, monitored, cleaned out and repaired by GRPF Stewards. The boxes are placed in suitable tracts of natural habitat, at exactly the right distance apart and facing south east.
In May, June and July, Stewards carefully monitor the boxes, checking for species, number of eggs, number of live young and number fledged. In 2012, we counted 5 Bluebird young in one nest box. By 2018, we had 15 nests and 72 fledged young. This year, despite a cold spring that impacted insect food supplies, 59 Bluebirds fledged from 12 nests, along with 200 Tree Swallows from 37 nests.
The rewards of our fence line walks include seeing 6 well-fed hatchlings in the nest and later in July, we watched these young Mountain Bluebirds in the aspens near by, learning to catch insects with their parents. This summer, we also saw a female Bluebird working hard to feed her young. Where was the male? We discovered it not far away, dead. Four of the five hatchlings survived and fledged with only one parent on insect duty.
The data we collect is sent into the Calgary Nest Box Monitoring Society. The GRPF team is one of 66 teams monitoring nest boxes in this area. Many on the other teams also band Mountain Bluebirds. This data is used to track longevity, migration, breeding patterns and more. All data is sent on to the North American Bluebird Society.
All this is done in the interest of Mountain Bluebird conservation – one of the largest grassroots conservation activities in North America.
Respectively submitted, Susan Church. Our team, also includes Gerald Kvill, Ken Wright, Clay Hunt and Shirley Leew.
For more information on this Steward project, contact schurch@shaw.ca.