Without a doubt, spring arrived early this year. With wonderfully warm, sunny weather earlier in the month, the plants that time their flowering by temperature and not by length of day got an early start this year. We have been enjoying their blossoms for several weeks.
The magnolias on the Riverview Hospital grounds in Coquitlam are now at their most magnificent. And not far away, at Colony Farm Regional Park, beautiful mountain bluebirds are touching down to rest and feed for a few days while working their way further north to nesting areas.
Similar to the colourful lazuli buntings that arrive at Colony Farm Park in late May to nest, mountain bluebirds are another bird species that has a remarkable sky-blue colour. In the case of mountain bluebirds, the males are almost entirely a stunning blue while females are a more drab greyish blue with a splash of very pale red on the breast.
Within Metro Vancouver, Colony Farm is a hot spot for mountain bluebird stopovers every spring. Reliably, they show up in late March and, with luck, can be seen into early April. They migrate from Mexico and the southern U.S. to fly as far north as Alaska to nest - as their name suggests, they do so at higher elevations in the mountains. While their main migration route is further inland, there appears to be a small population that follows a coastal route.
Somewhat larger than a song sparrow, mountain bluebirds can be a challenge to see even at Colony Farm as they are never abundant. One recent spring, a group of 40 was observed by delighted birders but, more typically, mountain bluebirds number a dozen or fewer.
Mountain bluebirds are closely related to the western bluebirds that nest in the Interior of B.C. Both species are secondary cavity nesters, which means they must rely on finding natural cavities in trees as their small and delicate beaks are not well suited for drilling into wood.
Decades ago, western bluebirds nested in the Lower Mainland but the arrival of starlings, which compete with them for nest sites, led to their disappearance. Starlings, a species inadvertently introduced from Europe, are more aggressive birds that also nest in cavities. The worrying decline of western and mountain bluebirds wherever starlings appeared led to the introduction of nest box programs along "bluebird trails" throughout the southern Interior. These nest boxes, installed on the tops of fence posts and maintained by volunteers, provide an abundance of nest sites for them and nest box programs have helped stabilize bluebird populations in the Okanagan.
The nesting habitats of mountain and western bluebirds overlap only in the southern Interior as western bluebirds do not migrate further north. Under natural conditions, these birds compete for nest sites in burned-over, lightly-forested areas where the decay of fire-damaged trees creates the cavities they both require. A study recently published in the journal Science has shed some light on how mountain and western bluebirds compete for nesting sites over several generations.
In areas where the nesting sites of mountain and western bluebirds overlap, mountain bluebirds are typically the first species to take advantage of post-fire habitat as they are more likely to disperse and search for new habitat areas. After a few generations, western bluebirds arrive. These birds are more aggressive than their mountain counterparts and usually force them out of the nesting area in a few years.
What scientists discovered in western Montana, where the two species overlap, is that the first few generations of male western bluebirds are extremely aggressive but they tend to lose this trait over a few generations. This helps to ensure western bluebirds will successfully eradicate mountain bluebirds.
Bluebirds lay clutches of eggs that range up to 10 in number. These eggs hatch asynchronously (one after the other, a day or so apart). Thus, when food sources are scarce, only the first few hatchlings will survive. The scientists discovered the most aggressive male western bluebirds were those that hatched first and that, when competition for nesting sites is high, more male birds hatch first.
This research suggests environmental stress can alter the sex of eggs, likely by increasing the level of the hormone androgen in the nesting females. It's an interesting example of how the species composition of an ecological community can be affected by hormone levels in nesting females.
The mountain bluebirds found at Colony Farm Regional Park are seen there only in the spring; they apparently follow a different route south when the time comes to return to their winter habitat in late summer. Birders report they are most likely to be observed in the fields north of the main access road to the park, Colony Farm Road, just off Lougheed Highway in Coquitlam. If you want to catch a glimpse of these beautiful visitors to Colony Farm Park, the best time will be in the next week or so.
Elaine Golds is a Port Moody environmentalist who is conservation/education chair of the Burke Mountain Naturalists and member of the boards of the Colony Farm Park Association and the Port Moody Ecological Society.
