Mountain Bluebird Season
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First nest box monitoring of the season.
For the last four years between April and August I have been fascinated with small vividly blue migratory birds - yes mountain bluebirds. During this timeframe they fly back to Alberta from their wintering grounds in the southern US and northern Mexico. It is a long way for these small birds to travel and their return to this area is specifically for nesting and raising new generations of mountain bluebirds.
Male and female mountain bluebird scoping out a potential home for the season despite late spring snow. (EXIF data f6.3, 600mm, 1/1250s, ISO250)
I was able to get out this week and do a nest box monitoring run to see if they have started nest building. The last time I was out was towards the end of April and I saw a number of mountain bluebirds, but with the changeable weather that included snow and cold spells - there was no nest building happening.
Mountain bluebirds return to the area almost a month before other species (especially the tree swallow) in order to secure the best nesting locations. It’s an interesting strategy that can have serious consequences if we have a late spring and insects are not plentiful. Once they get here their energy reserves are low and they need to build up strength for the nesting/breeding season.
Mountain Bluebird Advantage
Female mountain bluebird flying out of the nest box. (EXIF data f7.1, 600mm, 1/1250s, ISO 400)
In addition to arriving back to their nesting areas early, they have an advantage of being primarily a ground feeder and they feast off of beatles, grasshoppers and caterpillars as well they are able to capture flying insects mid air. They have the ability to hover above the ground and then dive to capture an insect once it is spotted. When insects are scarce (such as during a late spring) they can adapt and switch to eating primarily berries such as juniper or mistletoe. This adaptability makes them a more resilient species.
In contrast, tree swallows feed primarily in the air or on the surface of the water- flying open mouthed to scoop their prey on the fly. They can switch to berries or seeds when insects are scarce, but it is not their preferred feeding method.
Last year when we had a late snowfall in April, I was surprised to find a dead adult tree swallow in a nestbox. One of my primary resources for excellent information on all things mountain bluebirds and tree swallows is the Calgary Area Nestbox Monitoring Society (CANMS) and I found out that when this sort of late cold snap weather pattern occurs during the return of migrating tree swallows it can seriously impact their survival rate. Depleted energy stores and a lack of flying insects can make survival difficult during this timeframe.
Ant hill chaos reminiscent of how my work life felt some days.
This year we have had a very late start to spring with a lot of snow and cold temperatures. I was concerned about finding deceased tree swallows again and in fact 8 out of the 60 nest boxes had dead adult tree swallows in them. They will go into the nest boxes when it’s cold and often not have the strength to get back out. It’s a sad sight to see.
I also saw something unusual this year with two of those eight boxes containing a live adult bird along with the dead one. I didn’t think that tree swallows mated for life - they form bonded pairs for the nesting season, but not for life as some other birds do. When I looked up information about this situation I came up with two possible explanations. If a pair of tree swallows have formed a bonded pair before one of them dies then the other may stay in the nest box trying to establish the nest site - being somewhat confused that the other adult isn’t moving. An alternate explanation is that tree swallows are very territorial and fight over nest box locations - if one dies due to injuries then the other swallow may stay in the box to establish rights over the nesting site.
I’m not sure which scenario was in play, but it is sad to see these birds perish after such a long flight back to their nesting grounds.
This year I’ve applied the CANMS stickers which will hopefully prevent anyone opening the boxes or removing them during the nesting season.
2026 Season Off to a Good Start
On a more positive note, my first run of the season produced excellent observations about the mountain bluebirds with 27 out of 60 nest boxes showing nest building activity. I spent time observing mountain bluebirds gathering dried grasses and taking them into the nest boxes. The male and female stay close to the nest box during this phase, but only the female builds the nest - I suppose she has exacting standards on construction.
Female mountain bluebird gathering grasses for the nest. (EXIF data f6.3, 600mm, 1/1250s, ISO200)
In addition, I noted mountain bluebirds nesting in the far western end of the bird run which has boxes that I’ve not seen bluebirds claim over the last 4 years. We were even talking about relocating these boxes to more desirable locations, but I’m glad that we held out to see if they used the boxes.
I was also fortunate to see a male and female mountain bluebird feasting on caterpillars which made for some fun photography (it can’t be all work and no fun during a nest box run!).
Male mountain bluebird eating a caterpillar. (EXIF data f6.3, 600mm, 1/1250s, ISO200)
Lots of activity
In addition to observing mountain bluebird activity I like to spend time seeing what else has returned to the area and I was rewarded with a lot of activity yesterday. I heard the whirling sound of Wilson’s Snipes as they dip and dive through the air producing this unique sound with their tail feathers called winnowing. Both male and females make this sound, but males do it more frequently to warn off others trying to enter their territory and also to attract females.
Northern Harrier swooping in looking for prey. (EXIF data f7.1, 1/1250s, 600mm, ISO100)
Snipes are difficult to see as they blend in with the marshy areas they frequent and they are very skittish - taking flight at the slightest disturbance. We have snipes in the marsh behind our home and it is a delight to hear their sounds.
In addition to snipes I was fortunate enough to see a few different raptors including a Swainson Hawk, a Kestrel and a Northern Harrier doing aerial acrobatics as it came in low over a field looking for prey. I enjoy working on some of my photography skills (like panning) when I spot birds of prey in flight.
The Local Bird Pond
Eared grebes in the local pond. (EXIF data f7.1, 1/1250s, 600mm, ISO400)
I even made a stop at the local bird pond on my bird run to see what is nesting. There were a whole host of birds on the pond, but most were too far away to be positively identified. One pair that did stand out were the Eared Grebes which are odd looking birds with their glowing red eyes and golden feathery whisps at the sides of their heads. They are in fact called Eared Grebes because of these golden feathers which appear as part of their breeding plumage.
A couple of muskrats were sunning themselves in a marshy area, but my approach caused one to hop off the log and dip under the water.
Shaping up to be a Good Year.
I enjoy being in sync with the natural rhythm of the mountain bluebirds’ nesting cycle. Seeing these resilient birds return each year and go through the efforts of building nests and raising broods of new mountain bluebirds is a delightful experience. I’m looking forward to watching this year’s antics unfold as adults pair up and start the cycle all over again.
Are you seeing signs of spring and new life in your area? I’d love to hear about what you’re seeing this year in the comments below or reach out to me directly by clicking on the Connect With Me button.
Female mountain bluebird showcased against the rocky mountains. (EXIF data f7.1, 1/1000s, 600mm, ISO200)
I hope you’ll come back soon, share a cuppa, relax and enjoy more of my musings.
