Volunteers have recorded what they found in every box, every spring, since 1991 — more than three decades of nesting data around Henry's Lake. This page gathers what those records, paired with the area's weather, reveal about the birds and their changing seasons.
Henry's Lake sits at nearly 6,500 feet, and the bluebirds nest right at the edge of winter — May nights still drop to freezing and the snowpack often lingers into spring. Across the fifteen years with complete counts (2012–2026), spring weather leaves a modest fingerprint on nesting: snowier Mays tend to bring somewhat fewer bluebird fledglings, but no single weather measure dominates and the year-to-year swings are large.
The clearest signal in the record is the contest between bluebirds and tree swallows for the same boxes. Warmer springs tend to favor swallows, which take a larger share of the boxes, while bluebird box use stays roughly flat. And the balance has tipped sharply toward swallows in the most recent seasons — from rough parity through the 2010s to swallows holding far more boxes in 2025 and 2026.
Snowmelt timing sets when the ground opens up and insects emerge — the start of the season. The Island Park SNOTEL station beside the lake has measured the snowpack daily since 1982: the snow melts out between late April and late May (median around May 10), swinging a month from year to year. That variability shapes when each season can begin, though across the full record its link to how many boxes each species claims turns out to be weak.
The chart below plots how many boxes each species claimed against that spring's warmth. As Mays get warmer, tree swallows tend to take more boxes, while bluebird use stays roughly flat — so warm springs seem to hand the extra boxes to swallows rather than hurt bluebirds directly. It's a tendency, not a rule (the points scatter a lot), but it points the same direction as the recent swallow surge.
These are modest tendencies, drawn from the fifteen years with complete counts — real patterns worth watching, not strong or proven effects. The clearest, most reliable finding is simply that tree swallows have taken a growing share of the boxes in recent years.
Mountain bluebirds are slowly disappearing across the continent. The North American Breeding Bird Survey estimates the population has fallen about 1.55% a year — roughly a million birds lost since 1970, leaving around four million today. The decline has been sharper recently: independent surveys put the drop at 26% (Breeding Bird Survey) to 34% (eBird) between 2007 and 2021. The species is also considered highly vulnerable to a warming climate — under a +3°C scenario, more than half of its summer breeding range could become unsuitable.
Against that backdrop, one region stands out: Idaho, Montana, and Oregon have stayed relatively stable while the broader population has slipped — and long-running nest-box efforts are part of why. The Henry's Lake project sits squarely in that stronghold. For more than three decades it has provided steady, maintained nesting habitat exactly where the species has held on. The main pressure here isn't a regional collapse — it's local competition with tree swallows for the boxes, which the long record lets us actually watch and manage.
A note on what the boxes can and can't do: nest boxes provide safe nesting sites, but they can't offset range-wide pressures like climate change. The value of this 35-year record is that it documents one place where bluebirds are persisting — and gives a rare, box-by-box look at how weather and competition shape that persistence.
