“When Bonnie asked me whether Barbara and I wanted to have the Thursday Birders again this year,” Bill Simms began – and then paused before continuing. “It’s an important story to tell – we need to do it.”
When Bonnie introduced Bill for those who were attending for the first time, she explained that she met Bill in 2002 shortly after moving to New Mexico. Another Thursday Birder, when he learned where she lived, asked whether she knew Bill Simms – and discovered they were neighbors.
Bill began building and installing bluebird boxes on his property six miles south of Chillili in 1998, installing 18 the first year. Over the ensuing 23 years, he has kept perfecting the design and adding boxes. Currently he has 50 boxes – 3 more than in 2007 when I first visited with the Thursday Birders.
Bill, an geologist, has approached record-keeping for his boxes with scientific rigor, keeping meticulous records and submitting his nest box data to Cornell Lab of Ornithology’s Nest Box program. He usually provides us with a one to two-page handout with graphs. This year’s handout was four pages and has provided the backbone of this story.
Last year during the pandemic, the Thursday Birders were not meeting as a group, so we didn’t make our annual trek to his and Bonnie’s houses. I last wrote about our visit in 2016, shortly after the Dog Head Fire ripped through this area. (You can read about it here: Bluebirds and Hummingbirds – After the Wildfire – Forest Renewal in Action. As Bill began speaking, I knew I had to document 2020-2021 as well.
“Our bluebird season really started last September of 2020,” he started. “Despite little monsoonal rains, we had a generally successful 2020 season. We fledged 154 Western Bluebirds, which is above average for the past decade.”
By September, the Ash-throated Flycatchers that also use his boxes, had migrated south to spend the winter along the eastern and western coasts of Mexico and Central America.
The following graph documented at his weather station, and included in his handout, shows the extreme weather between September 4 and 11, 2020. On September 4 – 7, high temperatures were 92 – 93 F and low temperatures were around 58 F. On September 8 the high was 93, but during the night a cold front moved in and the temperatures plummeted to below freezing.
While it was cold enough to wear a parka and wool hat in Albuquerque,
more than a foot of snow fell in the east mountain area south of Chillili. Bill’s handout Bill stated that Albuquerque’s temperatures for the same period went from a high of 97 F to a low of 39 F – and that “The lows marked the coldest recorded temperatures for early September in more than a century and were accompanied by high, sometimes hurricane-force winds.” The precipitation totals on the graph reflect the amount of melted snow in his heated rain gauge (according to Bill, the water/ snow ratio being close to 12 to 1 means that it takes about a foot of snow to equal an inch of rain.)
“Initially we were not too concerned,” Bill told us, “because every winter the bluebirds have survived below-freezing temperatures with no ill effect.”
One of their survival strategies is to roost communally in family groups – and, if they don’t migrate, in the same bluebird box or other cavity they used for nesting. By crowding together in a single box, they use each other’s body heat to keep warm.
“I don’t know what made me check some of our bluebird boxes,” Bill continued. “When I checked the first one, I found four dead adult bluebirds. The next box I checked, I found four more.”
He then proceeded to check all of the boxes and continued to find one to three in several more boxes. No one from the Thursday Birders uttered a sound as he told this tale of woe.
“When we were done, we had counted 28 dead,” he relayed solemnly. “Even though our bluebirds had seemed to be in good health, we did not realize the toll the drought had been taking,” he concluded.
During the nesting period, the diet of Western Bluebirds is primarily protein-rich insects. While it wasn’t evident to most of us, the drought and lack of rain that characterized 2020 produced far fewer insects needed by the bluebirds. When the cold snap happened prematurely, the birds had not had enough time to build up their body fat.
“While we have far fewer boxes, we had the same experience,” Bonnie told us. Later that day Bonnie reminded me that when she had submitted her Climate Watch point counts for the Winter 2021 season (conducted on a day between January 15 and February 15), she and her count partner had observed very few bluebirds on her route in the same area.
While hummingbirds are able to survive cold temperatures by going into torpor, Bonnie maintained their food supply at her many feeders by bringing them in at night, and taking them back out in the daytime so they could continue to feed, even as ice was forming along the edges of the feeders.
By mid-September most hummingbirds still migrating through central New Mexico are juveniles. Since many birders in the Albuquerque area have reported they have far fewer hummingbirds visiting their feeders this year, other hummingbirds might not have had someone as conscientious as Bonnie attending to their food supply.
During that same period of time, there were reports of a large number of migratory birds, particularly those that are insect-eating, dying en masse as they were winging their way south through New Mexico during the near-freezing nighttime temperatures. It was so dramatic, the event was even covered by the New York Times.
The follow-up and analysis of many of the dead birds was done by a graduate student at the University of New Mexico and can be found here: http://news.unm.edu/news/unm-biology-student-documenting-unusual-nm-bird-die-offUNM biology students documenting unusual bird die-off.
“While we can’t be sure how many we lost, the number of birds that returned to the nest boxes in 2021 may give us an indication,” Bill stated. In past years, Bill has shared information with the Thursday Birders about how he has determined that birds will return to the same nest box they previously used. And, since they are year-round, they usually have started nest-building and egg-laying before the Ash-throated Flycatchers arrive from Mexico. “This year we only had five active nests at any one time, meaning around 21 pair presumably lost their lives in this event.”
According to Bill’s graph of bluebird box nest occupants from 1999 – 2021, in 2020 there were 154 bluebirds and 36 flycatchers. In 2021, there were 21 bluebirds and 54 flycatchers!
I asked Bill whether any bluebird pairs had a second nesting. ”I think there was one 2nd nesting,” Bill said in an email, “however it was not in the same nest. A flycatcher took over that nest after the fledglings left, and about the same time another nest had 6 blue eggs… So, I assumed that was the same bird that just fledged 5 chicks earlier … so, I think there was only one 2nd nest, if I’m right…
After I got home that day, I realized I had not seen any Western Bluebirds at the Simms, which is unusual for our visits. I contacted Bill who responded: “Bluebird sightings with so few birds are rare… saw a few just as I was checking nests earlier. The last bluebird fledged here around July 13 or 14, about a week before our get together…. Remember that we only had 5 adult pair, and 21 fledglings. We have not seen any around the house or around our ponds, which is pretty unusual… “
The data that Bill has been collecting, clearly demonstrating the effects of drier, warmer weather in our area on the viability of Western Bluebirds during freezing weather, provides a case study for climate change.
The monsoon rains that have blessed central New Mexico during July 2021 will hopefully generate sufficient insects to allow this year’s Western Bluebirds to thrive and return to nest in Bill’s and Bonnie’s nest boxes next year.