The deadly heatwave of 2021

No recap of the 2021 bushtit field season can fail to omit the effects of the unprecedented heat wave on bushtit nestlings.  And it wasn't good news.  It was, in fact, quite sad.  And informative.  Unfortunately.  

In late June, a "heat dome" settled over the Pacific Northwest for 3 interminable days.  It was record-setting and completely out of the range of normal for the area.  Completely.  Each day the temperature climbed.  By the 28th of June it was 116 degrees in the shade.  Walking to the grocery store from my house -- only a 5 block trek -- felt risky.  My daughter, her partner, and their cat joined us in my 800 sf house which we tried to cool to barely acceptable with 2 ACs.  Even so, we had to partition the house into one small space, leaving the rest of the house to bake.  We all became vampires...avoiding the day and going out only at night for "fresh" 100 degree air and short strolls around the neighborhood.  

But what of the bushtits?  How were they faring?  It was the tail end of the field season and we had only 8 active nests.  One of them was close to fledging age.  One was still incubating.  The other 6 had nestlings....some very young, some older.   One of these was a nest (WT 12) we were particularly interested in as there were two males and one female.  All three birds had built and incubated and were now feeding.  We were, understandably, anxious to get blood samples from the nestlings once they were old enough.   Were both males co-dads??  It seemed highly probable.  So that was the only nest we kept tabs on for those 3 days.  One of us would head out at dawn, watch it for 30 minutes in the 90 plus heat, and then crawl back into whatever cool cave we had devised for ourselves to wait out the day. 

By the 29th the heat had abated somewhat so we set out to check the 8 nests we had.  I won't get into the all the sad details of what we found.  I'll just summarize:  

One nest had been torn apart by predators, the contents most certainly devoured.  That's not unusual.  Another had fledged prematurely and a grisly fledgling corpse was hanging from the entrance -- sans eyes and brain -- apparently entangled in the artificial poly the parents had used to line the entrance.  Ok.  Gross, weird........and huh???

Two others were silent and when we opened them, contained dead nestlings.  The adults were no longer even in attendance.  (We did, I might add, relocate every single adult with an active nest during the heatwave and could verify none of them had perished from the heat.)  

Happily, 3 nests had survived:  one still had eggs and the other 2 were feeding kids, although we were to later discover that only some of the nestlings had survived in each.  And only one egg hatched from the nest with eggs.  So even those nests had not survived unscathed.   

By far the saddest result of the heatwave was at WT 12 -- the nest we had such fond hopes for.  When I arrived to watch it at 6am on the 29th, all 3 adults were bringing food to the nest.  That was encouraging!  But it didn't take long for me to discover the sad reality.  Yes, they were bringing food in, but they were also bringing it out.  It was clear that whoever was in there was no longer capable of eating.  But could they still be alive?  I rushed home to get some sugar water thinking that a bit of that might revive the nestlings and save their lives.  (Bad science, but sometimes I just can't help it.) But, alas, when we opened the nest we found 6 tiny dead perfect nestlings....smaller than they should have been for their age.  They must have died not long before given the behavior of their parents.  So sad.  We collected the little bodies to take samples from the livers for DNA. 

As we encounter more of these catastrophic heating events, most certainly due to human-mediated global climate change, local birds and other animals will no doubt be affected as were the Portland bushtits.  In fact, it's highly likely that other breeding birds were impacted in a similar way during the 2021 heatwave.  It was only the fact that we were already closely monitoring bushtit nests, and have been for many years, that we were able to observe the effects of the heatwave on them and compare that to previous years.  

A sad end to the season and an ominous warning for the future.