Thoughts on bushtit numbers after the heatwave

I've noticed quite a bit of conversation in OBOL re the heat dome and resulting bushtit numbers.  Rather than comment in OBOL, I thought I'd offer my thoughts here so that a larger audience can see them if they want.  These are just thoughts.  I have no answers! 

First, every single banded adult at the eight nests survived the event. So, at least from that small sample, there wasn't any adult mortality.  In addition, many other banded birds have been seen since.  I'll have a better idea of adult mortality when the breeding season begins next month.  But even then, I won't know the cause if the % survival is lower than usual.   

We have found about 100 nests/year over the last 4 years in Portland.  I have never had a nest with dead nestlings before.  The only other time was just once in Arizona after a freak cold spell: 3 out of 4 banding-age nests contained dead nestlings.  The only surviving brood had 3 adults feeding at (and sleeping in) the nest.  

On the other hand, predation rates were exceptionally high this year in Portland.  Personally, if there is a dip in bushtit numbers, I would expect that had a greater effect on the population than the heat dome, given that the heat came very late in the nesting season.  

Bushtit numbers in the winter are hard to come by.  As they are in large and mobile flocks, you either see them.....or you don't.  Many CBCs miss bushtits.  But that doesn't mean they aren't there!  I think the best way to get an indication of the robustness of a population is to count flock size.  Not estimate.  Count.  That means catching them as they cross a street or from tree to tree and counting them as they cross.  Big flocks in winter=healthy population.  

The problem is the occasional small flock doesn't mean much.  This November and December, I found the same bird in both a monster flock of >50 and messing around for over an hour in a smaller flock of 10.  So....she's was doing both.  I think if you go out often and see only small flocks of <15 birds, that may indicate a problem.  

The heavily-feathered bushtit nest is great at insulating against cold.  But it also serves to protect against heat.  I did a short study in AZ several years ago and found that the interior of a bushtit nest stays at a reasonable temperature even in full sun on a very hot day when the exterior nest surface temp rose above 120 degrees.  In Portland this year,  WT 12---the 3-bird nest that lost all 6 nestlings during the heatwave---was a small nest with very little insulation.  It was mostly in the shade, BTW.  The one nest with eggs during the heatwave was a pretty bizarre nest (the 3rd nest for the pair that year) with uncharacteristically thick sides and many feathers.  Perhaps that saved it?  Who knows.  It was also partly shaded as were most of the nests at that time.  

One more point:  Nests that survived were  significantly closer to water.  Water is essential to prevent dehydration which is the primary cause of death in the heat for birds.  We (Amit Gordon, Ian Connelly, and I) wrote all these observations up for publication and it is currently in press in The Wilson Journal of Ornithology.   

Hope all that is of some interest!  Comments and additional ideas welcome.  

What is it about bushtits??

I am often asked "what's so interesting about bushtits?"  The answer to that is "it would fill at least one long book."  And I am in the process of writing it.  In the meantime, I thought some of you may be interested in seeing a very brief list of some of the odd, uniquely bushtit, behaviors I have seen.  

First you need to know that bushtits live in tightly knit family flocks of from 10 to 15 birds that combine with other flocks as the breeding season winds down.  During the winter, flocks became hard to find because they travel over several flock home ranges. Combined winter flocks may be huge.....even this year after the heat event, we often ran into a flock on Reed campus that had at at least 50 birds, some of whom were old friends of ours.  

The family and extended family flocks are maintained throughout the breeding season.  And that's what makes bushtits truly unique.  Although pairs (or more than a pair) maintain a weakly defended area around the nest, flock members frequently visit each other's nests and hang out when not at their own nest. They all know exactly where all the flock nests are and who is where and what they are up to.  They even seem to have "best friends" or birds they are seen with frequently and nest near.   

That's the skeleton version as there's much more complexity to the story!  But it's enough for now.  Here's some of the fun stuff I have seen over the years.  Teasers, as you will.  BTW, none of these observations would be possible without color-banded birds.  

1. Musical nests (nest ownership exchanges -- and back):  One day XXXX and YYYY will be building at nest and the next day they are nowhere to be found.  Instead it's ZZZZ and WWWW.  Sometimes XXXX and YYYY may return, and ZZZZ and WWWW will be building a new nest elsewhere.  I'm not the first one to observe this.  Steve Ervin did as well in CA in the early 70s. But he wasn't focused on that aspect of bushtit behavior so he didn't follow up on it.  

2.  Bushtit cads:  Males who cavort with a neighboring female even while he has a nest elsewhere.  I've detailed one situation like this from last year.  There are more.  

3.  Deadbeat dads:  Males who not only cavort, but takeover a nest while their first mate handles incubation alone (both male and female usually take turns).  They then desert the 2nd female to return to being a dad at the first nest, leaving the 2nd female to fend for herself.  

4.  Extra birds ("helpers"):  These are usually males and usually there's only one.  But it varies; in AZ I did have one nest with 6 males and one female. There's a good story in that re how and why this happens!  Hint: is it really helping.....?

5.  More than one pair at a single nest:  two males and two females have been observed.  More on those complicated stories later.  

That's a smattering of the convoluted shenanigans bushtits can get up to.  They seem a cheery and cooperative little bunch, don't they?  But I believe it's actually competition that drives the system.  At least that's what I think as I learn more about them over the years.....stay tuned!       

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.              

   

Blogging woes and bushtit funny business

I am a bad blogger.  I will readily admit that.  I start the field season fresh and enthusiastic and fizzle out as the season progresses.   I have a pretty good excuse:  as I find more and more nests (about 100 each year the last 3 years) I get side-lined into my research and am too exhausted at the end of the day to sit down and write about all the cool things I saw.  If I could clone myself, I'd be in business.  But that's not happening.  

So, once again, the bushtit breeding season looms and, once again, I am faced with the excitement of sharing the excitement----and the reality that I will do a pretty bad job of it.  Ah well.   

In this lull before my 2022 research in Portland and during my sojourn in the New England winter,  I'd like to share a few highlights from last year's bushtit research that never made it into the blog.  

The first is what was happening at Nest 28 and Nest 20 near the border between Sellwood Park and Oaks Bottom.  

Nest 20 was in a monster pine tree on a very (very) steep slope.  When we first found it, it was being built in the "lower" branches  (30 or so feet up) in almost the exact location as nests in 2018 and 2019.  Same branch.  Same awkward position for watching.  The builders this year were W-X -- a male who hatched nearby in 2019 and was rebanded as WUUX -- and an unbanded female.   WUUX had been around in 2020, and we assumed he had a nest somewhere, but we never found it.  His sister (also originally W-X) nested that year in a tree not far from her natal nest as well.  (That throws a bit of a monkey-wrench into my assertion that females don't hang around, but disperse.  I'll just ignore that for the moment...).

[BTW, both W-X female and WUUX were kids of PYLX who, if you've read some of the earlier posts, you may recognize as the second male at Nest 11 in 2018.]  

A week after finding Nest 20 we found Nest 28 in a pine over-hanging a very steep slope just on the edge of Sellwood Park near the parking lot.  It was almost finished and was being built by an unbanded male and a female (eventually banded as XYYY and XEEE).  It was about 200 meters east of Nest 20.  Not far. But not all that close either.  

Neither nest was in a particularly favorable position for climbing up and banding the nestlings, so we put them both in a low priority category and watched them infrequently until.......

......very interesting stuff started to happen. On several watches (which later turned out to be during egg-laying when the female mates) WUUX showed up at Nest 28 chasing and following the female relentlessly while her male sort of fluttered around after them. WUUX even visited the nest several times...peering in and then taking off again after the female.   This would go on for over an hour and seemed to be almost a daily occurrence for a week.  WUUX was still seen at his own nest on and off, where that female was also laying eggs.  (It certainly does beg the question:  what was the female at Nest 20 doing while WUUX was off dallying with the female at Nest 28?  Huh.  Interesting.  While the cat's away....??)

After a week of this foolishness, WUUX was back at Nest 20 behaving as a dutiful dad: sharing incubation duties with the female until the eggs hatched and they began to feed the nestlings.  Which is when Male #2 (banded as RRRX) showed up and began to help.  Because of the difficult position of the nest, we weren't quite sure when he arrived but by the time we did see him, he was merrily feeding as if he belonged there.  And WUUX was perfectly fine with it.  

Because of WUUX's frequent visits Nest 28, in particular, suddenly became a nest of great interest.  Was it possible that the nestlings that eventually hatched were not just those of XYYY?  Was it possible that WUUX has also managed to mate with XEEE and was therefore also a dad there?  It seemed very possible.  And now that it was possible, we needed to get to those kids and get blood samples for DNA as well as blood from both XEEE and XYYY.  Remarkably, we already had WUUX's blood from when he was a nestling.  I say remarkably because in most cases where there is an interloping male chasing a female at a nest, he is unbanded and we have no idea where he came from. And we never get his blood for paternity analysis.  So this was a golden opportunity.  We think we know what WUUX was trying to do.  We know when he was trying to do it.  And, most importantly, we know who he is and we have his blood already.  

Perfect.  As long as we can also get blood samples from the parents at Nest 28 and from the kids we would know if he had been successful.    

But that nest.....Nest 28.......it was a challenge.  It seemed a risky business to climb up to it.  Nonetheless, we were determined.  We dragged in a long, heavy ladder and found 2 limbs close enough together to lean it against at an awkward angle of maybe 20 degrees.  I crawled up very cautiously and looped a rope around the branch the nest was on and pulled it carefully towards me.  This is when a hanging, enclosed nest is a big help.  No matter how much it swings or tilts, those kids can't fall out.  

No problem.  We got to the nest.  But the kids were a few days too young. In the end we had to wrestle the ladder back down and up again twice before the nestlings were "ripe."  Then it was a simple matter to band them and take blood samples.  

That same day we successfully banded the kids two of us stayed behind and set up a net to get samples from mom and dad.  This was also a bit of challenge because there was no good place to set up the net.  My assistant finally sat under the net with tape of begging nestlings and the male magically hopped right into the net and we had him.  Right before the nest fledged, we got samples from the female too.  Eureka!   A "complete set!" (says the vampire).  

Now I also think it's very possible that RRRX was a father at Nest 20 along with WUUX, especially since WUUX was frequently absent and misbehaving at Nest 28.  But we'll never know because that nest was truly impossible to reach.  We did, however, get a blood sample from RRRX and hope to find out later if he is somehow related to WUUX.  That's yet another possibility......that males who show up to help are helping close relatives.  

We shall see....only the DNA holds that answer. Until then, the mystery remains a tantalizing mystery.