[Tweeters] How do Cassin's Auklets work?

[Bob Boekelheide via Tweeters]

Hi, Steve,

I think accoustic surveys have been used in some burrowing seabird colonies, like with shearwaters, with uncertain success.  I suspect accoustic surveys to estimate an entire Cassin’s Auklet colony size would be fraught with problems.  Colonies are spread out over big areas, with nesting densities varying a lot throughout the colony.  Auklets may vocalize more in the pre-season, then get quieter after they lay eggs.  Their vocalizations vary within and between nights.  Weather doesn’t cooperate - it’s often windy.  Somebody would need to ground-truth at least some of the recordings.  Many of Washington's offshore islands (Alexander Island, for example) are difficult if not impossible to land on without creating havoc for birds and endangering lives.  

One method used on accessible islands is to estimate the total number of burrows in a colony, then determine what proportion of burrows are occupied by nesting birds (using endoscopes to peek into burrows), then multiplying the number of burrows by the occupancy rate to estimate the size of the breeding population.  That is how WDFW estimated the number of Rhino Auklets on Protection Island.

There’s more to a population than just breeding birds in burrows.  There are also young prebreeders, floaters, and unpaired adults that may or may not get counted, depending on the method.  The accoustic survey method might overcount these birds if they're really vocal, whereas the burrow occupancy method may not count them at all, since they’re gone from the colony during the day.

I’ll gladly leave the population estimates to the professionals…
Bob 



> On Jun 17, 2024, at 11:04 AM, Stephen Elston <stephen.elston at gmail.com> wrote:

> 

> Very interesting, Bob. Thank you for writing down all this information.   

> 

> I am wondering if anyone has tried to do a population survey accounstically. If these birds are consistent singers, it might be the case that one can perform a population survey by analysis of sound recorded at the nesting sites. Nowadays, there are sophisticated signal processing algorithms that can separate a great many sources.     

> 

> Regards to all, Steve

> 

> 

> On Sun, Jun 16, 2024 at 8:44 PM Bob Boekelheide via Tweeters <tweeters at u.washington.edu <mailto:tweeters at u.washington.edu>> wrote:

>> Hi, Tim and Tweeters,

>> 

>> I spent a few years studying Cassin’s Auklets at the Farallon Islands, so I’ll try to answer your auklet questions.  

>> 

>> If conditions are favorable, Cassin’s Auklets at the Farallones mostly feed krill to their chicks.  In less favorable years, they switch to eating a more diverse diet of larval fish and other pelagic crustaceans, along with occasional small squid.  They feed mostly in loose groups at the edges of the continental shelf, so they might fly considerable distances from their coastal nesting colonies to feed during the day.  Sometimes you see big feeding groups of them, likely if there is a patch of krill, but they’re usually more spread out.  

>> 

>> They fly back and forth to and from their colony every day, ideally not too far, but regularly 20-40 miles to feeding areas, often more.  A Cassin’s Auklet might travel 40-45 mph in fast flight depending on winds, so 20-40 miles doesn’t seem too far for them.  In poor feeding years they might have to travel much further to find food, or return smaller meal loads to their chicks, or else give up.  

>>   

>> They are totally nocturnal on land, other than of course during the nesting season when one adult stays in their burrow all day incubating their egg or brooding their young chick.  They leave their chick alone in the burrow at a fairly young age, so both parents can return food to the chick.  Their flights ashore to nesting islands occur well after dark, as they are sensitive to light levels even at night.  Because of predation, they are slow to come onshore during moon-lit nights, but on dark moonless nights they come ashore right away.  Sometimes they all come ashore in a giant wave, and sometimes they trickle in over a long period.  They seem to be able to locate things fairly well even on dark nights, so they must have excellent night vision.  Most departures in the morning occur well before dawn, but there are sometimes late departures that may end up in the belly of a gull or a Peregrine Falcon. 

>> 

>> When flying ashore, they usually fly in very quickly, plop down, get their bearings, and quickly make their way to their burrows.  They often collide with things on their way, including people, but almost always they quickly shake it off and keep going. They do everything they can to avoid predation by gulls, which nest nearby and lurk in the auklet colonies at night. The auklets dig their own burrows or else nest in rock piles or rock cavities.  Most burrows are about 2 to 4 ft deep, so once inside predators hopefully can’t get to them.  Breeding pairs are very faithful to their burrows between years.

>> 

>> Cassin’s Auklet adults have a nifty sublingual (under-tongue) pouch they use to carry prey to their chicks.  The consistency of the goo they carry in their sub-lingual pouch is kind of like shrimp cocktail, which they lap out to the chicks when they reach the burrows.  Meal loads with krill are mostly pink because of their photophores, whereas meal loads with fish are mostly gray fish chyme.  We randomly captured auklets flying in with pouches full of food and sampled their pouch contents. It’s quite amazing how large their meal loads can be relative to the size of the bird — a 180-200 g adult sometimes carried a 40-50 g meal load, or about 1/4 of their body weight.  They can cram a lot of krill and larval fish into their bulging sub-lingual pouch.  

>> 

>> Unfortunately many Cassin’s Auklet populations have been shrinking, between marine heat waves, El Ninos, predation, and who knows what.  The 50,000 auklets estimated nesting on Alexander Island by Speich and Wahl in the 1970s might be much smaller now.  But realistically, how do you estimate the numbers of a small seabird that only comes ashore at night on remote islands and then nests out-of-sight in underground burrows?  It’s a shot in the dark — ha ha!

>> 

>> The best thing about Cassin’s Auklets is their singing — imagine thousands of them chirping away on a windswept island in the middle of the night.  They scream their three-note songs while sitting in their burrows, repeating things like “LET ME OUT, LET ME OUT, LET ME OUT” and “IT’S ALL RIGHT, IT’S ALL RIGHT, IT’S ALL RIGHT,” over and over.  Totally wild!

>> 

>> Hope this helps,

>> Bob Boekelheide

>> Sequim

>> 

>> From: Tim Brennan via Tweeters <tweeters at u.washington.edu <mailto:tweeters at u.washington.edu>>

>> Subject: [Tweeters] How do Cassin's Auklets work?

>> Date: June 14, 2024 at 7:33:14 PM PDT

>> To: "tweeters at u.washington.edu <mailto:tweeters at u.washington.edu>" <tweeters at u.washington.edu <mailto:tweeters at u.washington.edu>>

>> Reply-To: Tim Brennan <tsbrennan at hotmail.com <mailto:tsbrennan at hotmail.com>>

>> 

>> Hey Tweets!

>> 

>> I've been plugging away at the Jefferson and Kitsap County year lists, and most recently made a trip to the coast, adding 8 more birds to the year list. This included some Black Swifts over a meadow behind a gift shop on the way up to the Hoh, and a few stray pelicans. 169 for the year in Jefferson was a Common Nighthawk over a clear cut (clearcut? Clear-cut?) off of FR-3000 the other night. 

>> 

>> The goal is two hundred species for the year. My bet is that I'll come up a little short of that, but have a great time trying. One thing that has been eluding me is some open-minded conversations about seabirds, and maybe more specifically, I am trying to understand Cassin's Auklets. A couple things I do understand about them. They are usually seen very far out from shore. Yep. The pelagic trips from westport head out far enough, but not into Jefferson. Repositioning cruises pass through Jefferson waters, but they pass through a lot of other waters, to my understanding, and might be a more extended trip than I'd be keen on doing.

>> 

>> So, I've researched a little, and come across an interesting fact. 50,000 or so Cassin's Auklets nest on Alexander Island, Jefferson County. And this is like... A mile off shore. They go out far. I understand this. 😄 But... Then they come back, yes? Is their return usually in full dark? Late in the day? It may be information that's hard to pull out, given that anyone with some sense, and a desire to see these birds would just hop on a pelagic trip, go a billion miles out, see them in any old county and call it a day. But if anyone knows a little more about how these birds work, I'm curious to hear more. Maybe they return via undersea tunnels, sporting transparent plumage? 

>> 

>> I've talked to one person who has kayaked to these islands (I'm not kayaking to these islands), and to a fishing charter that may be willing to do a trip out to some of these Jeffersonian Islands. I'm just slowly trying to extract teeth to determine. . . How late the boat might be able to be out there, and how late these birds return. This may be some really easy math, such as: "the birds come back after​ dark" and "the boat has to be back before dark", but it's been a challenge to get these two numbers. I'm not dumb enough to even think about pursuing this if it's a purely nocturnal endeavor, but. . . I'm just dumb enough to get to the bottom of this. 50,000 birds a kayak's paddle away seems too interesting to not even ask!

>> 

>> TLDR: How do Cassin's Auklets work? 

>> 

>> Auklets aside, this goes through Tufted Puffin habitat (yes, I know where to find them in Island and Clallam Counties, but thank you!) - I think it'd be a beautiful trip, regardless of any auklet goings-on. Feel free to reach out through my blog (jkcountybirding.blogspot.com <http://jkcountybirding.blogspot.com/>) if a trip like that would have your interest at all! If it feels like it would be worthwhile, that boat would hold six passengers. 

>> 

>> Cheers, 

>> 

>> Tim Brennan

>> Renton

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