Comments in the YouTube chat show some misconceptions about loon anatomy, particularly about anatomical structures lacking in loons. Here are some features found in a wide range of birds but not found in loons:
The Crop – A crop is an enlargement of the esophagus that allows storage of food prior to continuing to the stomach (more properly known as gizzard or ventriculus). It allows birds to gorge on food where it is plentiful and then digest the food when they’ve moved to a safer location. It also does some predigestion preparation and may be useful in combating harmful bacteria. Omnivorous and herbivorous birds are most likely to have a crop, and to have a well developed, complex, lobed crop. Loons are nearly exclusive fish eaters (piscivores) and that may have something to do with why they don’t have crops. Penguins are another piscivorous bird without a crop. Cormorants have a rudimentary crop, which is nothing more than an extra wide section in the esophagus.
Brood Patch – A brood patch is a featherless area on the underside of an incubating bird. It usually has a number of blood vessels near the skin and it aids in heat transfer to the egg. Brood patches typically are only present during breeding season. Loons seem to manage well without a brood patch. Exactly why loons don’t have a brood patch is unknown but it might have something to do with waterproofing. A loon’s feathers form a watertight envelope and they can control buoyancy by expanding and contracting their feathers. Perhaps a brood patch could compromise the watertight seal.
Egg Tooth – An egg tooth is a protuberance used by the offspring of egg-laying animals to break through the eggshell. On birds, it is normally found on the top of the upper mandible and falls off within a few days after hatching. Loon chicks can do well without an egg tooth. Their bill is well formed at hatch time, and although it isn’t as sharp and dagger-like as an adults, it’s still more than adequate for punching a hole in the eggshell. Loon chicks are precocial, meaning that they are fully developed and ready to jump in the water and swim with their parents the same day that they hatch. They are well past the stage where they would need an egg tooth.
Our Loon Cam 2 pair has so far had an uneventful incubation process. These two loons just don’t seem to present the non-stop drama of the Loon Cam 1 pair. But that’s good for us; we don’t need the stress of anxiety. And it’s good for the loons; they can concentrate on taking care of the eggs.
Now that the eggs are barely more than a week away from hatching, let’s see if we can nail down the hatch times. We only have two years of to-the-minute data that we can use but they are in close agreement. If the loons hold true to form, we should be able to accurately predict hatch times within a few hours. Incubation periods for egg 1 average 27 days and 13.5 hours. That would put this year’s first egg hatch at 5:30 AM on Thursday, July 9. Egg 2 is a little tougher to predict because only one egg hatched and the timing suggested it was egg 1. So, going by the one known incubation period for egg 2, we would expect the second egg to hatch around midnight (12:00 AM, July 10).
Taken together, these two loon pairs have a very similar and consistent egg-laying-incubation-hatch record. The two eggs are laid about 60 hours apart, on average. Incubation is very sporadic until the second egg is laid. The time from laying to hatch is about 27.5 days +/-10 hours for the first egg and a little over 25.5 days for the second egg. The result is that the eggs hatch about 1 day apart. Because this year the first egg was laid late in the day (June 11) and the second was laid early in the day (June 14), there’s a slight chance they will both hatch on July 9, one predawn and one well after dark.
Now that the Loon Cam 2 pair is almost half-way through its incubation period, it’s time to clear up some confusion about the history of the pair and reading the bands on the loons’ legs.
In 2016, intruding loons interfered on this territory enough to cause a nest failure. Without a nest or chicks to defend, the bond deteriorated between the pair, which had been together on the territory since 2013. The rest of the 2016 season was chaos with no clear resident pair.
In 2017, the current male and female emerged as the new resident pair and immediately began nesting. They successfully hatched and raised a chick, which suggests that both of these loons probably had previous nesting experience on other territories. We know that the male did because he was banded in 2006 on a nearby territory on the same lake. We banded the female this same year (2017), so we don’t know her previous history.
Both loons have two bands on each leg.
Female left: A white stripe band (white band with a dark stripe through the middle) over a blue band
Female right: A silver band (the aluminum USFWS band with a unique number) over a yellow stripe band (yellow band with dark stripe in middle)
Male left: A red band over a white band
Male right: A silver (aluminum) band over a red dot band (a red band with a white dot in the middle)
And by one band being over the other, it means it’s the closer one to the location the leg is attached to the body. It’s easy for people to mess that up when the loon is sitting on the nest. Closer to its rear end might be a better way of putting it. The standard practice is to put the silver band on the right leg when the loon is banded as an adult and on the left leg when the loon is banded in its hatch year.
This territory has been monitored since the mid 1980s. The nest site was originally on an island but new development in the 70s and 80s caused a deterioration of the nesting habitat that resulted in increased terrestrial egg predation. The raft was added in 1992. Since then, the average annual chicks surviving rate has been 0.643, which is higher than the statewide average. This pair has fledged 2 surviving chicks in the three years it has been on territory (0.667).
Now that the loon cam season is complete, we can review the events we witnessed over the past two months and see how they fit with the conventional wisdom of loon behavior and ecology. We think we know so much but we are constantly reminded that there is always more to learn. Here’s a few things that added to or reinforced our knowledge base.
Nesting loons have more ways of losing eggs than we thought. Disappearing eggs are nothing new. It’s more common than you might think. Loons can accidentally knock an egg out of the nest. Boat wakes can wash an egg out of the nest. Some predators can carry eggs away from the nest (raccoons and eagles are good examples). We’ve even had some suspected human thievery. But a loon accidentally burying an egg wasn’t on our radar until the Nest Cam #1 loons demonstrated that it could happen. Had we known that there were two eggs on the nest but didn’t have the camera to witness the occurrence, we would have listed the ultimate fate of the egg as unknown, or possibly unknown predation if a biologist had a chance to survey the area shortly after the egg disappeared.
An egg in the middle of the incubation phase can remain unattended for 10 hours and still remain viable. The Loon Cam #2 loons demonstrated this. This is just one data point and certainly doesn’t mean that all eggs would remain viable. Had the day been sunnier and warmer, or much cooler, the outcome may have been different. But each new observation narrows the unknown range.
Predation by eagles is increasing in NH. This isn’t really new, nor is it unexpected. In fact, LPC Senior Biologist John Cooley recent published a paper concerning this in the Wilson Journal of Ornithology. But watching it happen live on Loon Cam #1 certainly left an indelible impression on the minds of the viewers. And it demonstrates that even the smallest loon pond can be subject to predation by an expanding eagle population.
Loons have a wide variety of nest sitting schedules. The literature says that female loons are more likely to do the nighttime incubation and they tend to invest more time to incubation as the hatch date approaches. Observation of the Loon Cams over the past few years show that this is not always the case. The male on Loon Cam #1 does a lot of the nighttime sitting and he is consistently on the nest during hatch, whereas the female has been known to take off for extended periods when hatching is imminent. All pairs we have observed seem to have a very fluid schedule. As soon as we start predicting who will be on the nest at a certain time, the pair will call our bluff.
It all adds to our knowledge base and reminds us that we don’t know everything and sometimes we don’t even know what we think we know. Here’s looking forward to next year’s humbling lessons from the Loon Cam loons.