Wakes on Nest Cam
One of the opportunities in designing a new loon raft was to investigate the threat of wake boat wakes on nesting platforms. After the 2020 nesting season was over, our nest camera caught the effect of a passing wake boat on two separate occasions. In one case (left photo above) the platform tipped to such a degree that an egg could have rolled out. On a second occasion (center and left photos) the wake washed through the raft, flooding it such that it could have carried an egg out of the nest.
Earlier that season, we did find a whole, undamaged egg at the bottom of the lake just below the platform. However because we had not yet set up the camera, we do not know if that egg loss was the result of a wake or a predation attempt.
Traditional Raft Experiments
Since the threat of wake boats has not been well documented, we decided to run some experiments both on the old PT platform shown above as well as the new rafts. Neither is immune to the damage from these tall wakes, but in the process we discovered some important ideas to improve the eggs’ chances on these, or any type of raft.
The first tests were done on the traditional PT wood raft previously photographed with our nest cam. We put two chicken eggs in the nest and asked a wake boat owner to throw a good wake at it. The eggs did not roll out or break. To begin, his wake was not as dramatic as the 2020 nest cam wakes, as he was concerned about damaging the shoreline.. Secondly, after 2020, we changed the siting and orientation of the raft to keep it as protected from wakes as possible– a tweak that appears to have helped. Finally, chicken eggs are not loon eggs. They are thinner shelled, smaller, and have a lower center of gravity. Given the same wake and nest bowl, a loon egg would probably roll out of the nest more readily than a chicken egg, but perhaps be less likely to crack on impact.
A third lesson learned from this test has to do with the amount of nesting materials and nest shape (see photo above). When we set the nest out at the beginning of the season, there was an old nest with a very deep bowl, but no other soil or nesting materials surrounding the nest, probably because they were washed out by last season’s wakes passing through the raft. Our plan was to return to add additional soil and plant material surrounding the nest, but the birds nested before we had the chance. In retrospect, that may have been a help. This is because during our test, when the wake passed through the avian guard, rather than pouring into the nest, it drained rather quickly around the sides of the nest and off of the platform. In addition, the unusually deep nest bowl kept the eggs contained. So while we prefer to leave nest building up to the birds, for the few cases where platforms are exposed to wakes, it may make sense to nudge the nesting materials to form a drainage ditch surrounding the nest bowl and the beginnings of a bowl that is deep enough that the eggs would not easily roll out.
Robinson Raft Experiments
Raft with outriggers (top row) and without (bottom row). In both cases the angle of tilt, causing the eggs to roll when hit by a wake, was significant. In both cases the raft resisted the wakes washing through due to its buoyancy. This reduces the chances that eggs would be washed out, although rolling is still an issue.
We then tested the new raft in an open area of the lake where it could be hit directly with wakes that were higher than in the first experiment. We fixed experimental outriggers to the raft to see if they could provide any additional stability. While the outriggers provided great stability in flat water and while towing the raft, they did not make a significant difference when the wakes hit.
That said, the new - both with and without outriggers raft behaved differently than the traditional one in that it did not appear to flood as readily because it is more buoyant (see above pictures).
One of the two chicken eggs did break from rolling and colliding with the other egg. Loon eggs differ from chicken eggs in that they are larger, have a higher center of gravity, and more mass, suggesting that they might roll more easily and with greater momentum. However, this vulnerability is countered by tougher shells. Therefore, while it is not possible to make a direct correlation between the damage to chicken egg and the fate of a loon egg, the broken egg does illustrates a potential danger for eggs colliding or rolling out of the nest when a platform is tilted to the significant degree that occurs when hit by a large boat wake.
Conclusions
The potential danger that wake boat wakes pose to loon nesting platforms was illustrated by the photographs of platforms being tilted and washed out by the wakes of passing wake boats- both as seen by our nest cam in 2020, and in subsequent tests. The cracked chicken egg suggests that there is a potential for loon eggs to be damaged by colliding with each other when the raft is rocked to such a degree. While we expected to see an improvement when we added outriggers to the raft, the stabilization was no match for the tall wakes generated by the wake boat. The experiments suggest that beyond siting the raft in a protected area, adequate nest depth, and the presence of drainage ditches surrounding the nest may be the most important factors to focus on in the short term.