What factors influence loon nesting success?

loon with eggIdeal loon nesting sites are located in less developed areas where human disturbance is minimal. They are often located near the water’s edge on the leeward side of islands or peninsulas. However, many factors influence loon nesting success. These include:

  • Fluctuating water levels caused either by dams or storms events can interfere with nesting success. High water levels can flood the nest, while low water levels make it more difficult for loons to slip on and off the nest undetected by predators.
  • Human activity can reduce nesting success, driving loons off their nests. During the summer, when loons are driven off nest, high temperatures can kill the eggs. Boat collisions can separate chicks from their parents, as well as cause chick and adult mortality. Additionally, there are more egg predation events in developed areas because raccoon, skunk and crow numbers are generally higher in these areas.
  • Predation is an important factor limiting nesting success. Raccoons, skunks, crows, minks, otters, birds of prey, snapping turtles and even large fish pose dangers for either eggs or chicks.
  • High insect numbers can drive loons off nest. In Wisconsin, 70% of loons nests were abandoned this year because of black flies.black flies
  • Loons with higher mercury levels have less nesting success. High mercury levels interfere with egg development and decrease the number of hatched eggs. Lead poisoning can also interfere with the ability of loons to take care of their chicks.



Moberg, G. Loons abandon their eggs due to black fly outbreak in Northern Wisconsin. WPR(2014).Accessed July27th 2014.From: http://www.wpr.org/loons-abandon-their-eggs-due-black-fly-outbreak-northern-wisconsin.

Radomski, P.J., Carlsom, K., & Woizeschke, K. Common Loon(Gavia immer) nesting habitat models for north-central Minnosota lakes. Journal of the Waterbird Society 37 (2014): 102-117.

Schoch, N., Glennon, M.J., Evers, D.C., Duron, M., Jackson, A.K., Driscoll, C.T., Ozard, J.W. & Sauer, A.K. The impact of mercury exposure on the Common Loon (Gavia immer) population in the Adirondack park, New York, USA. Journal of the Waterbird Society 37 (2014): 133-146.

Spilman, C.A., Schoch, N., Porter, W.F., * Glennon, M.J. The effects of lakeshore development on Common Loon (Gavia immer) productivity in the Adirondack park, New York, USA. Journal of the Waterbird Society 37 (2014): 94-101



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