Common Loon Mortality

                                                                       Common Loon 

The population of Common Loons in Canada has declined over recent years.  In this post I will discuss a relatively recent case of loon mortality, followed by a general discussion.

The loon family, Graviidae, is one of the oldest avian families.  We in Canada are proud of our loons and consider them as symbols of the wonderful wilderness which is one our our treasured resources.  We think enough of this species to immortalize it on our coinage.  Loons breed on our northern lakes and we are all delighted to hear their calls and yodelling as they feed and raise their young.  They winter off our ocean shores and southward only to return the next spring to the same lake when the ice is barely opened up.  Banding records reveal that they live for 20 to 30 years and it is thought that they mate for life.  

Loons breed first at the age of 2 years.  The nest is built by both adults very near the water's edge on an island or shoreline hidden by vegetation.  The nest itself is a mound of reeds, grasses and twigs and is often reused year after year.  Two eggs are laid and are incubated by both adults.  The young hatch after 24 to 31 days and leave the nest within 1 to 2 days.  They learn to swim and dive after 2 to 3 days on the water.  Both parents feed, protect and care for the young.  We have all seen the small chicks riding on the backs of the adult birds. 

Two years ago a friend and I were working on a plant survey in the Kennedy Lakes area of New Brunswick and came upon the remains of a deceased bird.  A photograph of that bird is shown below.  CAUTION, please scroll down if you do not wish to see it.  The remains were collected and submitted for examination.  

                                                Remains of Common Loon  [E Mills Photo]

The autopsy was conducted by Andrew Sullivan, NB Museum, and identified the remains as that of a Common Loon.  It showed two levels of trauma.  The first, fractured sternum and furcula (wishbone) had been sustained some time before and were partly healed.  See photo below.  The second traumatic event had obviously been lethal.  There were gun pellet holes in the pelvis which were not healed.  This individual had obviously endured two levels of pain and suffering.  The first could have been from a collision while in flight and the bird was recovering and functioning from that.  It could also have been caused by a collision with a boat.  The second was probably accompanied by significant additional soft tissue damage which was enough to end the bird's life.  The fact that it was on land in a wilderness area may mean it had been trying to care for young or that it crawled on shore to die.  Whatever the circumstances, it was a painful,  traumatic event caused by a human.  That is inexcusable human behaviour and whether it was a trigger-happy teenager (or adult) or a duck hunter who wasn't careful about the species he/she was shooting, it just should not have happened.  

 Furcula of Loon Showing Healed Fracture  [Andrew Sullivan Photo]

The loss of this adult loon resulted in the breakup of a pair of loons that may have been nesting on that lake for many years.  It may have resulted in the death of that year's chicks.  It certainly upset the ecological balance of that lake.  We humans must be more mindful of our actions and how seriously we can (and do) negatively influence the environment and its animal and plant species!

Relevant Common Loon mortality studies have been conducted in Maritime Canada and New England.  These reveal some interesting facts.  The Maritime study (Daoust 1998) looked at 31 moribund or dead Common Loons from the 3 Maritime provinces.  Eight of these birds were in good body condition and died acutely by drowning or trauma.  23 of the birds were in poor body condition and died of chronic lead poisoning, respiratory mycosis, or oil contamination of their plumage.  The poor body condition was studied further and these birds also had high numbers of intestinal trematodes and significantly higher levels of total renal mercury.    

The New England study (Sidor 2003) examined 522 dead or moribund Common Loons taken from the New England area.  They found the causes of mortality differed significantly in breeding and wintering habitats.  Wintering adults died mainly of trauma and infection and had poorer body condition than breeding loons.  In breeding adults lead toxicosis from ingested fishing gear accounted for almost half of all mortality.  Direct anthropogenic factors accounted for 52% of loon mortality in that study!  They also studied mortality in loon chicks and they could identify that infraspecific aggression (from one loon chick to another) caused 25% mortality and other causes of trauma were responsible for 32%.  

So, considering the Maritime study, humans were responsible either directly or indirectly for much of the mortality.  Eight out of 31 cases were caused by drowning or trauma.  Humans were not responsible for all of that but certainly caused some of the trauma as in the case cited above.  23 out of the 31 cases had lead poisoning, respiratory mycosis or oil contamination.  Humans caused all the lead poisoning and the oil contamination.  We are looking really bad here!  Those birds in poor body condition had toxic levels of renal mercury.  Humans again!  What is not mentioned here as well is poisoning from PCBs which can also be a factor.  The New England study showed human causes in 52% of the loon mortality.  

The picture as presented by the case cited above and these studies is bleak.  Humans are a significant cause of loon mortality.  There is no easy way to look at this without putting the blame squarely on humans.  We must change our behaviour and we must continue to clean up our environment.  The Common Loon is perceived as a regal representative of our wilderness environment.  We have not protected it properly.  We can and must do better.

                                                     Common Loon on Canadian Dollar Coin

 Reference:

Daoust PY, Conboy G, McBurney S, Burgess N.  Interactive mortality factors in common loons from Maritime Canada.  J Wildl Dis. 1998 Jul 34(3) 524-31.

Sidor Inga F, Pokras Mark A, Major Andrew R, Poppenga Robert H, Taylor Kate M, Miconi Rose M.

Mortality of common loons in New England, 1987 to 2000. J Wildl Dis. 2003 Apr  39(2): 306-15.