Mystified by the Marbled Murrelet

TRU Environmental Sciences Seminar

January 20, 2011 3:30-4:30

Alan E. Burger

Department of Biology, University of Victoria

"Managing a threatened species with widely differing foraging and nesting habitats: The importance of understanding population limitation in Marbled Murrelets".

Image from: www.sierraclub.bc.ca/endangered-species

Dr. Alan Burger has studied the marbled murrelet (Brachyramphus marmoratu) for 20 years but says he still has a lot to learn. The distribution of this sea bird encompasses Alaska and the North American pacific coast where they spend roughly 80% of their life foraging underwater in near shore habitat and 20% nesting on mossy platforms of old-growth conifers.

According to Burger, copious amount of research on habitat parameters has been carried out and results show forest age, tree height and distance from ocean to be of importance. Roughly 1/3 of nestlings fledge and predation is the primary cause of nest failure. Despite the parents best attempts at hiding their offspring, predators such as crows, steller’s jays, squirrels and mice effectively stumble across eggs and young chicks. Marbled murrelets are long-lived and this coupled with low reproduction rates equates a low population turnover.



So why is the marble murrelet threatened? A closer look into marine and/or terrestrial factors limiting population size may be the answer. Burger discussed that at sea the limiting factor in population growth is prey availability while on land it’s nesting habitat, predation and social factors. The evidence is contradictory. Research from South West Vancouver Island, such as at-sea-counts and juvenile recruitment, illustrates marine factors to effect populations in the short-term. Radar counts at watersheds tracked low variability across years but high spatial changes amongst sites. In California there is a sink population (reproductive output is inadequate to maintain the local population levels) and prey availability effects breeding in some years.  However, there is immigration so food cannot be limiting. Watersheds where logging occurred showed a decrease in population size while the opposite was seen with intact forests. In Alaska, where terrestrial studies are lacking, researchers blame prey scarcity.  

Population loss is linked to logging, especially in BC and USA, says Burger. However, if we look at habitat availability, present data shows about 10-200 trees with platforms ha^-1 and an average of 1 nest per 33ha. It is not the trees with platforms that are limiting. Why then is the population struggling? An explanation:  The birds want to be spaced out. Flight and vocalization could be presented as spacing behaviour to reduce chances of a predator locating the nest. Further studies on social behaviour of these birds (although an unusual parameter in forest management) may be the key to understanding population decline of the marbled murrelet.   

My opinion:  A great lecture filled with valuable information. But we have much to learn. It’s interesting to see an example where the species’ niche is not the direct limiting factor in population reduction. A situation where the assumption of habitat loss is not to blame and there is a deeper-seeded issue to decipher.

Word Count: 453

When Populations Are Too Healthy...

Mech, D. 2010. Considerations for Developing Wolf Harvesting Regulations in The Contiguous United States. Journal of Wildlife Management. 74:1421-1424.

Link to Article:

http://www.swetswise.com.ezproxy.tru.ca/FullTextProxy/swproxy?url=http%3A%2F%2Fwww.wildlifejournals.org%2Farchive%2F0022-541X%2F74%2F7%2Fpdf%2Fi0022-541X-74-7-1421.pdf&ts=1295291936003&cs=66506344&userName=5786541.ipdirect&emCondId=5786541&articleID=154167520&yevoID=3155513&titleID=116602&referer=4&remoteAddr=192.146.156.172&hostType=PRO&swsSessionId=56eaBqrIySZGe0QuskFdBA__.pasc1

Mech (2010) discusses the likelihood of a permanent harvesting season of gray wolves (Canis Lupus) in the contiguous United States within the next few years. He comments that since being placed on the United States Endangered Species List since 1967 and Endangered Species Act in 1973 gray wolf populations have successfully recovered and continue to increase in population size. Harvesting wolves is a sensitive topic and Mech (2010) explains the species has been delisted twice and relisted due to technical legal issues.

The act of hunting, trapping, and harvesting of wolves is an extremely controversial topic with the general public in addition to ranchers, outfitters, sportsmen, animal welfare advocates amongst others. A large number of public citizens find it hard to believe and are dismayed that it may become legal to trap or kill wolves.

I understand Mech (2010) to be accurate in stating this “divided opinion” of taking wolves makes it crucial for each state to strategically develop proper fair-chase wolf harvesting regulations. Decision making must take into account the desired harvest objectives (for hunters as well as conservation goals) in addition to meeting public acceptance.

Further, Mech (2010) explains the difficulties of harvesting many wolves and the challenges with fair-chase hunting. Tactics such as aerial shooting, tracking by snowmobile, and/or spotting by helicopter and landing to shoot are opposed by much of the public. Trapping and snaring are techniques accepted by some wolf advocates but is expensive, time-consuming, and difficult. There are also other means of control mentioned in the article.

Considering the continuously growing populations of gray wolves there is a strong probability of harvesting management being put forth in the United States. Although it is difficult to convince the public that wolf harvesting is necessary, it may be possible to decrease people’s opposition by setting restrictions such as not killing individuals readily identifiable as pups or gravid females.

This topic is exceedingly sensitive and as someone who is keen on wolves, understands biological conservation, and an open-minded individual I understand both ends of the problem. Essentially, the best case scenario for the wolf is that humans all disappeared – or at least stopped growing exponentially – and the rancher’s would probably prefer the wolves didn’t exist at all. I think Mech successfully achieved an unbiased standpoint and considered both sides of the issue and it appears he agrees that the regulated ‘culling’ of gray wolves in the near future is essential for successful management of the species. The question is: How does one convince the public that shooting a cute fluffy animal is the ‘right thing to do’?

Word Count: 430