Thursday, December 26, 2013

Birds and Daylight Length

Dad makes a scrape in the snow
Many animals and birds react to daylight length. This phenomenon, known as photoperiodism, allows their physiology and behavior to adapt to seasonal changes in the environment, and indicates the most favorable time of year to produce offspring. Although bird species vary in their responses, the annual cycle of birds overall is driven by daylight length.

How do birds detect changes in day length? Like many other creatures, they use photoreceptors – specialized cells that detect light and initiate a physical response to it. The photoreceptors in birds are not in their eyes (as they are in mammals like us), but deep in the brain, in an area called the ventromedial hypothalamus. The receptors react to light that penetrates birds’ thin skulls and surrounding tissues. Changes in day length (and possibly strength and angle, at least in non-equatorial latitudes) initiate major changes in birdie physiology and behavior.

To quote Scott Weidensaul, "Changes in the photoperiod pull many strings in a bird's body".  As daylight length grows longer, the gonads of birds grow larger and produce more sex steroid hormones. This stimulates changes in behavior and sometimes plumage: depending on the bird, it may grow colorful plumage, choose and defend a territory, spend time vocalizing and flying to attract a mate, and engage in nest building. The Decorah eagles will begin rapidly responding to day length now that we are past the solstice. As the days grow longer, the eagles' gonads will swell in response. They will move deeper into courtship and nest-building activities will increase in frequency, duration, and intensity. Mom and Dad will spend more time bringing in sticks for the outer cup and crib rails, and softer materials, including corn stalks, for the inner bowl. We may see scraping as Dad did today in the snow: Copulation should begin in late January to early February, followed by egg laying in mid-to-late February.

Daylight hours will exceed nighttime hours on March 20th, although the eagles will have already experienced a new set of hormonal changes brought on by egg-laying and eaglet care. After June 21st, daylight hours will begin decreasing, which will trigger another set of biological changes in many birds. By late summer and early fall, birds might begin moving away from natal or home territories, packing in calories, gathering or flocking together in larger groups, including mixed age and species flocks, and in many other ways preparing for migration and overwintering. This year's young eagles will disperse and we'll see less and less of the adult eagles until early winter, when the cycle will begin anew.

Some exploration points:
  • Is there a predictable increase in frequency of nest visits as daylight length increases?
  • Do Mom and Dad differ in their nest building behavior? 
  • Do Mom and Dad spend more time interacting as daylight length increases?
  • Does weather also appear to impact nest-building activities?
I would love to hear from any teachers that end up exploring any of these points in the classroom. Email me at and let me know about it, or friend us and share it on our facebook page:

Some reference materials:
  • Living on the Wind: Across the Hemisphere with Migratory Birds (thanks, Joan!)
  • Adaptation and evolution of photoperiod response systems in birds (
  • Explanation of the word Recrudescence (I didn’t know Senescence had an antonym!):
  • Photoperiodism: Deep Brain Light Reception:
  • Photoreceptor Cell:

Wednesday, December 11, 2013

Lead Poisoning, Toxic Shot, and Lead-Free Hunting

Volunteer Ron Andrews with lead-poisoned bald eagle
On the evening of December 9, 2013, Bob Anderson of the Raptor Resource Project received a phone call about a sick and possibly injured eagle. The story of how he responded to it can be found here. Despite the best efforts of everyone involved, the eagle died of lead poisoning roughly two days after it was rescued. To quote Bob: “I have reached a point regarding these lead poisoned eagles that surprises me.  I do not get hardened and begin acceptance for picking up these sick eagles on the verge of death and clearly in severe pain.  To look at an adult bald eagle gasping for breath and making what can only be described as cries of pain; is something that never gets easy and to think it is clearly preventable.”

So how serious is lead poisoning? SOAR has wonderful information on their website at A few figures that struck me:
  • 56% of all eagles admitted to Iowa rehabilitators between 2004 and 2008 had abnormal lead levels in their blood. This ranged from a low of 37.5% in 2004 (with 62.5% of eagles being tested) to a high of 70.0% in 2005 (with 90.0% being tested).
  • The University of Minnesota’s Raptor Center in St. Paul received 117 lead-poisoned bald eagles during the winter of 2009.
  • While lead poisoning can kill directly, as it did with the eagle we tried to rescue, lead toxicity is also a factor in collision deaths and injuries. According to the Raptor Center, about 85% of eagles that come in with collision injuries also have elevated lead levels. This video from the UK shows the effects of lead on a duck's coordination and motor skills:
Lead poisoning is primarily the result of exposure to leaded or toxic shot. In 1991, the US Fish and Wildlife Service banned lead shot in waterfowl hunting, although it can still be used for some other types of hunting, depending on your state's laws and regulations. A survey of ducks on the Mississippi Flyway found that the ban on lead shot reduced lead poisoning deaths of Mississippi Flyway mallards by 64 percent, while overall ingestion of toxic pellets declined by 78 percent over previous levels. By significantly reducing lead shot ingestion in waterfowl, the ban prevented the lead poisoning deaths of approximately 1.4 million ducks in the 1997 fall flight of 90 million ducks.

Did the ban on lead shot prevent successful waterfowl hunting? No. The total number of geese and ducks harvested nationwide declined steeply beginning in about 1984, but started rising again in roughly 1992, as shown by this chart: Requiring the use of non-toxic shot did not negatively impact waterfowl hunting, but did prevent ducks, geese, and many other animals from coming into contact with lead shot by ingesting it directly or feeding on lead-poisoned animals or carcasses containing shot.

There are alternatives to toxic shot. A few links:
There are a number of groups that advocate for non-toxic shot. The movie Scavenger Hunt chronicles the efforts of a small team of biologists and hunters to convince hunters in northern Arizona to use non-toxic shot. As the director points out, many hunters have been deeply involved in conservation efforts. This method could also provide a model for lead-reduction efforts in other places. You can watch a trailer here:

If you hunt or shoot, please use non-toxic shot. It does your prey well, it does you well, and it does the environment well. We aren’t anti-hunting and we aren’t anti-gun, but handling lead-poisoned eagles has made us anti-lead shot.