I. WHY MIGRATE? (related to function of behavior. In what way does migration promote reproductive success? A cost/benefit analysis can help to understand some of the possible reasons)

Example: The arctic tern circumnavigates the globe every year, breeding in the Arctic and overwintering in the Antarctic (see a videoclip of this amazing feat)

Not all migrants travel the distances of the arctic tern. Why do birds fly south for the winter and why do birds return north the next spring?

A. Going South

1. Benefits

a. ___________________________________

 

b.____________________________________

 

c. ____________________________________

2. Costs

a.____________________________________

 

b.____________________________________

 

c.____________________________________

 

d.____________________________________ 

 

Because many birds migrate, it is assumed that the benefits outweigh the costs. But keep in mind that not all bird species migrate and furthermore, in some species, only some of the birds migrate whereas the others stay put.

Most of these same disadvantages are present when returning north, so they will not be repeated below, leaving us with the consideration of why come back at all?

B. Returning North (Why come back?)

1. Benefits

a._____________________________________

 

b._____________________________________

 

c._____________________________________

Lets explore the longer daylength hypothesis (aka longer days hypothesis)

2. Longer Daylength Hypothesis

a. Do longer days allow birds to get more food to their offspring causing them to grow faster and permitting a 2nd clutch?

b. A comparison of breeding success of Robins at different latitudes (fill in blanks below)

	OHIO ROBINS	ALASKAN ROBINS
# feeding visits/day	-	137
# days to fledging	13.2	-
Probability of 2nd clutch	-	50%

c. What do the data show?  

 

 

 

 

II. HOW DO BIRDS MIGRATE? (We now turn to an exploration of the mechanisms birds use to migrate).

A. Orienting Mechanisms

1. Piloting is defined as the use of landmarks

1. Vector navigation is defined as an ability to maintain a predetermined orientation, typically a compass bearing (direction) for a specified period of time or distance to reach a migratory goal location. Animals can use a variety of cues to maintain the orientation.

2. __________________________ ability to navigate to a migratory goal location even after displacement to unfamiliar locations outside of the animal's previous experience.

a. reverse displacement (retracing one's path)

b. map-based navigation (reliant on a learned representation of a mosaic of local cues or landmarks)

b. grid-based navigation (reliant on a learned representation of environmental physical or chemical gradients)

B. Piloting (an in depth examination of this mechanism)

1. procedures (to study the effects of landmarks)

a. moving landmarks (example, digger wasp on video clip). The videoclip describes digger wasp behavior, the importance of the nest tunneled into the ground, and how the digger wasp finds its nest when returning to it.

 

 

What does the digger wasp do when the landmarks surrounding its nest are moved to a new location?

 

 

 

 

 

b. preventing animals from seeing landmarks (example, homing pigeons)

1. Homing pigeons were released far away from the home loft

2. They were prevented from seeing landmarks by wearing ________________

2. The pigeons reached the general vicinity of the home loft (without using landmarks)

Did they reach the home loft?

 

What does this suggest?

2. Memory: Landmarks must be stored in memory

3. Landmarks cannot explain:

a. Successful migration by young birds because they have no landmarks stored in memory

 

b.______________________

 

4. landmarks may be important at the end of migration in terms of locating a specific site. Once the bird gets close enough, then landmarks might be used to zero in on a particular territory.  But birds appear to use something other than landmarks to fly over great distances.

C. Differentiating Vector Navigation from True Navigation Using Displacement

1. one procedure is to displace birds during migration and determine the effects of the displacement

a. If displaced birds can adjust and get to their overwintering area then they show true navigation

b. If they merely maintain the same direction without taking into account the displacement and do not get to the same overwintering area, then they only show vector navigation

2. Perdek's displacement study of migrating starlings (1958)

a. The subject population were 11,000 starlings migrating southwest from Norway/Finland to northern France (their overwintering area).

b. A large number of birds were captured and transported east to Switzerland; where did the birds go?

c. It depended on their age and hence their experience at migrating. Fill in the table below

AGE	Direction after displacement	Final Location	Adjusted for displacement	Type of Navigation
Adults (Experienced)	Northwest	Northern France (OW)	YES	-
Juveniles (inexperienced)	Southwest	Spain	-	-

d. Thus migrating at least once in this species is necessary to adjust for displacement.

e.Starlings are short distance social migrators, and it is unclear whether they were using a map or grid based system.

3. Continental displacement of white crown sparrows

a. A population of white crown sparrows spend the summer in Washington state and then migrate in a southern direction to southern California for the winter. They migrate alone thus eliminating social influences during migration.

b. In a recent study by Thorup et al., 2007, 15 white crown sparrow juveniles and 15 adults were transported to New Jersey (thus exposed to a continental displacement). Their migration pattern was monitored using very small, light weight radio transmitters attached to the birds. Fill in the table below to see whether they showed a pattern similar to the starlings

AGE	Direction after Displacement	Final Location	Adjusted for displacement	Type of Navigation
Adults (Experienced)	WSW	Southern California (OW)	YES	-
Juveniles (inexperienced)		-	-	-

c. More impressively, some adult white crown sparrows were able to adjust very rapidly to the displacement and had discerned the appropriate WSW direction within 15 miles (3 days) of the release site in New Jersey. In this case, birds had to be using some kind of grid navigation (no way to assess landmarks)

C. Cues for Vector Navigation - (early studies)

1. Can birds use the sun for determining and maintaining a direction? If so, the sun poses a challenge because:

a. The sun is not stationary (moving across the sky)

b. It requires the animal to make continual adjustments to the position of the sun throughout the day (time compensation).

2. Kramer Cage Set up

a. Early studies by Kramer showed the role of compass orientation in starlings

b. Description of the Kramer cage (draw the cage - how is it that birds can see only the sun? Why can't they use landmarks?)

 

 

 

 

 

c. Under sunny skies but not cloudy skies, startlings oriented in the migratory direction 

d. Starlings were then trained to find a feeder in a particular direction (EAST) using the sun as a cue; Following training some of the birds were clockshifted as described below

2. The Kramer Cage and Clockshifting: a form of misdirection was used to prove the importance of the sun.

a. misdirection can be created by shifting one's biological clock while remaining at the same location.

b. to create misdirection, two groups were trained to find the east feeder and then were exposed to the following light conditions

 

c. What were the light conditions for Group A?

 

 

 

d. What were their light conditions for Group B?

 

 

 

e. Both groups were tested at 6AM.

For Group A:

1. their internal clock was set to the actual time

2. At 6 AM, the sun is in the east

3. Birds should face the sun to arrive at the East feeder; and they did arrive at the east feeder

For Group B

1. their internal clock was different than the actual time, indicating that it was the middle of the day

2. In the middle of the day, they should turn to the left of the sun (because the sun is slightly to the south), to get to the East feeder

3. By turning to the left of the 6AM sun, they were deflected to the

_____________ feeder.

f. Misdirection studies:

 

1. ________________________________________________

 

2. Are particularly compelling because they ___________________________

 

3. Celestial Cues: Nocturnal migrants can't use the sun because they fly at night (see video clip)

a. What cues do young birds use?

 

b. What direction can be obtained? __________________________

c. How is it obtained?

 

III. USING HOMING PIGEONS AS A MODEL FOR MIGRATION

A. Training homing skills in pigeons (its not automatic)

1. Pigeons can be trained to find the home loft after being released hundreds of miles away

2. Training is progressive starting with short distances and increasing the distance up to 200-500 miles

B. Measurements (how is homing measured)

1. One measure is ________________(the direction in which a bird disappears on the horizon; how is this shown graphically?)

2. A second measure is travel time (time it takes after the bird is released to reach the home loft)