Knowledge Engineering: Flyway Management

Knowledge Engineering Session Notes:
Trumpeter Swan Migration Pathways and Chronologies

Southeast Idaho National Wildlife Refuge Complex, Pocatello, ID
1 June 1999
Present: Steve Bouffard, John Cornely, Rick Sojda, Gary Will

Some of the more important information garnered at this session has been summarized in tablular format, describing the movement of swans from one of 27 areas to another between life cycle events. This is presented as: "Of the swans that were present during a particular season at a particular area, what is the expected percentage of those birds that will spend time during the subsequent season at other areas?" These were provided as best estimates by the group. Also presented is the confidence that they had in the percentages provided. This migration is provided:

Additional Notes from the Session

Let LT = Leave Time Threshold and AT = Arrive Time Threshold

If LT_a > X, and if AT_b > Y, then use the probability of movement for time period ab from a lookup table

If LT_a < X, bird does not move

The following time periods were provided as guidelines:

breeding - on territories by mid April; fledging by mid-September
post-breeding/fall staging - mid-September through 1 December (is same as pre-breeding areas)
wintering (= time of "no" movement) - 1 December through 1 March
pre-breeding/spring staging - e.g., Camas, Ennis, Hebgen, Lake Helena, Freezeout - one March to mid-April
There may be three week differences in chronologies due to elevation and latitude.
Late spring and Island Park equals mid to late April in this may be the time of territory initiation.
Early spring Island Park equals mid March.

Factors influencing birds leaving a breeding area include:

food resources being inadequate

quality

species
density
quantity

availability

water depth
flows

Competition with other trumpeters (breeders)
"lateness" of the onset of breeding
inadequate water (e.g., Grays Lake situation)
disturbance (fishing/boating)
number of non-breeders and flock - non-breeders leave earlier
number of cygnets in flock - in increased number of cygnets will result in birds leaving later
day length
other comments

It is thought that day length may not be a dominant factor.
If there is no water, the birds must leave.
If food resources are excellent, birds are not likely to leave; but the opposite is not likely as definite.
A two-week delay and peak of hatch can delay leaving.
Even if food and water are adequate, birds may still leave if despair.

Factors influencing birds leaving a Fall staging area include:

food resources being inadequate

quality

species
density
quantity

availability

water depth
flows
ice

competition with other waterfall including Canadian trumpeters and under swans
whether, including snow and freeze-up
disturbance

hunting
winter recreation
fishing/boating

Factors influencing birds leaving a wintering area include:

food resources being inadequate
photo period
weather

South wind
warming

disturbance - less influential; local movements will occur, but these are not really "migratory" movements
percentage of flock the despair bounded

Factors influencing birds leaving a pre-breeding area include:

food resources being inadequate - not as important at this stage
As a quality of a pre-breeding area increases, the time needed to stay there decreases. Therefore, birds may leave sooner.
weather

South wind
warming

intra-specific aggression
photo period/biological clock

Some factors affecting whether birds will stop at an area include:

habitat
whether it is frozen
tradition
decoy effect
disturbance - affects whether they stay

Return to the Swan Management Decision Support System homepage.

USDI - Geological Survey
Biological Resources Division
Northern Rocky Mountain Science Center
Maintainer: Rick Sojda (sojda@swan.msu.montana.edu)