Autumn Migratory and Foraging Ecology of Eastern Population Sandhill Crane

Principal Investigator:
Everett Hanna, Ph.D. Candidate

Supervisors:
Dr. Scott Petrie, Long Point Waterfowl Executive Director
Dr. Jack Millar, University of Western Ontario
Dr. Michael Schummer, Long Point Waterfowl Senior Scientist

 

Sandhill Cranes (Grus canadensis) are the most numerous species of crane in the world. Migratory populations have broad breeding, migratory, and wintering ranges throughout North America that extend into Siberia, Russia (Fig. 1).  There are six migratory populations of Sandhill Crane, including: the Pacific Flyway Population (Lesser subspecies [G. c. canadensis]), the Central Valley Population (Greater subspecies [G. c. tabida]), the Lower Colorado River Valley Population (Greater subspecies; Central Valley Population), the Rocky Mountain Population (Greater subspecies), the Eastern Population (Greater subspecies), and the Mid-Continent Population (Lesser, Greater and Canadian subspecies [G. c. rowanii]; Mid-Continent Population).

Figure 1. From Case & Sanders 2009: Approximate nesting, wintering, and primary migration and staging areas of the six migratory Sandhill Crane populations (compiled from information in Lewis 1977, Drewien and Lewis 1987, Sharp et al. 2000, Tacha et al. 1994, and data from radio-telemetered birds provided by G. Krapu, Northern Prairie Wildlife Research Center, Jamestown, ND).

The Eastern Population (EP) traditionally breeds primarily throughout the Great Lakes region (including Wisconsin, Michigan, and Ontario) and winters in Florida and parts of southern Georgia.  During both spring and autumn migration, EP cranes stage throughout the east-central United States including Illinois, Indiana, Ohio, Kentucky, Tennessee, and Alabama, and, to the north, along the north shore of Lake Huron, Ontario, including Manitoulin and St. Joseph Islands.  The EP has been expanding in population size and breeding range; however, researchers are still seeking a precise estimate of the current extent of the EP throughout the annual cycle (Fig. 1).

At present, the EP’s population status is monitored by the Fall Sandhill Crane Survey coordinated by the United States Fish and Wildlife Service.  The fall survey is a long-term annual survey, first initiated in 1979.  The survey is conducted by volunteers and state/federal agency officials from the Atlantic and Mississippi Flyways (Wisconsin, Michigan, Indiana, Tennessee, Georgia, and Florida).  The primary objective of the survey is to count EP cranes that concentrate (staging and migrating) in Indiana, Michigan, and Wisconsin.  Recent estimates suggest that the population index is approaching 85,000 cranes with a five-year average (2005-2009) of approximately 40,000 ± 4968.4 cranes (Fig. 2).

Figure 2. Contemporary population estimate from US Fish and Wildlife Service Annual Fall Surveys collected during autumn migration.

Researchers and biologists are working to adapt survey methodology to provide more statistically robust data by reducing within and between year variation resulting from surveyor bias and survey timing.  To assist in this effort, researchers from Long Point Waterfowl partnered with the Canadian Wildlife Service and the Ontario Ministry of Natural Resources to collect the first minimum provincial population estimate in 2009.

With additional assistance from countless volunteers from the public, observers followed crane numbers at more than 20 roost sites from Sault Ste. Marie, ON. to Espanola, ON. along the north shore including Manitoulin and St. Joseph Islands to the south and counted nearly 9,000 cranes over two days in autumn 2009.

Figure 3. Sandhill Crane being released immediately after being outfitted with a solar-powered GPS transmitter mounted on a PVC leg-band after being captured in early August 2010 on Manitoulin Island, Ontario.

Satellite Tracking

As an integral component of Long Point Waterfowl student Everett Hanna’s M.Sc. thesis at the University of Western Ontario, a team of researchers from Long Point Waterfowl headed back into the field on Manitoulin Island to collect additional information relating to EP migratory ecology during summer and autumn 2010.  We captured cranes (n = 17) during July and August using rocket nets at baited sites throughout central Manitoulin Island.  We outfitted a subsample of captured cranes (n = 9) with solar-powered GPS tracking units affixed to leg-bands (Fig. 3).  We programmed tracking units to acquire GPS fixes at six hour intervals for 3-5 years.

 

Figure 4. Location of first stopovers made by Sandhill Cranes marked on Manitoulin Island, Ontario during autumn migration 2010. Dates of first GPS fix are displayed in white. Red arrows denote cranes that departed the study are before peak number of autumn migrants was recorded.

The primary application of these data will be to compare migration chronology between local (likely breed and spend the summer on Manitoulin) and migrant (likely breed and spend the summer elsewhere and migrate to Manitoulin from the mainland during late summer or early autumn) cranes.  We assumed that the cranes we captured and banded in 2010 local because of timing of capture (i.e., during summer before staging and migration commenced).  We conducted population surveys (roost counts) throughout autumn migration in 2010 to investigate migration chronology of non-marked cranes whereas remotely collected tracking data were used to calculate departure of marked (local) cranes.  Seven of nine marked cranes departed the study area prior to recording peak numbers at the study site in 2010 (Fig. 4).

Our preliminary findings suggest that local cranes depart the study site before migrants. This behaviour is likely a result of earlier nest initiation dates at lower latitudes and proximity to high quality food sources (i.e., agricultural grain fields).  These factors may have disparate implications for adult and juvenile age groups (e.g., juveniles continue structural growth during migration whereas adults are no longer growing).  Therefore, migration may be linked to age-specific factors, particularly because cranes remain in tightly-knit family groups during autumn migration.  To investigate family group migration, a new research programme was developed and proposed to transfer Everett’s project from the Master’s to the Doctoral program at UWO.  The new programme is entitled “Autumn migratory and foraging ecology of Eastern Population Sandhill Crane”. Thus, the proposed study is
an evaluation of the various factors that we believe affect migratory chronology of EP cranes at a key staging area in Ontario using data relating to movement patterns, foraging behaviour, and food density that will be collected during autumn migration, 2011 and 2012.

During autumn, EP cranes acquire energy to fuel migration by eating agricultural grains at staging areas along their migratory route to wintering areas in southeastern North America.  On the north shore of Lake Huron, Ontario, cranes primarily eat barley during staging and migration.  Although estimates of food availability and depletion exist for some staging areas for the Mid-Continent Population, no data have been collected at EP staging areas.  Density of food resources at staging areas may influence rates of lipid acquisition and subsequent timing of migratory departure during autumn.  Therefore, timing of migratory departure in cranes may ultimately depend on a combination of food availability and
environmental variables.  Migration chronology has been studied in birds with substantial parental
investment (e.g., post-fledging care), but no studies have compared adult and juvenile behaviour to determine which may influence migratory chronology.  Understanding factors that prompt or inhibit autumn migration in Sandhill Crane represents original scientific information that has not been studied in other species.

Our research has evolved to focus on how foraging behaviour of cranes and their migration off Manitoulin Island are influenced by availability and density of waste barley left after harvest.  In particular, we are questioning whether the crane giving-up density (GUD; a density of food below which it is no longer profitable to feed) is different than that of field-feeding waterfowl (~50 kg/ha).  Traditional GUD studies have focused on food densities within fields, but normally do not account for availability of food in nearby fields and wetlands (i.e., community effect).  Because cranes on Manitoulin Island only have a limited number of small barley fields to select from, the setting is ideal to study how animals make foraging decisions within and among fields (i.e., foraging scale).  The answers to this puzzle will provide information about how animals make foraging decisions as food densities decrease among available fields.  These answers are critical in developing conservation strategies for cranes and other birds that exploit waste grain during migration (e.g., waterfowl).

Figure 5. Mean wet weights (kg/ha± 1 SD) of grain samples (barley and wheat) collected during September and October 2011 and August – October 2012 at Manitoulin Island, Ontario, Canada. Focal fields were sampled five times maximum (four in 2012). Peak migratory departure for 2011 (A) and 2012 (B) are indicated.

In the field in 2011 and 2012, we sampled waste grain 5 times in 20 barley fields to estimate grain density, distribution, and depletion throughout autumn migration. Waste grain was depleted down to ~50 kg/ha in both 2011 and 2012 (Fig. 5). Interestingly, once the average grain density for the study site reached 50kg/ha, the majority of cranes using Manitoulin Island emigrated south (Fig. 5). However, within fields, the GUD of 50 kg/ha appeared to be more of a moving target than we had anticipated. Flocks of cranes rotated field use almost systematically to deplete grain density more evenly across the entire study site (Fig. 6). We propose that the crane GUD has population level implications for timing of migration and habitat suitability, but that GUD is a function of combined local food resources. That is, cranes do not simply locate a field with grain density above GUD and feed until it reaches 50 kg/ha, but instead forage throughout the entire study site treating the area as one food source. Analyses of

Figure 6. Relationship between crane field use and grain depletion throughout autumn migration for a single focal field from September – October 2012 at Manitoulin Island, Ontario, Canada. Daily grain density was estimated using linear interpolation from weekly sampling.

numbers of cranes using fields with known grain densities and their feeding behaviour within fields are ongoing. We also conducted an experiment by actively manipulating grain density in 0.25 acre plots in half of our focal grain fields in 2012. By collecting experimental data, we hope to test for a cause-and-effect relationship between grain density and behaviour.

The Sandhill Crane project has already greatly increased our understanding of migratory behaviour of EP cranes and Everett’s continued work will enable resource managers to determine impacts of landscape change and changing agricultural markets and practices on availability of crane food during migration and, subsequently, timing of migration.

 

Sandhill Cranes: Movement Maps

Past Movement Maps


Spring migration routes of Sandhill Cranes (n = 9) marked on Manitoulin Island, Ontario, Canada during July and August 2010. Eight of the nine marked cranes wintered in southern Georgia or Florida, USA; the remaining crane wintered in northwestern Tennessee, USA. All marked cranes returned to Manitoulin Island during April and May 2011.

Summer locations (June – August) of Sandhill Cranes (n = 9) marked on Manitoulin Island, Ontario, Canada during July and August 2010. One of nine transmitters failed (and subsequently went offline) in early June 2011. The remaining eight marked cranes followed traditional habitat use patterns targeting pastures and hay fields until the grain harvest started in mid-August. Traditional roost sites were also used throughout the summer months.

Fall migration routes of Sandhill Cranes (n = 8 ) marked on Manitoulin Island, Ontario, Canada during July and August 2010. Six of the remaining eight marked cranes departed Manitoulin Island between October 01 – 04, 2011. The final two cranes departed on October 22 and 26, 2011. Marked cranes followed traditional migratory pathways northwest along Manitoulin Island and south through upper Michigan, USA, subsequently stopping at staging areas in central Michigan and northwestern Indiana, USA where they remain at present.

 


Project Sponsors and Partners

Canadian Wildlife Service
Long Point Waterfowl
Ontario Ministry of Natural Resources
Ontario Federation of Anglers and Hunters
The University of Western Ontario
Wildlife Habitat Canada
Webless Migratory Game Bird Fund

Comments are closed.