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Brian Reports: What Affects the Nesting Outlook?
May 2, 2008
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As you read Brian's report this week . . .

1. When did the first whoopers reach the nesting grounds?

2. What things affect the number of chicks that will hatch and survive? How many chicks does Brian expect may hatch this spring?

3. How do water conditons (wet or dry) on the nesting grounds affect crane reproduction?

How many nests will Brian find?
Photos Brian Johns

Dear Journey North,

The first birds will have arrived on the breeding grounds in the past few days — the last week of April. They had been delayed a few days because of snow and unfavourable winds. In the next few days there will be a large influx of birds into the nesting grounds and a flurry of nesting activity. With no known deaths over the winter in Texas, the flock has 72 territorial pairs. In the last four years we've had over 30 young produced each year. The high was 45 young in 2006.

How Many Young Will Hatch in 2008?
Things that affect the numbers of young that hatch and survive are (1) predators and (2) weather conditions at time of hatching until about 2-3 weeks after hatching. Cool, wet weather means fewer chick survivals.

We're just coming to the end of a cycle of good production of young, so this year (2008) may not be as good as last year. In summer 2007, 84 young hatched, and 40 survived to flight stage and 39 of those 40 made it to the wintering grounds. I expect we will have 60+ nests. We had 65 last year (2007), and 62 nests in 2006.

Water Conditions Affect Crane Nests and Chick Survival
We're expecting lower water conditions this year. The worst year for water was 1981. May and August of that year had almost no precipitation. Those very dry conditions lead to some of the worst fires recorded in Wood Buffalo National Park. That particular year almost one-third of the park burned. It included a large portion of the crane nesting area. The dry habitat conditions resulted in only 3 young being produced; only 2 of them made it to Texas. This was the worst production year on record.

This tells us that dry conditions are bad for chick survival. The family groups have to forage over greater areas and likely outside their normal nesting territory. Also, dry conditions make crane areas easier for land predators, such as wolves and foxes, to reach the cranes.

Wet conditions are good because they give the cranes greater flexibility in choosing their nesting sites. Wet conditions provide greater foraging opportunities for the adults and chicks, and wet conditions restrict access by predators. On the other hand, extremely wet conditions are not necessarily good either.

Timing is Everything
Rain at hatching time and in the first couple of weeks after hatching can be as deadly as drought. Under rain conditions the young can become chilled and develop pneumonia. Food for the chicks may be harder to find, which could also result in poor survival of the young.

I will be starting aerial surveys to look for the nesting pairs beginning around mid May. I hope that we will have as many nests as last year. I'll be back with more news next week.

 

Brian Johns
Wildlife Biologist
Canadian Wildlife Service
Saskatoon, Saskatchewan, Canada

 

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