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Female Dispersal: Is it a matter of asking directions?

Posted: June 27, 2016

We recently published another paper on female dispersal in deer. Here are the highlights.

June is the month of newborn fawns.

It’s also the month when many 1-year-old deer – both male and female – disperse.

Last year we published a series of stories on dispersal in male and female deer. You can read them beginning here

The graduate student who conducted this latest research, Clay Lutz, just published a second paper focusing on factors that influence dispersal timing and paths in female deer.

This is based on monitoring 277 juvenile females (captured at ~8 months old) from 4 different areas of the state, WMUs 2D (western PA), 2G (northcentral PA), 3C (northeastern PA), and 4B (southcentral PA). Of those 277, 27 dispersed. 

What did he find?

  • Dispersal occurred at 1 year of age, which coincided with the fawning season.
  • Dispersal paths were generally non-linear and the dispersal process, on average, took 2 days, but sometimes weeks.
  • Roads, rivers, and human development influenced dispersal path direction and where dispersal terminated.
  • About 50% of yearling females made what Clay called “forays” outside their home range even if they did not ultimately disperse.

One GPS-collared female captures the essence of these findings. Here’s a map of her capture location, her natal home range, and 2 forays she made on 12 May and 17 May. Notice how a river and road stopped both forays.

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But that’s not the interesting part.

On the 25th of May she left her natal home range for good. She kept going… for 55 days and 10 hours.

She traveled 258 km (160 miles!), crossed I-80 twice, and crossed 3 major rivers 4 times.

For all this effort, she did not end up that far from home either! Only about 20 miles.

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On a scale of 0 (random motion) to 10 (straight line) of how straight the dispersal paths of females appear, they rate about a 6. In contrast, male dispersal paths are about a 9.

Why? Probably because males don’t ask for directions! They pick a direction and stick with it. Right or wrong, they are committed.

As fascinating as all this is, there are some important implications, especially as they relate to chronic wasting disease.

1. Reducing deer density will reduce female deer dispersal rates – and likely reduce disease spread. Female dispersal is density dependent  – higher deer densities lead to greater dispersal rates.

2. Containing the spread is going to be difficult when female deer disperse. Although not as many females disperse in Pennsylvania (8-24% of females versus 50-75% of males), there ends up being more of them (they live longer than males), they disperse farther (11 miles for females vs. 5 miles for males), and they take much more convoluted paths when they disperse (covering a larger area).

Whether females ask for directions or like to check all their options before settling down, they really get around.

-Duane Diefenbach

 

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