03 de marzo de 2020

What constitutes an identification?

There have been instances in which I have disagreed with an identification made by someone whom I consider to have knowledge superior to my own. In some of those cases I even think that they are probably right because I have so much confidence in their judgement. What do you do if you cannot make the same identification as an expert does by relying solely on your own knowledge?

In some other instances, the observer has added additional information in the form of an explanation that is not evident in the evidence provided. What do you do if the observer's explanation seems perfectly reasonable?

iNaturalist has addressed these issues.

"On iNaturalist, other users are encouraged to add identifications to each other’s observations, based on the evidence provided, in order to confirm or improve the Community Identification (see further discussion below on Research Grade status)."

"An identification confirms that you can confidently identify it yourself compared to any possible lookalikes. Please do not simply “Agree” with an ID that someone else has made without confirming that you understand how to identify that taxon. If you agree with the ID without actually knowing the taxon, it may reach Research Grade erroneously. "

iNaturalist is saying is that you should only make an identification at the level at which you can confidently identify it by relying solely on your own knowledge. If an expert opinion weakens confidence in your own opinion, then perhaps you should consider not making the identification. But, you should not agree with the expert simply because they are an expert. That would be a duplication of the expert opinion and would constitute two identifications by the same individual.

The same thing holds for cases in which the observer offers additional information in the form of an explanation. The explanation is not part of the evidence presented so it should be excluded in one's determination of the identification - even if it makes perfect sense. Otherwise, iNaturalist could devolve into something that is no longer useful to science.

Publicado el marzo 3, 2020 08:04 TARDE por ollerton ollerton | 0 comentarios | Deja un comentario

26 de diciembre de 2018

How to measure an animal track dimension from a photo containing a scale displayed on a monitor.

This requires that the viewer know the size of the scale beforehand.

  • Call the value of the size of the scale S.
  • Use a ruler to measure the size (e.g., length, diameter) of the scale on the monitor screen and call that value U.
  • Use the ruler to measure the dimension of the track (e.g., length, width) on the monitor screen and call that value M.
  • The size of the dimension, D is given by D = S * M/U.

    Example: Suppose you photograph a Bobcat track and with a coin such as a quarter near the track. Also suppose that you display the photo on your computer monitor and you measure the length of the track as displayed on the monitor as being 65mm (this is M). Next, suppose that you measure the diameter of the quarter as being 28mm (this is U). Next, suppose you either measure the diameter of an actual quarter or you do a web search and determine that a quarter is 0.955" in diameter (this is S).

    The length of the track, D, is 0.955" * 65mm/28mm = 2.31".

    Publicado el diciembre 26, 2018 07:03 TARDE por ollerton ollerton | 2 comentarios | Deja un comentario

    23 de diciembre de 2018

    How to distinguish between canine and feline tracks.

    See https://www.bear-tracker.com/caninevsfeline.html

    Feline tracks have a trapezoidal shaped pad with three lobes at the posterior of the pad and sometimes register two lobes at the anterior of the pad. The pad in feline tracks is proportionately larger than it is in canine tracks. The pad area of a canine front track is triangular. The pad area of a canine hind track can be triangular or even round in some species. The pad area of a canine track is not trapezoidal unless the animal slipped forward in mud.

    The toe arrangement in feline tracks is asymmetrical and there is a leading toe - toe number 3. The toes in feline tracks are also somewhat tear drop shaped. The toe arrangement in canine tracks is symmetrical and the middle toes are more oval shaped than they are in feline tracks.

    If you imagine lines being drawn between each of the pairs of side and middle toes it will form and "X". The lines of the "X" do not bisect the pad in canine tracks but they do bisect the pad in feline tracks.

    Finally, felids have to expend energy to extend their claws so their claws typically do not register in their tracks. Canid claws are always extended and often register in their tracks.

    Canine examples
    https://www.inaturalist.org/observations/18997094 - Coyote Front on the left and hind on the right.
    https://www.inaturalist.org/observations/17591110 - Domestic Dog
    https://www.inaturalist.org/observations/16578205 - Domestic Dog that had slipped forward in mud so that the pad area is trapezoidal.
    https://www.inaturalist.org/observations/19106805 - Gray Fox

    Feline examples
    https://www.inaturalist.org/observations/19106785 - Mountain Lion
    https://www.inaturalist.org/observations/18636765 - Bobcat, mud
    https://www.inaturalist.org/observations/17591112 - Bobcat, dry substrate
    https://www.inaturalist.org/observations/19176947 - Domestic Cat

    Additional Resources

  • You can find more extensive information here https://www.bear-tracker.com/caninevsfeline.html, https://bear-tracker.com/mammals.html, and here http://www.naturetracking.com/.
  • The most convenient source of North American Mammal track information is the iTrack Wildlife app for your smart phone.
  • The Field Guide to Animal Tracks and Scat of California by Elbroch, Kreskey, and Evans is my personal favorite.
  • Publicado el diciembre 23, 2018 07:07 TARDE por ollerton ollerton | 7 comentarios | Deja un comentario

    How to photograph animal tracks.

    @jonahevans made a video about how to photograph animal tracks. It is available here https://www.youtube.com/watch?v=HaLMQ2H6_PE.

    You don't always need shade if sunlight comes in at an angle and the track is in full sunlight.

    Publicado el diciembre 23, 2018 06:40 TARDE por ollerton ollerton | 2 comentarios | Deja un comentario

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