Tuesday, August 6, 2013

Definition for residency or site fidelity

Below is the working definition of residency or site fidelity of marine mammals compiled by Aine O’Shea, a member of the international MARMAM mailing list, posted on 13 July 2013. Thanks a lot Aine for allowing me to post the article in its entirety on my blog! If you want to contact Aine directly, her email is osheaine@gmail.com.

Aine's compilation helps my thoughts on the residency patterns of small cetaceans in Lovina (pix by myself)

Following a request I submitted to MARMAM last week regarding a definition for residency / site fidelity, I have received some information which I would like to share with the MARMAM site.  

- It varies and there is no standard definition

- The term "site fidelity" is borrowed from studies of terrestrial taxa, and in many cases those animals (whether they're mammals, lizards etc.) have very narrow ranges and/or territories that are easily defined.  This isn't the case with most cetaceans

- Residency is in the eye of the beholder

- There's no easy place to draw the line

- Residency suggests that animals are almost always present within a specific area, while site fidelity means that animals always return to the same location. Animals can show both residency and site fidelity, or they can show site fidelity without residency (as is the case in many migratory species)

- In both cases, the terms are scale-dependent; that is, whether you define an animal as showing residency or site fidelity will depend on the size of the area you are using as your sampling units (usually defined as a study area) e.g. an individual might not be resident in a study area that consists of a single bay, while it may be resident in a wider region

- Similarly, for site fidelity, an animal may not repeatedly return to the exact same bay, but may return to the same general area each year, e.g. a humpback whale might not show site fidelity to the island of Maui, but may show site fidelity for the entire Hawaiian archipelago

- Both site fidelity and residency may be interpreted as somewhat human constructs imposed on animals based on how we view a specific area of interest, and in all cases, they should be accompanied by a specific definition of the spatial area to which they are being applied

- Residency, and to a lesser extent site fidelity, are not particularly useful ecological concepts (the fact that there are no clear definitions is also an indicator of this). Instead, it would be better to use more ecologically-meaningful terms like home range (which captures all areas where an individual occurs and is based on its own distribution and not any human construct of a study area at a specific spatial scale)

- Levels of site fidelity can also be captured within the home range concept by looking at core areas within the total home range (for example, areas where an animal spends 50% of its time), and these can be identified using kernel density estimates (KDEs)

- There is no natural division between residents and visitors in the Bottlenose population, Adelaide - some are almost always seen, some seen many times, some quite a lot, some only occasionally, some rarely, etc.

- The terms may be defined by the conductor of the study

- The term residency depends on your research question and hypothesis

- Read studies outside the taxon which may or may not shed more light on definition

- There is no consistency in the definitions, as in most cases the definitions are based on the duration of the study and not in what the animals are doing

- The re-sighting pattern of dolphins will vary with time and if the study is short, their definition is not going to be very rigorous

- The best definition of the terms, have been defined for dolphins studies conducted in Sarasota Bay, Florida, and Shark Bay, Australia – as they are the two longest running projects of wild dolphins in the world

- One must be careful with definitions and understand that different species have different re-sighting patterns based on the way that their societies are organized

- The site fidelity or residency is dependent of the frequency and amount of individuals surveyed

- The terms vary also, like residence time (occupancy), annual return rate (recapture rate) and site fidelity - they are not the same, but reflect a tendency of animals coming back / using a particular area, in a certain period

- Specify individuals within the species, so you should document your identification process and results

- Specify GPS coordinates of location you are proving fidelity.  For example, resident Orcas may be loyal to a particular bay, cove, inlet while still being characterized by residents

- Specify dates/time of year so you can connect with migration patterns and/or all other known factors for the species and individual

- Specify criteria, i.e. how often does the animal return?  With what other animals does s/he aggregate?  For what duration?

- The method of residency / site fidelity is only a tool, not the truth

- Figure out if your definition is close to someone else’s and why

- Be careful not to miss factors that can drive the coincidence and determine if the pattern is biologically meaningful

- Explain also the meaning of any level of variability you observe and how it may overlap with someone else’s definition and why you stick to one or the other

- Regardless of the definitions used, the level of understanding of site fidelity for any particular species/population depends both on the actual movement patterns of the animals and the methods used to study them

Hope this information is of use.

Best Regards,


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