RESEARCH

SHORT-EARED OWL

PROJECT OUTLINE

Phase 3:  Stable isotope analysis and habitat usage


Objective:
To learn about local and long-range movements of Short-eared Owls, in an effort to better understand year-round habitat needs and identify linkages between breeding and wintering areas.  Habitat loss has been proposed as one of the key factors responsible for the sharp decline in Short-eared Owl populations, therefore tracking local movements in relation to habitat type and disturbance may provide useful data to help guide management and conservation efforts.  Meanwhile, population estimates continue to be confounded by uncertainty over the degree to which Short-eared Owls are nomadic, so exploring whether individuals show any consistency in the use of breeding or wintering areas may lead to an improved understanding of population dynamics on a continental scale.

Methods:
This phase of the project uses radio telemetry as a means of documenting the local movements of Short-eared Owls, and a combination of leg banding and stable isotope analysis to provide information on long-distance movements.  The work is being undertaken primarily by Kristen Keyes as part of her Master's thesis at McGill University, with assistance from local volunteers and other MRF partners.

The project currently focuses primarily on Amherst and Wolfe Islands near Kingston, Ontario, though other sites may be included depending on the distribution of the regional Short-eared Owl population during the course of the study. We have focused on Amherst Island in the past as it is one of the few locations in eastern Canada where Short-eared Owls are consistently observed in both summer and winter.  It is therefore particularly suited to this phase of research, as it provides an opportunity to test whether some individuals remain in the same territories year-round, or there is in fact a shift, with the wintering population coming from further north, and potentially taking the place of the individuals that breed there in summer.

While recoveries of banded Short-eared Owls have been fairly rare to date, marking this population as thoroughly as possible greatly increases the probability that at least some individuals will subsequently be reported.  Getting future locations for even a few owls will improve our limited understanding of their movement patterns, and possibly also longevity.  A subset of individuals banded are being fitted with lightweight radio transmitteres attached with natural rubber as a rump-mount.  These permit us to pinpoint the location of individuals as long as they remain in the local area.  Over the course of months, the data collected provide an overview of habitat usage that allows us to assess habitat associations, territory size, and in the case of juveniles, dispersal movements.

Small (<2 sq cm) feather samples are being collected from each individual for stable isotope analysis.  In the case of juveniles, the samples will play a key role in developing a species-specific "base map" with which to calibrate the patterns of distribution of deuterium (and possibly other isotopes) across North America. The isotopic signatures of adults can then be compared to this base map to estimate where they grew their feathers.  Depending on their age, this could identify where they hatched, and/or where they bred the previous summer.  While this technique is not nearly as precise as satellite telemetry, it should allow us to identify population connectivity at a coarse level.  To acheive good continental coverage, we are asking Short-eared Owl researchers elsewhere to contribute feather samples (from live-trapped individuals to those found dead) to the project for both development and testing of the base map.  We already have partners from several states and provinces who have agreed to contribute, but would benefit from a larger network - please e-mail us for details if you or someone you know will be working on Short-eared Owls in 2010 and expect to be able to collect any small feather samples, and see our call for feathers for further details. 

Preliminary results:
Field work begin in April 2009, by searching for courtship displays indicating the establishment of breeding territories.  This involved visiting sites known to be active in recent years, but also testing out a new roadside survey protocol aimed at discovering unknown territories.  Courtship was observed at six sites on Amherst Island, but no owls were seen on Wolfe Island.  This most likely reflects the relative abundance of voles on the two islands, which through informal field reconnaissance appeared to be high and low, respectively.  Three nesting pairs were located on Amherst Island through intensive search efforts in the areas where courtship was observed.  Attempts were made to band adults and young, but due to unexpectedly early nesting and challenges capturing adults, only one juvenile was banded and fitted with a radio transmitter. It was followed for just under one month, from June 10 to July 8, at which time it and all other owls occupying two adjacent territories appeared to relocate off the island.  For further details on these and other aspects of the project, please visit our notes from the field section of the website.

We are currently preparing for a second wave of field work this winter, with the goal of conducting regular volunteer-based visual surveys and attaching up to nine additional transmitters.

Partners and supporters:
MRF has already secured the support of several partners in this project, but is looking for additional partners to expand the geographic scope of the project and assist with funding - please e-mail us if you are interested in further details on becoming involved.  Partners and supporters to date are:

And the following, who have assisted with sample collection:

 

2002- The Migration Research Foundation Inc.