Long-eared Owl Trapping Research Update

Block title

Long-eared Owl Trapping Research Update

July 8, 2013

Kate Stone shares an update on long-eared owl research.

PDF icon Download (3.09 MB)

Long-eared Owl Trapping Research Update

This report summarizes spring trapping of long-eared owls (LEOW) on the MPG Ranch. Over the course of three weeks, HawkWatch International, Inc. (HWI) and MPG Ranch staff trapped long-eared owls at known nest sites and suspected breeding territories. We developed methods for capturing LEOW in a forested setting, a habitat type where few trapping efforts have been made. We successfully captured six owls. Though our intent was to affix satellite transmitters to captured owls, no owls met the size requirements for transmitter attachment. To increase the future potential for use of transmitters on long-eared owls, we made major advances in the design of the transmitter harness, reducing overall weight and the potential for harness failure. We tested the improved harness design on a captive LEOW, a testing process seldom undertaken. Staffing for this project included Shawn Hawks from HWI, and Kate Stone and William Blake from MPG Ranch.

We focused our field activities on trapping at known nest sites and searching for new nest sites. On this map, yellow polygons represent areas we searched on foot. Blue dots represent known or discovered nests. Green dots represent trapping locations where we found owl sign or detected owls earlier in the season, but failed to capture owls with this trapping effort.

Our trapping efforts extended throughout most of the month of May. We tried various combinations of mist nets, BC traps, and audio lures to capture owls. See the Capture Methods section for our thoughts on what methods worked best.

At the Tongue Creek nest, we captured the male on 5/10 and a female sharp shinned hawk on 5/23.

At the Little Baldy nest, we captured two owls the evening of 5/24. We sexed one owl as a male based on weight, though we observed what might have been a brood patch on “his” abdomen. We also called the second owl captured a male.

At the Becca Draw nest, we captured the female on 5/12 and the male on 5/24.

At the Rock Quarry nest, we captured the female on 5/25. The Owl Research Institute originally captured and banded this owl in February 2012 near Missoula. They sexed her as a male. Our observations of her behavior at the nest and an obvious brood patch suggested otherwise.

Capturing long-eared owls in a forested setting proved challenging, due to the continuous vegetative cover that allowed many options for owl movement. We tried various combinations of mist nets, bal-chatri (BC) traps, and audio lures in our attempts to capture long-eared owls.

9 Though the nooses on the BC traps ultimately proved ineffective for capturing owls, we believe the rustling of the mice in the dried leaves was essential to luring the owls to the nets.

Shawn and William set up an “L”-shaped mist net array near the Tongue Creek nest. They placed the baited BC traps on the far side of the nets from the nest, in between the two arms of the “L”.

11 In Becca Draw, we used the traditional method of daytime trapping where we set up mist nets perpendicular to the draw, near vegetation that we expected the owls to flush into. In several visits to the Becca Draw nest, we saw the owls flush into this clump of vegetation. In this picture, William extracts the female owl after an easy capture. At this trapping session, the male flew just over the net and avoided capture. To limit stress to the pair and their newly hatched nestlings, we returned and captured the male at a later date, using similar methods.

Though we hoped to affix 9 g satellite transmitters to captured owls, no owls met the size requirements for transmitter attachment; owl mass ranged from 221- 330 g and we needed them to weigh closer to 400 g, given the weight of the transmitter, associated harness, and leg band.

13 Figure 1. The original harness design contained two neoprene pads and four separate Teflon straps, each sewed and glued. This harness weighed 4.3 grams.

Figure 2. Our modified harness design features just one neoprene pad and two continuous Teflon strands and no sewed/glued attachment points. Depending on which width of Teflon used, we reduced the harness weight by 2.49 or 3.34 g.

We tested the redesigned harness system using both Teflon weights on a captive long-eared owl belonging to local rehabilitator, Judy Hoy. We did not glue the final top knots of the first harness we attached, using the 3/16” Teflon.

Testing pics Ears after two days and two nights wearing the transmitter without any problems.

Though we were disappointed that we could not attach transmitters to the owls we captured, we were pleased with the development of methodology that will increase our success at capturing long-eared owls in the future.

Previous Research Update

RVRI Research Update 04-30-13