Western Screech-Owl Inventory (Megascops kennicottii macfarlanei), Okanagan Region, 2007

Transcription

1 Western Screech-Owl Inventory (Megascops kennicottii macfarlanei), Okanagan Region, 2007 Prepared by Nigel Jackett, Megan Traicheff, Kersti Vaino, and Vicky Young British Columbia Conservation Corps Penticton, BC Prepared for BC Ministry of Environment Penticton, BC September 2007

2 Executive Summary The BC Conservation Corps South Okanagan Species at Risk crews were tasked with conducting Interior Western Screech-Owl (Megascops kennicottii macfarlanei) call playback surveys in the southern interior of British Columbia during the breeding season of The main objective of the project was to survey sites that had previous M. k. macfarlanei detections to assess multiple year occupancy. This effort resulted in a total of 429 call-playback stations. The total owl count was 69 and included 6 species of owl. Of these, the most numerous were the targeted species, Interior Western Screech-Owl, which totaled 28 (42%). Data gathered during this inventory will possibly be used to assist in making future management and conservation decisions. Acknowledgements We would like to thank: Ministry of Environment biologists Jared Hobbs and Orville Dyer for providing historical data, maps and guidance; Dick Cannings for providing the historical data spreadsheet of Western Screech-Owl sites; Tolko Industries and the BC Conservation Corps for providing funding for this project; and the BC Conservation Foundation for providing administrative support. We would also like to thank Tolko Industries for providing habitat suitability maps, and the BC Conservation Corps for providing all field equipment and supplies. 1

3 Table of Contents Executive Summary... 1 Acknowledgements... 1 Table of Contents... 2 List of Figures... 2 List of Tables... 2 Introduction... 3 Study Area... 3 Methods... 3 Results... 5 Discussion... 8 Conclusion and Recommendations... 8 References... 9 Appendix 1: Owl Survey Forms List of Figures Figure survey stations and Western Screech-Owl detections in the Okanagan, Kettle, Similkameen, Thompson and Shuswap drainages... 6 List of Tables Table 1. Numbers and relative percentages of each owl species detected during the 2007 BCCC Western Screech-Owl call playback surveys Table 2 Summary of survey results for previously detected sites that were resurveyed in

4 Introduction In British Columbia, there are currently two recognized sub-species of Western Screech- Owls: coastal (Megascops kennicottii kennicottii) and interior (M.k. macfarlanei). The interior Western Screech-Owl subspecies is provincially red-listed in British Columbia and is managed under the IWMS (Identified Wildlife Management Strategy). Federally, it is listed as endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and the Species at Risk Act (SARA). The South Okanagan is the distribution center for the interior subspecies of Western Screech-Owl in B.C. They are most frequently found in low elevation deciduous or mixed deciduous-coniferous forests (usually riparian) and typically nest in mature black cottonwood trees (Populus trichocarpa) (Cannings et al. 1987). Western Screech-Owls tend to use cavities in large diameter deciduous trees, usually made by Northern Flickers (Colaptes auratus) or Pileated Woodpeckers (Dryocopus pileatus), for nesting and roosting (Cannings 2004). The BC Conservation Corps (BCCC) was tasked in 2007 to conduct Western Screech- Owl occupancy surveys in the Okanagan, Kettle, Similkameen, Thompson and Shuswap drainages of British Columbia. The project concentrated on surveying areas with previous detections. This included detections from survey efforts by the BCCC in 2006 and other recorded detections within the southern interior of British Columbia as amassed by the Ministry of Environment (MOE), birders and other local biologists. Information gathered during these surveys could potentially be used to establish Wildlife Habitat Areas (WHAs) and help inform future management and conservation decisions. Study Area The main areas of interest for our project (BCCC South Okanagan Species at Risk) were the Okanagan, Kettle, Similkameen, Thompson and Shuswap drainages in the southern interior of British Columbia (Figure 1). Call playback transects were placed to target mature cottonwood riparian habitat and previous detections in these areas. Methods Occupancy surveys were conducted using a call playback method to determine a presence or a presence not detected. Broadcast stations were placed along a linear transect which usually followed a road. Two walking transects involved hiking a designated trail within the habitat. Transects typically consisted of 15 stations, located approximately 500 metres apart, and covered an average linear distance of 7.5 kilometres, depending on the amount of suitable habitat. Survey areas were selected based on historical detection locations and both habitat suitability maps and road maps to locate accessible potential habitat. Transect routes were laid out in advance during daylight hours to locate prime habitat to 3

5 target and locations with optimal acoustics. Stations targeting historic detections were placed as close to the location of the historic detection as possible. Call playback surveys started at sunset. Stations started with an initial broadcast bout of 1 to 1.5 minutes. Western Screech-Owl territorial calls (bouncing ball) were broadcast using a megaphone and attached CD player. Stations lasted 15 minutes with calling bouts of approximately 1 minute every 4 minutes. Surveyors listened for owl responses during and in between each broadcast. If an auditory response of the targeted species was heard, broadcasting was stopped to avoid harassment of the species and surveyors listened for the remaining time. Broadcasting was also stopped if a Barred Owl or Great Horned Owl was heard and surveyors moved on. These 2 species are potential predators to the Western Screech-Owl and surveyors wanted to limit the risk of a predatory attack if a Screech-Owl was nearby. Stations were also terminated if Western Screech-Owls from previous stations could still be heard calling to limit disturbance to the owl. Additional time was added to stations where there was loud traffic or other noise to compensate for the diminished ability to hear any owls. Data for the owl surveys was recorded according to provincial Wildlife Species Inventory (WSI) standards on the field forms in Appendix 1. For each transect, the names of the surveyors, the time of sunset, the date as well as a transect description including start and end UTMs (Universal Transverse Mercator units in NAD 83), a sketch of the transect area and a brief description of the targeted habitat was recorded. At the start and end of each transect, the wind speed (using the Beaufort scale), air temperature, precipitation (none, light rain, moderate rain, heavy rain) and cloud cover (clear, <50%, >50%, 100%) were recorded. At each station, the survey name, start and end time of the station and UTM from a GPS unit (Garmin, GPSmap 60Cx, Legend Cx, or Vista C) were recorded. Comments were noted for stations where background noise (eg. river noise, wind, or dogs barking) was prominent enough to affect the integrity of the survey. When an owl was detected, the station number, species code (ie. WSOW for Western Screech-Owl), call time, response time (time elapsed between the first broadcasted call and the time of the first detected owl call), call duration, call type (eg. territorial, juvenile begging, etc.), type of detection (visual or acoustic), call direction using a compass, approximate distance to the owl, age class (adult or juvenile), and sex were recorded. In some species the difference in calls between male and female can be quite obvious and in others it is more difficult to confirm. Thus, sex of the owl was recorded only when the surveyors were certain, otherwise it was marked as unknown. UTMs for detected owls were projected with a handheld GPS unit using the estimated distance and direction. The GPS co-ordinates (owl detections and survey stations) were uploaded onto field laptops using Garmin MapSource software. Surveyors also incidentally noted Common Nighthawks (Chordeiles minor) heard during the surveys since these have recently been listed as Threatened by COSEWIC. Common Poorwills (Phalaenoptilus nuttallii) were also noted. These birds are not federally listed but surveyors thought it worth collecting this information as they are from the same family as the Common Nighthawk and are also insectivores. 4

6 All data collected during the 2007 inventory was then entered into a MOE Species Inventory (WSI/SPI) Data System spreadsheet that will be added to the Species Inventory Web Explorer (SIWE) dataset. Maps were developed using Arcmap9 by creating shapefiles based on UTM locations. Results A total of 33 transects were surveyed by the BCCC crews throughout the 2007 field season. Surveys were interspersed throughout the season in the following manner: 7 transects between May 5 th -7 th, 2 transects June 29 th, 15 transects between July 24 th 31 st, 3 transects August 1 st and 2 nd and 6 transects from September 4 th 9 th. This effort resulted in 429 call-playback stations (Figure 1) with a total survey time of 6376 minutes ( hours). The surveys resulted in 67 owl detections representing 6 different owl species (Table 1): Western Screech-Owl, Great Horned Owl (Bubo virginianus), Barred Owl (Strix varia), Flammulated Owl (Otus flammeolus), Northern Pygmy Owl (Glaucidium gnoma) and Northern Saw-whet Owl (Aegolius acadicus). A total of 28 Western Screech-Owls were found at 24 of the 429 stations resulting in a detection rate of 5%. Western Screech-Owls and Great Horned Owls were detected at almost equal rates, 42% (28/67) and 39% (26/67) respectively. Table 1. Numbers and relative percentages of each owl species detected during the 2007 BCCC Western Screech-Owl call playback surveys. Owl Species Common Name Owl Species Scientific Name Number of Detections Relative Percentage Western Screech-Owl M. k. macfarlanei Great Horned Owl Bubo virginianus Barred Owl Strix varia 9 13 Flammulated Owl Otus flammeolus 2 4 Northern Pygmy Owl Glaucidium gnoma 1 1 Northern Saw-whet Owl Aegolius acadicus 1 1 All Owl Species Call response time for Western Screech-Owls was variable but 17 of the 24 owls detected (71%) responded within the first 12 minutes of the station. Great Horned Owls and Barred Owls, potential predators of the Western Screech-Owl, were each detected at one station where there was also a Screech-owl calling. 5

7 Figure survey stations and Western Screech-Owl detections in the Okanagan, Kettle, Similkameen, Thompson and Shuswap drainages. 6

8 As mentioned in the Methods section, the sex of an owl detected was only noted when surveyors were certain of it. Juveniles, whose calls are quite distinct, were also noted. Thus, of the 28 Western Screech-Owls detected 6 were noted as male, 6 were juveniles and 16 were unknown. Three of the 24 sites where Screech-Owls were detected had more than one detected owl, in each case an adult of undetermined sex and one or more juveniles. Adult pairs of owls were not detected at any of the sites. Reproduction was confirmed at 5 sites based on the presence of one or more juvenile(s) but this does not represent reproductive success as surveys were not all conducted during times when young could be detected. Of the 26 Great Horned Owl detections 4 were female, 4 were male, 14 were juveniles and 4 were unknown. For Barred Owls, 7 were adults (sex unknown) and 2 were juveniles. The 2 Flammulated Owls were males. The Northern Pygmy Owl was an adult (sex unknown) and the Northern Saw-whet Owl was a juvenile. Cannings (2007) identified 193 locations with previous detections of interior Western Screech-owls and categorized them as representing non-breeding (38), possible breeding (133) or confirmed breeding (22) records. The BCCC crew surveyed 62 of these sites in 2007 and Screech-Owls were detected at 10 of these sites. (Table 2) Table 2 Summary of survey results for previously detected sites that were resurveyed in Cannings breeding category Previous detections # Surveyed in 2007 # Detected in 2007 Confirmed Breeding Possible Breeding Non-breeding Total Transects were only surveyed once during the project, due to time constraints, with the exception of six transects: one transect at Douglas Lake Road, Mission Creek East, BX Creek and Chase Falkland Road and two along the Salmon River. These transects were each surveyed twice, in both July and September. During the Western Screech-Owl surveys 13 Common Nighthawks were detected; 4 of these were near Falkland, 1 near Vernon, 2 near Summerland, 1 near Penticton and 5 near Okanagan Falls. 7 Common Poorwills were also detected; 5 of these were near Vernon and 2 were near Okanagan Falls. 7

9 Discussion For a more effective assessment of re-occupation, transects should have been surveyed more than once during the breeding season. Multiple repetitions of survey transects are recommended for the Western Screech-Owl as response rates may vary throughout the breeding season (Hausleitner 2006, Cannings and Angell 2001). Furthermore, as some previous detections were within a few hundred metres of each other, they could in actuality be representing the same site. To avoid this, future re-occupancy studies might find a polygon approach to previous detections to be more accurate. Also, the spot check method utilized at some historic detections meant that the entire potential suitable habitat in the area might not have been covered by the survey. This was usually the case when access to the historical site was an issue due to private land or road accessibility. Reoccupancy of a site does not suggest it is the same owl as in previous years or that the owl is nesting at that particular site. Occupancy surveys simply determine the presence of a resident owl or a floater (Hausleitner 2006). Conclusion and Recommendations The 2007 BCCC survey provided information on the occupation and re-occupation of sites by the Interior Western Screech-Owl within the southern interior of British Columbia. A recommendation for future surveys is to have multiple repetitions of transects during the breeding season to better assess occupancy of sites. 8

10 References Cannings, R.J Western Screech-owl location database. BC Ministry of Environment working document. Penticton. BC. Cannings, R.J.and H. Davis The status of thewestern Screech-Owl (macfarlanei subspecies) Megascops kennicottii macfarlaneiin British Columbia. BC Ministry of Environment working report. Victoria. BC. Cannings, R.J Interior Western Screech-Owl. Accounts and measures for managing identified wildlife. Ministry of Water, Land and Air Protection, B.C. Accounts V. Cannings, R.J., and T. Angell Western Screech-owl. In the Birds of North America No. 597 (A. Poole, P. Stettenheim and F. Gill, eds.). Philadelphia: the Academy of Natural Sciences; Washington, DC: The American Ornithologists Union. Cannings, R.A., R.J. Cannings and S.G. Cannings Birds of the Okanagan Valley, British Columbia. Royal British Columbia Museum. Victoria, BC. Hausleitner, D Inventory methods for owl surveys: Nocturnal owls that respond to call playback of recorded calls. Standards for Components of British Columbia s Biodiversity No.42. V Prepared for the Ecosystems Branch of the Ministry of Environment for the Resources Information Standard Committee. 9

11 Appendix 1: Owl Survey Forms 10

12 11