Conserving Purple Martins on McDonald-Dunn Forest, Benton County, Oregon

Transcription

1 Conserving Purple Martins on McDonald-Dunn Forest, Benton County, Oregon 2011 Progress Report Dave Vesely Oregon Wildlife Institute

2 Introduction The purple martin (Progne subis) is the largest swallow in North America and among the largest in the world 1. The species was reported to be common in the southern Willamette Valley during the 1940 s 2, but populations appeared to be in steep decline through most of the state during the 1940 s 1980 s 3. It was during this period that forestry practices were causing a reduction in the number of snags in most regions, and thus decreasing the availability of cavity nesting sites for purple martins. Numbers of European starlings (Sturnus vulgaris), a serious, non-native competitor for nest sites, also dramatically increased in Oregon during this period and certainly contributed to lower productivity of martin populations 4. There is some evidence that populations may be undergoing a recovery in local areas (e.g., Oregon Coast, Fern Ridge Reservior), largely due to the effectiveness of artificial nest box programs 5. The purple martin is presently listed as state sensitive-critical by the State of Oregon and is listed as a species of concern by the U. S. Fish and Wildlife Service (USFWS). Local birders have been observing a small purple martin colony (probably three breeding pairs) in two clearcuts located at Oregon State University s (OSU) McDonald-Dunn Forest (T10S R5W Secs 15,17; Figure 1). Purple martins have been using cavities excavated by woodpeckers in snags that have been retained on clearcut harvest units. Informal, but regular observations suggest that European starlings are becomingly increasingly numerous near the McDonald- Dunn Forest martin colony and agonistic behavior between martins and starlings has been observed at the site (personal observation). What makes the McDonald-Dunn Forest colony particularly special is that the martins continue to nest in natural tree cavities. Only a small portion of the western U. S. population continues to use snags. Most known colonies in the Northwest now rely on boxes and gourds for nesting and the eastern U. S. population is entirely dependent on manmade structures 6. The primary objective for this first year of conservation actions by the Oregon Wildlife Institute (OWI) was to install two types of supplemental nesting structures in McDonald-Dunn Forest and monitor their use by purple martins. Observations this year will be used to guide the types of artificial nest structures used in the future, as well as their placement. A secondary objective was to begin marking individual martins with numbered leg bands to facilitate regional population analyses of the species. 1 Brown, C Purple martin (Progne subis). In, A. Poole and F. Gill (Eds.) Birds of North America. Number 287. The Academy of Natural Sciences (Philadelphia) and the American Ornithologist s Union (Washington D.C.). 2 Gullion, G. W Birds of the southern Willamette Valley. Condor 53: Sharp, B Guidelines for the management of the purple martin, Pacific Coast population. Sialia 8: Korpi., R. T European starling (Sturnus vulgaris). Pp In, D. B. Marshall, M. G. Hunter, and A. L. Contreras [Eds.]. Birds of Oregon: a general reference. Oregon State University Press. Corvallis, OR. 5 Horvath, E. G Distribution, abundance, and nest site characteristics of purple martins in Oregon. Oregon Dept. of Fish and Wildlife Technical Report Cousens, B. Personal communication. Oct. 25, Page 1

3 2011 Activities Nest Site Enhancements Two artificial gourd racks mounted on 14 ft. poles were erected during spring 2011 near natural snags that have been used for nesting by martins during the last several breeding seasons (Table 1, Figure 2). Each rack is capable of supporting 12 plastic gourds with starling-resistant entrances, although only 6 gourds were mounted on each rack during the 2011 breeding season. Two important design features of the gourd racks are 1) the ability to lower the aluminum arms supporting the gourds to ground level, and 2) a large access opening in the side of each gourd that is normally sealed with a threaded cap. These features permit easy inspection inside of the gourds and removal of nestlings for banding, thereby avoiding the need for a ladder or tree climbing. Table 1. Descriptions of eight known purple martin nest cavities and project activity sites. Site Identifier Description TAMS Cluster of conifer snags known to be used by purple martins since 2008 TAMR Artificial gourd rack installed spring S Single Oregon white oak snag known to be used by purple martins since 2008; 3 wood nest boxes attached to snag spring R Artificial gourd rack installed spring B 2 individual wood nest boxes attached to a snag in spring B 6 individual wood nest boxes attached to two snags in spring 2011 MAC1 Purple martin nesting activity at a conifer snag discovered in 2011 MAC2 Purple martin nesting activity at a conifer snag discovered in 2011 The racks were positioned near the known natural nest sites to increase the likelihood that they would be investigated by purple martins returning to the area. However the height of vegetation was also considered in selecting rack locations. Purple martins prefer open habitats and usually select nest cavities well above surrounding trees and/or shrubs. The rack locations selected in 2011 should be suitable for two or three more years. By then, the planted Douglas-firs will reach the height of the gourds and make the racks unsuitable for nesting. To our knowledge, these are the first artificial gourd racks that have been erected in the Willamette Valley, although they have been used along the lower Columbia River in Oregon. Eleven wood nest boxes designed specifically for purple martins were installed on snags in clearcuts at three locations in McDonald-Dunn Forest (Table 1, Figure 2). These nest boxes are of an identical design used on USFWS refuges in the Willamette Valley and at the U. S. Army Corp of Engineers Fern Ridge Reservoir colony in Lane County. The Natural gourds have been used to attract purple martins for more than 100 years. Artificial gourds are durable, easy to clean, and have an opening that makes nest inspection easy. Page 2

4 wood nest boxes are more familiar to at least some purple martins breeding in the Willamette Valley and wood boxes may be more attractive than the novel gourd racks to these individuals. Monitoring Observations were made at the gourd racks and individual nest boxes at least twice a week from March 7 to August 15, 2011 (Table 2). The first purple martins returning to McDonald- Dunn Forest were observed on April 28. As during previous years, martin activity centered on the oak snag at the 110S site and multiple conifer snags at the TAMS site (Figure 2). A male martin was also observed investigating a nest box at the 210B site, but was chased off by a pair of western bluebirds. Purple martins were observed entering and exiting two different cavities in snags for several weeks at the TAMS site. However, the height of the cavities prevented us from confirming the presence of nestlings in these cavities. The single cavity at the 110S oak snag was also the focus of activity for several martins and probably represents a third nest in a snag at our McDonald- Dunn Forest sites this year. We were especially pleased to discover purple martins using the gourd rack at the 110R site. We had assumed that it may take more than one breeding season for the birds to become sufficiently familiar with these structures before attempting to nest in them. The martin nest in gourd #1 was mostly constructed with fresh leaves and twigs from Oregon white oak and had a thin lining composed of a few feathers. An almost identical nest was discovered in a different gourd on rack 110R, but martins were never actually observed entering that gourd. It remains unknown whether this second nest was started and abandoned by the pair using gourd #1, or a failed attempt by a different pair. A high proportion of the artificial nest structures (gourds and wood boxes) were used by songbirds this year. Species that nested in these structures included violet-green swallows (Tachycineta thalassina), tree swallows (Tachycineta bicolor), One of the purple martin nestlings discovered in gourd rack 110R. This bird is approximately 12 days old. western bluebirds (Sialia Mexicana), and house wrens (Troglodytes aedon). No attempt was made to evict these birds since we could have hung additional gourds for martins if needed. Fewer European starlings were observed along Tampico Road near the TAMS site than in the recent past. Our observations indicate that there was probably only one pair nesting in the area, although numerous starlings were observed on agricultural lands less than one mile to the north. During July, Roberta Swift (U. S. Army Corp of Engineers) reported a sighting of multiple purple martins in a clearcut approximately 3.5 mi from the TAMS site. I made a 90 minute Page 3

5 reconnaissance visit later that month and observed at least 18 purple martins flying above the clearcut and martins entering cavities in two different snags (MAC1 and MAC2, Figure 1). Joan Hagar (U. S. Geological Survey/FRESC) and I have also observed martins flying above lower Soap Creek Valley on multiple occasions this year and we assume these birds are associated with the MAC1/MAC2 colony. This colony should be considered as a location for additional conservation activities. Banding Five purple martin nestlings found in gourd #1 at Rack 110R were banded by Joan Hagar on August 1. All of the nestlings appeared robust and had no signs of external parasites, a cause of mortality in many nestling birds. Federal (aluminum) bands with numbers to were attached to the left leg. Red color bands with codes corresponding to Federal bands, OR A220 to OR A224, were attached to the right leg. The gourd was last rechecked on August 15. No nestlings remained in the gourd and no martins were in close proximity of the gourd rack. It is assumed that the 5 juveniles fledged successfully. Table 2. Significant purple martin observations and project activities made during the 2011 season. Dunn Forest, Benton County, Oregon. Date Site Note Mar 7 All Observations begun; Rack 110R installed April 20 All Rack TAMR installed; first violet-green swallow observed this year April S A pair of martins observed at oak snag; first martins seen this year May 3 110S 5 martins observed flying near snag May 4 110S 3 wood nest boxes attached to oak snag May 7 240B Wood nest boxes installed May S Male & female martins observed bringing nest material to snag cavity June 6 110R Female martin flying close overhead as gourds were checked June R Two martins perched in snag near rack June R Female martin observed exiting gourd #1; gourd #1 lined with fresh oak leaves and a couple of feathers; gourd #3 has an identical nest; at least 6 martins flying near rack June 25 TAMS Two martin pairs observed frequently entering/exiting snag cavities July 2 110R Female martin perched on rack July 8 MAC1 At least 7 martins circling 50 ft snag; 1 martin observed entering snag cavity July 8 MAC2 Male and female martins observed entering/exiting snag cavity July 15 TAMS Two martins making repeated visits to a shrub to collect nest materials; martins active at 3 different snag cavities July R Martin observed entering gourd; 2 nd martin made repeated dives at volunteer observer July R 5 martin nestlings found in gourd #1 July S Martin chicks heard in snag July S 4 or 5 adult martins very active near nest cavity July R A martin was observed investigating several gourds August 1 110R 5 martin nestlings in gourd #1 are measured and leg-banded August 15 All Last observations Page 4

6 Approximately 120 purple martins were also banded by Joan Hagar at Fern Ridge Reservoir this summer. This represents the most intensive banding effort of purple martins in the Willamette Valley to our knowledge. Future Plans 2011 was the first year of planned 5 year project intended to increase the population of purple martins in northern Benton County. Providing martins artificial nest sites seems necessary at the McDonald-Dunn Forest colony where there is significant competition from starlings. However it is hoped that some of the martins produced at this location will colonize other forest sites deeper in the Oregon Coast Range where starlings are rare. Clearcut harvest units in which clusters of large diameter snags have been retained are probably suitable breeding habitat for the species, although there is almost no research or monitoring effort the precise nesting habitat requirements of the species in forested environments. During the next two breeding seasons we hope to see increased martin use of the artificial gourds and wood nest boxes at the McDonald-Dunn Forest sites. If the local martin population expands in response to the supplemental nest sites, our project will seek additional locations for installing nest structures on nearby private and public lands in the following years. The ODFW E. E. Wilson Wildlife Refuge is approximately 3 miles from the McDonald-Dunn Forest TAMS site and contains extensive wetlands that are likely to provide good foraging habitat for martins. E. E. Wilson also offers the opportunity to foster a stepping stone colony between McDonald-Dunn Forest and the Willamette River if sub-adult martins can be Joan Hagar weighing a purple martin nestling. Band numbers and other information about each nestling will be provided to the USGS Patuxent Wildlife Research Center. attracted to new artificial nest structures installed on the Refuge. OWI is collaborating with Oregon State University Horticulture and several farms along the Willamette River to establish new wildlife conservation projects. OWI will seek permission to install martin nest structures on these farms if the McDonald-Dunn Forest population expands. Our long-term goal is to create several colonies along Willamette River between U. S. Fish and Wildlife Service s Baskett Slough and W. L. Finley Refuges, where there are other ongoing purple martin conservation efforts. Page 5

7 Acknowledgments OWI would like to thank the following contributors to the project: Molly Monroe and the USFWS Willamette Valley Refuge System for the donation of wood nest boxes OSU College Forests for permitting us access to the purple martin sites and allowing us to conduct conservation actions on their lands OWI volunteer Carly Gerhardstein for the long hours devoted to monitoring purple martins this year Joan Hagar of the U. S. Geological Survey/Forest and Rangeland Ecosystem Science Center for contributing to project planning and performing the leg banding of martins And we are especially grateful for the grant provided to our project from the Oregon Wildlife Heritage Foundation. The Oregon Wildlife Institute is a non-profit organization dedicated to the conservation and enhancement of wildlife resources in both native and human-altered environments through research, education, and conservation planning. Visit our website at Page 6

8 Figure 1. Vicinity map of OSU McDonald-Dunn Forest with project activity sites. Benton County, Oregon.

9 Figure Detail aerial photo of project activity sites on OSU McDonald-Dunn Forest. Benton County, Oregon. Page 1