Raptor View Research 2013 Report

Raptor View Research 2013 Report

March 13, 2014

The annual report by Raptor View Research Institute on MPG Raptor Banding and Fall Migration for 2013

MPG Raptor Banding and Fall Migration Summary Report 2013 Raptor View Research Institute

Table of Contents Abstract.........................................................................................................1 Observation Effort and Methods ....................................................................................................1 Weather ...........................................................................................................................................1 General Raptor Migration Summary .............................................................................................2 Species Composition ......................................................................................................................3 Temporal Pattern of Raptor Migration ............................................................................................5 Seasonal Pattern of Raptor Migration .............................................................................................5 High Count Days...............................................................................................7 Species accounts..............................................................................................................................8 Northern Harrier...........................................................................................................................8 Osprey .......................................................................................................................................... 8 Turkey Vulture.............................................................................................................................9 Golden Eagle..............................................................................................................................10 Bald Eagle..................................................................................................................................10 Sharp-shinned Hawk..................................................................................................................11 Cooper’s Hawk ..........................................................................................................................11 Northern Goshawk.....................................................................................................................12 Red-tailed Hawk ........................................................................................................................12 Rough-legged Hawk ..................................................................................................................13 Swainson’s Hawk.......................................................................................................................13 Broad-winged Hawk .................................................................................................................. 14 Ferruginous Hawk......................................................................................................................14 American Kestrel .......................................................................................................................15 Merlin.........................................................................................................................................15 Peregrine Falcon ........................................................................................................................16 Prairie Falcon.............................................................................................................................16 Comparison Between Raptor Count Sites ....................................................................................17 Fall 2012 Trapping and Banding Results ...................................................................................... 18 Summary ........................................................................................................................................ 21

Table of Figures Figure 1: Total observations per day during 2011-2013 fall counts on the MPG Ranch............2 Table 1: Summary of raptors counted during fall surveys on the MPG Ranch .......................3 Figure 2: Percentage of raptors separated by group counted fall 2013 on the MPG Ranch..........4 Figure 3: The number of raptors counted in one-hour intervals during 2013 fall migration at the MPG Ranch..................................................................................5 Figure 4: Seasonal patterns of raptor migration during fall 2013 at the MPG Ranch. ................6 Figure 5: The number of raptors counted in ten-minute intervals during fall 2013 highest-count days..................................................................................7 Figure 6: The North American Range of Turkey Vultures................................................9 Table 2: Summary of fall 2013 count data and survey effort from four raptor count sites in Montana.............................................................................................17 Figure 7: Comparison of raptor observations between the MPG Ranch, Nora Ridge, Bridger Mountains and Jewel Basin during the fall 2012 counts.....................................18 Table 3: Number of raptors captured during fall migration 2011-2013...............................20 Figure 8: Proportion of Raptors Captured at Each Trapping Site by Group...........................20

MPG Fall Raptor Migration Summary Report 2013 Abstract: This report summarizes fall 2013 raptor counting and banding at the MPG Ranch. During 70 days of counting from 2 September to 12 November, we counted 5,077 diurnal raptors of 17 species. This total is higher than the sum of our two previous seasons. Additionally, we banded 81 raptors of 10 species from 9 September - 27 October. Observation Effort and Methods We counted migrating raptors from 2 September through 12 November for a total of 431.5 hours. Inclement weather prevented observations on 2 of the 72 days. As in previous years, West Baldy Ridge (GPS location: 46°42'19.49"N, 113°58'46.37") was our primary lookout. We used Indian Ridge (GPS location: 46°41'34.60"N, 114° 1'47.16"W) when West Baldy Ridge was engulfed in stratus clouds, and as an additional count site when the number of observers allowed. Counts were conducted from West Baldy Ridge 20 days, from Indian Ridge 18 days, and from both sites 32 days. Observers communicated with hand-held radios when using both count sites to ensure raptors were not double counted. This year’s count was conducted by three primary observers (Eric ‘Kerr’ Rasmussen MPG Ranch, Amy Seamen RVRI, and Kris Guymon RVRI). Primary observers had prior raptor counting experience, and used either 8X or 10X high-quality binoculars. Additionally, 20X – 60X spotting scopes were available for long-distance identifications. We recorded species, age, sex, altitude, lateral direction and distance, and approach and departure bearing for each bird that passed the observation site. We hope to identify patterns in the paths of migrating raptors as this dataset grows, and use this information to improve survey locations and methodology. Weather We recorded weather conditions each hour. Of the 70 days we conducted a count, 38 were overcast and cloudy. There was precipitation on 23 days. We were unable to count on two days, due to low visibility from heavy precipitation. The high temperature for the season was 30 °C (4 September), and the season low temperature was -5°C (30 October). Wind speeds were mild (0- 10 kph) most days, though on 28 days speeds >20kph were recorded. Winds were northern or southern most often (40% and 34% of observations respectively) and occasionally western (20%). As in the two previous falls, we rarely recorded winds from the east (6%). Visibility was good for the vast majority of count days; fog severely hampered visibility on just two surveys.

General Raptor Migration Summary We recorded 5,077 migrating raptors (Figure 1). This total compares to 2,375 in 2012 and 2,163 in 2011, and is the largest seasonal count of migrating raptors ever recorded in Montana. We observed 3,322 migrants, 65% of our season total, from 26 September-3 October, including a state record of 983 raptors on 1 October. This peak period was far earlier than those observed in previous seasons. We believe these unprecedented, high-count days were due to a period of severe, winter weather across the region. While most of western Montana was in the depths of a persistent, snowy system, the Bitterroot Valley and Mission Valley to the north had relatively good weather. Migrant raptors likely capitalized on these openings, and funneled into the Bitterroot Valley. While we saw record numbers of birds in late September-early October, Montana’s other raptor count sites tallied unusually few birds and/or were unable to survey because of inclement weather. Though we used the lower site more often this fall, which improved our ability to detect some migrants, we do not believe this accounts for the drastic differences between our totals and those of 2011 and 2012. Many of the birds recorded by the lower site were also observed from the higher site; had we used the West Baldy Ridge count site alone this fall, we would still have observed far higher numbers than in previous years. Figure 1: Total observations per day during 2011-2013 fall counts on the MPG Ranch. To compare 2013 totals to 2012 and 2011, we capped the vertical axis of the main figure at 250 observations per day. The actual values of six days whose total is greater than 250 can be seen to scale in the inset figure.

Species Composition We observed 17 species during fall 2013 counts. The five most abundant species included: Turkey Vulture (1,861), Red-tailed Hawk (973), Sharp-shinned Hawk (591), American Kestrel (344), and Cooper’s Hawk (288) (Table 1). Despite the large increase in total birds counted this season, we saw similar numbers of eagles, Prairie Falcons, Ferruginous Hawks, and Rough- legged Hawks as in previous years, and fewer Northern Harriers. Table 1: Summary of raptors counted during three fall surveys on the MPG Ranch. 

Turkey Vultures, which comprised an insignificant portion of the 2011 and 2012 fall counts, were the most observed group this season. Of the 3,322 raptors we counted from 26 September-3 October, 1,666 were Turkey Vultures. This total is staggering; a sum of just 73 total Turkey Vultures were counted in the 2011 and 2012 fall surveys. Apart from this major change, and a small decline in Northern Harriers, each group’s contribution to the total count was comparable to previous seasons (Figure 2). Figure 2: Percentage of raptors separated by group counted during the fall 2011-2013 surveys on the MPG Ranch.

Temporal Patterns of Raptor Migration As in 2011 and 2012, we counted few migrants before noon and after 5 P.M. each day, though counts were rarely conducted before 10 A.M. or after 5 P.M. Approximately 67% of migrants passed between 12-3 P.M. (Figure 3). Figure 3: The number of raptors counted in one-hour intervals during 2013 fall migration at the MPG Ranch.

Figure 4: Seasonal patterns of raptor migration during fall 2013 at the MPG Ranch. For illustrative purposes, numbers of detections were averaged over three day periods to minimize the effect of day-to-day variability.

High-Count Days Our highest counts occurred on 26 September, 1 October, and 3 October with 665, 983, and 541 raptors observed respectively. Turkey Vultures made up the bulk of the 26 September and 1 October totals, while Red-tailed Hawks, Sharp-shinned Hawks, and American Kestrels contributed more to the 3 October count. Most migrants passed between 11:30 A.M. and 3:00 P.M. on all three days. While we recorded high numbers of raptors until 6:00 P.M. on 1 October, the late-afternoon hours were relatively quiet on 26 September and 3 October (Figure 5). Figure 5: The number of raptors counted in ten-minute intervals during fall 2013 highest- count days.

Species Accounts Northern Harrier (NH): We counted 109 Northern Harriers from 5 September-9 November this season, compared to 203 in 2012 and 137 in 2011. As in previous years, we counted them fairly regularly throughout the entire season, though never in large numbers.Osprey (OS): We recorded 121 Osprey from 5 September-12 November. The peak of Osprey migration occurred during the last week of September. As in previous years, we infrequently saw Ospreys throughout the second half of the season; we counted only 12 (10% of this season’s count) after the first week of October. This season’s total count of Osprey was much higher than in previous years, largely due to a push of birds around the last week of September.

Turkey Vulture (TV): We counted 1,861 Turkey Vultures from 10 September-24 October, including 601 individuals on 1 October, making them this season’s most observed species. This total compares to a sum of 73 counted in the previous two seasons. We recorded over 90% of our Turkey Vulture count between 23 September and 3 October. Turkey Vultures are not known to regularly migrate through any specific area of Montana in great numbers. Montana’s three other fall migration count sites average less than 10 passing Turkey Vultures each season. Western Montana is at the northern limit of the Turkey Vulture’s breeding range; while we believe weather was responsible for diverting these birds into the Bitterroot Valley, it remains unclear where they were diverted from (Figure 5).

Sharp-shinned Hawk (SS): We counted 591 Sharp-shinned Hawks from 2 September-12 November, making it the third most observed species this season. Their numbers were evenly distributed around a peak in early October. The daily high occurred on 3 October when we recorded 76 individuals.Cooper’s Hawk (CH): We counted 288 Cooper’s Hawks from 2 September-22 October. Like Sharp-shinned Hawks, their numbers peaked around the start of October. Though we regularly observed Cooper’s Hawks until the third week of October, their numbers dropped sharply after peaking; we recorded less than 20% of the total after 1 October.

Northern Goshawk (NG): We counted 32 Northern Goshawks this season from 13 September- 30 October. Though less pronounced than that of the two other accipiter species, we observed a peak of Northern Goshawks around the beginning of October.Red-tailed Hawk (RT): Red-tailed Hawks were the second most observed species this season. We counted 973 between 2 September and 12 November. Our peak counts of Red-tailed Hawks occurred during the first few days of October, including a count of 162 on 3 October. Numbers stayed fairly high until the third week of October, after which we had few days with high counts. As in 2011 and 2012, our Red-tailed Hawk total was higher than that of Montana’s three other count sites.

Rough-legged Hawk (RL): We observed 101 Rough-legged Hawks this season from 1 October- 9 November. Rough-legged Hawks are a northern-breeding bird, and typically aren’t observed until the second half of our fall surveys. In the three fall counts conducted on the MPG Ranch thus far, we have not seen Rough-legged Hawk in the month of September, and saw less than 15% of the 412 total individuals recorded before October 15. Because they migrate later than other species, we did not see a dramatic increase in Rough-legged Hawk numbers due to weather patterns in September and October.Swainson’s Hawk (SW): We counted 16 Swainson’s Hawks from 20 September-4 October. Though it is difficult to draw conclusions from such a low number of observations, Swainson’s Hawk numbers also seemed to increase during the weather events of 26 September-3 October. We counted seven individuals on 27 September and four on 1 October; compared to a daily high count of two in previous years.

Broad-winged Hawk (BW): We saw many more Broad-winged Hawks this year compared to previous seasons. We counted 122 individuals from 12 September-3 October. We recorded a daily high count of 39 on 27 September. Like Turkey Vultures, Broad-winged Hawks often travel in groups on shared thermals known as kettles; we observed them moving in these groups more frequently than as individuals. Ferruginous Hawk (FH): As in the fall surveys of 2011 and 2012, we observed very few Ferruginous Hawks this season. We saw six between 18 September and 19 October. Because Ferruginous Hawks are rarely observed at raptor count sites across the U.S., we know little about their migration ecology.

American Kestrel (AK): We counted 344 American Kestrels from 2 September-29 October, including a daily high count of 78 on 3 October. American Kestrels migrate early; we saw less than 5% of the 759 individuals counted in the past three seasons after October 15. Our daily counts of American Kestrels peaked between 26 September and 3 October.Merlin (ML): We counted 30 Merlins from 10 September through 14 October, compared to just 9 in 2012 and 6 in 2011. We counted most Merlins between 8 October and 14 October, several weeks later than the peak migration of most other raptors.

Peregrine Falcon (PF): We counted 21 Peregrine Falcons from 9 September through 8 October. This total compares to 8 in 2012, and 4 seen in 2011. We recorded 9 individuals during our period of high daily counts from 26 September-3 October.Prairie Falcon (PR): We recorded 12 Prairie Falcons this season from 10 September-8 October. Prairie Falcons are relatively uncommon across the U.S., and are one of the most infrequently counted birds at most raptor count sites.

Comparison Between Raptor Count Sites Raptor counts took place at four sites in Montana during fall of 2013, though sites differed in start and end dates and overall effort (Table 2). While the MPG Ranch saw record numbers of migrants, the total counts of the Bridger Mountains and Jewel Basin were lower than their previous five-year averages. Nora Ridge saw a 14% increase in raptors counted, compared to its previous five-year average. Weather limited counts at the MPG Ranch on just two days and Nora Ridge five days, while the Bridger Mountains and Jewel Basin lost 14 and 19 days respectively. As in previous years, the species composition of Montana’s four count sites were very different (Table 2). Our totals of Turkey Vultures, Red-tailed Hawks, Broad-winged Hawks, Osprey, were much higher than the other three sites, while our total of Golden Eagles was much lower. Table 2: Summary of fall 2013 count data and survey effort from four raptor count sites in Montana.

Count metric

Fall 2013 Trapping and Banding Results We conducted our second full season fall banding effort. In addition to the banding site on West Baldy Ridge used in 2012, we constructed another station just above the Floodplain, west of the Rockpile. As in 2012, we used live Rock Doves, European Starlings, and House Sparrows to attract passing raptors. As raptors attempted to take the lures, they were captured in manually controlled bow nests. Trapping was conducted by Adam Shreading, Tyler Veto, Erick Enzien, Brooke Tanner, Jesse Varnado, and Pat Little. We banded from 9 September-28 October. We trapped from both sites 30 days, West Baldy Ridge only on six days, and from the Floodplain only on 12 days.

We captured 81 individuals of 10 species (Table 3). Though our total captures were similar at both sites, and Accipiters made up the majority of captures at both sites (Figure 8), we believe the addition of the Floodplain site allowed us to target some different species. This year we captured six Merlins, all at the Floodplain. Falcons commonly forage while migrating; the Merlins captured at the Floodplain were likely hunting in the vegetation along the Bitterroot River as they moved south.

Figure 8: Proportion of Raptors Captured at Each Trapping Site by Group. Though we were pleased with the productivity of the new Floodplain site, we had a difficult time attracting birds traveling east of the blind, just above eye level. We believe moving the trapping site to a slightly higher elevation to the southeast may increase the number of birds captured. We were surprised to see the number of captures at our site on West Baldy Ridge drop from 63 in 2012 to 37 this season. With only two trapping seasons conducted at the site thus far, it is impossible to know whether 2012 was particularly good for this location, or if 2013 was particularly unproductive.

Summary We counted markedly more raptors this year compared to 2011 and 2012, setting Montana state records for the most migrant raptors counted during a season (5,077), and most migrant raptors counted in one day (983). Turkey Vultures, typically one of the least counted species at Montana’s count sites, were our most counted species this year. Additionally, we recorded our highest annual tallies for 12 of the 16 other species observed. We believe our increased totals were most likely due to a regional weather pattern between 26 September and 3 October that funneled birds into the Bitterroot Valley. We recorded our lowest annual counts of Golden Eagles and Northern Harriers, while numbers of Bald Eagles and Rough-legged Hawks fell between the totals of 2011 and 2012. We captured a total of 81 raptors this season, an improvement from the 63 captured in 2012. We attribute this increase to the use of a second Floodplain blind used in conjunction with our site on West Baldy Ridge. Accipiters accounted for most captures at both sites. We captured more falcons at our lower trapping site, including six Merlins, a species not previously captured on the MPG Ranch. With just three years of fall counts conducted so far, we are still establishing what “typical” numbers of migrants are. While we may feel confident saying this year’s count of Turkey Vultures was high, we are still determining what range of totals are “normal” for other species. Similarly, we are still learning how to improve our capture strategies. We will continue to alter our trapping locations and methods, as we learn more about the flight paths raptors use as they migrate over the MPG Ranch.

Previous Research Report

2013 Mapping Songbird Territories in Woody Draws on the MPG Ranch

Next Research Report

Avian Acoustic Monitoring - Spring and Fall 2013

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