Small Mammal Trapping Baseline Surveys Mother Goose Lake
Alaska Peninsula/Becharof NWR, Alaska June-August 2003
Susan Savage
Key Words: Alaska Peninsula, Arctic shrew, Sorex articus, dusky shrew, Sorex monticolus, home range, masked shrew, Sorex cinereus, meadow jumping mouse, Zapus hudsonius, Mother Goose Lake, northern red-backed vole, Clethrionomys rutilus, Nyanzol-D fur dye, population cycles, pygmy shrew, Sorex hoyi, Sherman live traps, tundra shrew, Sorex tundrensis, tundra vole, Microtus oeconomus
U.S. Fish and Wildlife Service Alaska Peninsula National Wildlife Refuge Complex P.O. Box 277 King Salmon, AK 99613
February 2004 Abstract
Small mammal trapping at Mother Goose Lake continued on the Alaska Peninsula National Wildlife Refuge for the ninth consecutive year and the eighth year at the same location. We do not plan to return to the trapping grid in 2004. A trapping grid of one hundred Sherman live traps was used to conduct this study. Seven mammal species were captured in 2003: the Arctic shrew (Sorex articus) or tundra shrew (Sorex tundrensis), masked shrew (Sorex cinereus), pygmy shrew (Sorex hoyi), dusky shrew (Sorex monticolus), northern red-backed vole (Clethrionomys rutilus), tundra vole (Microtus oeconomus), and meadow jumping mouse (Zapus hudsonius). Shrew identifications are based on a modified dichotomous key and will be corrected or confirmed when specimens are sent to a museum for identification. Masked shrews were the most abundant species captured in 2003. The northern red-backed vole population did collapse this year, one year after predicted. Meadow jumping mice captures increased this year to tie the previous high capture year of 2000. Morphological measurements, sex, and the presence of ectoparasites were noted. Fur dye was used for the third year and we experimented with dye marking individual animals for the second year.
Introduction
Prior to this study at Mother Goose Lake, small mammals on the Alaska Pensinsula had received little attention from the scientific community. Work included inventories in the Meshik-Kujulik Bay area (Braided Creek), Ugashik-Wide Bay area (Dog Salmon), Herendeen-Balboa Bay drainages (Lawrence/Grass valley; Wilk et. al .1986), and Aniakchak Caldera and Bay (Jerrell 1987, Trapp 1993). Goals of the Mother Goose survey, and other subsequent inventories at refuge field camps, included determining species presence, obtaining morphological data, tracking population trends, and determining habitat relationships. The 2003 effort was prompted because the predicted decline of northern red- backed voles did not occur in 2002 and was anticipated this year. Further background is provided in Savage (2003). This year a concurrent small mammal trapping project was conducted at Puale Bay (Menard and Savage In Prep). Recently, other agencies have begun to show an increased interest in small mammals on the Alaska Peninsula (Larson 2002).
Study Area
Mother Goose Lake is located at 57°11' N, 157°15' W along the Alaska Peninsula within the Alaska Peninsula National Wildlife Refuge (Figure 1). The small mammal trapping grid is situated along the southeast portion of the lake and to the west of nets 2 and 3 of the MAPS LAKE Site (Figure 2). A cottonwood forest borders the grid on the southern, western, and eastern sides with a willow (Salix pulchra, S. barclayi and S. niphoclada) and alder (Abuts crispa) thicket bordering the northern side. The habitat within the study area consists largely of dwarf shrubs including crowberry (Empetrunt nigrum), Labrador Tea (Ledum palustre), and lowbush cranberry (Vaccinium vitis-idaea), and moss, lichens, forbs and grasses. The willow bushes are interspersed in pockets throughout the grid with taller thickets being found along the cottonwood edges. Gridlines A and B actually lie within the edge of the cottonwood / willow / alder thicket on the east. Although quantitative data does not exist
2 Alaska Peninsula and Becharof National Wildlife Refuges
Becharof • Alaska Towns N, Lake L 1 Becharof r--- 'National Wildli Becharof NWR Refuge Alaska Peninsula NWR
I (P„C.k. Chignik Unit ...Si ft.> Ugashik Unit ,10{
Mother Goose Lake Alaska Peninsula National Wildlife Refuge (Ugashik Unit)' Gulf ofAlack
Figure 1. Location of Mother Goose Lake field station within the Alaska Peninsula National Wildlife Refuge and the state of Alaska.
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30 0 30 60 90 120 150 Meters 1
• Traps Cottonwood forest Crowberry tundra Medium shrub ivHorsetail Creek
Figure 2. Location and details of small mammal trapping grid including mist net lanes and trails, Mother Goose Lake.
4 from early years, my impression is that low and medium shrub and cottonwood are increasing on the grid.
Methods
The trapping grid was established under the specifications provided by Eric Rexstand of UAF. One hundred folding Sherman live traps (22.5 x 7.5 x 8.8 cm) were placed approximately ten meters apart on a series of eight lines labeled A-H. Lines A, C, D, and E each contained 10 traps, while lines B and H consisted of 13 traps each, and F and G had 17 traps each (Figure 2). Plastic non-zip sandwich bags containing hulled sunflower seeds for food and cotton or polyester bat for warmth were placed in each trap. The traps were baited by scattering hulled sunflower seeds in and around the entrance to the traps. Each trap was checked four times a day at 5-6 hour intervals except overnight (trap checks at 0600-0645, 1100, 1600, 2100), during a seventy-two hour session in June (23-26), mid summer (July 31-August 3), and August (24-27).
The mammal captures were identified to species with the aid of External Key to Alaska Cricetal and Arvicolid Rodents (MacDonald, 1982a), External Key to Alaska Shrews (Soricidae) (MacDonald, 1982b), and Smithsonian Book of North American Mammals (Wilson and Ruff 1999). In past years the shrew key had been used as general guidance for shrews. This year, because of a greater confusion, and perhaps a closer examination of the shrews in the field, stricter adherence to this key was followed with some exceptions. See Appendix 1 for notes on shrew species determination.
Morphological data was collected on captured mammals in millimeters (mm) according to Ingles (1965), including measurements of total length (nose to tail), tail, hind foot, and ear. Morphological measurements were reported as ranges and averages. Additional information noted for each specimen included mass in grams (g), sex, and the presence/absence of ectoparasites. Morphological data is summarized only for first time captures.
Marking methods were modified slightly from 2002. Each new capture was marked with a fur clip. Shrews were fur clipped on the rump only. Voles and jumping mice were marked with individual fur clip and dye patterns using Nyanzol-D fur dye (see dye instructions in Leppold and Savage 2001). Simpler patterns using dots and lines were used; we avoided marking against the "hair grain" of the animals. Fur clips corresponded to dye patterns so individuals could be identified if the dye had not developed yet. A small squeeze bottle with a narrow tip was acquired for dye application. As recommended in 2002, the same staff members were present at all trapping sessions in order to improve individual recognition.
Because individuals were identified, additional information is summarized about individual patterns of trap use and home range. Maximum distance between traps where an individual was captured and Minimum Convex Polygon area (connect the outer dots of the polygon; only for animals captured at more than two trap locations) were calculated using ArcView for one northern red-backed vole, one tundra vole and two meadow jumping mice.
5 Habitat use, as determined by vegetation classes, was evaluated within a 5 m radius of each trap location. Vegetation categories included cottonwood forest, tall shrub (> 2.5 m), medium shrub (1.1 — 2.5 m), low shrub (0.4 — 1.1 m) and dwarf shrub (< 0.4 m). At each trap a shrub / forest category was selected as dominant; each forest / shrub category was given a percent score for canopy cover. In addition, herbaceous plant and some dwarf shrub species were quickly surveyed. Species of dwarf shrub present were also noted and the presence of tussocks was also recorded. Captures by small mammal species in specific vegetation categories were compared against the number of traps available within that vegetation type. When sample sizes were sufficient, log-likelihood tests for goodness of fit were performed to compare availability of habitat type vs. number of traps with captures of each species in a habitat type and vs. number of captures of each species in a habitat type.
As in 2002, animals are counted as "New" if they are unmarked, or in the case of an escaping animal, if presence of a marking was not determined before they escaped. Escapes will also be tallied in the "escape" column. To obtain the total animals captured, only the New and Recapture columns are summed. Escapes produce two kinds of errors: non-detection of a marked animal upon recapture and non-detection of a previously captured animal that was not marked. Mortalities will also be shown on the initial tally table.
Following refuge field camp tradition, incidental avian and mammal observations were taken while trapping crews were in the field.
Results
The 118 captures were identified to seven species and one genus (because of escapes) of insectivores and rodents. Of those 118 captures, 92 were new and 26 were recaptures; seven individuals escaped prior to being identified as marked or prior to being marked (Table 1). Masked shrews comprised 34% of all captures, dusky shrews comprised another 14%, meadow jumping mice comprised 14%, Arctic / tundra shrews comprised 13%, northern red- backed voles comprised 10%, pygmy shrews comprised 7%, unidentified shrews (escapes) comprised 5%, and tundra voles comprised 3%. No non-target species (weasels or squirrels) were captured. Of only new captures, masked shrews comprised 38%, dusky shrews comprised 16%, meadow jumping mice comprised 15%, Arctic / tundra shrews comprised 12%, pygmy shrews comprised 8%, unidentified shrews comprised 7%, and northern red- backed and tundra voles comprised 2% each. Voles have a higher tendency to be recaptured than other small mammal species; only 2 (16%) of the 12 northern red-backed voles captures were new captures, and 50% of tundra vole captures were new. By contrast, 88% of meadow jumping mice captures were new, 88% of all masked, dusky and pygmy shrew captures were new, and 73% of all Arctic / tundra shrews were new.
Twenty small mammals died during trap operations resulting in a mortality rate of 17%. Of these mortalities, 13 were masked shrews, one was a dusky shrew, three were Arctic / tundra shrews, and 3 were pygmy shrews. Two animals died in the June trapping session, seven died in the mid-season session, and 11 died in the August session. All mortalities except one were likely due to stress, hypothermia, or lack of appropriate food in traps for the shrews. One shrew was caught in a trap door. All animals that died were collected this year as specimens.
6 We are currently making arrangements with the University of Alaska — Fairbanks museum for identification and curation of the specimens.
Table 1. Small mammal captures by month, Mother Goose Lake - 2003.
23-26 June 31 July - 3 Aug 24-27 August Totals Species N R E M N R E M N REM N R E M TOT Arctic / Tundra Shrew 2 5 2 1 4 2 2 11 4 3 15 Masked Shrew 2 19 1 5 14 4 8 35 5 13 40 Pygmy Shrew 2 2 2 1 3 I 7 I 3 8 Dusky Shrew 1 3 11 2 1 15 2 I 17 Sorex sp. 2 1 2 2 2 2 6 0 5 0 6 N. Red-backed Vole 2 3 7 2 10 0 0 12 Tundra vole 2 2 2 2 0 0 4 Meadow Jumping Mouse 3 1 1 1 10 I 1 14 2 2 0 16 Grand Total 12 I 2 2 34 6 2 7 46 19 3 1 1 92 26 7 20 118 N= new captures R= recaptures E=escaped M= Mortality Escapes: animals that escape before they can be marked or before their marked status is determined (Assumed to be and recorded as new).
Morphological measurements for the seven potential species captured this year are reported in Table 2. Measurement ranges for total length, tail length and weight as reported in Wilson and Ruff (1999) are also displayed. Weather (excessive rain) created exceptionally challenging field conditions this year. Because of this, examination for ectoparasites and for sex was much abbreviated. In addition, the field observers continued to have a difficult time determining sex on shrews and some of the other animals. With these limitations in mind, meadow jumping mice are the only species worthy of comment on sex ratio. Considering two out of 12 individuals were unidentified to sex, the ratio of the remaining sexed animals was approximately even. Few external parasites were detected included one tick on masked shrews, fleas on one dusky shrew and one jumping mouse, orange fungus on one red-backed vole, and mites on one tundra vole (five infestations were found on 92 animals).
We continued to track the number of disturbed traps. We noted one disturbed (seed and insulation removed from trap) and ten snapped traps in June, five snapped traps in mid- season, and one broken trap, 15 disturbed traps and 47 snapped traps in August. Thirty of the August disturbances including the broken trap were attributed to the 1600 trap run on 25 August. It appeared that one animal systematically disturbed a large part of the grid. Another major source of disturbance this year was thought to be birds that removed seed and insulation from the traps. The total disturbance rate over 3600 trap sets was 1.8%, slightly higher than the rate of 1.2% last year.
7 Table 2. Morphological data for small mammal first time captures, Mother Goose Lake, 2003.
Arctic / Tundra Masked Shrew N. Red-backed Shrew Pygmy Shrew Dusky Shrew Tundra Vole Meadow Jumping Vole Mouse sample literature sample literature sample literature sample literature sample literature sample literature sample literature Total Avg. 95.9 84.1 81.3 102.9 124.0 149.5 204.9 Length (aim) N 10 35 7 15 2 2 12 *A:100-124 Range 85-109 T:85-120 73-98 75-125 74-88 60-105 84-114 95-140 115-133 Tail 127-161 145-154 152-225 194-219 180-235 Avg 34.3 35.1 29.7 45.2 29.5 40.5 122.7 Length (mm) N 10 35 7 15 2 2 A:36-45 12 Range 28-48 T:20-35 33-37 30-50 24-32 20-40 38-51 30-60 24-35 30-48 Foot (mm) 38-43 30-54 114-132 100-135 Avg. 11.4 10.3 9.7 11.8 17.5 17.5 29.6 N 10 35 7 15 2 2 12 Range 10-13 9-11 8-11 10-13 17-18 15-20 Ear (mm) Avg. 26-33 11.0 N 12,0 9.8 1 2 Range 12 11 12 Weight (g) Avg. 7-12.5 5.8 3.4 3.7 4.6 29.3 51,3 20.0 N 11 35 7 15 2 2 A:5-13 12 Range 4-9 T:5-10 2.5-6.5 2-5 2.5-5.5 2-7 3-6 4-10 27.5-31 23-40 50-52.5 25-80 Ectoparisitcs Mites 14.5-31,5 12-30 Number of Fleas 1 1 Animals Fungus 1 1 Infected Ticks 1 Sex Female 0 3 2 1 1 1 6 Male 1 0 1 0 0 1 4 Unknown 10 32 4 14 1 0 2 * A = Arctic Shrew, T = Tundra Shrew As in 2002, the crew visited traps on a regular schedule this year making it easy to quantify captures by capture time. Total captures by species are corrected by the number of hours between trap checks giving a "relative capture rate." 1 Capture rates are displayed by time and species in Figure 3. Capture rates for all animals were 7 capture / hour at 0600, 2.4 captures / hour at 1100, 4.4 captures / hour at 1600 and 4.2 captures / hour at 2100. The most striking patterns are found in the species with the highest number of captures. Masked shrew and red- backed voles avoided traps in mid morning. Dusky shrew avoided mid morning and sunset, and jumping mice were almost exclusively caught at sunrise.
Figure 3. Captures rates by time of day and species, Mother Goose Lake - 2003.
2.50 A— Dusky Shrew 2.00 Masked Shrew 1.50 MJ mouse 1.00 NRB Vole 0.50 - n 0.00 4 :— Pygmy Shrew 600 1100 1600 2100 —A-- T. Vole —II— Tundra Shrew Capture Time
Figure 4 shows 2003 captures per trap and vegetation types as categorized this year. Habitat data as represented by vegetation types was collected at each trap and is listed in Appendix II. As demonstrated in Figure 4, trap use was not random across the grid. Of the 100 traps on the grid only 61 traps captured the 118 captures recorded. Two traps had six captures, six traps had four captures, six traps had three captures, 17 traps had two captures, and 30 traps had one capture. Recapture of the same animal did not always account for the high individual trap use. Up to four different species were caught in some of the individual traps.
This year we found 57 traps where dwarf shrub dominates, three traps where low shrub dominates, 28 traps where medium shrub dominates, one trap where tall shrub dominated and 11 traps where cottonwood dominated (Table 3; Figure 4). Many of the traps in crowberry- dominated habitat had no captures. However, traps in cottonwood, medium shrub or near the cottonwood edge were more likely to have captures. While examining use of vegetation, I also noted patterns between small mammal species. Contrary to 2002, meadow jumping mice were captured in at least one trap used frequently by voles. As in 2002 shrews used traps that were used by voles or by jumping mice.
To give a real rate this number should be divided by the number of traps (100) and the number of days (9), but since all relative rates would be divided by these same numbers giving very small numbers, this relative rate is used.
9 Clif-6•F_6 00/4 .00,011.1.0 4. G-5 eF-5
Key 3 Number of Captures at Traps c3t_2 c)-2 dr 0 C11-1 0 1 GAF-1 C) 2 GO •F.° ED 3 al 4 011 •G1 •F1 al ci e131 0A1 @ 5 - 6 Q.1 2 2 •A2 elks/Horsetail Creek alE2 CDI•eC2D2 eleG3 (1)13 Vegetation Types at Traps 414 • Cottonwood G4 F4 C134 0A4 n Q-15 •G5 FICE 5 B 50A 5 Tall Shrub 0-16 Ao F6 0E6 417 .G6 $ G7 CF7 CD7 Medium Shrub 0E7 Q-18 038 *F48 LD8 Low Shrub H9 CFR9 QD9 C8 Ctsi €110 • G9 011041P9 n 0A10 Dwarf Shrub G10 Cb10 Cho Q310 **we
20 20 40 60 80 100 Meters
Figure 4. Habitat at each trap site and total captures by trap, Mother Goose Lake, 2003. Number of traps used and total captures were tallied by small mammal species and by dominant vegetation category (Table 3). Captures of pygmy shrews and both vole species were too few to comment on habitat use patterns. Dusky shrews were captured in all habitat types, but medium or low willow was present at all capture locations. Dusky shrew trap use or captures per habitat type were not significantly different from the available habitat on the grid. Masked shrew and meadow jumping mouse trap use and number of captures per habitat type were significantly different from the available habitat (number of traps: G=6.93, 6.93, p <0.05 for both species; number of captures: G=5.85, 6.93, p <0.1 for masked shrew, p<0.05 meadow jumping mouse). Masked shrews and meadow jumping mice were captured more often in medium shrub and cottonwood when compared to the number of traps available in those habitats. Arctic shrew captures (but not number of traps used) were also significantly different from trap availability (number of captures: G = 14.06, p<0.001). Arctic shrews were captured in dwarf shrub in greater proportion to traps available in that habitat. This is a simplistic view of habitat use patterns. Because habitat is a many dimensional feature, greater understanding of habitat preferences might be obtained through the use of multivariate statistics.
Table 3. Habitat characteristics of trap sites and capture sites by species, Mother Goose Lake - 2003.
Dwarf Low Med Tall Cotton- Shrub Shrub Shrub Shrub wood Total Notes Traps 57 I 3 28 1 11 100 "[raps with captui es (Total Captures) Arctic / Tundra 10 dwarf shrub present at all cap Shrew (11) 2 (3) 1 (1) 13 (15) loc. med or low willow present at 11 14 Masked Shrew 7 (8) 32 (40) all cap loc, dwarf shrub (13) (19) present at most and grass present at most Pygmy Shrew 3 (3) 3 (3) 2 (2) 8 (8) dwarf shrub present at all cap loc. Dusky Shrew 6 (9) 1 (1) 5 (5) 1 (1) 1 (1) 14 (17) med or low willow present at all cap loc N. Red-backed Vole 1 (1) 1 (3) 3 (8) 5 (12) Tundra Vole 3 (4) 3 (4) Meadow Jumping Mouse 4 (4) 8 (8) 4 (4) 16 (16) medium or low shrub found at all cap loc 38 33 ) 91 Total Used 1 (1) 1 (1) 18 (24) (45 ) (41 (112)
In addition to using individual dye marks on voles and mice as in 2002, we used individual fur clip patterns. We marked two individual northern red-backed voles, two tundra voles and ten meadow jumping mice. One northern red-backed vole was marked twice because on the third recapture of the animal we recognized that the rump fur was "worn" but did not recognize it as a fur clip, i.e., recapture. Only two individual meadow jumping mice were recaptured.
11 We were able to recognize one individual northern red-backed vole, one individual tundra vole and two individual meadow jumping mice with our marking method. This northern red- backed vole was recaptured ten times over two months and one tundra vole was recaptured two times. Table 4 displays individual capture patterns, furthest distance documented, and home range by minimum convex polygon for the one animal captured in more than two traps. Furthest distance between traps for both vole species this year was about 25 m and for meadow jumping mice ranged from 72 to 111 m. Home range for the northern red-backed vole was 49 sq. m. This was small compared to most measured home ranges for voles in 2002.
Table 4. Individual animal data showing number of captures, distance documented and home range, Mother Goose Lake — 2003.
Approx. time Total Species Dye Mark btw first and last # traps Furthest Area captures capture visited Distance sq in N. Red-backed Vole Center Dot 1 month 11 4 25.2 49 Tundra Vole Rt. Hip 1 day 3 2 25.4 NA M. Jumping Mouse Center Dot 1 day 2 2 71.5 NA M. Jumping Lt. Hip Mouse 2 months 2 2 110.7 NA
Incidental observations of birds and mammals detected no species that had not previously been noted at Mother Goose Lake (Appendix III).
Discussion
Another year of capture data has added additional insight about small mammal population fluctuations. Northern red-backed vole numbers did fall to a record low this year. As surmised last year, northern red-backed vole peaks lasted for two years (Table 5, Figure 5). Our trapping project indicated the population cycle was five years long during this period at Mother Goose Lake. Running simultaneous trapping projects at other field locations also provides evidence that northern red-backed vole cycles are not synchronized across the entire Alaska Peninsula, Northern red-backed vole capture rates at Puale Bay were greater in 2003 than in the previous two years (Menard and Savage In Prep.). Incidental observations in King Salmon also indicated that northern red-backed voles were numerous during the summer of 2003. Tundra voles have been missing on the grid since 1999. Continued trapping at Mother Goose might give some insight into factors affecting their populations.
Meadow jumping mice captures fluctuate more subtly with a low of four captures in 2002 and a high of 14 captures in 2000 and 2003. Jumping mice exhibited highest captures during years of low northern red-backed vole captures and vice versa. The lowest capture of jumping mice occurred in 2002 when northern red-backed vole captures were were extremely high. Jumping mice captures may be an artifact of trap availability or exclusion by northern
12 •
Table 5. Comparison of captures over all years, Mother Goose Lake 1996 - 2003. All previous year escapes summed with New.
1996 1997 1998 1999 2000 2001 2002 2003 N R N R N R N R N R N R N R N R Arctic / Tundra Shrew I I 4 Masked Shrew 41 2 0 33 1 1 29 1 45 3 43 1 35 5 Pygmy Shrew 7 I Dusky Shrew 4 7 1 2 15 2 Total Shrews 41 4 40 1 29 45 45 68 N. Red-backed Vole 48 83 60 76 4 19 24 12 35 60 91 37 143 2 10 Tundra Vole 19 48 14 7 1 2 2 M. Jumping Mouse 9 6 8 4 6 2 8 4 14 7 6 1 4 2 14 2 Brown Lemming I Least Weasel i Short-tailed Weasel I 1 Arctic Ground Squirrel 1 TOTALS _ 158 139 92 87 90 4 _ 32 28 85 43 156 95 131 146 _ 154 26
Figure 5. Small mammal fluctuations, Mother Goose Lake 1996 - 2003 (new captures only).
80 70 60 E' 50 —4—N. Red-backed Vole tz 40 —a— M. Jumping Mouse C.% 30 —X-- Tundra Vole 20 —a-- Total Shrews 10 0 red-backed voles as much as an indication of their population trends. Because shrew identifications are still preliminary it is difficult to draw many conclusions about shrew population trends. Total shrew captures fluctuated from high to low over a two-year cycle from 1996-2000. But shrew captures have been consistently high since 2000. Peak highs and lows vary interspecifically indicating that different factors affect the populations of each species. Because of the limitations of study design and resources, causes of population fluctuation at the Mother Goose Lake site are unknown. Summer weather data has been collected at Mother Goose Lake from 1994 - 2000 and year round weather has been collected since the instillation of a Remote Area Weather Station in July 2000. Examination of summer (June - August) precipitation, minimum monthly temperature and maximum monthly temperature show no correlation to small mammal population trends. If year round weather data was available, analysis of winter trends might show significant patterns. In Savage (2003), I speculated that trapping effort may not have been uniform across years. I also speculated on the negative impact of toe-clipping on captures and recaptures.
Rates of recapture continue to vary greatly from species to species and year to year. Northern red-backed voles generally show the highest recapture rate and this year it increased to 5.0. This recapture rate was attributable to one animal. This is the highest recapture rate ever documented (Table 6). Tundra voles show the next highest recapture rate although this year's rate was second to 1996. As noted in 2002, the cessation of toe-clipping may be responsible for the marked increase in recaptures. Some voles now exhibit what is known in mark- recapture literature as "trap happy," probably in response to the reliable food source and nesting material and with little aversive stimuli.
Table 6. Recapture rates (Recapture / New) for commonly captures species, Mother Goose Lake, 1996 - 2003. 1996 1997 1998 1999 2000 2001 2002 2003 Masked Shrew 0.05 0.03 0.03 0.07 0.02 0.14 N. Red-backed Vole 1.73 1.27 1.26 2.92 1.52 3.86 5.00 Tundra Vole 2.53 0.50 1.00 M. Jumping Mouse 0.67 0.50 0.33 0.50 0.50 0.17 0.50 0.14
Meadow jumping mice recapture rate fell this year. Even if the two escapes had been detected as recaptures instead of assumed to be a new, the recapture frequency would have only been 0.33. Note that the two jumping mice that were recaptured moved over a large distance. Perhaps many mice were dispersing and thus reduced the possibility of being recaptured. Masked shrews had a lower recapture rate when compared to the rodents. However, this year's rate was higher than all other years and was twice the previous high rate of 7%. Two contributing factors to the particularly low recapture rate in shrews are mortality, and non-detection of recaptures. This year mortality was lower in shrews than in other high shrew capture years (not 1997 or 1999; see Table 7). Only a few shrews were released without being marked or without being carefully checked (when environmental conditions were poor to reduce mortality) and most of these were late in August when the probability of recapture was low anyway. This year escape rate was also lower in shrews
14 compared to most years and especially compared to 2000 and 2001. Decreased mortality and fewer escapes increases the proportion of animals marked and thus increases the probability of detecting a recapture.
Table 7. Mortality rates (number dead / total capture) of small mammal species, Mother Goose Lake, 1996-2003. Only shrews and northern red-backed voles have died during trapping.
1996 1997 1998 1999 2000 2001 2002 2003
Sorex sp. 0.49 0.50 0.12 0.00 0.57 0.29 0.48 0.23 N. Red-backed Vole 0.02 0.01 0.00 ' 0.00 0.00 0.02 0.01 0.00 Total Animals 24 3 5 0 17 17 24 20
Morphological measures can be compared to previous years and to the literature (See Table 2). Since morphological measures were heavily used to identify Sorex species, most animals sampled fall within the published ranges (Kays & Wilson, 2002) for their species. Note that eight of ten shrews identified as Arctic / tundra fall within the ranges for tundra shrews for total length and tail length and below the range for Arctic shrews (i.e., they are more likely to be tundra shrews by morphology). The other two animals fall within either species' range for total length and in the Arctic shrew range for tail length. As size was used heavily to separate dusky and masked shrews, masked shrews sampled fall toward the lower end of the range reported in the literature. Masked shrew average measurements for 2003 are more similar to those reported in 1995, 1996, 1998, 2000 and 2002 than for those reported in 1999 and 2001 (Leppold & Savage 2001, Savage 2003). Dusky shrews also fall below and toward the lower end of their reported range for total length possibly indicating misidentification or immature animals, although all tail lengths are within reported range. Comparative data for past years is limited for dusky shrews. Measurements for pygmy shrew also fall within the reported ranges for this species. One of two captured voles measured less than the minimum range for total length and tail length reported in Kays and Wilson (2002). Since only two animals constitute the 2003 sample, comparison to other years means little. One of two tundra voles fell below the reported range for total length. All meadow jumping mice fell into the measurement range reported for their species except one weighed slightly heavier than the reported limit. Measurements from 2003 for jumping mice generally fell in the middle ranges of other years' averages.
In all years marking has been used to identify previously captured animals from those that had not been captured that season. This was the second year we made an attempt to mark individual animals. Most of the recommendations made in 2002 regarding marking were adopted. In 2002 we recommended having at least one staff member present at all trap sessions to facilitate individual recognition. Even with the same staff on hand, individual recognition was not always improved, probably because of the challenging weather. However, copious notes allowed any recognition errors to be reconciled later. Fur clipped rumps were successful in identifying recaptured shrews. Because of excessive rain this year, we were not as successful marking animals with Nyanzol-D dye. Recapture rates were much reduced and two errors in following the marking patterns occurred on jumping mice this year so it is more difficult to comment on the success of the individual marking program.
15 As recommended in 2002, a larger area was considered around each trap for vegetation analysis and percentage score of each vegetation type were collected. When examining the influence of vegetation on animal captures it is difficult to tease out whether habitat type presence alone or its dominance is of importance to the animal. Vegetation type use by each species generally agreed with those described in Wilson and Ruff (1999). Dusky shrews are described as the most general of the shrews with regard to habitat and we captured them in traps located in all vegetation types. Arctic / tundra shrews were captured mostly at dwarf shrub locations which concur with their reported use of the boreal forest region with preference for the non-forested habitats. Masked and pygmy shrews were intermediate in the distribution of vegetation types used as described. Tundra voles were found preferentially in dwarf shrub dominated vegetation types; this finding also agrees with the habitat preference described in the literature. Meadow jumping mice were found in three vegetation types and Wilson and Ruff describe them as users of grass fields and woods.
Previous Mother Goose reports indicate that capture rates for crepuscular and diurnal hours vary from year to year, with little to no correlation to the capture patterns of the previous year (Savage 2003, Leppold & Savage 2001, Young 2000, Margulies 1999, Foster 1998). This year I corrected captures by approximate length of trap set and re-examined capture rate for time of day. Because in 1996 — 2001, traps were not checked on a regular schedule across the season or even within a trapping session, it was difficult to compare between years. Only enough data existed for northern red-backed vole, masked shrew and meadow jumping mice. Most species of shrew are reported to be active primarily at night with dusky shrews reported to have short bursts of daytime activity (Wilson & Ruff 1999). Wilson and Ruff make no comment on northern red-backed vole activity patterns. No clear pattern emerged for northern red-backed voles or shrews; patterns varied from year to year as reported above. However, meadow jumping mice do tend to be captured more frequently in the dawn or early morning trap checks. This does agree with literature reports of primarily nocturnal activity (Wilson & Ruff 1999).
This project is the longest continuing small mammal study undertaken along the Alaska Peninsula and has contributed important long-term biological information. Information has been gained about the presence, abundance, morphology, and vegetation use patterns of various species. Defining population cycles continues to be a challenge. This basic information will contribute to our understanding of mammal and bird species that are dependent on small mammals as a primary food source. Thus an understanding of small mammal populations adds to our understanding of ecosystem function in general.
Recommendations
• Although further effort at Mother Goose Lake would add additional insight to northern red-backed vole, tundra vole and meadow jumping mouse population trends, perhaps more insight about small mammal species and populations in general can be gained by directing effort elsewhere. Therefore, I recommended small mammal projects should be moved to other locations on the refuge.
16 For all recaptured animals, take measurement of at least total length, tail length and weight to assist in confirming individual identification.
Develop a mobile shelter to use when raining to protect animals from wetting and improve morphological sampling.
Continue to experiment with individual animal marking (also see recommendations from 2002).
Obtain further information on ectoparasites including collecting samples if a cooperator for identification is available.
Acknowledgements
Thanks to field staff volunteer Bob Blush for his work through lots and lots of rain and long hours to assist the author in the field. Funding for the small mammal survey was provided by the USFWS — Alaska Peninsula / Becharof National Wildlife Refuge. Thanks to Birchwood Air and Branch River Air for safe transportation to the field. Thanks to Wildlife Biologist Ron Squibb for reviewing this report.
Literature Cited
Foster, J. 1998. Small Mammal Mark/Recapture Baseline Surveys Mother Goose Lake Alaska Peninsula/Becharof National Wildlife Refuge Complex, Alaska. USFWS, King Salmon, AK (Unpubl.). 9 pp.
Ingles, L.G. 1965. Mammals of the Pacific States. Stanford University Press.
Jerrell, G.H. 1987. Small mammal survey of Aniakchak Caldera. Nat'l. Park Serv., King Salmon, Alas. (Unpubl). 11 pp.
Kays, R.W. and D.E. Wilson. 2002. Mammals of North America. Princeton University Press, Princeton.
Larson, K.R. 2002. BLM Summer Field Work Mammal Report. Mammal Collection, Univ. Alaska Museum, Fairbanks, Alas. (Unpubl.) 63pp.
Leppold, A. and S. Savage. 2001. Small Mammal Trapping Baseline Surveys, Mother Goose Lake, Alaska Peninsula/Becharof National Wildlife Refuge, Alaska, June-August 2001. USFWS, King Salmon, AK (Unpubl.). 23 pp.
MacDonald, S. 0. 1982a. External Key to Alaska Cricetid and Arvicolid Rodents. University of Alaska, Fairbanks. Fairbanks, AK. 2 pp.
17 MacDonald, S. 0. 1982b. External Key to Alaska Shrews (Soricidae). University of Alaska, Fairbanks. Fairbanks, AK. 4 pp.
Margulies, M. 1999. Small Mammal Mark/Recapture Baseline Surveys Mother Goose Lake Alaska Peninsula/Becharof National Wildlife Refuge Complex, Alaska. USFWS, King Salmon, AK (Unpubl.). 15 pp.
Menard, N. and S. Savage. In Prep. Small Mammal Trapping Baseline Surveys, Puale Bay, Alaska PeninsulalBecharof National Wildlife Refuge, Alaska, June — August 2003. USFWS, King Salmon, AK (Unpubl.).
Nott, P. 2000. Monitoring Avian Productivity and Survivorship (MAPS) Habitat Structure Assessment (HAS) Protocol: describing vertical and horizontal spatial habitat patterns at MAPS stations. Institute for Bird Populations, Point Reyes Station, CA. (Unpubl.).
Savage, S. 2003. Small mammal trapping baseline surveys, Mother Goose Lake, Alaska Peninsula / Becharof NWR, Alaska, June — August 2002. USFWS, King Salmon, AK (Unpubl.). 22 pp.
Trapp, T.W. 1993. Notes on Small Mammal Trapping project, Aniakchak Bay and Aniakchak Caldera, summer 1002, Katmai National Park, King Salmon, AK (Unpubl.)
Wilk, R.J., C.L. Kranich, D.C. McFarlane. 1986. Wildlife and Vegetation studies in the Meshik-Kujulik Bay, Ugashik-Wide Bay, and Herendeen-Balboa Bay Drainages, Alaska Peninsula National Wildlife Refuge. USFWS, King Salmon, AK (Unpubl.). 116 pp.
Wilson, D.E. and S. Ruff. 1999. The Smithsonian Book of North American Mammals. The Smithsonian Institute Press, Singapore.
Young, R. 2000. Small Mammal Trapping Baseline Surveys Mother Goose Lake Alaska Peninsula National Wildlife Refuge, Alaska. USFWS, King Salmon, Alaska (Unpubl.). 13 pp.
18 Appendix 1. External Key to Alaska Shrews (Sorididae) - Interpretation Summer 2002
Original Rule Interpretation Species 1 Total length greater than 140 mm; upper parts Sorex palustris, blackish to blackish-gray, with silvery white or water shrew gray underparts; hind foot 18 mm or more, with conspicuous fringe of stiff hairs on edge of toes.
l' Total length less than 140 mm; body color not as Go to 2 above; hind foot less than 10 mm, without conspicuous fringe of stiff hairs on toes.
2 Body conspicuously bicolored when viewed from All bicolored animals (aka two-toned in Go to 3 the top, the dark back sharply set off from paler notes); Also note many of these animals were sides vocal, while no other unicolored animals were. 2' Body unicolored when viewed from the top. All "blended" or unicolored animals Go to 5
3 Weight of males and non-pregnant females Weighing equipment not accurate to 0.5 g so S. arctieus , arctic greater than 5.5g (avg 7.4 g); body length (tot len all animals were >5 g. except 1; many < 65 shrew - tail len) averaging more than 65 mm; tail, mm for body; all had tail:total ratio < 50%. averaging less than 50% of total length, usually Note 2 animals were sign. Larger than others. conspicuously tipped with tuft of long hairs Key says Arctic shrew but tundra shrew is slightly darker than rest of tail. more appropriate for this range.
3' Weight less than 5.5g (avg 7.4 g); body length one fell in this category Go to 4 averaging less than 65 mm; tail, averaging more than 50% of total length, not conspicuously tufted at tip. 4 Restricted to St. Paul Island, Pribilof Islands. NA S. pribilofensis , Pribilof shrew 4' Absent from St. Paul Island, but present on St. NA S. cinereus, Lawrence Island and on mainland north of the masked shrew Brooks Range. 5 Total length of adults averaging more than 110 11 of 17 animals < 110 mm; all had tails > 37 S. monticolu.s. , mm; tail long, usually more than 37 mm (avg mm. dusky shrew 45). 5' Total length of adults less than 110 mm; tail All animals < 110 mm; all had tails < 37 mm Go to 6 shorter, usually less than 37 mm. (5 = 37 mm). 6 Total length usually less than 90 mm (avg. All animals < 90 mm; tail < 32 mm. S. hovi , 85mm); snout appears blunt and the tail short pygmy shrew (avg 30 mm). 6' Total length usually more than 90 mm; snout Some animals < 90, but all > 73; tail > 33 and S. cinereus, longer and more pointed, tail longer (avg 36 < 37 mm. masked shrew mm) and thicker looking; (Note should use skull characters for positive ID).
19 Appendix II. Habitat characteristics recorded within a 5 m. radius circle of each trap, Mother Goose Lake, 2003
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22 Appendix III. Incidental avian and mammal observations at Mother Goose Lake, June - August 2003,
July 31 - Aug 24 - 23-26 July 31 - Aug 24 - Birds* 23-26 June Aug 3 Aug 27 June Aug 3 Aug 27 Red Throated Loon X X Tree Swallow P X Common Loon X X X Black-capped Chickadee P X X Grebe sp. X Gray-cheeked Thrush Tundra Swan X X Hermit Thrush P X X Mallard X American Robin P X X American Wigeon X American Pipit X Greater Scaup X C X Orange-crowned Warbler P X X Red-breasted Merganser X C X Yellow Warbler Northern Harrier X Wilson's Warbler P X X Bald Eagle X X X American Tree Sparrow X Sandhill Cranes X X X Fox Sparrow X X Gambel's White-crowned Greater Yellowlegs X X X Sparrow P X Least Sandpiper 0 Golden-crowned Sparrow P C X Wilson's Snipe P Pine Grosbeak X Arctic Tern X Common Red pol I P C X Murrelet SP. MAMMALS** Bonaparte's Gull X Brown Bear T T T Mew Gull X X Moose V Glaucous-winged Gull X X X Caribou V Belted Kingfisher X Wolf T T Downy Woodpecker X X Shrew sp. V Alder Flycatcher P Meadow Jumping Mouse V Black-billed Magpie C X X River Otters S S S Common Raven X X ** Key to Mammal Observations: * Key to Breeding Status: T=Tracks 0= Observed/non-breeding P= Probable Breeder V=Visual X= Observed in breeding Habitat C= Confirmed Breeder S=Sign / Scat