PROGRESS REPORT
PROJECT TITLE: American black bears (Ursus americanus): Reliance and impacts on corn
production in northwestern Minnesota
PROJECT NUMBER: 4087-12SP (UM project 00032727)
REPORTING PERIOD: 1/1/2015- 3/31/2015 – Last Report
PRINCIPAL INVESTIGATOR: Mark Ditmer
ORGANIZATION: University of Minnesota – Dept. of Fisheries, Wildlife and Conservation Biology
PHONE NUMBER: 651-895-9883
EMAIL: ditme004@umn.edu
1.) PROJECT ACTIVITIES COMPLETED DURING THE REPORTING PERIOD. (Describe project
progress specific to goals, objectives, and deliverables identified in the project workplan.)
One manuscript that identifies the MNCGA as a funding source was accepted for publication by Ursus
and will be in print inMay. A second manuscript at the Journal of Mammalogy should be accepted
formally in the coming month.
2.) IDENTIFY ANY SIGNIFICANT FINDINGS AND RESULTS OF THE PROJECT TO DATE.
From previous resports:
From previous report:
Here are a few results from the isotope manuscript (preliminary). Below is a table highlighting
bear reliance on different food during different seasons among demographic groups followed by
the abstract from the manuscript.
Population estimates of diet for spring/summer and fall food sources broken down by demographic groups found to have a
strong influence on IDE crop estimates. FWOC = Females w/o cubs, FWC = Females with cubs.
Food Source
Adult Males
Immature Males & Females
FWOC
FWC
Ants
0-11%
2-12%
0-13%
0-7%
Corn
9-23%
0-7%
3-16%
0-11%
Deer
0-3%
0-2%
0-3%
0-2%
Spring Veg. & Summer Fruit
70-85%
84-94%
75-90%
84-95%
Sunflowers
0-7%
0-5%
0-10%
0-2%
Corn
19-39%
1-11%
10-30%
0-11%
A ) Spring/Summer Mixing Model (2/3rds Distal End)
B ) Fall Mixing Model ( 1/3 Root End)
rd
Fall Fruit & Nuts
59-75%
87-96%
67-83%
88-99%
Annual Diet from Crops
12-31%
0-10%
5-24%
0-12%
The American black bear is an omnivore and ecological opportunist currently expanding
both geographic range and population size throughout North America possibly due to the
abundance and availability of anthropogenic food sources. To gain a better understanding of the
causes and consequences of anthropogenic foraging, we studied the diets of a newly established
population of bears living in a highly-fragmented, agricultural region of northwestern Minnesota
from 2006 - 2012. Our objectives were to 1) estimate dietary contributions of seasonally
available foods; and 2) explore relationships between contributions from agricultural food
sources and metrics for physical size, health, demographics, wildland and agricultural food
availability, and for a subset of GPS-collared bears, home range size and landscape composition.
We conducted stable isotope analysis (δN15 and δ13C) on 110 American black bear (Ursus
americanus) hair samples from a total of 51 bears. We estimated the dietary contributions of
early season vegetation, ants, white-tailed deer, fruit and nuts, corn and sunflowers. We found
that males and some females without cubs of the year (FWOC) consumed corn in the
spring/summer (95% credible intervals: males = 9-23%, FWOC = 3-16% ) and to a greater
extent in the fall (corn + sunflowers, males = 19-46%, FWOC = 10-40%) relative to immature
bears (spring/summer = 0-7%, fall = 1-16%) and females with cubs of the year (spring/summer =
0-11%, fall = 0-13%). We corroborated the results of our individual dietary estimates of crop use
by comparing the proportion of diet associated with agricultural sources to the proportion of GPS
locations in corn and sunflower fields (β = 1.99, p < .001, r2 = .43, n= 33). Male bears’ crop
consumption was positively associated with age, increased size, fat thickness and negatively
associated with fall home range size. Females exhibited increased crop consumption with age,
size, and fat thickness while decreasing crop consumption in years with high availability of fall
wildland foods and cub rearing. Male bears were not strongly influenced by landscape
composition or agricultural availability, unlike females whose agricultural consumption was
more closely tied to home range size, local crop availability and landscape composition. Overall
males and females without cubs of the year demonstrated very different levels of risk-adversity,
with male bears more likely to seek out anthropogenic food sources on the landscape. Males and
females benefited similarly from consuming agricultural food sources. More agricultural
consumption was associated with more weight, fat levels and home range size although
discerning the cause and effect relationship between size and agricultural foraging is difficult due
to social dominance behavior.
From the MN DNR technical report for ECOLOGY AND POPULATION DYNAMICS OF
BLACK BEARS IN MINNESOTA (published in 2013) regarding interviews with farmers:
Crop Damage by NW Bears
During 2009–2012 we conducted 38 interviews with growers (36) and apiarists (2) in the
NW study area. Most were long-time residents of the area (average ~30 years). Growers reported
differing amounts of bear damage among crops and crop varieties (Table 7). Among the 25
survey participants who had grown corn in recent years, 91% reported damage from bears. Those
who grew hybrid/grain corn reported more bear-related damage than those who grew field corn
for silage (Table 7). Among 19 sunflower growers, 16 had grown oil sunflowers (used for
cosmetics, cooking, birdseed), 9 confection sunflowers (used for human consumption, birdseed)
and 6 had experience with both varieties. The mean level of bear damage in oil sunflower fields
was significantly higher than confectionary sunflower fields (Table 7). Bears are likely attracted
to the black oilseed for its high fat content (Figure 6). Apiarists (2 of 2, but highly dependent on
year) and oat growers (9 of 9) also reported significant amounts of bear damage. Of 25 growers
of soybeans, the crop with the most areal coverage, only 1 reported bear damage (rated as
minor). Those who grew wheat, canola, barley, alfalfa, sugar beets, and rye grass, grains, or hay
reported low or no distinguishable bear damage.
Tolerance toward bear damage was largely related to the perceived level of past damage: 5
of 26 growers had not incurred any bear damage and all considered themselves tolerant of bears;
among 21 respondents that had incurred bear damage, only 6 (29%) classified themselves
tolerant, 8 (38%) had tolerance “contingent on level of damage” and 7 (33%) were classified as
having no tolerance for bear damage. Accordingly, 5 of 7 (71%) growers who did not report
any damage from bears had not killed or attempted to kill bears and 50% said they would prefer
the same or more bears in the region. Conversely, of 16 growers who reported crop losses to
bears, 10 (63%) had attempted nuisance killing or additional hunting pressure and 73% indicated
that they would prefer fewer or no bears in the region.
Table 7. Extent of black bear-related damage to cropfields in NW Minnesota perceived by
interviewed farmers, 2009–2012. Growers were asked to subjectively rate levels of bear damage
to their crops based on a scale of 0 (no damage) to 5 (major damage).
Number of
Bear damage rating
interviewees
Mean
Hybrid/grain corn
13
3.61
Silage corn
10
1.83
Oilseed sunflowers
15
2.20
Confection sunflowers
9
0.28
Oats
9
2.94
Crop
95% CI
2.71 – 4.51
1.30 – 2.68
1.17 – 3.23
0.04 – 0.52
1.96 – 3.93
3.) CHALLENGES ENCOUNTERED. (Describe any challenges that you encountered related to project
progress specific to goals, objectives, and deliverables identified in the project workplan.)
None during this period.
4.) FINANCIAL INFORMATION (Describe any budget challenges and provide specific reasons for
deviations from the projected project spending.)
The remaining funding from the MNCGA was used during this period for journal page charges (Ursus).
5.) EDUCATION AND OUTREACH ACTIVITES. (Describe any conferences, workshops, field days,
etc attended, number of contacts at each event, and/or publications developed to disseminate project
results.)
Ditmer M.A., T.E. Burk and D.L. Garshelis. Do innate food preferences and learning affect
crop raiding by American black bears? In press at Ursus.
Ditmer M.A., D.L. Garshelis, K.V. Noyce, A. Havales and J.R. Fieberg. Are American black
bears in an agricultural landscape being sustained by crops?
In review at Journal of Mammalogy.