Table Of Content.
J. RaptorRes. 31 (2):191—196
© 1997 The Raptor Research Foundation, Inc.
CONCLUDING REMARKS ON RAPTOR RESPONSES TO
FOREST MANAGEMENT: A HOLARCTIC PERSPECTIVE
Gerald Niemi and JoAnn M. Hanowski
J.
Natural Resources Research Institute, University ofMinnesota, 5013 Miller Trunk Highway,
MN
Duluth, 55811 U.S.A.
Recent and Historical Trends Europe. Hayward stated that although the Boreal
Participants were asked to provide perspectives Owl was not known as a breeding bird in the lower
on the current (past 30 yr) and historical (past 48 U.S. until the early 1970s, the increased obser-
100+ yr) population trend for each species (Table vations over the past 20 yr is likely due to increased
search efforts rather than a population increase. In
1). Both Pertti Saurola and Peter Ewins present
Fennoscandia, especially in Finland, an increase in
strong evidence that Osprey Pandion haliaetus
( ) nest boxes for owls (22 691 nest boxes for owls
populations have increased in both North America
and Europe since the 1960s when populations of checked in 1994) has likely increased populations
many fish-eating birds declined due to the inges- in many areas and also our understanding of this
species’ biology.
tion of pesticides such as DDT. Historically, how-
Geir Sonerud presents data showing an apparent
ever, Osprey populations varied considerably over
recent increase in Northern Hawk Owl Surnia ulu-
the past 100+ yr on both continents. (
Per Widen has shown that the Northern Gos- la) populations in northern Europe during the last
hawk Accipter gentilis has likely declined during part of this century. Over the past 90 yr, the pop-
( ) ulation was high in the early part of the century,
recent years in Fennoscandia, possibly due to frag-
followed by a decline, and then a recent increase.
mentation of forests and reductions in total
In North America, Patricia Duncan and Wayne
amounts of mature forest and associated prey pop-
Harris speculate that the population appears to be
ulations such as grouse. In North America, Patricia
Kennedy found no evidence for a decline in this relatively stable but that it fluctuates in response to
available food supplies.
species based on its range, population demograph-
There is relatively strong evidence for an in-
ics (density, fecundity and survival) and population
crease in the Great Gray Owl (Strix nebulosa) pop-
trends. She suggested that a more detailed meta-
ulation in northern Europe over the past 30 yr, but
analysis is required to further address this ques-
Seppo Sulkava and Kauko Huhtala present evi-
tion. The historical trend for this species is un-
dence that the long-term trend is highly variable.
known on either continent, although she speculat-
They suggest that the recent increase is due to a
ed that the Northern Goshawk may have been
combination offactors including reduced killing of
more abundant in the eastern U.S. prior to the
owls by humans, increased availability of artificial
extinction of the Passenger Pigeon Ectopistes mig-
( nest sites (hundreds of twig nests and nest plat-
ratorius and the deforestation in this region at the
) forms), but warn that although regional Great
end of the 19th century.
Gray Owl populations have been relatively stable
Like most of the raptor species included here,
both recently and historically, local populations
there is little information on Long-eared Owl (Asio fluctuate widely with available food supply.
otus) trends for North America. Based on admit-
tedly sparse data, Denver Holt hints at a possible Forest Management
recent decline in the species in some parts of Stand Size and Shape. In general, we know very
North America. Nothing is known about historical little on how species might respond to variations
population trends for this species. No paper was in the size and shape of logged stands (Table 1)
included for this species from Europe. The Osprey is likely not affected directly by stand
Neither Greg Hayward nor Harri Hakkarainen size and shape. However, availability of suitable
were willing to speculate as to whether there were nest trees, effects oflogging on aquatic systems and
recent or historical population trends for the Bo- fish supply and populations of major nest preda-
real Owl (Aegoliusfunereus) in North America and tors (e.g., Eagle Owl, Bubo bubo, in Europe or Great
191
192 Niemi and Hanowski Vol. 31, No. 2
Table 1. Summarization of trends and possible responses to forest management of six forest raptors in Europe and
North America.
Forest Management
Trend Stand Size Stand Shape
Species Continent Recent Long-Term Small Medium Large Simple Complex Residuals
Osprey Europe Increase Variable Neutral Neutral Neutral Neutral Neutral Essential
N America Increase Variable Neutral Neutral Neutral Neutral Neutral Essential
Northern Europe Decline Unknown Negative Negative Negative Unknown Unknown Negligible
Goshawk N America No evidence Possible de- — — — — — Unknown3
cline in
Eastern US
Long-eared N America Possible Unknown Positive Unknown Negative Negative Positive Negligible
Owl decrease
Boreal Owl Europe Unknown Unknown Unknown Unknown Positive? Neutral Positive Essential
N America Unknown Unknown Unknown Unknown Unknown Unknown Positive Essential
Northern Europe Possible Possible Postive Unknown Negative Neutral Positive Positive
Hawk Owl increase decrease
N America Stable Stable Positive Unknown Negative Neutral Neutral Positive
Great Gray Europe Increase Variable Positive Unknown Negative Negative Positive Positive
Owl N America Stable Stable Positive Unknown Negative Negative Positive Positive
AAll factors were not examined for this species because of the focus on the species demography.
Horned Owl, Bubo virginianus in North America) derstories where it makes short flights between
may indirectly affect Osprey populations. Perth perches. The species seldom uses recently cut areas
Saurola points out thatyoung Ospreyvocalizing for for foraging presumably because of the dense un-
food in a single tree in the middle of a clear-cut is derstories where prey is hard to detect. He also
a dinner bell to an Eagle Owl. Although more is suggests that the Northern Goshawk prefers larger
known about the ecology of Ospreys relative to the tracts of forest for foraging and, hence, is further
other five species included here, Peter Ewins affected by fragmentation of forested areas. There-
points out that remarkably little is known about fore, logging offorests, especially clear-cuts that re-
Osprey nesting ecology relative to timber extrac- duce foraging area and fragment large blocks of
tion. He concluded based on his review that there mature forest, appears to be contributing to de-
is a need for a systematic field study and no firm clines of the Northern Goshawk in Fennoscandia.
generalizations can be made. His discussion on the Based on a variety ofevidence for Northern Gos-
discrepancy between protection standards for nest- hawks across North America, Patricia Kennedy con-
ing Ospreys and the potential costs associated with cludes that there is no strong evidence to support
that protection are thoughtful. The recently devel- the contention that goshawk populations are de-
oped guidelines on Osprey nests presented by Pert- clining. She emphasizes two possible conclusions
ti Saurola provides a step toward improving this based on her analysis: (1) either the goshawk is not
situation. declining or (2) current sampling techniques are
Although his conclusions are based on admitted- insufficient to detect population trends. Reynolds
ly sparse data, Per Widen finds that the Northern et al. (1992) provide comprehensive guidance on
Goshawk has declined in Fennoscandia due to the forest management for the Northern Goshawk in
loss of mature forests and consequent reductions the southwestern U.S. In addition, Kenward (1996)
m
available foraging areas and food resources. points out additional complexities in understand-
Northern Goshawks forage primarily on grouse ing Northern Goshawk ecology, especially differ-
(many species of which are also declining in Fen- ences that may be operating in North America and
noscandia) squirrels and lagomorphs; the former Europe. He indicates that further study is needed
,
two ofwhich are found primarily in mature forests. on interspecific interactions, winter diet and life
Per Widen emphasizes that the species primarily history information between fledgling and breed-
forages in mature and older forests with open un- ing periods. Clearly, additional data are needed on
) -
June 1997 Raptors and Forestry 193
responses of this species to forest management real Owl throughout its annual cycle. For instance,
practices that will help us understand how to main- Microtus voles may not be available in some clear-
tain adequate populations of Northern Goshawks, cuts in winter wrhen the snow has a hard crust or
yet provide sustainable and ecologically sound har- in summer when the vegetation is too thick. Dur-
vest levels. These studies, however, will not be easy, ing these times, mature forests provide the best
must be long-term, and will not be cheap because cover and available prey populations.
the Northern Goshawk has relatively low popula- Greg Hayward’s data for the Rocky Mountain re-
tion levels, a large home range and a food base gion suggest that Boreal Owls primarily forage in
that varies substantially. Moreover, despite some of mature and older spruce-fir forests in the western
the differences that exist between North America U.S. In these forests, the red-backed Able Cleth
(
and Fennoscandia (e.g., available food supply), rionomys gapped is the dominant prey. Similar to
there appear to be many opportunities to better Sonerud (1986), he suggests that there is less snow
our knowledge on how Northern Goshawks react crusting in mature and older forests relative to
to variations in forest management by additional openings and young forests and, therefore, less
comparisons and coordination of studies on the prey is available in openings and young forests dur-
two continents. ing winter months. He emphasizes that the ecology
Again using a limited amount of published in- of this species appears to vary considerably geo-
formation on the ecology of Long-eared Owls, graphically, such as northern and southern popu-
Denver Holt suggests that forest management mea- lations of the Boreal OwTl in North America (Hay-
sures producing relatively small and open cut areas ward and Aferner 1994).
in which owls can forage juxtaposed with forested It is obvious that studies from northern Europe
areas with nest sites provide ideal habitat. Hence, and western North America may not be compara-
this species may be negatively affected by large ble, although greater quantification of nesting and
cuts, unless the shape is relatively complex to pro- foraging habitat, landscape context ofnesting hab-
vide access to forested areas. There is some ques- itat and improved understanding of the food base
tion on the extent to which the Long-eared Owl for the Boreal Owl on both continents wrould aid
uses contiguous forested areas because data from comparisons. In northern Europe, nest boxes,
these areas are limited. Forest management that hunting perches and adequate food have allowed
provides habitat for prey, plus roost and nest-site Boreal Owls to nest near clear-cuts. However, pro-
cover for Long-eared Owls will be most beneficial. viding nest boxes over large geographic areas is a
Summaries by Greg Hayward and Harri Hakka- daunting task and likely not an economicallyviable
rainen for Boreal Owls in Fennoscandia and North means to manage a species. The work by Hakka-
America are enigmatic. Harri Hakkarainen and his rainen and Korpimaki (1996) also illustrates the
colleagues show that, in Fennoscandia, nesting suc- influential role of interspecific interactions with
cess is highest in landscapes with relatively large other owl species, Boreal Owl distribution and re-
proportions of recently clear-cut areas (e.g., 35- production. Data like these are not available for
70%) compared with landscapes with small pro- North America and nest-box studies are likely the
portions of clear-cut area (10-30%). However, in only way to address these questions. Although pa-
their studies, nest boxes were provided presumably pers on the Boreal Owl from the two continents
due to the lack ofnatural nest cavities. In contrast, may be enigmatic, they are fascinating in terms of
Greg Hayward states that clear-cutting creates providing insights on complexities involved in
stands without habitat value for Boreal Owls for a studies forjust one species in regard to forest man-
century or more. Harri Hakkarainen reasons that agement issues.
clear-cut areas in Finland create suitable habitatfor Based on limited knowledge on Northern Hawk
held voles Microtus spp.), the primary prey for the Owl ecology, Patricia Duncan, Wayne Harris and
(
Boreal Owi in this region. Those factors (stand and Geir Sonerud conclude that this species likely ben-
landscape characteristics) that contribute to high efits from relatively small and complex cut sizes in
vole densities appear to be most critical for suc- forests. Key issues for this species are hunting
cessful nesting of the Boreal Owl. In contrast with perch availability, nest trees and cover for protec-
these data, Sonerud (1986) and Jacobsen and So- tion within a logged landscape. Geir Sonerud de-
nerud (1993) emphasize the considerable variation scribes a relatively intense, albeit with limited spa-
in prey availability and foraging habitat for the Bo- tial replication, study of foraging by Northern
194 Niemi and Hanowski Vol. 31, No. 2
Hawk Owls. He emphasizes that hunting perches cut areas for nesting is unclear. In Finland, some
within logged areas are required. Ifno live or dead nests have been found in open habitats (e.g., clear-
residuals are left in clear-cuts, the only hunting cuts) or near openings. Geir Sonerud indicates
perches that allow this species to use these areas that few breeding opportunities exist in recently
for foraging are trees remaining along the edges. cut areas because of the lack of suitable older trees
The species can tolerate larger clear-cut areas ifthe for nest sites. He points out that the decline in
shape is convoluted providing edges or if many Northern Hawk Owls in Finland from the 19th
suitable hunting perches are left distributed within century to the 1950s was thought to be due to the
the cut areas allowing access to most of the clear- disappearance of suitable nest trees. Patricia Dun-
cut area. In addition, suitable areas for cover and can and Wayne Harris suggest that areas that offer
nesting are also required. year-round habitat are cut-overs containing
As with the Northern Hawk Owl, evidence pre- enough stumps and trees for nest structures.
sented byJames Duncan, Seppo Sulkava and Kau- Hence, it would appear that recently logged areas
ko Huhtala show the Great Gray Owl responds fa- may be suitable nesting areas for both the North-
vorably to relatively small and complex cuts that ern Hawk Owl and Great Gray Owl if suitable re-
provide suitable foraging perches along edges and siduals are left. On a local scale it is also possible
suitable cover for nesting and protection in the ad- to actively manage for these species by placing nest
jacent forest habitat. We do not know how the spe- boxes (Northern Hawk Owl) or nesting platforms
cies would respond to intermediate-sized cuts but, (Great Gray Owl), but several authors point out
based on the species’ ecology, large clear-cuts with that this type of mitigation is impractical at larger
no hunting perches would be of little use. Larger spatial scales.
cuts with well-distributed hunting perches, convo- In northern Europe, Boreal Owls nest success-
luted edges and adjacent areas that provide cover fully in a landscape with a high proportion ofclear-
and nesting may be suitable. Little is known of the cuts when provided with suitable nest boxes. Nev-
size requirement of a forest area for nesting or cov- ertheless, Hard Hakkarainen and his colleagues
er. In addition, the nesting forest requirements of point out that modern forestry practices must pro-
large raptors which produce most nesting plat- vide suitable snags and patches of old mature for-
forms for the Great Gray Owl also need to be con- est with large trees dense enough to support the
sidered. hole-nesting Black Woodpecker Dryocopus mar-
(
Residuals. With the possible exception of the tins) The Black Woodpecker excavates most natu-
.
Northern Goshawk and Long-eared Owl, the re- ral nest cavities for the Boreal Owl in Finland. Greg
maining four species require residuals in logged Hayward points out that, in North America, avail-
areas for the species to use this habitat (Table 1). ability of nest cavities depends upon available nest
For species that often use residuals for nesting such trees (especially aspen, Populus spp.), insects and
as the Osprey and Boreal Owl, they are essential. pathogens necessary to create suitable, weakened
It is unclear to what extent the Northern Goshawk trees and primary cavity nesters such as Pileated
or Long-eared Owl require residuals as hunting Woodpecker (Dryocopus pileatus) to create cavities.
perches. Certainly these species use them occasion- In a nest-box experiment in Idaho, he found that
ally as hunting perches or resting sites, but their the Boreal Owl selected nest boxes within forests
importance to their overall fitness is unclear. of more complex structure (e.g., multiple canopy
Based on the evidence from Fennoscandia, the layers and many tree size classes) and did not use
Boreal Owl, Northern Hawk Owl and Great Gray boxes in forests with a more simple structure (e.g.,
Owl all use residuals left within logged areas for single canopy layer and more uniform tree diam-
hunting perches to forage for small mammals (es- eters). More information is needed to address the
pecially Microtus voles). Seppo Sulkava and Kauko combination of nesting, foraging and cover needs
Huhtala suggest that the Great Gray Owl popula- of the Boreal Owl.
tion has increased in many parts of Finland be- In general, residuals in logged areas are clearly
cause ofthe increased populations ofMicrotusvoles beneficial to a variety of forest raptors, including
and the ability of the Great Gray Owl to forage in most of those considered here. Quantitative data
these logged areas. obtained through replicated field studies are need-
The extent to which either the Northern Hawk ed to address specific issues on species, sizes, spa-
Owl or Great Gray Owl use residuals within clear- tial distribution and number of residuals (dead or
June 1997 Raptors and Forestry 195
alive) required in logged areas. For instance, leav- Raptors, by virtue of their position in the forest
ing a few dead trees in the middle of a clear-cut food chain and their potentially important role in
for Ospreys may be detrimental. If a goal of forest ecological processes of forests, will always be of
management is to simulate natural forest condi- high concern in forest resource management de-
tions to the extent possible, then the natural dis- cisions. If we are to maintain healthy forest ecosys-
turbance forces for most of the northern boreal tems, then it is imperative for society to increase
forests considered here are fire, insect outbreaks its investment in understanding these systems.
and wind (Pastor et al. 1996). In these systems, re-
Acknowledgments
siduals in the form of burned trees, patches ofun-
We appreciate the constructive comments on these
burned forest, charred trees from fire, dead trees
concluding remarks from many of the contributors to
from an insect outbreak or trees with broken tops this issue including Patricia Duncan,James Duncan, Har-
from excessive wind were much more common in ri Hakkarainen, Greg Ha)ward, Denver Holt, Patricia
the past. Kennedy, Geir Sonerud, Seppo Sulkava and Per Widen.
We thank the following organizations for their financial
Conclusions support of the symposium and this issue of theJournal of
Raptor Research US Bureau of Land Management; the
:
Although only six species of raptors were consid- North Central Forest Experiment Station in St. Paul,
ered here, they illustrate that forest management Chequamegon National Forest, Chippewa National For-
aimed toward logging wall benefit some species, est, Nicolet National Forest, Ottawa National Forest and
Superior National Forest; Boise-Cascade, White Paper Di-
while alternative management measures aimed at
vision; Georgia-Pacific Corporation; Lake Superior Paper
the maintenance of mature and old forest will ben- Industries; National Council of Stream and Air Improve-
efit other species. For instance, clear-cutting in ment Inc.; Potlatch Corporation, Northwest Paper Divi-
small units (2-5 ha) has increased populations of sion; Minnesota State Legislature (through the Minne-
Microtus voles in Fennoscandia and this habitat in- sota Environment and Natural Resources Trust Fund as
recommended by the Legislative Commission on Min-
termixed with suitable forested areas for nesting
nesota Resources); and the University of Minnesota
and cover are beneficial to the Northern Hawk through its Natural Resources Research Institute, Raptor
Owl and Great Gray Owl. There is a potentially Center, Department of Biology and University College.
important role of large fields and large dear-cuts This is contribution number 207 ofthe Center for Water
and the Environment, Natural Resources Research Insti-
in supplying source populations of Microtus voles
tute, University of Minnesota, Duluth.
to the smaller, isolated clear-cuts. In contrast, re-
duction in mature and old forest may lead to re- Literature Cited
duced populations of the Northern Goshawk. Hakkarainen, H. and E. KorpimAki. 1996. Competitive
The key is to understand predator and prey re- and predatory interactions among raptors: an obser-
sponses to forest changes at a variety of spatial vational and experimental study. Ecology 77:1134-
scales including microhabitat, landscapes and land- 1142.
scape mosaics. Individual species responses could Hayward, G.D. and J. Verner. 1994. Flammulated, Bo-
then be incorporated into forest change simula- real, and Great Gray Owls in the United States: a tech-
nical conservation assessment. USDA For. Ser. Gen.
tion models that consider both spatial and tem- CO
Tech. Rep. RM-253, Ft. Collins, U.S.A.
poral scales (Pastor et al. 1996). These simulation Jacobsen, B.V. and G. Sonerud. 1993. Synchronous
models will allow us to assess the effects of a range switch in diet and hunting habitat as a response to
of management scenarios on species populations, disappearance of snow cover in Tengmalm’s Owl Ae-
other species complexes (e.g., plants, insects, mam- goliusfunereus. OrnisFenn. 70:78-88.
mals, etc.), ecological processes (e.g., nutrient cy- Kenward, R.E. 1996. Goshawk adaptations to deforesta-
cles, plant growth and decomposition) and com- tion: does Europe differ from North America? Pages
modity production. The models should be devel- 233-243 in D.M. Bird, D.E. Varland and J. Negro
oped with the best available knowledge and ap- [Eds.], Raptors in human landscapes. Academic
UK
Press, London,
plied with an understanding of the degree of
uncertainty produced with the output. The models Pastor, J- DJ. Mladenoff, Y Haila, J. Bryant and S.
Payette. 1996. Pages 33-69 in H.A. Mooney, J.H.
can be improved as our knowledge of these organ-
Cushman, E. Medina, O.E. Sala and E.D. Schulze
isms and processes increase. Similarly, factors that
[Eds.], Functional roles of biodiversity: a global per-
contribute most to output uncertainty should pro- spective. Wiley and Sons Ltd., London, UK
J.
tide a framework for prioritizing additional re- Reynolds, R., R.T. Graham, M.H. Reiser, R.L. Bassett,
search activity. P.L. Kennedy, D.A. Boyce,Jr., G. Goodwin, R. Smith
196 Niemi and Hanowski Vol. 31, No. 2
and E.L. Fisher. 1992. Management recommenda- Sonerud, G.A. 1986. Effect of snow cover on seasonal
tions for the Northern Goshawk in the southwestern changes in diet, habitat, and regional distribution of
United States. USDA For. Serv. Gen. Tech. Rep. raptors that prey on small mammals in boreal zones
CO
RM-217, Ft. Collins, U.S.A. of Fennoscandia. Holarct. Ecol. 9:33-47.
