LAND MANAGEMENT HANDBOOK

35

The Ecological Roles of Wildlife Tree Users in Forest Ecosystems

1995

Province of British Columbia Ministry of Forests Research Program The Ecological Roles of Wildlife Tree Users in Forest Ecosystems

Marlene M. Machmer and Christoph Steeger

Province of British Columbia Ministry of Forests Research Program Canadian Cataloguing in Publication Data Machmer, Marlene M. The ecological roles of wildlife tree users in forest ecosystems

(Land management handbook ; 35)

“This handbook prepared by Pandion Ecological Research Ltd.”--Verso of t.p. Includes bibliographical references: p. ISBN 0-7726-2418-6

1. Forest fauna – Ecology - British Columbia. 2. Forest fauna - Feeding and foods - British Columbia. 3. Forest insects - Biological control - British Columbia. 4. Trees -Wounds and injuries - British Columbia. 5. Forest management - British Columbia. I. Steeger, Chrisoph, 1958– . II. British Columbia. Ministry of Forests. Research Branch. III. Pandion Ecological Research Ltd. IV. Title. V. Series.

SB764.C3M32 1995 574.5’2642’09711 C95-960108-2

Prepared by Pandion Ecological Research Ltd. P.O. Box 26, Ymir, BC V0G 2K0

© 1995 Province of British Columbia Published by the Research Branch B.C. Ministry of Forests 31 Bastion Square Victoria, BC v8w 3E7

Copies of this and other Ministry of Forests titles are available from Crown Publications Inc. 521 Fort Street Victoria, BC v8w 1E7 SUMMARY

This report synthesizes North American litera- in pest density. They also affect pest abundance ture about the effects of wildlife tree users on indirectly by altering the microclimate of their invertebrate and vertebrate pest populations. prey and by increasing pest susceptibility to The feeding habits of 92 species of wildlife tree other mortality agents such as parasitism, pre- users in British Columbia are described along dation, disease and weather. The relative effect with the forest pest species (vertebrate and in- of predation by these guilds is greatest at low vertebrate) they prey on. By examining the pest densities; thus they play a significant role trophic relationships of wildlife tree users, in maintaining pests at endemic levels by delay- knowledge of their other ecological roles is ing the onset of outbreaks or by accelerating gained. These roles are identified and discussed their decline. The ground- and aerial-foraging in the context of forest management. Manage- (hawking) birds, terrestrial and arboreal ment recommendations and research directions rodents, and aerial-foraging and gleaning bats are discussed. all consume injurious insects. However, the Wildlife tree users are arranged into foraging quantitative effect of these wildlife tree-using guilds, and studies that investigate the effects of guilds on pest populations requires further individual species or entire guilds on the abun- investigation. There is little evidence that dance and distribution of forest pests are re- vertebrate forest pests are regulated by wildlife viewed. These effects are quantified when tree-dependent carnivorous birds and mam- possible and anecdotal information is presented mals. However, their actions may reduce pest and discussed for guilds where quantitative damage by slowing the rate of an outbreak, studies are lacking. This information is used to accelerating its decline, or interacting with evaluate the potential capacity of specific wild- density- dependent factors to lowe r equilibrium life tree users to regulate forest pests in a pest densities. density-dependent manner. Other ecological roles of wildlife tree users The impact of wildlife tree users on forest in British Columbia include dispersing mycor- pests is most apparent in the bark-foraging and rhizal inoculum, seeds and other materials, foliage-gleaning guilds, which have been studied providing nesting, feeding and roosting oppor- extensively. Members of these groups (e.g., tunities for wildlife, accelerating decomposition woodpeckers, nuthatches and chickadees) exert in dead and decaying trees, nutrient cycling, a direct influence on pest abundance, exhibiting transmitting tree and insect pathogens, consum functional and numerical responses to increases ing seeds, and damaging healthy trees.

iii ACKNOWLEDGEMENTS

We would like to thank Daniel Lousier (Minis- Idaho, Moscow), Professor Robert Barclay (Uni- try of Forests, Prince George Forest Region) for versity of Calgary) and Grant MacHutchon sup- initiating and supporting this project. Dale Seip plied background reference material. Joan (Ministry of Forests, Prince George) provided Siderius assisted with information gathering. We helpful comments on an earlier version of this also thank Susan Bannerman for her thorough document. Professor Oz Garton (University of editing of the manuscript.

iv CONTENTS

Summary...... iii

1. Introduction ...... 1

2. Methods and Materials ...... 2

2.1 General Approach ...... 2

2.2 Forest Pests in British Columbia ...... 2

2.3 Information About the Feeding Habits of Wildlife Tree Users ...... 2 2.4 Information About the Regulating Effect of Wildlife Tree Users on Forest Pests ...... 3

3. Results ...... 4 3.1 Feeding Habits of Wildlife Tree Users ...... 4 3.2 Regulation of Abundance and Distribution of Forest Pests by Wildlife Tree Users ...... 5 3.2.1 Bark-foraging birds ...... 5 3.2.2 Foliage-gleaning birds ...... 6

3.2.3 Terrestrial and arboreal rodents ...... 8

3.2.4 Ground-foraging birds ...... 8

3.2.5 Aerial-foraging and hawking birds ...... 8 3.2.6 Terrestrial-foraging raptors ...... 8 3.2.7 Aerial-foraging and gleaning bats ...... 9 3.2.8 Carnivores ...... 9 3.2.9 Amphibians ...... 10

3.3 Summary of Impact of Wildlife Tree Users on Forest Pests ...... 10 3.4 Other Ecological Roles of Wildlife Tree Users ...... 10 3.4.1 Dispersal of mycorrhizal inoculum ...... 11

3.4.2 Dispersal of seeds and other materials ...... 11

3.4.3 Provision of nesting, roosting and feeding opportunities ...... 12

3.4.4 Accelerating decomposition in dead and decaying trees ...... 13 3.4.5 Nutrient cycling ...... 13 3.4.6 Vectors for the transmission of tree pathogens ...... 13 3.4.7 Seed predation ...... 13 3.4.8 Damage to healthy trees ...... 14

4. Management Implications for Wildlife Tree Users ...... 39

5. Directions for Future Research ...... 41 5.1 Primary Cavity Excavators ...... 41 5.2 Secondary Cavity Users ...... 41 5.3 Bats ...... 41 5.4 Small Mammals ...... 42

Appendix 1. Forest insect pests and their associated taxonomic classification ...... 43

Literature Cited ...... 44

v Tables 1 Food habits of aquatic-foraging birds...... 15 2 Food habits of terrestrial-foraging raptors ...... 16

3 Food habits of bark-foraging birds ...... 18

4 Food habits of foliage-gleaning birds ...... 19 5 Food habits of aerial-foraging and hawking birds ...... 21 6 Food habits of ground-foraging birds ...... 22 7 Food habits of aerial-foraging and gleaning bats ...... 23 8 Food habits of terrestrial and arboreal rodents ...... 25 9 Food habits of carnivores ...... 27 10 Summary of quantitative studies of avian predation on forest pests ...... 28

11 Summary of quantitative studies of mammalian predation on forest pests ...... 37

vi 1 INTRODUCTION

Wildlife trees are an integral component of forest invertebrate and vertebrate forest pests ecosystems and have become the focus of inte- (Lousier 1989). In this context, pests are species grated forest management in British Columbia. A that damage and kill trees. However, it is recognized wildlife tree is “atree (dead or alive) which pro- that these species are natural components of forest vides present or future critical habitat for mainte- ecosystems. The role of insectivorous birds in con- nance or enhancement of wildlife”(Backhouse and trolling invertebrate pests has received considerable Lousier 1991). Its value for wildlife may be provided attention in the European (Bruns 1960; Franz 1961; by one or more physical attributes such as struc- Herberg 1967) and North American literature ture, age, condition, species, geographic location or (Beebe 1974b; see references in Dickson et al. 1979; surrounding habitat features. In British Columbia, Thomas et al. 1979, Takekawa et al. 1982). Much of more than 90 wildlife species, or approximately the information on this topic was collected from 16% of the province’s indigenous birds, mammals other parts of North America and focuses on agri- and herptiles depend to some extent on wildlife cultural systems, on bird species that do not de- trees for reproduction, feeding or shelter pend on wildlife trees, and on forest ecosystems (Backhouse and Lousier 1991). with different tree and pest species and forest man- The forest’s potential to produce and retain agement practices from those occurring in the Pa- wildlife trees can be eliminated by intensive forest cific Northwest. The relevance of this literature to management and silvicultural practices (e.g., British Columbia forests requires some clarification. clearcut harvesting, short harvest rotations, even- This report synthesizes North American litera- aged stand management, and multiple thinning), ture about the effects of wildlife tree users on in- snag and associated Workers’ Compensation Board vertebrate and vertebrate forest pest populations. safety regulations, fire-prevention activities, and This is accomplished by: public gathering of firewood (McClelland 1979; 1. describing the feeding habits of wildlife tree Thomas et al. 1979, Cline et al. 1980; Miller 1985). species and the forest pest species (vertebrate Consequently, these activities constitute a serious and invertebrate) they prey on; and threat to the viability of associated wildlife tree 2. identifying the quantitative effects of wildlife users (Bunnell and Alleye-Chan 1984; Raphael and tree users on specific pest prey populations White 1984; Zarnowitz and Manuwal 1985; (invertebrates are stressed because there are few Lundquist 1988). quantitative studies on vertebrate pests). The British Columbia Wildlife Tree Committee Information about tree species, forest pest spe- (WTC) is developing management strategies and a cies and forest management practices in British research program to conserve the province’s wild- Columbia is emphasized. By examining the trophic life tree resource and its dependent wildlife species relationships of wildlife tree users, knowledge of (Backhouse and Lousier 1991). Part of the interest their other important ecological roles is gained. in conserving these species stems from the poten- These roles are identified and discussed in the con- tial role that wildlife tree users play in regulating text of forest management.

1 2 METHODS AND MATERIALS

2.1 General Approach the information compiled about diet into context. In general, members of the insect orders The literature review covered the following general Coleoptera and Lepidoptera constitute some of the subject areas: most damaging insects in the province. The moun- • diet, food habits, foraging behaviour and con- tain pine beetle continues to be the most damaging sumption rates of wildlife tree species; and bark beetles as a group (mountain pine beetle, • forest pests, forest damage, and wildlife tree spruce beetle, western pine beetle, Douglas-fir bee- species interactions; and tle, western balsam bark beetle, Ips spp., ambrosia • general ecology, habitat requirements, and forest beetles, northern spruce engraver beetle, pine management of wildlife tree species. engraver beetles, fir engraver beetles) constitute a Most of the relevant mammalogy, ornithology, greater source of tree mortality and economic loss entomology, and wildlife and forest management- than any other group of forest insects (Wood and related literature was found by searching the Fish van Sickle 1992). Spruce budworm, Douglas-fir and Wildlife and Agricola databases on CD ROM tussock moth, western hemlock looper and gray disk. Under each of the three general subject areas, spruce looper have caused the most significant databases were searched for each individual wildlife recent defoliation of coniferous hosts over wide- tree species (common and Latin names), by species spread areas in the Interior (Wood and van guild (e.g., swallows, woodpeckers, owls, etc.), by Sickle 1992). foraging or nesting guild (bark-foraging birds, Many vertebrate species impede reforestation in foliage-gleaning birds, insectivorous bats, cavity- the province by consuming large quantities of nesting birds, etc.), by taxonomic guild (e.g., small seeds and seedlings, clipping off and browsing mammals, raptors, bats), by vertebrate class (e.g., seedling shoots, gnawing and stripping the bark, or bird, mammal, amphibian), and by larger group- girdling the boles of sapling or pole-sized conifers. ings (e.g., vertebrate). Additional literature was Members of the orders Rodentia and Lagomorpha found by consulting a U.S. Forest Service cavity- constitute some of the more damaging vertebrate nesting bird bibliography (Fischer and species with significant losses in young regenerat- McClelland 1983). More recent government publi- ing stands attributed to voles, squirrels, cottontail cations were obtained directly through the Provin- rabbits, snowshoe hares and porcupines (Sullivan cial Forest Service library in Victoria. and Sullivan 1982; Finck et al. 1989; Wood and van Sickle 1991, 1992). However, the effect of vertebrate 2.2 Forest Pests in British Columbia pests is generally negligible when compared to that of insects, disease and abiotic injury. Shrews, mice, Each year in British Columbia forests are damaged pocket gophers, pikas, chipmunks, wood rats, bea- by a variety of vertebrate and invertebrate pest spe- vers, mountain beavers, deer, elk, moose, black cies. These pests cause mortality by reducing tree bears and woodpeckers are responsible for only growth and vigour, thereby negatively affecting sporadic damage and minor economic losses forest management and the economic potential of (Finck et al. 1989). our forests. Predominant invertebrate and verte- brate pests in British Columbia are reviewed else- 2.3 Information About the Feeding Habits of where (Pank 1974; Harestad 1983; Harper and Wildlife Tree Users Harestad 1985; Finck et al. 1989; Wood and van Sickle 1991, 1992); however, brief mention of some Species that depend on wildlife trees were arranged of the most damaging pests is made here to place into foraging guilds, based on their primary forag-

2 ing mode and location, and vertebrate class. The efficiency can be achieved in two ways. As prey following foraging guilds are represented: density increases, predators can respond function- • aquatic- foraging birds ally by attacking more prey or numerically by • terrestrial-foraging raptors aggregating or increasing their survival or repro- • bark-foraging birds ductive rates. Both of these responses were studied • foliage-gleaning birds by Holling (1959) and their sum is the total • aerial-foraging and hawking birds number of prey killed by the predator population. • ground-foraging birds Vertebrate predators show functional and numeri- • aerial-foraging and gleaning bats cal responses to some forest insect pests and are • terrestrial and arboreal rodents capable of exerting direct control over the density • carnivores of their prey under some conditions (Holling 1959; • ungulates Berryman 1986). • amphibians There are many difficulties associated with Some of these designations are not mutually studying the effects of insectivorous predators on exclusive but they facilitate later discussion of the forest pests. Insects exhibit complex life cycles and role of wildlife tree users. the susceptibility of each life cycle stage to the The information about the feeding habits of predator and the predator’s response to changes in wildlife tree users was compiled from a variety of the density of vulnerable pest stages must be meas- sources including original research and many refer- ured. This must be accomplished against a back- ence texts and guidebooks. Where quantitative data ground of several interacting predators, prey, were available, primary foods are listed in decreas- parasites and abiotic factors. For bark-foraging and ing order of their occurrence in the diet (by vol- foliage-gleaning birds, and terrestrial and arboreal ume). Only foods that constituted 10% or more of rodents, many quantitative studies address a guild’s the diet volume in any season are listed. Foods or a specific guild member’s (the predator) effect eaten “occasionally” are only included when quali- on a forest insect pest (the prey). These studies are tative data were available. Estimates of the percent summarized in Table 1o for avian predators and in animal food or the percent of a certain food type Table 11 for mammalian predators. Only studies (e.g., insect, fungi) are given when relevant. When- that explicitly include one or more wildlife tree- ever possible, primary foods eaten (e.g., insects) dependent species in their predator guild are in- are broken down into orders and, in some cases, cluded in these tables. The studies listed in the into families eaten. Specific pest species eaten are tables either: included in the comments section of each food 1. investigate the functional or numerical responses habit table in Section 3.1 and in each quantitative of predators to changes in pest species density; study summary table in Section 3.2. A list of the 2. estimate the rate of mortality in a pest popula- common names and associated taxonomic classifi- tion attributable to the feeding activity of the cation (order and family) of all forest insect pests predator; referred to in the tables is provided in Appendix 1. 3. quantify the rate of pest consumption by the Common and scientific names of all wildlife tree predator at a known pest density; or users are included in Tables 1–9. 4. combine some of the above. This information is used to evaluate the effects 2.4 Information About the Regulating Effect of of specific wildlife tree users on forest pests. Wildlife Tree Users on Forest Pests For the other guilds, little quantitative informa- tion is available; however, qualitative information Predators may exert density-dependent regulatory pertinent to the potential impact of these guilds on pressure on their prey by increasing their predation forest pests is presented and discussed. efficiency as prey density increases. This increased

3 3 RESULTS

3.1 Feeding Habits of Wildlife Tree Users well, but they do not specialize as much as the other three species. The feeding habits of 92 species of wildlife tree Three members of the guild (Williamson users listed in Backhouse and Lousier (1991) are Sapsucker, Northern Flicker, Pi leated Woodpecker ) described in Tables 1–9. The diets of aquatic- feed heavily on ants that construct their galleries in foraging birds are listed in Table 1. Five of the nine moist wood, which weakens trees and increases species take predominantly fish, three of the four their susceptibility to windthrow (Knight and remaining species which do eat insects take mainly Heikkenen 1980). aquatic forms. Only the Wood Duck feeds on ter- Larval, pupal and emergent adult stages are all restrial insects and these form a small proportion preyed on by the bark-foraging guild and differ- of its summer diet. This group therefore has a neg- ences in bill morphology and foraging mode be- ligible influence on forest pest species. tween guild members result in the division of The food habits of 16 terrestrial-foraging raptors insect prey resources. Nuthatches and creepers use are shown in Table 2. Rodents and lagomorphs superficial foraging techniques (e.g., peer and (e.g., pikas, rabbits, hares) are the most common poke, probe, scale) to chip away bark flakes, locat- food of 12 of the 16 species. Vertebrates that can ing insect prey on or near the bark surface negatively affect forest management and regenera- (Stallcup 1968; McEllin 1979; Franzgreb 1985; tion activities (e.g., voles, mice, shrews, chip- Lundquist and Manuwal 1990). Woodpeckers (par- munks, pocket gophers, squirrels, pikas, rabbits, ticularly the Hairy, Three-toed, Black-backed, and hares and porcupines) are the predominant prey of Pileated Woodpeckers) use subsurface foraging these 12 species. At least four species (Barn Owl, techniques (e.g., drilling, excavation) to penetrate Northern Hawk-Owl, Spotted Owl and Northern the subcambium layer where beetle larvae and ants Saw-whet Owl) are considered small mammal are extracted (Stallcup 1968; Jackson 1970; “specialists”— that is, small mammals make up Connor 1979; 1981; Lundquist and Manuwal 1990). more than 90% of their diet volume. Numerous studies address the effects of this guild The food habits of bark-foraging birds are listed on forest insect pests and these are reviewed and in Table 3. Terrestrial insects are the “primary” their findings discussed in Section 3.2. food item (i.e., ≥75% of the diet volume) for 11 of Foliage-gleaning wildlife tree users are listed in the 15 species, and at least 50% of the annual diet Table 4. Insects are the most common food item in volume for the remaining four species. Either the diets of all four species and larvae and adults of Coleoptera or Lepidoptera are the first or second the order Lepidoptera are ranked first in the diets most common insect orders consumed by all spe- of three of the four species. This guild consumes cies, and 13 of the 15 species are known to prey on various injurious insects. various injurious insects (see general comments in The food habits of aerial-foraging and hawking Tables 3 and 1o). This is most obvious in the Hairy, birds are listed in Table 5. This guild includes a Three-toed and Black-backed Woodpeckers, all of diverse assemblage of species, and insects consti- which consume primarily insects and, in particular, tute the primary food (i.e., ≥75% of the diet vol- wood-boring beetle larvae of the families ume) of 9 of the 1o species. Most members prey Buprestidae (wood-boring metallic beetles), exclusively or primarily on flying insects or emer- Cerambycidae (wood-boring long-horned beetles), gent phases. Five of the 1o species are known to and Scolytidae (bark beetles and ambrosia beetles). prey on injurious insects. All species are to some Representatives of these insect families are the extent migratory and their consumption is there- most injurious insects in temperate coniferous for- fore limited to a fixed breeding period. ests (Knight and Heikkenen 1980). The Pileated The diets of ground-foraging birds are shown in Woodpecker, Downy Woodpecker, the Williamson Table 6. The Bewick’s Wren and House Wren eat Sapsucker and, to some extent, the White-headed primarily insects (i.e., ≥75% of the diet volume), Woodpecker feed on members of these families as the Common Grackle is an omnivore and the

4 House Finch eats mainly seeds and other plant The primary foods of eight members of the or- products. Three of the four guild members prey on der Carnivora are shown in Table 9. Small- to me- forest insect pests. dium-sized mammals (rodents and lagomorphs) All 12 wildlife tree-dependent bats found in the are the first-ranked foods for five of the eight province are primarily insectivorous (Table 7) and members listed. The diets of the three remaining eight of 12 species are thought to prey exclusively species are relatively varied. on flying insects. Bat diets are correlated with The Caribou (Rangifer tarandus) and the tooth and jaw morphology (Freeman 1981) as well Clouded Salamander (Aneides ferreus) are the only as body size and echolocating abilities (Barclay and ungulate and amphibian wildlife tree users in the Brigham 1991). Strong dentition and muscular jaws province. Caribou eat lichens, grasses, sedges, are characteristic of species that eat relatively hard- shrubs, leaves and other vegetation (Cowan and bodied insects (e.g., Coleopterans). Species with Guiget 1978). They are unique in their almost ex- small teeth tend to specialize on soft-bodied insects clusive dependence on arboreal lichens in winter (e.g., Lepidopterans, Dipterans). Small bats are (Simpson et al. 1987). The Clouded Salamander capable of detecting smaller insects, thereby defin- eats primarily insects and other invertebrates. Ants, ing the size classes of prey available (Barclay and particularly carpenter ants which inhabit moist Brigham 1991). Lepidopterans are the most com- wood, constitute most of the diet (Orchard 1984). mon insects taken by six of the 12 species and Fifty-one studies were found that deal explicitly Coleopterans and Lepidopterans make up part of with the impact of the province’s wildlife tree users the diet of 11 of 12 species. on specific forest insect pests. These studies use a Although numerous studies have investigated variety of experimental and observational methods bat diets using fecal and stomach content analyses to quantify effect: artificial stocking of prey; com- (Black 1974; Whitaker et al. 1977, 1981a, 1981b; parisons of mortality between prey populations of Warner 1985; Brigham 1990; Brigham and different densities; consumption estimates based on Saunders 1990; Brigham et al. 1992; Whitaker and observation, metabolic requirements, digestive rate Lawhead 1992), insects consumed are usually iden- studies or captive feeding experiments; determinis- tified by order, and in some cases, by family tic modelling; predator exclusion experiments; prey (Whitaker 1988). There is little information available and predator censuses; and predator stomach and on the specific forest pest species consumed by bats fecal content analyses. Eight more quantitative (R. Barclay, University of Calgary and M. Brigham, studies pertinent to the topic were found but these University of Regina, pers. comm., February 1993). failed to identify the specific guild species The diets of terrestrial and arboreal rodents are (Dowden et al. 1953; Morris et al. 1958; Amman and listed in Table 8. Diet information was not found Cole 1983; Campbell and Torgerson 1983; for the Sitka Mouse and the Red-tailed Chipmunk. Campbell et al. 1983; Carlson et al. 1984; Takekawa Fungi were the primary food eaten (i.e., ≥75% of and Garton 1984; Torgerson et al. 1990). the diet volume) by three species; they constituted 50% or more of the diet volume in at least six of 3.2 Regulation of Abundance and Distribution of the 12 species, and appeared as a food item for Forest Pests by Wildlife Tree Users every guild member. The predominance of fungi in these rodents’ diets has far-reaching implications 3.2.1 Bark-foraging birds for forest health and productivity. The ecological Thirty-four studies investigated the impact of guild role of forest rodents in the obligate symbiosis be- members on insect pests and 25 of these focused tween trees and mycorrhizal fungi is discussed in specifically on woodpeckers (Table 1o). These stud- Section 3.4.1. ies indicate that bark- foraging wildlife tree users Insects are part of the diet in nine of the 1o spe- show a density-dependant response to changes in cies for which diet information is available, but pest population densities. Bark foragers increase insects are the first-ranked food item only for the the proportion of insects in their diet as the pest Deer Mouse and possibly for the Columbia Mouse. populations gradually increase (a functional re- Four members of this guild are known to prey on sponse: Buckner and Turnock 1965; Koplin and forest insect pests. Their role in controlling these Baldwin 1970; Koplin 1972; Crawford et al. 1983). pests is discussed in Section 3.2.3. They also aggregate in pest-infested areas (a

5 numerical response: Rust 1929, 1930; Baldwin 1960; content analyses but the additional information Buckner and Turnock 1965; Otvos 1965; Mattson (e.g., digestive passage rate or number of times the et al. 1968; Koplin and Baldwin 1970; Koplin 1972; stomach is filled per day) required to calculate Crockett and Hansley 1978; Kroll and Fleet 1979; daily consumption rates is not given. These data Kroll et al. 1980; Lester 1980; Villard and are nevertheless presented for comparisons of rela- Beninger 1993). Such aggregations are particularly tive consumption rates between species. A rough well documented for woodpeckers feeding on bark estimate of daily consumption can be calculated by beetles. Winter densities can increase up to 85-fold dividing the number of prey per predator stomach by during infestations (Blackford 1955; Yeager 1955; an estimated digestive passage rate (1.2 hours; Baldwin 1960; Koplin 1972; Massey and Takekawa and Garton 1984) and then assuming the Wygant 1973; Kroll and Fleet 1979; Kroll et al. 1980) bird forages 8–16 hours per day. and the Downy, Hairy, Three-toed and Black- Some of the most impressive rates of consump- backed Woodpeckers seem to be the most flexible tion are shown by woodpeckers. For example, species in this regard. Observations of 2-12 wood- stomachs of Three-toed Woodpeckers contained an peckers feeding unhindered at the same tree are average of 915 spruce beetle larvae during an out- not uncommon during such post-breeding break and woodpeckers are expected to fill their aggregations (Baldwin 1960; Koplin 1972). During stomachs several times to capacity each day. This the breeding season, woodpecker densities can could result in an individual consuming many increase up to seven-fold during infestations thousand larvae per day (Koplin 1972). (Koplin 1972). Factors such as breeding territory All 34 studies concluded that bark-foraging birds requirements, the availability of nesting and roost- contribute significantly to prey mortality through ing sites (snags of sufficient size and suitable decay their feeding activity. The estimated percent mor- stage), and food availability between pest outbreaks tality in prey populations ranged from 0.5–98%, may limit the size of breeding aggregations (Kroll depending on whether a study took the indirect et al. 1980). During long-term infestations, wood- effects of predator feeding into consideration (see pecker populations also respond numerically (by comments in Table 1o). This is particularly impor- increased reproduction) to the greater availability tant in woodpecker predation on bark beetles of nesting and roosting sites provided by insect- (Otvos 1979), where birds flake, puncture, excavate killed trees (Baldwin 1968; Otvos 1979). It is not and remove bark during the process of feeding. A clear to what extent the fecundity of individual general reduction in bark thickness changes the birds can increase during infestations. microhabitat of the prey and reduces subsequent The value of the bark-foraging guild in regulat- prey survival. Indirect effects of woodpecker feed- ing the abundance of their prey populations is en- ing activity on bark beetle mortality include in- hanced by at least 12 of the 15 bark-foraging species creased parasitism of intact beetle broods (up being year-round residents (Campbell et al. 1990). to 1o-fold in winter; Otvos 1965) by parasites with During winter months, these species are the major short ovipositors, and increased brood mortality avian insectivores in forests and their consumption because of the dessication and lethal temperatures of overwintering pests is an important factor in associated with bark thinning (Moore 1972; diminishing the pests', potential for rapid popula- Otvos 1979). Beetle broods dislodged in bark flakes tion increase in the spring (Jackson 1979a; Kroll suffer high mortality as well (Otvos 1965; Kroll and and Fleet 1979). Avian-insect interaction models Fleet 1979). The mean density of predatory insects demonstrate that when insects are exposed to pre- attacking bark beetle broods may decrease dation over a prolonged period, such as winter, the (Otvos 1965) or increase (Kroll and Fleet 1979; Kroll size of the area of “local stability” (i.e., stable equi- et al. 1980) because of woodpecker activity. librium densities of predator and prey) can be Several studies pose the question of whether quite extensive (Otvos 1979). avian predation complements or diminishes the Predator consumption estimates are given (or efficiency of other mortality agents, such as insect could be calculated with available information) in predation or parasitism on forest pests. Birds can eight studies. Four other studies report the number influence these other mortality agents by: of prey per predator stomach based on stomach 1. consuming insect predators and parasites directly;

6 2. preferring or discriminating against parasitized est at low to moderate prey densities, and this prey; or seems to be the case for insectivorous birds in gen- 3. changing the microhabitat of the prey so that eral (McFarlane 1976; Otvos 1979; Holmes 1990). they are more or less susceptible to these other Although this guild exhibits both functional and mortality agents (Otvos 1979). numerical responses to increasing prey densities, Clearly, woodpecker activity indirectly increases they are unable to keep up with rapidly expanding the susceptibility of beetle broods to other mor- epidemic prey populations. In two studies, wood- tality agents. peckers exerted their greatest predatory impact at Most avian predators consume beneficial insect epidemic prey densities (Koplin and Baldwin 1970; predators and parasites; however, their relative fre- Koplin 1972); however, unusually high levels of quency in the diet as compared to their availability winter aggregation are reported in these studies. In in trees is usually low (Otvos 1979). Bruns (1960), general, the reproductive rates, breeding territory Buckner and Turnock (1965), MacLellan (1958), requirements, availability of nesting and roosting Sloan and Coppel (1968), Sloan and Simmons sites and food supply between outbreaks limit the (1973) and Schlichter (1978) all report that birds are effectiveness of birds in controlling large-scale epi- highly discriminating in prey selection and that demic infestations (McFarlane 1976; Otvos 1979; they take a significantly lower proportion of Moeck and Safranyik 1984). The major role of birds parasitized versus non-parasitized prey. is to maintain endemic pest levels, delaying the In addition to their influence on insect preda- onset of an outbreak and accelerating the decline tors of bark beetles, woodpeckers may attract or in an outbreak that has peaked, which increases the increase the susceptibility of beetle broods to other time span between outbreaks (see literature reviews vertebrate predators through their feeding activity. in Buckner 1966; van den Bosch 1971; Beebe 1974b; Brown Creepers and Red-breasted Nuthatches are McFarlane 1976; Otvos 1979; Crawford and reportedly drawn to recently “woodpeckered” bark Jennings 1982; Takekawa et al. 1982; Fischer and where they can gain access to beetle larvae (Kroll McClelland 1983; Moeck and Safranyik 1984). and Fleet 1979; Otvos 1979). It is conceivable that other beetle predators would be attracted by such 3.2.2 Foliage-gleaning birds activity. Birds contribute indirectly to the mortality Nineteen studies in Table 1o deal with the role of of their prey by transmitting entomogenous patho- foliage-gleaning wildlife tree users in regulating the gens during feeding (Franz et al. 1955; Bruns 1960; abundance of forest pest insects. Members of this see references in Otvos 1979). All of these indirect guild search for insects on the terminal branches effects are not considered in most studies listed in and foliage of conifers and they respond function- Table 1o, but they could substantially increase the ally and numerically to increased prey density prey population mortality rate attributed to the (Buckner and Turnock 1965; Dahlsten and predator. Herman 1965; Mattson et al. 1968; Gage et al. 1970; The rates of prey mortality reported in Table 1o Crawford et al. 1983; Crawford and Jennings 1989; depend on stand-level factors such as density, Crawford et al. 1990). All species are resident and elevation, and site-specific silvicultural practices. territorial, and some studies conclude that they are Petit and Grubb (1988) correlated the relatively low responsible for up to 95% mortality in endemic mortality rate of hardwood borers in the clearcuts pest populations (Coppel and Sloan 1971). Sug- they studied to the dense vegetation and lack of gested limits to the numerical response of this guild large snags. Woodpeckers were more than two are suitable snags for nesting and roosting (Langelier times as prevalent in surrounding uncut forests. and Garton 1986; Garton 1987). Shook and Baldwin (1970) suggested that wood- Although their consumption rates are generally peckers are more effective at reducing spruce not as high as those of woodpeckers (e.g., 6.1 large beetles in semi-open stands than in dense stands western spruce budworm larvae/hour for the because more dead and windthrown trees (which Black-capped Chickadee: Garton 1987), foliage attract woodpeckers) are present. gleaners prey on both larval and adult forms and Eleven studies explicitly concluded that the play a major role in reducing defoliation rates and regulatory influence of bark- foraging birds is great- in maintaining sparse populations of western

7 spruce budworm and other injurious insects indicate that this species feeds on spruce budworm, (Langelier and Garton 1986; Garton 1987). sample sizes were insufficient to evaluate its effect All but one of 19 studies concluded that this quantitatively. Two of the four ground-foraging guild plays a role in regulating the abundance of wildlife tree users have relatively broad diets (Table forest pest insects. These birds also probably con- 6) and their potential influence as a group on pest sume insect predators and parasitoids of their prey species abundance is probably negligible. in the process of feeding (Otvos 1979) but this 3.2.5 Aerial-foraging and hawking birds effect has not been measured. Members of this Only two studies were found that investigate the guild are known to eat emergent bark beetles role of specific guild members on forest pests (Table 4) and the “in-flight” mortality beetles (Table 1o). Baldwin (1968) concluded that the incur may be significant because it acts on the pre- Mountain Bluebird and five other species which ovipositing female (see Moeck and Safranyik 1984). prey on adult Engelmann spruce beetles were re- Six studies explicitly state that impact was greatest sponsible for 24– 32% mortality in the population. at endemic prey densities. As with bark foragers, A mortality rate of 8–26% was estimated for an members of this guild maintain sparse pest aerial foraging guild (including the Violet-green populations between outbreaks but are not capable Swallow) preying on western pine beetle (Otvos of stopping an existing outbreak. 1979). In both cases, mortality was incurred during 3.2.3 Terrestrial and arboreal rodents the short period of bark beetle emergence, flight Eight quantitative studies were found that investi- and attack on trees and coincided with the nestling gate the role of wildlife tree-dependent small feeding period of several of the predator species. mammals on forest pests (Table 11). Although Although other guild members (e.g., Ash- consumption estimates (e.g., 400–500 prey per throated and Pacific-slope Flycatchers) have predator per day for red squirrel feeding on spruce received little attention, Stallcup (1963) observed budworm) suggest that guild members can poten- several unidentified flycatchers (Emphidonax sp.) tially consume large numbers of pests, only Holling eating flying spruce beetles. He estimated the (1959) and Dowden et al. (1953) concluded that in-flight mortality to be approximately 10%. small mammals contribute to pest regulation over Similarly, other members of the same genus (e.g., a range of prey densities. Four studies are incon- H ammo n d’s Flycatcher ) a re sign ifican t consume rs clusive and two studies conclude that guild mem- of spruce budworm moths (Langelier and Garton bers are not important predators of the prey under 1986; Garton 1987). investigation. Aside from Hollings’ work, all studies There are many difficulties in studying the im- failed to examine predator feeding responses over a pact of aerial foragers on forest pests. Their con- range of prey densities and were limited to labora- sumption is limited to the brief “in-flight” phase of tory observation or trapping a few animals for the pest life cycle, and predation is inconspicuous stomach content analysis. No predator exclusions and difficult to quantify without sacrificing the nor estimates of mortality by predators were at- animal. However, mortality incurred by aerial for- tempted. Clearly, the role of small mammals in agers on pre-ovipositing females is considered pro- regulating forest insect pests requires further inves- portionately more important than that on earlier tigation. Given the impressive consumption esti- life cycle stages (Moeck and Safranyik 1984). The mates attributed to guild members, they may act as quantitative effects of this guild on forest pests a significant density-independent mortality factor, merits further investigation. by slowing the rate of pest increase during an epi- 3.2.6 Terrestrial-foraging raptors demic, accelerating the rate of decline of a pest, or Unlike the relationship between some insectivorous interacting with density-dependent factors to pro- birds that depend on wildlife trees and forest pests, duce a lower equilibrium pest density. there is little quantitative evidence that raptors can 3.2.4 Ground-foraging birds regulate the abundance of their vertebrate prey. Only one study listed in Table 1o addresses the Data on their quantitative food intake in the wild role of this guild (and the Common Grackle, and their response to changes in prey availability in particular) in the control of a forest pest are lacking for most raptor species (Marti 1987). (Crawford et al. 1983). Although stomach analyses The most reliable data available are for owls, where

8 pellet analyses can be used in conjunction with Barclay 1992). Bats use prey-generated sound and consumption studies on captive birds. Barn Owls movement cues as well as echolocation when are resident small mammal specialists and consume gleaning (Fenton 1990). an estimated seasonal average of 60–110 g of whole Members of this guild are clearly efficient preda- small mammal prey per day which represents ap- tors and consume large quantities of insects annu- proximately 1o–18% of their body weight, or ally. Juvenile, pregnant and lactating Little Brown roughly 1.7–3.1 voles (Microtus sp.) or 3.1–5.8 deer Bats consume an estimated 1.8, 2.5 and 3.7 g of mice (Peromyscus sp.) per day (Marti 1970, 1973; insects, respectively, each night (Anthony and Steenhof 1983). Great-horned Owls consume an Kunz 1977). This amounts to 818, 1136 and 1682 estimated seasonal average of 63–119 g of prey per insects per individual per night, respectively, as- day, which represents 4.7–8.9% of their body weight suming an average prey weight of 2.2 mg (Griffin or 0.33–0.63 adult Red or Douglas squirrels per day et al. 1960). Most insectivorous bat species con- (Marti 1970,1973; Steenhof 1983). These consump- sume between 30–50% of their body mass in insects tion rates are expected to increase during the every night (Anthony and Kunz 1977; Fenton 1990) breeding season with the higher metabolic require- and wildlife tree-dependent species in the province ments of incubation, feeding nestlings and range from 4.3–27.6 g, on average. Larger species fledglings. (e.g., Hoary Bat, Big Brown Bat, Pallid Bat) tend to Thirteen of the 16 members of this guild are consume larger prey (Anthony and Kunz 1977; resident (Campbell et al. 1990) and are capable of Barclay 1985,1986; Brigham 1990; Brigham and exerting predation pressure throughout the year. Saunders 1990), so the number of insects con- Although there is little evidence that this guild sumed per individual per night is expected to be regulates prey in a density-dependent manner, by comparable. consuming vertebrate pest species, terrestrial- Some bat species (e.g., Little Brown Bat, Big foraging raptors may slow the rate of an epidemic Brown Bat, Silver-haired Bat) are known to pest outbreak or accelerate its decline. This group opportunistically exploit rich patches of prey such therefore plays a potentially significant role in lim- as hatches of emergent insects (Buchler 1976; iting damage to forests. Barclay 1985; Brigham and Fenton 1991; Brigham et al. 1992). It is tempting to speculate that they 3.2.7 Aerial-foraging and gleaning bats would behave similarly during pest irruptions or Although it is generally assumed that insectivorous during the emergence phase of certain adult pests bats play a role in controlling forest pests (Bruns but there are no direct empirical data available to 1960; Ross 1967; Constantine 1970; Hill and Smith support this. Interestingly, a few studies address the 1984), an objective assessment is not possible now strong convergence in foraging behaviour and diet because good qualitative and quantitative data are between Big Brown Bats and Common Nighthawks lacking. (Brigham 1990; Aldridge and Brigham 1991; Several characteristics of this guild could poten- Brigham and Fenton 1991). Common Nighthawks tially affect forest pests. Bats are nocturnal hunters are reported to be an important avian predator of so their predatory behaviour can be considered the mountain pine beetle (Rust 1929). Stomach complementary to that of the previous guilds dis- analyses showed an average of 76 adult beetles cussed. Lepidoptera is the first-ranked insect order — 20% of the total food volume consumed. It would consumed by 6 of the 12 bats in the province that be interesting to investigate the diet of Big Brown depend on wildlife trees (Table 7) and many are Bats and other guild members in beetle-infested active primarily at night (references in Holmes areas during the period of adult emergence, flight 1990). Bats of this guild prey mainly on flying in- and attack. sects (Whitaker et al. 1981a) and would be expected to affect mainly the “in-flight” phases of pest life 3.2.8 Carnivores cycles. However, at least four members take flight- Data on the rates at which carnivores consume less insects and spiders (Table 7) and gleaning from vertebrate pests are lacking. Although some repre- the ground or foliage is a well-documented forag- sentatives of this guild (e.g., marten, ermine, least ing strategy in two of these species (Pallid Bat: weasel) prey heavily on rodents, there is little evi- Bell 1982; Western Long-eared Myotis: Faure and dence that wildlife tree-dependent carnivores can

9 regulate the abundance of their prey. By consuming sects and may also have a regulating influence on small mammals, this group may act as a significant forest pests, but these groups require further inves- density-independent mortality factor, slowing the tigation. rate of pest increase or accelerating its decline. This Vertebrate forest pests (e.g., voles, squirrels, would reduce seed consumption and damage to hares) do not seem to be regulated in a density- young, regenerating forest stands. dependent manner by carnivorous birds or mam- mals. Nevertheless, predation by these guilds may 3.2.9 Amphibians cause significant mortality, which reduces the im- Because of their dependence on fresh water, am- pact of vertebrate pests. Ecologists have debated phibians are not considered as important predators whether intrinsic or extrinsic factors are the most of forest insects (Buckner 1966). No references con- important in regulating vertebrate prey popu- cerning the Clouded Salamander’s consumption of lations. The general consensus is that the two specific forest pests were found. The Spotted Sala- classes of factors interact to affect prey population mander, a related species found in the northeastern abundance (see discussion in Southern 1979). United States feeds on the late larval stages of The discussion of the effects of predators on spruce budworm (Jennings et al. 1991). However, forest pests has focused only on short-term nu- predation of spruce budworm by this species is merical responses. However, another effect of sus- considered unimportant when compared with tained predatory pressure is evolutionary. other vertebrate predators (e.g., birds). Insectivorous bark-foraging and foliage-gleaning birds, because of their regulatory influence on en- 3.3 Summary of Impact of Wildlife Tree Users on demic prey populations, have a strong selective Forest Pests influence on their prey that can determine certain traits in their populations. For example, selective Some species that depend on wildlife trees clearly play a role in regulating the abundance of insect predation of defoliating Lepidoptera larvae pests in forests. This influence is most apparent for (Garton 1979) can influence its choice of feeding substrates, feeding schedules, plant species prefer- the bark-foraging and foliage-gleaning guilds, which have been studied extensively. These groups ences, life history patterns, body pattern and col- oration over an evolutionary time scale (see directly influence prey abundance by consuming large numbers of pest individuals and by altering references cited in Holmes 1990). These traits, in their foraging and reproductive behaviour with turn, determine the pattern and extent of damage changes in pest density. They also indirectly influ- by defoliators, so that birds, through selective for- ence prey populations through their feeding activ- aging, indirectly affect other ecosystem compo- ity, by altering the microclimate of their prey and nents and processes. Because of their quick by increasing prey susceptibility to other mortality generation times and high reproductive rates, in- agents such as parasitism, predation, disease and sects are capable of genetically-based changes over a relatively short time. For example, the peppered weather. Quantitative studies show that the magni- moth exhibited a change in the frequency of the tude of these indirect effects is considerable. melanistic coloration gene from 1–98% of the It should be stressed, however, that the relative population within fifty generations (references in influence of bird predation on pest populations is greatest at low pest densities. Once an epidemic Holmes 1990). outbreak is established, birds alone are generally 3.4 Other Ecological Roles of Wildlife Tree Users unable to control it, unless extremely high levels of predator aggregation overwhelm a very localized Wildlife tree-dependent species have other im- infestation. However, insectivorous birds play a portant ecological roles in addition to their influ- significant role in maintaining pests at endemic ence on the abundance and distribution of forest levels by delaying the onset of an outbreak or by pests. Some of these are perceived as extremely accelerating its decline. valuable to forest ecosystems whereas others have The ground-foraging and aerial-foraging/hawk- traditionally been viewed as negative from a forest ing birds, terrestrial and arboreal rodents, and management and economic perspective. aerial-foraging and gleaning bats all consume in- By transporting and consuming fungi, terrestrial

10 and arboreal mammals spread mycorrhizal mycorrhizal fungi which produce their sporocarps inoculum, which is critical to forest health and (fruiting bodies) belowground (Maser et al. 1978). nutrition. This same guild, along with seed-eating These fungi lack spore dispersal mechanisms and birds, disperses seeds. Terrestrial and arboreal ro- depend on small mammals for spore dissemination dents function as dispersal agents of organic and (Fogel and Trappe 1978). Mycophagists consume inorganic materials, increase soil aeration, enhance the sporocarps of mycorrhizal fungi, which contain drainage and ultimately accelerate organic decom- nutrients, water, viable fungal spores, nitrogen- position. All guilds, but most notably birds and fixing bacteria and yeast (Maser 1990). These bats because of their mobility, contribute to nutri- sporocarps emit species-specific odours that attract ent cycling in forest ecosystems. Primary cavity- mycophagists and, once consumed, pass through nesting and bark-foraging birds provide feeding, the digestive tract and are excreted in pellets with- roosting and nesting opportunities for other cav- out loss of viability (Trappe and Maser 1976). The ity-dependent species as well as increase the rate of spores from pellets can then contact and inoculate tree decomposition. susceptible host roots, being washed into the soil To some extent, primary cavity-nesters damage by rain or transported by the tunnelling and bur- healthy trees through their feeding and nesting rowing activity of small mammals. Alternatively, activites and all forest birds have been implicated germinated spores may fuse with an existing fungal in transmitting plant pathogens (e.g., wood-decay- thallus, thereby contributing new genetic material ing fungi, arboviruses). Some small mammals (Maser 1990). impede reforestation by consuming seeds and seed- By enhancing the spread of hypogeous lings and by debarking or girdling juvenile trees. mycorrhizal fungi, terrestrial and arboreal rodents maintain their own food supply and disseminate 3.4.1 Dispersal of mycorrhizal inoculum the spores that are critical for the growth and sur- Mycorrhizae are symbiotic associations between vival of conifers and deciduous hardwoods. Small fungi and the roots of vascular plants. The fungal mammals that feed in forested sites and adjacent hyphae act as extensions of the host’s own root clearcuts (e.g., deer mice, chipmunks) aid in refor- system, absorbing nutrients, minerals and water estation by depositing spore-containing pellets in from the soil and translocating them to the host cutover areas. Seeds of mycorrhizal hosts that ger- plant. Some mycorrhizal fungi also produce growth minate nearby are thereby inoculated (Maser et regulators that can create new root tips or com- al. 1978). The obligatory relationship between pounds that enhance the host plant’s resistance to mycorrhizal fungi and trees is traceable to the ear- pathogens (Maser 1990). In turn, the host supplies liest known fossils of plant-rooting structures sugars produced photosynthetically to the (Marks and Kozlowski 1973; Harley and mycorrhizal fungi. Mycorrhizal fungi are thought Smith 1983). In an old-growth Douglas-fir stand in to occur in 90% of all plant families. Woody plants Oregon, the top 1o cm of soil was estimated to con- in the families Pinaceae (e.g., pine, fir, spruce, tain over 5000 kg/ha of mycorrhizae (Trappe and larch, Douglas-fir, hemlock), Fagaceae (e.g., oak) Fogel 1977). The enhanced dissemination of these and Betulaceae (e.g., birch, alder) have developed symbionts by small mammals is an integral com- an obligatory dependence on root-inhabiting fungi ponent of forest health. to absorb adequate nutrients from the soil (Marks and Kozlowski 1973; Harley and Smith 1983). Ex- 3.4.2 Dispersal of seeds and other materials periments show that without mycorrhizal Through their feeding activities, birds and mam- inoculum, commercially valuable tree seedlings mals act as important dispersal agents of seeds. (e.g., pine) fail to grow. Such dispersal is important to maintain and spread The consumption of fungi (mycophagy) by woody plant populations, particularly in recently mammals and the strong reliance of some small logged areas. It also promotes plant gene flow and mammals (e.g., squirrels, chipmunks, voles) on population differentiation (van der Pijl 1972). fungi as a primary food source is well documented Most wildlife tree-dependent birds are insectivo- (Table 8; see also Fogel and Trappe 1978; Maser rous for at least part of the year (Tables 1–6) but only et al. 1978). This reliance is mutual; small mammals the ground-foraging guild is expected to disperse consume primarily (88%) hypogeous fungi, that is, appreciable numbers of seeds.

11 Rodents (e.g., squirrels, chipmunks, mice) col- woodpecker cavities (Scott et al. 1977; Raphael and lect and store several kilograms of seeds annually White 1984). Roosting cavities are also excavated by (see references in Golley et al. 1975). By caching these species. Roosts provide resting, security and these seeds, they may satisfy the dormancy require- thermal cover, and winter roosts are considered ments for germination. They also consume seeds, critical for all of the nuthatches and chickadees some of which are adapted to pass through rodent and at least nine woodpecker species that are digestive tracts unharmed. Digestive juices may resident in the province (Cannings et al. 1987; weaken the seed coat, which favours water absorp- Campbell et al. 1990). tion and germination (Kreftig and Roe 1949). The There are 31 species of secondary cavity-using digging and burrowing activities of various mam- birds in British Columbia which depend on va- mals expose mineral soil that provides a seedbed cated or natural cavities for nesting (Backhouse favouring seedling establishment. and Lousier 1991). Some require cavities for roost- Caches of seeds are deposited in areas of intense ing as well (Scott et al. 1977; Campbell et al. 1988). rodent activity where feces are abundant. As Beebe (1974b) reviewed studies that suggest scarcity discussed above, these fecal pellets contain yeast of natural or vacated cavities, or, alternatively, suit- and nitrogen-fixing bacteria in addition to able trees in which to excavate them, is the chief mycorrhizal spores. The yeast stimulates growth limiting factor for hole-nesting bird populations. and nitrogen fixation in the nitrogen-fixing Numerous examples of nest site competition and bacteria (Li et al. 1986) and spore germination in avian counter-adaptations to such competition are the mycorrhizal fungi (Maser 1990). Transportation cited. of seeds to areas where pellets are concentrated Twelve bat species in the province use natural or may therefore encourage establishment and early vacated cavities for hibernation, maternity colo- growth of seedlings (Maser 1990). nies, maternal roosts and day or night roosts (Fitch Small mammals accelerate organic decomposi- and Shump 1979; Barclay 1985; Barclay et al. 1988; tion through the cutting and transportation of Backhouse and Lousier 1991). Hollow trees, tree leaves, stems, fungi and fruits which act as input to crevices or openings under loose bark are occa- litter. Stark (1973) quantified the effect of squirrel sionally used (van Zyll de Jong 1985; Nagorson and feeding activity on the pine ecosystem as an in- Brigham 1993). Suitable hibernacula and sites for creased litterfall of 18 g/m2 per year. This effect maternity colonies and roosts may be the limiting could be important in nutrient-poor soils. factors for some bat species (Hill and Smith 1984; The physical and chemical properties of soils are van Zyll de Jong 1985). Twelve rodent and seven improved by small mammals. Through their dig- carnivore species depend to some extent on vacated ging and burrowing activities, this guild mixes ho- or natural tree cavities for nesting and denning in rizons of the soil profile. This increases nutrient summer or winter (Backhouse and Lousier 1991). availability in the soil, improves soil aeration, Primary cavity excavators provide a vital service to moisture-holding capacity and drainage from seep- all these other wildlife tree-dependent groups, by age areas (Spurr and Barnes 1980). excavating cavities directly and by loosening bark during their feeding activities. 3.4.3 Provision of nesting, roosting and feeding Woodpeckers also provide other insectivores and opportunities herbivores with access to food resources. Some Primary cavity excavators play an important role in birds (e.g., Brown Creepers, Red-breasted Nut- forest ecosystems by providing other cavity- hatches) are attracted to woodpecker feeding exca- dependent species with this critical habitat element vations, where they feed on beetle broods, ants or (Beebe 1974b; Thomas et al. 1979). Nineteen spe- exposed grubs (Kroll and Fleet 1979; Otvos 1979). cies of birds in British Columbia are capable of Similarly, Hairy and Downy Woodpeckers are excavating their own nest cavities. These include 12 attracted to excavations made by Pileated Wood- woodpecker, 3 nuthatch and 4 chickadee species peckers because they can forage more deeply than (Backhouse and Lousier 1991). Nuthatches and they could by their own efforts (Lawrence 1967; chickadees are classified as weak excavators and Maxson and Maxson 1981). Sapsuckers create sap will occasionally nest in natural cavities or vacated wells in the bark of coniferous and deciduous trees

12 and shrubs (Tate 1973). Sap is an important sea- In temperate old-growth redwood forests, bats sonal component in the diet of these birds (Table 3; contribute an estimated 1o-1o0 g/tree per year of see also Tate 1973; Jackman 1975) and the use of sap guano which contain 10% N, compared to a back- wells by other birds (e.g., Williamson, Downy, ground of 2–3 g of N/m2 per year (Rainey et Hairy and Three-toed Woodpeckers, White- al. 1992). Values for guano deposition in provincial breasted Nuthatch, House Wren, Mountain forests are not available now, but nutrient input by Chickadee, Ruby-crowned Kinglet, Yellow-rumped bats is expected to be significant (R. Barclay, Uni- Warbler, Pine Siskin, American Goldfinch, Rufous versity of Calgary, pers. comm., February 1993). and Broad-tailed Hummingbirds), mammals (e.g., Birds and bats are probably more effective chipmunks, squirrels) and insects (e.g., wasps, than any other group in transferring nutrients bees) is well documented (Batts 1953; Kilham (e.g., calcium, nitrogen, phosphorus, sulfur, potas- 1953,1958; Foster and Tate 1966; Jackman 1975; sium, sodium, magnesium) within and between Miller and Nero 1983; Ehrlich and Daily 1988). The forest ecosystems because of their relative mobility heavy use of late-summer sap wells by some groups (Sturges et al. 1974; DeGraaf 1977). Estimates of (e.g., warblers, hummingbirds) suggests that this annual nutrient loss for birds are given in Sturges food resource could provide a dietary supplement et al. (1974), with migratory species accounting for during times of declining insect and floral nectar up to 16% of all phosphorus lost. At least 34 of the availability (Miller and Nero 1983; Ehrlich and province’s 58 (i.e., 59%) wildlife tree-dependent Daily 1988). Sapsuckers can therefore be considered birds are resident species so nutrient loss attributed as “keystone herbivores” (Ehrlich and Daily 1988) to this group is probably much less. by supplying other groups with access to a rich 3.4.6 Vectors for the transmission of tree pathogens food source. Forest birds and mammals are implicated in the 3.4.4 Accelerating decomposition in dead and spread of tree diseases, both directly and indirectly decaying trees (Otvos 1979; Ostry et al. 1982). Warner and French Woodpeckers prefer to excavate nesting and roost- (1970) demonstrated that Common Grackles could ing cavities in dead or decaying trees softened by transfer rust spores (Puccinia sp.) from infected to fungal heart rots (Shigo and Kilham 1968; healthy seedlings. These spores remained viable Kilham 1971; Conner et al. 1976; Bull and and were recovered from the plumage up to 45 Meslow 1977; McClelland 1977; Mannon et al. 1980; days after application. Similarly, forest birds (e.g., Harestad and Keisker 1989; Bull et al. 1992). Such Mountain Chickadee) and mammals (e.g., Least trees reduce the energetic requirements of cavity Chipmunk) may accelerate the spread of dwarf excavation, while maintaining a tough outer pro- mistletoe by transporting the seeds on their plum- tective shell. Similarly, dead and decaying wood is age or fur, and depositing them at uninfected sites a preferred foraging substrate for woodpeckers, (Zilka and Tinnin 1976; Ostry and Nicholls 1979; probably because it harbours an abundance of Hudler et al. 1979; Nicholls et al. 1986). Ostry et al. bark-dwelling insects (Connor and Crawford 1974; (1982) suggested that Downy Woodpeckers play a Bull and Meslow 1977; Mannon et al. 1980; Raphael role in the spread of Hypoxylon sp. fungus, either and White 1984; Bull 1987; Steeger et al. 1993). by carrying fungal spores directly or by creating While feeding and excavating nest and roost cavi- favourable conditions (through their feeding activ- ties, woodpeckers provide secondary sites for insect ity) for infection by airborne spores. Unidentified attack and fungal infection. Ultimately, they accel- fungi invaded the galleries of southern pine beetle erate the rate of tree decomposition and nutrient through openings created by woodpecker foraging cycling in forest ecosystems (Otvos 1979). (Dahlsten 1982). The extent of such transmission and its effect on forest health require further inves- 3.4.5 Nutrient cycling tigation. Because of their numbers and daily movements, bats may significantly enhance the nutrient status 3.4.7 Seed predation of regularly occupied roost trees, and on a larger Although seeds are included in the diet of 14 wild- scale, of entire forest ecosystems by depositing life tree-dependent birds (Tables 3–6), they do not nitrogen-rich guano (Hutchinson 1950; Kunz 1982). constitute the primary food for these species

13 (except for the House Finch). The most voracious 3.4.8 Damage to healthy trees avian seed predators in coniferous forests are not Woodpeckers tend to select dead or decaying trees wildlife tree users (e.g., juncos, sparrows, towhees, for nest or roost cavity excavation. However, thrushes; see references in Wiens 1975). Therefore, sound, live trees are occasionally used for nesting wildlife tree-dependent birds, as a group, are not by Pileated Woodpeckers (McClelland 1979; Miller expected to have a large impact on reforestation and Miller 1980; Harris 1983) and as foraging efforts. substrate by other woodpecker species (Conner Seeds are consumed by all terrestrial and arbo- and Crawford 1974; Mannon et al. 1980; Bull 1987). real rodents listed in Table 8 and some group Some damage to isolated trees has been observed members (e.g., Peromyscus sp., Clethrinomys sp., (Ziller and Stirling 1961); however, economic losses Eutamias sp.) are significant consumers of seeds because of woodpecker activity are considered neg- during reforestation efforts (Radvanyi 1970; review ligible (Finck et al. 1989). in Pank 1974). An estimated five mice per hectare Red Squirrels are considered the most important will remove 50 ooo direct-seeded Douglas-fir seeds damage agents of juvenile lodgepole pine stands in from a cutover area during a 15-day period the central Interior of British Columbia damaging (Sullivan 1978). Numerous techniques have been up to 37% of the potential crop (Sullivan and employed to control or eliminate seed-eating small Sullivan 1982; Sullivan and Vyse 1987). Squirrels mammal populations (e.g., slashburning, poison strip bark from the stem and feed on the cambium baiting, rodenticide-treated seeds, use of alternative and exposed sapwood. This can reduce the growth foods, altering the timing of direct-seeding, etc.). and vigour of a tree, increase its susceptibility to These efforts have generally been unsuccessful fungal attack or eventually kill the tree through (Sullivan 1979). girdling (Sullivan and Vyse 1987).

14 TABLE 1 Food habits of aquatic-foraging birds

Species Primary foodsa % A.F. b General comments Sources

Wood Duck Aquatic plants, seeds and fruits of shrubs and 13 Insects increase to 16–27% of the diet Martin et al. 1951; (Aix sponsa) trees, aquatic and terrestrial insects, other in spring and summer Ehrlich et al. 1988 invertebrates Common Goldeneye Crustaceans, aquatic insects, molluscs, fish, 74–85 Aquatic insects make up 28% of the Cottam 1939; (Bucephala clangula) aquatic vegetation annual diet Martin et al. 1951; Ehrlich et al. 1988 Barrows Goldeneye Aquatic insects, molluscs, crustaceans, aquatic 78–85 Aquatic insects make up 36% of the Cottam 1939; (Bucephala islandica) vegetation annual diet Martin et al. 1951; Campbell et al. 1988; Ehrlich et al. 1988 Bufflehead Aquatic insects, crustaceans, molluscs, seeds 75–80 Aquatic insects make up 70% of the Martin et al. 1951; (Bucephala albeola) of aquatic vegetation, fish annual diet in freshwater Erskine 1971; Scott et al. 1977; Ehrlich et al. 1988 Hooded Merganser Fish, crustaceans, aquatic insects, molluscs, >90 Aquatic insects make up 13% of Palmer 1976; (Lophodytes cucullates) frogs and tadpoles, snails the annual diet Scott et al. 1977; Ehrlich et al. 1988 Common Merganser Fish, crustaceans >90 Palmer 1976; (Mergus merganser) Ehrlich et al. 1988 Great Blue Heron Primarily fish; occasionally small mammals, — — Campbell et al. 1988; (Ardea herodias) reptiles, amphibians, birds, invertebrates, Ehrlich et al. 1988 aquatic vegetation Osprey Primarily fish 100 — Beebe 1974a; Machmer (Pandio n haliaetus) and Ydenberg 1990; Steeger et al. 1992 Belted Kingfisher Primarily fish; occasionally aquatic 100 — Ehrlich et al. 1988 (Ceryle alcyon) invertebrates, reptiles, amphibians, insects a Primary foods = foods that make up ≥10%, of the diet volume in any season or foods eaten “occasionally” when only qualitative data were available. b % A.F. = estimated percent of the diet volume consisting of food of animal origin. TABLE 2 Food habits of terrestrial-foraging raptors

Species Primary foods a % A . F .b General comments Sources

Turkey Vulture Primarily carrion >95 — Beebe 1974a; (Cuthartes aura) Ehrlich et al. 1988 Bald Eagle Fish, small- to medium-sized birds, small 100 Gallinaceous birds, waterfowl, Beebe 1974a; Fielder (Haliaeetus leucocephales) mammals, carrion seabirds 1982b; Stalmaster and Gessaman 1984; Ehrlich et al. 1988

Northern Goshawk Small- to medium-sized birds, small 100 Gallinaceous birds, passerines Beebe 1974a; (Accipiter gentilis) mammals, lagomorphs, weasels waterfowl Campbell et al. 1988; Ehrlich et al. 1988

Red-tailed Hawk Small- to medium-sized mammals and 100 Pocket gophers, ground squirrels Beebe 1974a; Bruce et al. (Buteo jamaicensis) birds; occasionally reptiles, amphibians weasels, lagomorphs 1982; Ehrlich et al. 1988 and insects Golden Eagle Medium-sized mammals, medium-sized 100 Marmots, lagomorphs; grouse, Beebe 1974a; (Aquila chrysaetos) birds; occasionally carrion ptarmigan, pheasant Marr and Knight 1983; Ehrlich et al. 1988

American Kestrel Small mammals; wide variety of large 100 Voles, mice, pocket gophers, Beebe 1974a; (Falco sparverius) insects and small birds; occasionally chipmunks, ground squirrels Campbell et al. 1988; reptiles and bats Ehrlich et al. 1988 Merlin Primarily birds; occasionally insects and 100 >80% birds by biomass Beebe 1974a; Scott et al. (Falco columbarius) small mammals 1977; Ehrlich et al. 1988 Barn Owl Primarily small mammals; occasionally 100 Voles, mice, shrews, pocket gophers Fielder 1982a; (Tyto alba) birds Taylor 1984; Bull and Akenson 1985; Campbell et al. 1988; Ehrlich et al. 1988 Western Screech - 0 w l Small mammals, arthropods, amphibians, 100 Generalist; diet varies regionally Marks and Marks 1981; (Otus kennicottii) reptiles, fish Ehrlich et al. 1988

Great Horned Owl Lagomorphs, rodents, birds 100 Rabbit, snowshoe hare, pika; Ehrlich et al. 1988 (Bubo virginianus) grouse, pheasants, waterfowl, passerines

Northern Hawk Owl Primarily small mammals; occasionally 100 Voles, mice, shrews, lemmings Bent 1961b; (Surnia ulula) insects and birds Ehrlich et al. 1988 TABLE 2 (Continued)

Species Primary foods a % A.F. b General comments Sources

Northern Pygmy-Owl Primarily small mammals and small birds; 100 Voles, mice; finches, sparrows, Bent 1961b; (Glaucidium gnoma) occasionally reptiles, amphibians, large starlings, thrushes Ehrlich et al. 1988 insects Spotted Owl Primarily rodents and lagomorphs; 100 Mice, rats, chipmunks, Bent 1961b; (Strix occidentalis) occasionally birds, reptiles and insects squirrels; >9o% mammals by Forsman 1976; biomass Ehrlich et al. 1988 Barred Owl Small- to medium-sized mammals; some 100 Mice, voles, shrews, chipmunks, Bent 1961b; (Strix varia) birds, reptiles and amphibians squirrels, lagomorphs, weasels Marks et al. 1984; Campbell et al. 1988; Ehrlich et al. 1988 Boreal Owl Primarily small mammals and birds 100 Chipmunks, squirrels Ehrlich et al. 1988 (Aegolius funereus) Northern Saw-whet Owl Primarily small mammals; occasionally 100 Mice, voles, gophers; >95% small Boula 1982; (Aegolius acadicus) birds mammals in winter by biomass Grove 1985; Campbell et al. 1988; Ehrlich et al. 1988 a Primary foods = foods that make up ≥10% of the diet volume in any season or foods eaten “occasionally” when only qualitative data were available. b % A.F. = estimated percent of the diet volume consisting of food of animal origin. TABLE 3 Food habits of bark-foraging birds

Species Primary foods a % A.F. b Major insect orders eaten General comments Sources

Yellow- bellied Insects, sap, bast, 50 Hymenoptera, Coleoptera, Most insects taken in spring and Beal 1911; Bent 1964c; Sapsucker cambium, fruit Lepidoptera summer; eats spruce budworms, tent Lawrence 1967; (Sphyrapicus varius) caterpillars, sawflies Tate 1973 Red-naped Sapsucker Insects, sap, bast, 50 Coleoptera, Hymenoptera, Most insects taken in spring and Beal 1911; Bent 1964c; ( Sphyrapicus cambium, fruit, Orthoptera summer Ehrlich et al. 1988 nuchalis) spiders Red- breasted Insects, sap, bast, 53–69 Hymenoptera, Coleoptera, Most insects taken in spring and Beal 1911; Bent 1964c; Sapsucker cambium, fruit Homoptera, Trichoptera, summer Jackman 1975; Otvos (Sphyrapicus ruber) Lepidoptera and Stark 1985; Ehrlich et al. 1988

Williamson Insects; occasionally 87–92 Hymenoptera, Coleoptera Ants comprise most of diet; eats Beal 1911; Bent 1964c; Sapsucker cambium, sap bark beetles Otvos and Stark 1985 (Sphyrapicus thyroideus) Downy Woodpecker Insects; occasionally 76–97 Coleoptera, Hymenoptera, Beetles make up >40% of diet Beal 1911; Bent 1964c; (Picoides pubescens) sap, fruits, Lepidoptera volume; two-thirds are wood- Otvos and Stark 1985 cambium, seeds boring buprestids, cerambycids and scolytids; eats larch and pine sawflies, codling moth Hairy Woodpecker Insects; occasionally 77–93 Coleoptera, Hymenoptera Beetles make up >60% of diet Beal 1911; (Picoides villosus) fruits, seeds volume; most beetles are wood- Bent 1964c; Otvos and boring buprestids, cerambycids and Stark 1985; Villard and scolytids; eats larch sawfly, codling Beninger 1993 moth White-headed Insects, pine cones, 40–80 Coleoptera, Hymenoptera, Most cones taken in spring, insects Beal 1911; Bent 1964c; Woodpecker spiders Homoptera in summer, cones and insects in Ligon 1973 (Picoides fall/winter; eats bark beetles albolarvatus) Three-toed Insects 89–96 Coleoptera, Lepidoptera >75% of diet volume consists of Beal 1911; Woodpecker wood-boring beetles; eats larch Stallcup 1962; (Picoides tridactylus) sawfly Bent 1964c; Otvos and Stark 1985; Goggins et al. 1989 TABLE 3 (Continued)

Species Primary foods a % A.F. b Major insect orders eaten General comments Sources

Black- backed Insects; occasionally >90 Coleoptera, Hymenoptera >75% of diet volume consists of wood- Bent 1964c; Woodpecker fruit, mast, cambium boring beetles; consume ~13,675 beetle Goggins et al. 1989; (Picoides articus) larvae per bird annually Villard and Beninger 1993 Northern Flicker Insects; occasionally 61–95 Hymenoptera, Coleoptera, Strong seasonal diet trends; ants Beal 1911; (Colaptes auratus) nuts, grains and fruits Orthoptera, Lepidoptera comprise ~75% of insect food by Martin et al. 1951; volume Bent 1964c; Otvos and Stark 1985; Campbell et al. 1988 Pileated Insects; occasionally 73–75 Hymenoptera, Coleoptera, Ants (Camponotus sp.) comprise Beal 1911; Bent 1964c; Woodpecker fruits and nuts Lepidoptera >50% of diet volume; eats bark Beckworth and (Dryocopus beetles and spruce budworms Bull 1985; Otvos and pileatus) Stark 1985; Bull et al. 1992 Red- breasted Insects; occasionally 70–88 Coleoptera, Hymenoptera, Diet includes bark-dwelling forms Bent 1964b; Nut hatch seeds and spiders Hemiptera, Dermaptera such as bark beetles, weevils, Stallcup 1963; (Sitta canadensis) wood-borers; eats spruce and jack Anderson 1976; pine budworm, Douglas-fir tussock Campbell et al. 1988 moth White-breasted Insects; occasionally 83–92 Coleoptera, Hymenoptera, Diet includes bark-dwelling forms Bent 1964b; Nuthatch spiders, seeds and nuts Lepidoptera, Dermaptera, such as bark beetles, weevils, Stallcup 1963; (Sitta carolinensis) Hemiptera wood-borers; eats gypsy moths, Anderson 1976 tent caterpillars, spruce budworm Pygmy Nuthatch Insects; also conifer 83 Coleoptera, Hymenoptera, Diet includes several bark beetles, Stallcup 1963; (Sitta pygmaea) seeds and spiders Hemiptera, Lepidoptera wood-boring beetles, leaf bugs and Bent 1964b; weevils; eats spruce budworm Anderson 1976; Otvos and Stark 1985 Brown Insects and spiders; >85 Lepidoptera, Diptera, Diet includes many injurious forms Beal 1911; Stallcup 1963; Creeper occasionally nuts and Coleoptera, Hemiptera, such as bark beetles, wood-borers, Otvos and Stark 1985; (Certhia seeds Homoptera larch sawfly, spruce budworm Mariani and americana) Manuwal 1990 a Primary foods = foods that make up ≥ 10% of the diet volume in any season or foods eaten “occasionally” when only qualitative data were available. b % A.F. = estimated percent of the diet volume consisting of food of animal origin. 0 TABLE 4 Food habits of foliage-gleaning birds

Species Primary foods a % A.F. b Major insect orders eaten General comments Sources

Black-capped Chickadee Insects; occasionally 70 Lepidoptera, Coleoptera, Eats codling and gypsy Martin et al. 1951; (Parus atricapillus) seeds, fruit and Hemiptera, Hymenoptera moth, spruce and jack pine Bent 1964a; spiders budworm, larch and pine Scott et al. 1977 sawfly, larch casebearer, Douglas-fir tussock moth, forest loopers, wood-borers, bark beetles and weevils Mountain Chickadee Insects; occasionally 75–98 Hymenoptera, Lepidoptera, Eats spruce budworm, Scott et al. 1977; (Parus gambeli) seeds, nuts, berries Coleoptera, Diptera, Douglas-fir tussock moth, Dahlsten and and spiders Homoptera sawflies, spruce aphids, Copper 1979; needle miners, forest Campbell et al. 1988; loopers, injurious Grundel and geometrids and tortricids Dahlsten 1991 and bark beetles Boreal Chickadee Insects; occasionally - Lepidoptera, Homoptera, Eats spruce and black- Bent 1964a; (Parus hudsonicus) seeds, berries and Coleoptera headed budworm, larch Scott et al. 1977; spiders sawfly, forest loopers and Campbell et al. 1988 bark beetles Chestnut-backed Insects; occasionally 65 Lepidoptera, Hemiptera, Eats spruce budworm, Bent 1964a; Chickadee seeds, fruits and Homoptera, Coleoptera Douglas-fir tussock moth, Scott et al. 1977 (Parus rufescens) spiders forest loopers, sawflies and bark beetles

a Primary foods = foods that make up ≥ 10% of the diet volume in any season or foods eaten “occasionally” wh en only qualitative data were available. b % A.F. = estimated percent of the diet volume consisting of food of animal origin. TABLE 5 Food habits of aerial-foraging and hawking birds

Species Primary foods a % A.F. b Major insect orders eaten General comments Sources

Flammulated Owl Insects; some 100 Lepidoptera, Coleoptera, Bull and Anderson 1978; (Otus flammeolus) spiders, birds and Orthoptera Campbell et al. 1988; mammals Ehrlich et al. 1988 Lewis Woodpecker Insects, fruit, nuts, 37 Coleoptera, Hymenoptera, Most insects eaten in Beal 1911; Bent 1964c; (Melanerpes lewis) berries, seeds, Orthoptera, Hemiptera, summer; eats adult emergent Bock 1970; Jackman 1975 spiders Diptera insects (no wood-boring larvae); eats tent caterpillars Vaux’s Swift Insects 100 Diptera, Coleoptera, Eats exclusively flying insects Martin et al. 1951; (Chaetura vauxi) Hymenoptera, Hemiptera Scott et al. 1977 Pacific-slope Flycatcher Insects 100 Hymenoptera, Diptera, Eats bark beetles Martin et al. 1951; (Emphidonax difficilis) Hemiptera, Coleoptera, Bent 1963; Stallcup 1963; Lepidoptera Scott et al. 1977 Ash- throated Flycatcher Insects; occasionally 92 Hymenoptera, Hemiptera, Bent 1963; Scott et al. 1977, (Myiarchus cinerascens) spiders, fruits and Coleoptera, Lepidoptera, Otvos and Stark 1985 berries Diptera Purple Martin Insects; occasionally 100 Hymenoptera, Diptera, Bent 1963; Scott et al. (Progne subis) spiders Hemiptera, Coleoptera, 1977, Walsh 1978; Otvos Lepidoptera, Odonata and Stark 1985 Tree Swallow Insects; occasionally 80 Coleoptera, Hymenoptera, Eats larch sawfly and Bent 19 63; (Tuchycineta bicolor) spiders, seeds and Odonata, Ephemeroptera, bark beetles Campbell et al. 1988 berries Orthoptera Violet-green Swallow Insects 100 Hemiptera, Diptera, Preys on several injurious Bent 1963; (Tachycineta thalassina) Hymenoptera, Coleoptera, insects including scolytids Otvos and Stark 1985 Lepidoptera and engraver beet les Western B l u e b ird Insects; occasionally 80 Coleoptera, Hymenoptera, Bent 1964d; (Sialia mexicana) spiders and fruits Hemiptera, Lepidoptera, Herlugson 1982 Orthoptera Mountain Bluebird Insects; occasionally 90 Coleoptera, Hymenoptera, Eats bark beetles Stallcup 1963; (Sialia currucoides) fruits and spiders Lepidoptera, Hemiptera, Bent 1964d; Power 1980; Orthoptera, Homoptera Herlugson 1982 a Primary foods = foods that make up ≥ 10% of the diet volume in any season or foods eaten “occasionally” when only qualitative data were available. b % A.F. = estimated percent of the diet volume consisting of food of animal origin. TABLE 6 Food habits of ground-foraging birds

Species Primary foods a % A.F. b Major insect orders eaten General comments Sources

Bewick’s Wren Insects 97 Hemiptera, Coleoptera, Eats injurious forms Bent 1964b; (Thryomanes bewickii) Orthoptera (e.g., weevils, bark Ehrlich et al. 1988 beetles, locusts) House Wren Insects; also spiders, 98 Hemiptera, Lepidoptera, Eats bark beetles Bent 1964b; (Troglodytes aedon) snails and millipedes Coleoptera, Hymenoptera, Scott et al. 1977; Orthoptera Ehrlich et al. 1988 Common Grackle Insects, spiders, 32 Hymenoptera, Orthoptera Omnivorous; eats spruce Martin et al. 1951; (Quiscalus quiscula) crustaceans, and jackpine budworm Ehrlich et al. 1988 earthworms, snails, birds’ eggs, small vertebrates, fruit, grain, seeds and nuts House Finch Seeds, fruits, buds and - - - Ehrlich et al. 1988 (Carpodacus mexicanus) tree sap a Primary foods = foods that make up ≥ 10 % of the diet volume in any season or foods eaten “occasionally” when only qualitative data were available. b % A.F. = estimated percent of the diet volume consisting of food of animal origin. TABLE 7 Food habits of aerial-foraging and gleaning bats

Species Primary foods a Major insect orders eaten General comments Sources

Pallid Bat Insects, spiders, Coleoptera, Lepidoptera, Prefers insects >17 mm; prey Easterla and Whitaker 1972; (Antrozous pallidus) small vertebrates Orthoptera includes flightless forms Whitaker et al. 1977; Bell 1982; gleaned from the ground or Nagorson and Brigham 1993 foliage Big Brown Bat Insects C ol eoptera, Lepido p t e r a, Prefers insects 6-12 mm; prey Whitaker et al. 1977, 1981a; (Eptesicus fuscus) Diptera, Isoptera, Hemiptera includes flightless forms such Brigham 1990; Brigham and as beetle larvae and spiders Saunders 1990; Nagorson and Brigham 1993 Silver-haired Bat Insects Le pidopter a, Homoptera, Diet is extremely flexible Whitaker et al. 1977, 1981a, (Lasionycteris noctivagans) Hymenoptera, Diptera, 1981b; Nagorson and Coleoptera, Isoptera Brigham 1993 Hoary Bat Insects Lepidoptera, Coleoptera, Prey size range: 6-30 mm Whitaker et al. 1977, 1981a; (Lasiurus cinereus) Diptera, Odonata Barclay 1985; Nagorson and Brigham 1993 California M yo t is Insects; occasionally Le p id o p t e r a, Trichoptera, Prey includes flightless forms Whitaker et al. 1977, 1981b; ( My0tis californicus) spiders Diptera, Coleoptera gleaned from the ground or Nagorson and Brigham 1993 foliage Western Small-footed Myotis Insects Trichoptera, D i pte r a, Whitaker et al. 1981b; (Myotis ciliolabrum) Lepidoptera, Coleoptera, Woodsworth 1981; Nagorson and Hemiptera Brigham 1993 Western Long-eared Myotis Insects; occasionally Lepidoptera, Coleoptera, Preys on many flightless Whitaker et al. 1977, 1981a; Faure (Myotis evotis) spiders Diptera forms and Barclay 1992; Nagorson and Brigham 1993 Keen’s Long -eared Myotis Insects Lepidoptera Very little information Van Zyll de Jong 1985; Nagorson (Myotis keenii) available on diet and Brigham 1993 Little Brown Myotis Insects Diptera, Lepidoptera, Prefers insects 6-10 mm Whitaker et al. 1977, 1981a; Herd (Myotis lucifugus) Coleoptera, Trichoptera and Fenton 1983; Nagorson and Brigham 1993 Northern Long- ea red Myotis Insects Trichoptera, Lepidoptera, Whitaker 1972; Nagorson and (Myotis septentrionalis) Coleoptera, Diptera, Brigham 1993 Homoptera, Hymenoptera TABLE 7 (Continued)

Species Primary foods a Major insect orders eaten General comments Sources

Long-legged Myotis Insects Lepidoptera, Hymenoptera, - Black 1974; Whitaker et al. 1977, (Myotis volans) Diptera, Coleoptera, 1981a; Nagorson and Brigham Homoptera 1993 Yuma Myotis Insects Ephemeroptera, Trichoptera, Feeds mainly on aquatic insects Easterla and Whitaker 1972; (Myotis yumanensis) Diptera, Lepidoptera, Whitaker et al. 1977, 1981a; Coleoptera, Isoptera, Brigham et al. 1992; Nagorson Homoptera and Brigham 1993 a Primary foods = foods that make up ≥ 10% of the diet volume in any season or foods eaten “occasionally” when only qualitative data were available. TABLE 8 Food habits of terrestrial and arboreal rodents

Species Primary foods a General comments Sources

Southern Red-backed Vole Fungi, lichens, seeds, berries, 72% fungi in the diet by Cowan and Guiget 1978; Fogel and Trappe (Clethrionomys gapperi) shoots and petioles of volume; eats larch sawfly 1978; Maser et al. 1978; Gunther et al. 1983; graminoids, forbs and shrubs, Stevens and Lofts 1988 insects Bushy-tailed Wood Rat Green and dry foliage of forbs, 34% fungi in the diet by Cowan and Guiget 1978; Fogel and Trappe (Neotoma cinerea) shrubs and trees; fungi, lichens, volume 1978; Maser et al. 1978; Stevens and Lofts 1988 fruits and seeds; occasionally insects and carrion Deer Mouse Arthropods, seeds, fruits, fungi, 46% animal food and 10% Martin et al. 1951; Cowan and Guiget 1978; (Peromyscus maniculatus) lichens, stems and roots of grasses fungi in the diet by Fogel and Trappe 1978; Maser et al. 1978; volume (e.g., Coleoptera, Gunther et al. 1983; Stevens and Lofts 1988 Lepidoptera, Diptera); eats gypsy moth and pine sawfly Columbian Mouse Arthropods, seeds, fruits, fungi, No information on Cowan and Guiget 1978 (Peromyscus ureas) lichens, stems and roots of grasses fungus consumption

Sitka Mouse No specific dietary (Peromyscus sitkensis) information available Northern Flying Squirrel Primarily fungi and lichens; 78% fungi in the diet by Martin et al. 1951; McKeever 1960; Cowan and (Glaucomys sabrinus) occasionally buds, fruits, seeds, volume; insect orders Guiget 1978; Fogel and Trappe 1978; shrubs, mosses, forbs and insects consumed include Maser et al. 1978; Stevens and Lofts 1988 Lepidoptera and Coleoptera

Ye I low - pi ne Chip mu n k Fungi, seeds, flowers, fruits, 50% fungi in the diet by Cowan and Guiget 1978; Fogel and Trappe (Tamias amoenus) bulbs, tubers and insects volume 1978; Maser et al. 1978; Maser and Maser 1987; Stevens and Lofts 1988 Least Chipmunk Seeds, fruits, fungi and insects No information on Martin et al. 1951; Cowan and Guiget 1978; (Tamias minimus) fungus consumption; eats Fogel and Trappe 1978 jack pine budworm TABLE 8 (Continued)

Species Primary foods a General comments Sources

Red-tailed Chipmunk - No specific dietary information - (Tamias ruticaudus) available Townsend’s Chipmunk Primarily fungi; occasionally 77% fungi in the diet by volume Cowan and Guiget 1978; Fogel and (Tamias townsendii) berries, seeds and nuts Trappe 1978; Maser et al. 1978 Douglas Squirrel Fungi, conifer seeds, fruits, buds, 70% fungi in the diet by volume Cowan and Guiget 1978; Fogel and (Tamiasciurus douglasii) insects, sap, cambium Trappe 1978; Maser et al. 1978 Red Squirrel Primarily fungi; also seeds, nuts, 77% fungi in the diet by volume; eats Cowan and Guiget 1978; Fogel and (Tamiasciurus lichens, fruits, buds, insects, small jack pine budworm and spruce Trappe 1978; Maser et al. 1978; hudsonicus) vertebrates, sap, cambium budworm Stevens and Lofts 1988 a Primary foods = foods that make up ≥ 10% of the diet volume in any season or foods eaten “occasionally” when only qualitative data were available. TABLE 9 Food habits of carnivores

Species Primary food a General comments Sources

Marten Rodents, lagomorphs; occasionally birds, fish, Voles, mice and squirrels Stordeur 1986; (Martes americana) vegetation, insects and crustaceans Stevens and Lofts 1988 Fisher Lagomorphs, porcupine, rodents, birds, carrion, Squirrels, voles, mice and shrews Cowan and Guiget 1978; Powell (Martes pennanti) insects, fruit and berries 1982; Stevens and Lofts 1988 Ermine Small mammals, birds, fish, amphibians and Voles, squirrels, chipmunks and Stordeur 1986; Stevens and (Mustela erminea) insects; some vegetation mice Lofts 1988; Nagorson et al. 1989 Long - t ailed Weasel Small mammals, pikas; occasionally birds Voles, mice and squirrels Cowan and Guiget 1978; (Mustela frenata) Stevens and Lofts 1988 Least Weasel Primarily microtine rodents; occasionally small — Cowan and Guiget 1978 (Mustela nivalis) birds, amphibians and reptiles Spotted Skunk Mice, birds, amphibians, reptiles, insects, fungi; Fogel and Trappe 1978; (Spilogale putorius) occasionally fruit Cowan and Guiget 1978 Raccoon Arthropods, birds, small mammals, fish, frogs, Omnivorous Cowan and Guiget 1978; (Procyon lotor) berries, fruits, nuts, seeds and eggs Stevens and Lofts 1988 Black Bear Leaves, shoots, buds, sapwood, fruits, fungi, Omnivorous Cowan and Guiget 1978; (Ursus americanus) insects, fish, carrion, small- to medium-sized Stevens and Lofts 1988 mammals and ungulates a Primary foods = foods that make up ≥ 10% of the diet volume in any season or foods eaten “occasionally” when only qualitative data were available. TABLE 10 Summary of quantitative studies of avian predation on forest pests

Prey Prey Predator Prey General comments/ Predator a Prey densityb stage c consumption d mortali t y e S o u rce conclusions

Order Coleoptera

Woodpecker guild Engelmann EPI L 99% of woodpecker 55% Hutchinson 1951 Mortality estimated for 3 species. (TTWO, HAWO, spruce beetle diet in winter DOWO) (Dendroctonus consisted of spruce engelmanii) beetle larvae - Woodpecker guild Engelmann END L 45–98% Knight 1958 Mortality estimated for 3 species. (TTWO, HAWO, spruce beetle Prey mortality depended on DOWO) intensity of localized woodpecker activity; mortality per tree was highly correlated with % bark removed by woodpeckers. Conclude: 3 species are important in control of spruce beetle. Woodpecker guild Engelmann EPI L 45–98% Baldwin 1960 Mortality estimated for 3 species; (TTWO, HAWO, spruce beetle includes direct and indirect DOWO) effects of woodpecker feeding activity. Strong nu mer i cal response by all 3 species (30-fold increase in woodpecker density during EPI). Avian guild Engelmann END-TR A - 24–32% Baldwin 1968 Mortality estimated for entire (incl. MOCH, spruce beetle guild (6 species). Conclude: birds MOBL, and 4 non- have an important impact on WT species) adult spruce beetles when prey at moderate densities. Woodpecker guild Engelmann END L - 52–83% Shook and Mortality estimated for both (TTWO, HAWO) spruce beetle Baldwin 1970 species. Prey mortality was influenced by stand density: semi-open = 83%; open = 71%; dense = 52%. Conclude: woodpeckers are important in controlling END spruce beetle populations. TABLE 1o (Continued)

Prey Prey Predator Prey General comments/ Predator a Prey densityb stage c consumption d mortality e Source conclusions

Woodpecker guild Engelmann END L TTWO: 400 L/ha per yr 19% Koplin 1972 Mortality estimated for 3 species; (TTWO, HAWO, spruce beetle HAWO: 50 L/ha per yr all 3 species: functional and DOWO) DOWO: o L/ha per yr numerical response to increased prey density. Combined predatory impact was greatest at EPI L TTWO: 178 ooo L/ha 83% EPI prey density. Decreased per yr effect at END prey density HAWO: 110 ooo L/ha because of availability of per yr alternative prey; decreased DOWO: 49 250 L/ha impact at PAN prey density per yr because of limits imposed by nesting territoriality on PAN L TTWO: 1 165 250 L/ha 55% numerical response. From END per yr to EPI prey density, 50–85-fold HAWO: 535 750 L/ha increase in woodpecker winter per yr density and 6–7-fold increase in DOWO: 387 250 L/ha woodpecker breeding density. per yr Conclude: woodpecker predation can limit EPI but not PAN spruce beetle infestations. Woodpecker guild Engelmann END L TTWO: 42 L/predator 20–29% Koplin and Mortality estimated for 3 species; (TTWO, HAWO, spruce beetle stomach Baldwin 1970 all 3 species: functional and DOWO) HAWO: 7 L/predator numerical response to increased stomach prey density. Spruce beetle larvae L TTWO: 915 L/predator 45–98% made up 2–7% and 4–29% of the stomach items in woodpecker diet at END HAWO: 154 L/predator and EPI prey densities, stomach respectively. Conclude: DOWO: 45 L/predator woodpeckers are important stomach regulators of spruce beetle. - Woodpecker guild Spruce beetle EPI L 24–98% McCambridge Mortality estimated for 3 species; (TTWO, HAWO, (Dendroctonus and Knight includes direct and indirect DOWO) rufipennis) 1972 effects (e.g., dessication, changes in parasite and predator density) of woodpecker feeding activity. 30 TABLE 10 (Continued)

Prey Prey Predator Prey General comments/ Predatora Prey densityb stage c consumption d mortality e Source conclusions

Avian guild Mountain EPI A TTWO: 3–75 — Rust 1929, 1930 Woodpeckers showed a numerical (incl. TTWO, pine beetle A/predator stomach response to localized increases in HAWO, and non- (Dendroctonus HAWO: 2–14 mountain pine beetle density. WT species) ponderosae) A/predator stomach

Avian guild Mountain EPI A guild: 2358 A/acre per 11.6% Stallcup 1963 Mortality estimated for entire (incl. RBNU, pine beetle season guild (? species). Most important BRCR, PYNU, and predators were RBNU, BRCR, non-WT species) PYNU and Emphidonax spp. flycatchers. Conclude: birds contribute to control during the flight and attack period of adult beetles. - Woodpecker guild Mountain END L, A 27–54% Amman 1973 Mortality estimated for both (HAWO, DOWO) pine beetle species. Woodpecker predation on adults increased with elevation; larvae are smaller and less preferred at higher elevations. Woodpecker guild Mountain EPI L, A Beetle adults and 45–95% Crockett and Mortality estimated for 3 species; (TTWO, HAWO, pine beetle larvae made up 67–99% Hansley 1978 estimates include direct and DOWO) of the winter diet indirect effects (e.g., dessication, volume for all freezing, changes in parasite and predator species predator density) of woodpecker feeding activity. 2–3.5-fold increase in woodpecker density during outbreak. Secondary infection by other wood-borers increased intensity and duration of predator response. - Woodpecker guild Mountain EPI L, A 30% Lester 1980 Mortality estimated for 5 species. (DOWO, HAWO, pine beetle - HAWO and TTWO: strong TTWO, BBWO, numerical response in EPI vs. PIWO) END areas. Conclude: woodpeckers more important at END prey density. TABLE 10 (continued)

Prey Prey Predator Prey General comments/ Predatora Prey densityb stage c consumption d mortalitye Source conclusions

Avian guild Mountain END-EPI L,A HAWO: 21 108 L/ha per Korol 1985 Consumption is likely (HAWO, RBNU, pine beetle season (theoretical underestimated because only data BRCR) maximum) on 3 species were adequate for inclusion in the model. Guild: 329 A/ha per Conclude: birds may suppress season prey growth and maximum prey density; silvicultural methods and retention of wildlife trees could prevent growth of EPI from END prey densities. Downy Mountain EPI L 50–90% Bergvinson Herbicide-treated trees increased Woodpecker pine beetle and Borden DOWO predation efficiency to 1992 90% from 50% in control trees. Conclude: treating trees would enhance woodpecker nesting and feeding habitat and decrease beetle impact. Woodpecker Western pine EPI L, A — 31.8% Otvos 1965 Mortality estimated for entire guild (HAWO, beetle guild; includes only direct impact DOWO, WHWO, (Dendroctonus of woodpecker feeding activity. PIWO) brevicomis) Woodpecker activity increased beetle parasite densities 4-fold and decreased insect predation on beetles slightly. Avian guild Western pine EPI A 8–26% Otvos 1969, Mortality estimated for entire (incl. VGSW, beetle 1970 guild; range is over 3 years. RBNU, and 4 Conclude: avian predation can non-WT species) contribute to control of adult beetle densities. Downy Southern EPI L 7% in Moore 1972 Mortality estimate includes Woodpecker pine beetle winter and direct effect of woodpecker (Dentroctonus spring; 2% feeding only. Woodpecker feeding frontulis) in summer increased dessication of inner bark and caused weather and disease to increase brood mortality; this effect was not quantified. 32 TABLE 1o (Continued)

Prey Prey Predator Prey General comments/ Predator a Prey density b stage c consumption d mort ali t y e Source conclusions

Woodpecker g uild Southern EPI E, P, A - 3.5% E; Kroll and Fleet Mortality estimated for entire (incl. DOWO, pine beetle 12–30% P, A 1979; Kroll guild. Woodpecker density HAWO, PIWO) in summer; et al. 1980 increased 6–33-fold in EPI vs. 36–63% P, A END prey areas. Conclude: in winter woodpeckers play a role in stabilizing southern pine beetle population densities. Woodpecker guild Ips beetle END 1 1–76 % Shook and Mortality estimated for both (TTWO, HAWO) (several Baldwin 1970 species. Beetle mortality species) influenced by stand density: 76% = open; 11% = semi-open. Conclude: woodpeckers contribute to control of END beetle densities. Black-backed Oregon fir EPI L BBWO: 10–12 L/day 90% Wickman 1965 Conclude: BBWO feeding activity Woodpecker sawyer is an important source of pest (Monochamus control. o regon ensis) Woodpecker guild Hardwood EPI L - 13–6 5 % Solomon 1969 Mortality estimated for entire (incl. HAWO, borers guild. Woodpeckers preyed on 14 DOWO, PIWO) (14 species) species of borers. Tree diameter at breast height was inversely related to woodpecker predation success. Woodpecker guild Red oak END L - 9.4% Petit and Mortality estimated for both (DOWO, HAWO) borer Grubb 1988 species. Study conducted in (Enaphalodes clearcut where woodpecker rufulus) densities were low, probably because of lack of nest sites.

Order Lepidoptera

Avian guild Larch case- END L — 23.5% Sloan and Mortality estimated for entire (incl. BCCH) bearer Coppel 1968 guild (? species). Conclude: (Coleophora predation by birds contributes to laricella) prey population stability. TABLE 10 (continued)

Prey Prey Predator Prey General comments/ Predator a Prey density s t age c consumption mortality e Source conclusions

Mountain Lodgepole EPI L Larvae made up >9o% - Telford and MOCH: functional and Chickadee needle miner of the stomach volume Herman 1963 numerical response to increased (Coleotechnites of overwintering Dahlsten and prey density. starki) MOCH Herman 1965 Mountain Douglas-fir END L, P, E - 16.7% Dahlsten and MOCH fed mainly on egg masses Chickadee tussock moth Copper 1979 and cocoons. Predation rates (Orgyia were correlated with MOCH nest TR L, P, E - 66.7% pseudotsugata) densities. Conclude: bird density may be important in moth EP I L, E - P, 71.7% suppression.

Avian guild Douglas-fir - L, P Used number of 43% Torgerson et al. Mortality estimated for entire (incl. RBNU, tussock moth observed predation 1984 guild. MOCH and RBNU are the MOCH, BCCH, events as an indication two most important predators CBCH, and 17 of relative based on their density and non-WT species) consumption: observed consumption. Loss rates RBNU: 24 events of prey were positively associated MOCH: 4 events with concurrent densities of BCCH: 1 event avian predators. CBCH: 2 events Woodpecker Codling EPI L — HAWO: MacLellan 1958 Only 3% of larvae eaten by guild (DOWO, moth 34.8% woodpeckers were parasitized; HAWO) DOWO: 14% of escaped larvae were 17.2% parasitized. Orchard density effected mortality by woodpecker predation: dense = 64%; semi- open = 49%; open = 35%. Conclude: both species important in control of moth larvae. Avian guild Black-headed END L, P 15 prey/predator per 3–14% Gage et al. Mortality estimated for entire (incl. BOCH) budworm day 1970 guild (? species). BOCH: positive (Acleris functional and numerical variana) response to increased prey density.

33

34 TABLE 10 (continued)

Prey Prey Predator Prey General comments/ Predator a Prey density stag e c con s u m pti0n d mortality e Source conclusions

Avian guild Jack pine END L, P BCCH: 7 prey/predator 40–65% Mattson et al. Mortal ity estimated for entire (incl. BCCH, budworm stomach 1968 guild (? species). BCCH and RBNU, COGR) (Choristoneura RBNU: 2 prey/predator RBNU: strong numerical pinus) stomach response. Conclude: birds play a COGR: 43 prey/predator role in moth control at END prey stomach density. Avian guild Jack pine END L, P BCCH: 8.4 prey/predator - Mattson 1975 BCCH: no functional response (incl. BCCH) budworm stomach observed from END to TR prey densities. Conclude: birds TR L, P BCCH: 6.3 prey/predator important at END prey density stomach only. Avian guild Eastern EPI L 40 L/predator per day 4.3% Kendeigh 1947 Mortality estimated for entire (incl. BCCH) spruce guild (? species). budworm (Choristoneura fumiferana) Avian guild Eastern EPI L 65–100 L/predator 3.5–7% George and Mortality estimated for entire (incl. chickadees, spruce per day Mitchell 1948 guild (? species). Conclude: birds nuthatches, budworm more important at END prey creepers) densities.

Avian guild (incl. Eastern END L, P BCCH: 2.9 87% Crawford et al. Mortality estimated for entire BCCH, RBNU, spruce prey/day per ha 1983 guild (15 species). BCCH and COGR, and 12 budworm RBNU: 3.6 RBNU increased consumption other non-WT prey/day per ha rates from END to TR prey species) densities; no increased TR BCCH: 17 L, P 23% consumption rates from TR to prey/day per ha EPI prey densities. Conclude: RBNU: 30 some species (e.g., BCCH, prey/day per ha RBNU) are important in pest EPI L, P BCCH: 122 2 % suppression and may prevent or prey/day per ha reduce the severity of budworm RBNU: 124 outbreaks. prey/day per ha TABLE 1o (Continued)

Prey Prey Predator Prey General comments/ Predatora Prey density stage c consum ption d mortality e Source conclusions

Avian guild Eastern END L, P BCCH: 2 120 prey/ha 84% Crawford and Mortality estimated for entire (incl. BCCH, spruce per season Jennings 1989; guild. RBNU: positive functional BOCH, RBNU, budworm BOCH: 890 prey/ha Crawford et al. response to increased prey BRCR, and 20 per season 1990 density. Conclude: birds are other non-WT RBNU: 1 760 prey/ha capable of reducing growth loss species) per season in spruce-fir forests and TR L, P BRCR: o prey/ha per 22% dampening the severity of season budworm infestations when habitats are suitable for supporting adequate numbers of avian predators. Avian guild Western - L, P BCCH: 6.1 L - Garton 1987 Conclude: BCCH and MOCH (incl. BCCH, spruce or P/predator per hour play a role in maintaining sparse MOCH, and 24 budworm MOCH: 6.1 L budworm densities during non-WT species) (Choristoneura or P/predator per hour intervals between outbreaks. occidentalis) Avian guild Western EPI L, P - 66–72% Torgerson and Mortality estimated for entire (incl. MOCH, spruce Campbell 1982; guild (? species). Conclude: birds RBNU) budworm Takekawa and contribute significantly to Garton 1984 regulation of budworm populations.

Order Hymenoptera

Avian guild European END L - 95% Coppel and Mortality estimated for entire (incl. BCCH, pine sawfly Sloan 1971 guild (? species). Conclude: DOWO) (Neodiprion resident birds (e.g., BCCH, sertifer) DOWO) are most important in control of sawfly densities. 35 36 TABLE 10 (Concluded)

Prey Prey Predator Prey General comments/ Predator a Prey densityb stage c consumption d mort ality e Source conclusions - Avian guild Larch sawfly END L, A 5.9% L; Buckner and Mortality estimated for entire (incl. BCCH, (Pristiphora 64.9% A Turnock 1965 guild (? species). BCCH and YBSA) erichsonii) YBSA: functional and numerical TR L, A BCCH: 1 054 A/predator 0.5% L; response to increased prey per season 5.6% A density. Conclude: birds are most YBSA: 76 L/predator likely to impact prey at low prey per season densities.

a Predators are abbreviated according to species codes in Cannings and Harcombe (1990): BBWO = Black-backed Woodpecker; BCCH = Black-capped Chickadee; BOCH = Boreal Chickadee; BRCR = Brown Creeper; CBCH = Chestnut-backed Chickadee; COGR = Common Grackle; DOWO = Downy Woodpecker; HAWO = Hairy Woodpecker; MOBL = Mountain Bluebird; MOCH = Mountain Chickadee; PIWO = Pileated Woodpecker; PYNU = Pygmy Nuthatch; RBNU = Red-breasted Nuthatch; TTWO = Three- toed Woodpecker; VGSW = Violet Green Swallow; WHWO = White-headed Woodpecker; YBSA = Yellow-bellied Sapsucker; non-WT species = species that are not consid- ered wildlife tree users. b Prey density = codes: END = endemic; EPI = epidemic; PAN = panepidemic; TR = transitional. c Prey stage = prey life cycle stage (A = adult; C = cocoon; E = egg; L = larvae; P = pupae). d Predator consumption = rate of prey consumption by the predator. e Prey mortality = rate of prey mortality attributed to the predator. TABLE 11 Summary of quantitative studies of mammalian predation on forest pests

Prey Prey Predator Prey General comments/ Predator Prey density a stage b consumption c mortality d Source conclusions

Order Lepidoptera

Deer Mouse Gypsy moth EPI P 28 P/predator per day - Smith and Consumption estimate based on Lau ten- metabolic requirements. Possibly schlager 1981 a weak numerical response to increased moth density. Red Squirrel, Jack pine END L, P — Mattson et al. Found negligible budworms in Least Chipmunk budworm 1968 analysis of stomach contents of 1o chipmunks. Conclude: small EPI L, P — mammals are not important budworm predators. Red Squirrel Eastern EPI L, P 400–500 prey/predator - Dowden et al. Budworms made up 51% of red spruce per day 1953 squirrel diet. Conclude: red budworm squirrels could contribute to control of budworm densities. - Red Squirrel Eastern L, P 600–700 prey/predator - Morris 1963 Estimate based on laboratory spruce per day feeding trials; no alternate prey budworm available. - Red Squirrel Eastern EPI L, P 0–39 prey/predator Jennings and Estimate based on stomach spruce stomach Crawford 1989 content analyses. Consumption budworm was lower than previously estimated potential consumption. — Small mammal Eastern EPI L, P Jennings et al. Digestive tracts of 2 Red-backed guild spruce 1991 Voles examined contained no (incl. Red- budworm budworm larvae or pupae backed Vole) although other guild members did. 37

38 TABLE 11 (Continued)

Prey Prey Predator Prey General comments/ Predator Prey density a stage b consumption c mortality d Source conclusions

Order Hymenoptera

Small mammal Pine sawfly END C 25 C/predator per day 5% Holling 1959 Mortality estimated for entire guild guild (3 species). Deer Mouse: 135 C/predator per day (incl. Deer functional and numerical TR C 15% Mouse and 2 240 C/predator per day response to increased prey other non-WT density. Conclude: small species) EPI C 14% mammals can theoretically control or dampen oscillations in sawfly densities.

Small mammal Larch sawfly - C ≤600 C/predator per - Buckner 1955 Study inconclusive; the role of guild day small mammal predation on (incl. Red- sawflies requires further backed Vole) evaluation.

a Prey density codes: END = endemic; TR = transitional; EPI = epidemic. b Prey stage = prey life cycle stage; codes used: L = larvae; P = pupae; C = cocoon. c Predator consumption = rate of prey consumption by the predator. d Prey mortality = rate of prey population mortality attributed to the predator or predator guild. 4 MANAGEMENT IMPLICATIONS FOR WILDLIFE TREE USERS

Wildlife tree-dependent insectivorous birds, bats, In addition to snag management, silvicultural and small mammals are of potential economic im- practices favouring primary cavity excavators include portance because of their food habits and their reducing the size of clearcuts (Kroll et al. 1980), alter- capacity to consume large amounts of injurious ing the shape of clearcuts to generate long, narrow forest insects. Although these biological agents in- openings (Kroll et al. 1980), increasing the rotation teract with a host of other factors to influence the age (Kroll et al. 1980; Raphael and White 1984; abundance and distribution of forest pest popu- Keisker 1987) and retaining old-growth forest 1 ations, managing for h ea1 thy, sustain ab1 e islands until the harvested stand regenerates populations of insectivorous predators can be cost (Raphael and White 1984). The spatial distribution effective (Takekawa et al. 1982; Takekawa and of these islands and their proximity to other ma- Garton 1984; Garton et al. 1984). The value of forest ture or old-growth stands should also be consid- birds in the biological control of spruce budworm ered (Lousier 1989). Uneven-aged management or alone in Douglas-fir stands in Washington is esti- periodic thinning to create openings in the canopy mated at $18.15 per hectare (Garton et al. 1984). for regeneration of deciduous trees is also advo- Furthermore, natural predators reduce our growing cated (Crawford et al. 1983; Keisker 1987). dependence on pesticides to control forest pests Food supply between insect outbreaks may also (DeGraaf 1977; Miller 1985; Lousier 1989). limit the density of primary cavity excavators The quantitative effect of bark-foraging and foli- (Kroll et al. 1980; Moeck and Safranyik 1984), who age-gleaning birds on forest pest populations is forage on a variety of substrates such as standing clearly documented and these groups should be dead or live trees, stumps, downed logs and woody considered a priority for management. All are pri- debris. Foraging methods and associated foraging mary cavity excavators except the Brown Creeper. habitat requirements change seasonally (Jackson The response of primary cavity excavators to insect 1970; Conner 1979; Bull 1980; Lundquist and outbreaks is partly limited by the availability of Manuwal 1990), and in winter, standing trees are suitable nesting habitat (Kroll and Fleet 1979; the primary foraging substrate (Conner et al. 1975; Moeck and Safranyik 1984). To meet the nesting, Bull and Meslow 1977; Bull 1980). Woodpeckers roosting and feeding requirements of these species, prefer snags as foraging substrates (Rapheal and wildlife trees of sufficient diameter, height and White 1984; Lundquist and Manuwal 1990); how- density and appropriate species and decay classes ever, they may tolerate more size and decay stage must be retained (Mannon et al. 1980; Raphael variation in feeding trees than in nesting trees and White 1984; Zarnowitz and Manuwal 1985; (Mannon et al. 1980; Raphael and White 1984; Lundquist 1988). Although some of these factors Bull 1987; Swallow et al. 1988; Steeger et al. 1993). vary according to species-specific requirements, Brown Creepers, Red-breasted Nuthatches and primary cavity excavators generally prefer to nest Pygmy Nuthatches use live trees and snags in pro- in large-diameter snags with decayed heartwood portion to their respective occurrence (Raphael and broken tops (Conner et al. 1976; Mannon et and White 1984; Lundquist and Manuwal 1990), al. 1980; Raphael and White 1984; Neitro et al. 1985; while Chestnut-backed Chickadees prefer live trees Lundquist 1988; Harestad and Keisker 1989; over snags as foraging substrate. Lundquist and Mariani 1991). Management guide- Bark-foraging primary cavity excavators gener- lines for the retention of wildlife trees of sufficient ally prefer large-diameter trees (i.e., > 50 cm at size and density to support cavity-nesting bird breast height as foraging substrate) (Mannon et populations are discussed in Thomas et al. (1979), al. 1980; Bull 1987; Swallow et al. 1988; Lundquist Mannon et al. (1980), Raphael and White (1984), and Manuwal 1990; Mariani and Manuwal 1990; Neitro et al. (1985), Zarnowitz and Manuwal (1985), Steeger et al. 1993). A preference for tree species Lundquist (1988), Wildlife Tree Committee of with deeply furrowed bark such as Douglas-fir is British Columbia (1992) and Steeger et al. (1993). also shown by some species (Lundquist and

39 Manuwal 1990; Mariani and Manuwal 1990). Trees secondary cavity-using birds is a common manage- of large diameter with furrowed bark provide opti- ment technique in Europe (Thomas et al. 1975; mal temperature and moisture conditions for McFarlane 1976; Otvos 1979). Increases in bird den- insect larvae and pupae to overwinter, and sity and diversity and decreases in lepidopteran support a greater abundance and diversity of larval densities (compared to control areas) have insects (Jackson 1979b; Bull 1987; Mariani and been associated with this technique (see references Manuwal 1990). They also increase the available in Takekawa et al. 1982). Although nest boxes foraging substrate without increasing a bird’s area - should not be considered as an alternative to snag of-search for prey (Mariani and Manuwal 1990). management (Mannon et al. 1980; Brawn and Therefore, by preferring deeply furrowed, large- Balda 1983), they may be useful to enhance diameter trees, birds can reduce their energetic populations of secondary cavity users in chronic costs of foraging (i.e., search and travel costs). outbreak areas (Langelier and Garton 1986). Primary cavity excavators should be provided Horizontal and vertical diversity should be con- with sufficient numbers of standing, large-diameter sidered to enhance the habitat for aerial-foraging feeding trees, in addition to those required for and ground-foraging secondary cavity users nesting (Lundquist 1988; Steeger et al. 1993). This (Langelier and Garton 1986). Thinning of dense will sustain woodpecker population densities dur- stands, group selection cutting or interspersing ing periods of low food availability (e.g., winter, small- to medium-sized clearcuts throughout a between insect outbreaks). The spatial distribution stand will provide different degrees of canopy clo- of feeding trees within a stand must also be consid- sure and augment the shrub understorey for these ered. A closely clumped pattern of feeding patches species (Garton and Langelier 1983). may be advantageous, both to satisfy the cover re- Species-specific habitat requirements for bats have quirements of foraging birds and to minimize the yet to be established in British Columbia; however, travel time within and between patches (Raphael some roosting and foraging requirements are com- and White 1984). mon to a number of species. Wildlife tree-depend- Other options to enhance the food supply of ent bats use tree hollows and cavities or cracks primary cavity excavators include maintaining in and under tree bark for roosting (Fitch and standing snags or killing trees to increase popu- Shump 1979; Kunz 1982; Barclay 1985; van Zyll de lations of secondary insects (Koplin 1972), cultur- Jong 1983; Barclay et al. 1988; Nagorson and ing and dispersing insects eaten by these species in Brigham 1993). Studies in Oregon (Perkins and areas susceptible to insect outbreaks (Koplin 1972), Cross 1988) and in coastal forests of the Pacific high-stumping to provide additional foraging Northwest (Thomas 1988) indicate that bats prefer substrate (Kroll et al. 1980, Moeck and to roost in Douglas-fir/western hemlock stands Safranyik 1984), and treating trees with herbicide to that exceed 200 years of age. Preference for this age enhance the foraging efficiency of woodpeckers class is linked to bark crevices, which first appear (Bergvinson and Borden 1992). To ensure an ad- at about 80 years and become apparent in trees equate supply of alternative food sources (e.g., of 150 years or older, and to snag density (Perkins berries, nuts, seeds), limiting post-harvest site and Cross 1988). Snag management for suitable preparation and vegetation control are also sug- species, ages, decay classes and densities of roosting gested (Kroll et al. 1980). trees is critical to maintain viable populations of Less is known about the roosting habitat re- insectivorous bats. quirements of cavity nesters (Backhouse and Bat activity patterns near roost sites led Thomas Lousier 1991). Nesting and roosting requirements (1988) to conclude that although old-growth stands may differ for individual species (Bull et al. 1992) are critical for roosting, bats may be foraging in and providing suitable nesting habitat does not younger age classes. Edge habitat and habitat near necessarily ensure that roosting habitat is adequate. water are considered important foraging habitat By meeting the habitat requirements of primary elements (Mayle 1990). To improve bat foraging cavity excavators, it is generally assumed that the habitat, travel corridors with an abundant shrub habitat needs of other wildlife tree-dependent layer and sheltered areas around riparian zones groups are also met (Thomas et al. 1979; Neitro should be maintained (Mayle 1990). et al. 1985). Providing nest boxes for insectivorous To ensure viable populations of small mammals

40 that will disperse mycorrhizal inoculum, coarse tion and cover, reproduction, feeding, food storage woody debris (e.g., logs, stumps, root wads, bark, and as runways. Through appropriate management piles of limbs) must be available as well as wildlife of wildlife trees, requirements for coarse woody trees. These features are used for thermal protec- debris should also be satisfied (Maser et al. 1979).

5 DIRECTIONS FOR FUTURE RESEARCH

5.1 Primary Cavity Excavators evaluated. Modified silvicultural systems which potentially enhance the efficiency of natural preda- The studies reviewed here clearly document tors should be developed and tested in operational that primary cavity excavators have a significant trials. beneficial effect on the abundance and distribution of forest pests. Therefore, management goals 5.2 Secondary Cavity Users should promote and maintain healthy, sustainable populations of these insectivorous predators. Although secondary cavity users do consume inju- Emphasis should be placed on research that rious insects, their quantitative effect on forest determines: pests in the Pacific Northwest is not well studied. 1. the density, size, decay stage, species and associ- Future research should investigate the degree of ated characteristics of wildlife trees required to dietary opportunism shown by various species in meet the specific nesting, foraging and roosting response to changes in pest insect density. This requirements of each primary cavity excavator; type of research can be facilitated by encouraging and predators (e.g., Tree Swallows, Violet-green Swal- 2. the effectiveness of different silvicultural systems lows, Western Bluebirds, Mountain Bluebirds, and practices in meeting these habitat require- House Wrens) to use nest boxes and by using spe- ments in representative biogeoclimatic zones cialized techniques for diet determination (e.g., across the province. cameras, artificial nestlings). Through comparative The latter could be addressed through compara- studies of different pest densities or by artificially tive or experimental studies that investigate the stocking pests, the effect of pest density on the reproductive success and foraging energetics of diet, foraging behaviour and reproductive success woodpeckers nesting in areas with different har- of secondary cavity users can be investigated. An vesting regimes. Useful and feasible parameters to excellent example of this type of research initiative measure include fledging success, food delivery is Dahlsten and Copper’s (1979) study of Mountain rates to nestlings and energy expenditure of breed- Chickadee predation on the Douglas-fir tussock ing woodpeckers. moth in northeastern California. Primary cavity excavator habitat research has mainly focused on nesting requirements and on 5.3 Bats foraging behaviour during the breeding or post- breeding season. However, winter may represent an Studies of the effect of bats on forest pest insects energetic bottleneck due to the lack of flying insects are lacking, presumably because of the difficulties and because ground-based foraging substrate is in observing and measuring predation in nocturnal snow-covered. The capacity of the habitat to meet aerial insectivores. Such research should be con- each species’ w inter food requirements must be ducted in the broader context of species-specific evaluated. Research which integrates the manage- foraging behaviour, foraging habitat requirements ment of pests and predators with operational and prey selection. By measuring insect density forestry is also needed. The effects of current pest and diversity while concurrently monitoring the management practices (fire suppression and sal- foraging activity and diet of bats, inferences can be vage harvesting, pheremone baiting, pesticide made about the degree of selectivity or opportun- application) on predator populations need to be ism shown by different species. Radiotelemetry

41 could be used to monitor the foraging activity of 5.4 Small Mammals larger species; smaller species could be marked with light tags and their foraging observed. Fecal Few quantitative studies of small mammal preda- analysis would provide an indication of diet com- tion of insects exist, presumably because of obser- position and breadth. vational difficulties. An alternative approach would Comparative studies of the foraging behaviour be to study small mammal foraging behaviour in and prey selection of different bat species in areas outdoor enclosures where a natural feeding envi- of endemic versus epidemic pest densities (e.g., ronment can be mimicked while pest densities can emergent mountain pine beetles) would establish be readily manipulated and predation rates quanti- to what extent pest species are included in the diet. fied. This would allow the effect of other habitat Parameters that could be measured include the elements (e.g., forest cover, coarse woody debris) number of feeding passes and buzzes, time spent on foraging behaviour and diet selection to be ex- away from the roost, and diet composition and amined concurrently. breadth.

42 APPENDIX 1 FOREST INSECT PESTS AND THEIR ASSOCIATED TAXONOMIC CLASSIFICATION

Common name Order Family

Ant Hymenoptera Formicidae Bark beetle Coleoptera Scolytidae Black-headed budworm Lepidoptera Tortricidae Codling moth Lepidoptera Olethreutidae Douglas-fir tussock moth Lepidoptera Liparidae Eastern spruce budworm Lepidoptera Tortricidae Engelmann spruce beetle Coleoptera Scolytidae Engraver beetle Coleoptera Scolytidae European pine sawfly Hymenoptera Tenthredinidae Forest looper Lepidoptera Geometridae Geometer moth Lepidoptera Geometridae Gypsy moth Lepidoptera Liparidae Hardwood borer Coleoptera Buprestidae Ips beetle Coleoptera Scolytidae Jack pine budworm Lepidoptera Tortricidae Larch casebearer Lepidoptera Coleophoridae Larch sawfly Hymenoptera Tenth redinidae Leaf bug Hemiptera Miridae Locust Orthoptera Acrididae Lodgepole needle miner Lepidoptera Gelechiidae Long- horned beetle Coleoptera Cerambycidae Metallic wood-boring beetle Coleoptera Buprestidae Mountain pine beetle Coleoptera Scolytidae Needle miner Lepidoptera Gelechiidae Oregon fir sawyer Coleoptera Cerambycidae Pine sawfly Hymenoptera Tenthredinidae Round-headed wood-borer Coleoptera Cerambycidae Sawfly Hymenoptera Tenthredinidae Southern pine beetle Coleoptera Scolytidae Spruce aphid Homoptera Aphididae Spruce beetle Coleoptera Scolytidae Spruce budworm Lepidoptera Tortricidae Tent caterpillar Lepidoptera Lasiocampidae Tortricid moth Lepidoptera Tort ricidae Weevil Coleoptera Curculionidae Western pine beetle Coleoptera Scolytidae Western spruce budworm Lepidoptera Tortricidae

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