Edge Effects and Ecological Traps: Effects On

Home , Cardinal (bird), Ecological trap, Edge effects

.EDGE, EFFECTS AND ECOLOGICAL TRAPS: EFFECTS ON SHRUBLAND BIRDS IN MISSOURI

APRILA. WOODWARD,1,2Departmentof FisheriesandWildlifeSciences,302Anheuser-BuschNaturalResourcesBuilding,

ALIXD.FINK,Departmentof FisheriesandWildlifeSciences,302 Anheuser-BuschNaturalResourcesBuilding,Universityof UniversityMissouri,Columbia,ofMissouri,MOColum65211,bia,USAMO 65211,USA ,__.!.i_ii_,7_!_,_i_1__. / FRANKR.THOMPSON,III, U.S.ForestService,NorthCentralResearchStation,202Anheuser-BuschNaturalResources _,_; :, _._.._ Building,UniversityofMissouriC,olumbia,MO65211,USA !_.:

_._¢ Abstract: The effect of habitat edge on avian nesting success has been the focus of considerable debate. We studied relationships between habitat edges, locations of nests, and predation. We tested the ecological trap hypothesis for 5 shrubland bird species in the Missouri Ozarks. We compared habitat selection and daily nest predation rates among 3 distance-to-edge categories. Edge effects were species specific. Indigo bunting (Passerina cyanea) - _ and northern cardinal (Cardinalis cardinalis)preferred nest sites that were close (<20 m) to habitat edges. Yellow- _+, i,,_,: bre_ted chat (Icteriavirens)and prairie warbler (Dendroicadiscolor)preferred nest sites >20 m from the edge. Fielcl ' ...... sparrow (Spizellapusilla) used habitat in proportion to availability. Daily nest predation varied by as much as , . +."_ " 200-300% among distance-to-edge categories but did not decrease monotonically with distance from edge. The ...... ' * ° nest predation models without distance-to-edge categories were ranked the best models based on Akaike's Infor- :., _. , mation Criterion; however, Akaike weights indicated some support for alternative models with distance-to-edge cat- " " egories. Edges did not act as ecological traps for shrubland birds in this study because habitat preference was not + positively correlated with nest predation across the 3 distance-to-edge categories. Researchers and land managers should not assume that shrubland birds respond to edges in the same way that forest species respond to edges .... , Furtherrnore, species with similar nesting ecology do not necessarily have similar nest-site preferences or nest predation rates in relation to distance to habitat edges.

JOURNAL OF WILDLIFE MANAGEMENT 65(4):668-675 _, ,...., Keywords:.Cardinaliscardinalis,. Dendroicadiscolorecological, traps, edge effects, field sparrow, Icteriavirens,indigo bunting, .+_...... i_,_i:;,_._;i,i_...... Missouri, nest predation, northern cardinal, Passerinacyanea,prairie warbler, Spizellapusilla, yellow-breasted chat.

t • . Habitat edge is the boundary or ecotone between varies among habitats; and (3) that trap habitat is adjacent habitats. Avian species richness and abun- preferred and the animal has lower fimess there . _, dance often are elevated at or near habitat edges (Donovan and Thompson 2001). Few tests of the (StrelkeandDickson 1980, Chaskoand Gates 1982, ecological trap hypothesis apply to edges and Morgan and Gates 1982, Hansson 1983). Nest pre- songbirds (Ratti and Reese 1988); however, habi- + dation and brood parasitism, however, also may tat selection has been inferred by comparing bird _ ' _ • . /" be greater near edges (Gates and Gysel 1978, Tem- abundances in edge and interior (Strelke and , ¢ " pie and Cary 1988, Johnson and Temple 1990). Dickson 1980, Morgan and Gates 1982, Noss 1991), j_ Bii-ds may be more vulnerable to nest predation and numerous studies have compared reproduc- and brood parasitism in edges than in the interior tive success in habitat edge and interior of a habitat because predators and brood parasites (reviewed by Paton 1994, Andr_n 1995). Van

• . (.sUch as brown-headed cowbirds; Molothrus ater) Home (1983) and Vickery et al. (1992) cautioned may be more abundant-or active in the adjacent that high densities might not always be associated ,, habitat and edge. or because nests are more with quality habitat or breeding success. The detectable near edges (Paton 1994, Andrrn 1995). conservation implications of ecological traps This paradox of high bird abundance and rich- depend on population and landscape conditions. _- " ness but .low nesting success near edges was If the trap habitat is abundant across a landscape, termed an ecological trap by Gates and Gysel numerous individuals select it, and reproductive (1978). Ecological traps require (1) that an ani- success (or survival) is low, traps can act as a pop- ., " mal exhibits habitat preferences; (2) that fitness ulation sink that drains source populations and threatens viability (Donovan et al. 1995, Donovan

1E-mail: [email protected], andNaturalThompsonselectio2001).n should favor individuals that 2 Present .address: Arizona Game and Fish Depart- ment,-Nongame and Endangered Wildlife Program, accurately assess the relative quality of habitats 2221 West Greenway Road, Phoenix, AZ 85023, USA. and prefer high-quality habitat (Lanyon and 668 j. Wildl. Manage. 65(4):2001 EDGE EFFECTS AND ECOLOGICAL TRAPS • Woodwardet al. 669 \

ThompsOn 1986). Birds largely select habitats addressed the 3 conditions for an ecological trap " based on vegetative structure; this relationship is by determining whether (1) birds exhibited nest- partially genetic but also modified by experience site preferences among 3 distance-to-edge cate- (lames 1971). Birds depend not only on factors gories; (2) daily nest predation varied among dis- " directly related to survival (ultimate factors) but tance-to-edge categories; and .(3) nest predation

factors;also on landscapeHildrn 1965).and vegetationBreeding cuesterritories(proximateoften wasencespositivelyacross thecorrelated3 distance-to-edgewith nestcategories.site prefer- l • are occupied, long before factors that affect breed- __ ...... _: ing success are observable. Therefore, cues may ME/HODS ...._i,i!)ii,ii(:_ be misleading. As a result, several circumstances _,:.... . , might result in ecological traps. For example, Study Area , . the mechanisms that evolved to guide birds to Our study was conducted from 1 May to 15

suitable habitat may no longer work because of August 1997, 1998, and 1999 on 9 study sites on •. ..., changes in the environment. Dramatic landscape the Rolla-Houston Ranger District of the Mark '_::c__"....

changes m_ty occur too quickly for birds to adapt, Twain National Forest in Laclede and Pulaski __",...... :i_'_.....; . • and the type of terrain that induced individuals counties in the Missouri Ozarks. The area is , _-. " " to setde may no longer provide the best nest sites characterized by moderate to steep sloping hills. ,_'!( " (Hildrn 1965). Some of the best examples of Approximately 56% of the landscape surround ...... : " ., ecological traps for songbirds may be in agricul- ing our study sites (10-km circles around the cen- _ ,_ tural habitats,affected by intensive grazingl mow- ter point of each site) was .oak (Quercus ....:.. ing, or tillage (Best 1986, Bollinger and Gavin spp.)-hickory (Carya spp.) forest, 11% shordeaf 1992, Purcell and Verner 1998)reconditions only pine (Pinus echinata) forest, _7% grassland, and _.. recer/fly faced by songbirds. 5% cropland (Woodward 2000). Most research on edge effects has been on for- We studied 3 types of shrubland habitat: regen- est-interior species and examined differences in erating forest, glades, and forest-pasture edge. _ii_ _:_i': " nest sUccess between the edge and interior of These habitats are the dominant types of shrub- _'_:....__;__::_.__, .forested habitats. These studies often classify land or early successional habitat in the Missouri . _ 'shrubland birds as edge species because in this Ozarks. They also are related to forest manage- context they are limited to forest edges. Some ment issues concerning clearcutting and pre- . species_such as the indigo bunting_select edges scribed fire. We located 3 study sites, 2-13 ha in and are successful there (Suarez.et al. 1997), but size, for each habitat. Each site was surrounded II9, others_such as the prairie warbler and yellow- by forested habitats. Regenerating forest sites breasted chat_require larger shrubland patches were clearcut in 1994 and had a thick understory (Annand and Thompson 1997). Little research of oak and hickory saplings and some residual _ h_ addressed the influences of edges on shrub- trees and snags. Glades are fire-maintained habi- ' /'41' land birds or whether edge effects occur between tats and were managed by prescribed burning; all _ the edge and interior of shrubland habitats, sites were last burned in 1992. Glades were char- jt_ S-hrubland birds have some of the same charac- acterized by dolomite outcrops, a scattering of terisfics (open-cup nests near the ground) that overstory trees and shrubs, and grassy areas. make f0rest-nesting species vulnerable to nest pre- Dominant tree species were Eastern red cedar .dati0n; however, shrubland habitat may support _uniperus virginiana), white and red oaks, elms " v.ery different predator assemblages (Thompson (Ulmus spp.), shorfleaf pine, and hickories. For- , et al. !999). Although many shrubland birds are est-pasture edge sites were the interface between abundant, most are declining, and some regional a mature upland forest and a grazing allotment or global popuiations are of conservation con- (see Woodward 2000 for detailed site descrip- ° Cern (Askins 2000, Pashley et al. 2000). tions). Site boundaries were mapped with a We conducted a comprehensive study of spa- Trimball Pathfinder Pro (realtime mode) Global tial, temporal, and habitat-specific factors that Positioning System (GPS)unit, which is accurate .,. • affect avian reproductive success. Our goal was within approx. 1 m. to identify.potential factors that limit shrubland bird populations. The objective of this compo- Nest Surveys and Monitoring nent of the study was to determine whether We located nests of 5 abundant, breeding bird shrubland birds suffer from edge effects and species: indigo bunting, yellow-breasted chat, whether edges act as ecological traps. We field sparrow, prairie warbler, and northern car- 670 EDGE EFFECTS AND ECOLOGICAL TRAPS • Woodwardet al. J. Wildl. Manage. 65(4):2001 "\

dinal. We systematically searched for nests on an distance-to-edge contour lines in a computer geo- approx. 4-day rotation. We used behavioral cues graphic information system. We calculated the and systematic searches _of potential nest sub- expected number of nests in each edge category strates to locate nests. Nest contents, species, as the proportion.of total area in a category times approximate height of nest, and nest substrate the total number of nests for a species. We used °

.weretions recwereordedmarkedwhenatnestsdistanceswere f_>5ound.rn withNestplasticloca- witha maximum2 df (3likelihoedge odcategchi-squaredories- 1) statisticto test (G)the I flagging and Universal Transverse Mercator coor- hypothesis that the distribution of nests among • _!!i!__ !_!_!i_'_!'_!_il dinates Were later determined with a GPS unit. the distance-to-edge categories was in proportion ::_ , We monitOred nests every 3 to 4 days early in the to habitat availability (Alldredge and Ratti 1986, nest periOd but every 1 to 2 days within approx. 4 White and Garrott 1990). If we rejected this " days of the estimated fledging date. The date, hypothesis, we used procedures by Neu et al. . ' ' time ofvisit, number ofeggs, number of nestlings (1974) to determine which distance-to-edge cate- ' __ (with a description, of development of yolang), gories were preferred or avoided (P < 0.05). .,:_. _!_,,. presence of adults, brood parasitism, and preda- We calculated daily predation rates (DPR) by )_ _:_:!?i . . ' tion events were recorded during each visit. We the Mayfield method (Mayfield 1961, 1975) We -/i ....._.,. - . followed accepted conventions (Martin and Geu- used program MICROMORT (Heisey and Fuller _--_i_';'_ pel 1993, Ralph et al. 1993, Martin et al. 1997) 1985) to calculate daily predation rates (DPR) and considered nest_ successful (not depredat- and standard errors for each distance-to-edge cat- _,_ _' ._ . ed) if at least 1 young (host or cowbird) fledged, egory and likelihood values for models with and ::; _'_" _,

signs of predation and there was fledgling activi- pared DPR (as opposed to nest slaccess) to direct- _ ...... _'.:_-' - " _- We.assumed fledging occurred if there were no without distance-to-edge categories. We com- ty nearby, and we estimated fledging or predation ly address the hypothesis that nest predation was '_ _" _:_: ' 4 •date as the midpoint between the last 2 visits, related to distance to edge because additional factors affect nest success. Data Analysis We compared model (1) with constant preda- :_...... _._: We Classified nests into 3 distance-to-edge cate- tion and no edge categories to 4 alternative mod- go'ties: <20, 21--40, and >40 m. We determined els with predation rates for the following dis-

•nesting habitat preference and nest predation tance-to-edge categories: (2) <20 m and >20 m; • . ratesfor each class. We selected these intervals to (3) _<40rn and >40 m; (3) 21--40 rn and <20m + obtain-an adequate distribution of habitat and >40 m; and (4) <20 m, 21-40 m, and >40 m. We _" _, nests across :all intervals for statistical tests and used an information-theoretic approach and cal- because the strongest evidence for edge effects is culated Akaike's Information Criterion, delta , y

fortheedgedistanceswas the<50 borderm (Patonbetween1994).the Inshrubland-all cases, AIC,respectively;and AkaikeBurnhamweightsand (AIC,AndersonAAIC, 1998)and tow, _ .." habitat patch and adjacent mature forest. We identify the best models. The model with the _g /" analyzed individual species and all species com- smallest AIC is the best approximating model for Jilt bined. Because our study focused on the effects the data, and primary inference should be drawn of distance to edge, we pooled nests from the 3 from models with a AAIC of 1 or 2 to perhaps as types of .shrubland habitats. In addition, not many as 3 or 4 when models are nested and differ "engugh nests existed in all categories to test for successively by 1 parameter; Akaike weights rep- • " interactions betweenhabitat and distance-to- resent the likelihood of a given model (Burnham • edge categories. We also pooled nests from all and Anderson 1998). We concluded there was an years because the proportion of nests in each dis- edge effect if strong evidence existed for a model tance-to-edge category did not differ among years with edge categories. We also compared the best for any species (_2,. p > 0.139) and pooling in- model with edge categories (as determined creased Sample sizes; we will focus on habitat and above) to the reduced model with no edge cate- year effects in'a forthcoming manuscript, gories with a likelihood ratio test (White 1983, ._ We determined whether each species and all spe- Heisey and Fuller 1985). . " cies pooled preferred or avoided each distance- We compared the results of the habitat prefer- to-edge category by comparing the distribution ence and DPR analyses to evaluate the ecological of nests to habitat availability. We determined the trap hypothesis for each species and all species number of nests in each of the 3 distance-to-edge combined. We calculated the Spearman-rank categories by intersecting nest coordinates with correlation between habitat preference and DPR.

• . . i ...... ,

!:i!_2i . , j. Wildl. Manage. 65(4):2001 EDGE EFFECTS AND ECOLOGICAL TRAPS * Woodwardet al. 671 '\

70] ,'Indigo Bunting Yellow-breastedChat 22-day nest interval; and northern cardinal nests, - 6o 0.033 + 0.0117 or 55% for a 24-day nest interval. 50 e¢ 40 - Edge Preference

, 2o30 , Nests ranged from 0.06 m to 122.76 m (E = i0 24.48) from the habitat edge. Neither preference '_, ' 0 nor avoidance existed of any distance-to-edge cat- ,, ,: ,, i .<20 21--40 >40 <_20 21-40 >40 egory by all species pooled (Z2 = 1.80, P = 0.595; __,_:% ...... J 70 " Field Sparrow Prairie Warbler Fig. 1). Habitat use by field sparrow was in propor- _'_'_' 6o fion with habitat availability (Z2 = 0.291, P= 0.865). !::!:J 4o o 30 0.005), yellow-breasted chat (Z2 = 13.14, P = _, 20 0.001) , prairie warbler (Z2 - 19.34, P< 0.001) , and 5010 Habitatnorthern usecardinalby indigo(Z2 bunting= 5.23, P=(Z20.022)= 10.63,was pnot= , _0, -" ' ' in proportion with available habitat. The indigo <_20 21-40 >40 _<20 21-40 >40 bunting preferred to nest in the <20-m distance- , . " 70 No_'themCardinal All Species to-edge category and avoided the >40-m distance- - " " 6o to-edge category (Fig. 1). The yellow-breasted " , 50 chat preferred to nest in the >40-m distance-to- :_--i_:;i_,::". " 4o edge category and avoided the <20-m distance-to- 2_+_-__;-_ ,:_ 2030 edge category (Fig. 1). The prairie:warbler avoid- _:__-_ 10 ed nesting in the <20-m distance-to-edge category • 0 and moderately preferred (P< 0.10) the 21-40-m _;i _:'_.; :': ' <_20 >20 _<20 21-40 >40 distance-to-edge category (Fig. 1). We used only -_)_i " " ' Distance from edge (m) 2 distance-to-edge categories (<20 m and >20 m) for the northern cardinal because only 1 nest was nestslocatedFig,1. Percent-of(whitehabitatbars)available<20m, 21-40(blackbars)m, andand>40percentm fromof >40 m from edge. The northern cardinal pre- 'habitat edgefor 5'speciesnestingin Missouri,1997-1999. ferred to nest in the <20-m distance-to-edge cate- Asterisks-denotesignificantdifferencesbetweenpercent gory and avoided the >20-m distance-to-edge cat- availabilityandpercentuse (Z2,P< 0.05). egory (Fig. 1). Edge Effects on Nest Predation _" We used the difference between the percent of Daily predation rates varied among distance-to- nests and percent of available habitat in each dis- edge categories by as much as 200-300%, and in tance-to-edge category as a measure of prefer- different directions for some species (Table 1). , /C ence (Alldredge and Ratti 1986). We concluded The nest predation models with no edge cate- , ,_ / that an ecological trap existed if a significant pos- gories were the best models for all species; how- itive correlation (P < 0.05) occurred, which indi- ever, supporting evidence existed for the alterna- cated birds preferred to nest in categories with tive models (Table 2). Akaike weights ranged high DPR. , from 0.519-0.649 for the no edge category model, and all species had alternative models 'RESULTS with AICs < 3, so not enough convincing evidence We found 339 nests of the 5 study species (93 in existed for any 1 model. The likelihood-ratio • ' 1997, 128 in 1998, and 118 in 1999). We moni- tests comparing models with distance-to-edge cat- tored 111_ 89, 57, 54, and 28 indigo bunting, yel- egories to models with all categories pooled were " low-breasted chat, field sparrow, prairie warbler, not significant for all species combined (P > and northern cardinal nests, respectively. Over 0.317), indigo bunting (P> 0.317), field sparrow all years and distance-to-edge categories, daily (P > 0.294), or northern cardinal (P > 0.584). ., , predation rate (_+SE) of indigo bunting nests was The likelihood-ratio tests for yellow-breasted chat 0.039 + 0.0052 or • 62% for a 24-day nest interval; and prairie warbler provided some support for yellow-breastedchat nests, 0.045 + 0.0065 or 64% edge effects. The models with edge categories for a 22-day nest interval; field sparrow nests, <40 and >40, and 21-40, <20 + >40, were margin- 0.051 + 0_0095 or 70% for a 23-day nest interval; ally different (P = 0.078 and P = 0.074, respective- prairie warbler nests, 0.032 +_0.0069 or 51% for a ly) than the model with all categories pooled for

,;_, _ ,...... - , 672 EDGE EFFECTS AND ECOLOGICakL TRAPS * Woodwardet al. J. Wildl. Manage. 65(4):2001

• . Table1. DaUy-nestpredationratesfor nests<20m, 21-40 m, and>40mfromedgeandrelationshipto nest-sitepreferencefor 5.songbirdspeciesbreedingin shrublandhabitatsin Missouri,USA,1997-1999. !_"'_: _-

<_20rn 21-40 rn >40m Rankcorrelationa Species DPR SE DPR SE DPR SE r P

-Yellow-breastedIndigobunting chat 0.0460.035 0.0120.006 0.0320.048 0.0080.011 0.0630.042 0.014 -1.000.50 0.6670.001 _ _'*_; '_._ / Fieldsparrow 0.043 0.013 0.064 0.018 0.044 0.019 0.87 0.333 " _:"_" Prairiewarbler 0.061 0.026 0.023 0.008 0.037 0.013 -1.00 0.001 _;_? Northerncardinal 0.048 0.015 0.036b 0.017 Allspecies 0.041 0.005 0.038 0.005 0.05 0.007 0.50 0.667 '

aSpearman-rankcorrelationof relationshipbetweendailynestpredationandnest-sitepreference(%use - %availability)for the3distance-to-edgecategories.

bIncludes1nest >40m. ,_ ,

the yellow-breasted chat. • The model with cate- Missouri (Annand and Thompson 1997), and ".- , gories 21-40, <20 + >40, was marginally different southern Illinois (Suarez et al. 1997); but lower (P = 0.129) from the model with all categories than in some more fragmented landscapes in the _:;_" • . pooled for the prairie warbler. Midwest (Robinson et al. 1995). We found some evidence that DPR varied in rel_don to distance " _: - Evaluation of the Ecological Trap to edge. Estimates of DPR varied greatly among Hypothesis , distance-to-edge categories for some species The only significant Spearman-rank correla- (Table 1), and the magnitudes of Akaike weights dons were for the indigo bunting and prairie war- for the models with no edge categories (Table 2) _ 5 _:: bier, and the correlations were in the opposite did not provide convincing evidence that they ' direction (.negative) predicted by the ecological were the best models (Burham and Anderson •trap hypothesis (Table 1). Correlations for the 1998, Anderson et al. 2000). other species were 'positive but not significant. We found some evidence of greater DPR closer Therefore, we found no evidence .that the eco- to edges for the yellow-breasted chat and prairie _, logical trap hypothesis applied to the 5 species we warbler and edge effects were nonlinear. Nest pre- studied in shrubland habitat patches, dation was high closest to the edge, declined in the • DISCUSSION 21-40-m distance-to-edge category, and then in- creased >40 m from edge (Table 1). High nest ' _"_ We observed species-specific patterns in prefer- predation near the edge likely is the result of activ- _# "/ ences for nest sites relative to distance to edge; ity patterns of nest predators in shrubland habi- some species preferred to nest near edges and tats. Thompson et al. (1999) used video cameras others away from edges. Previous studies have to determine that snakes (especially the black rat reporteda similar range of results. Territory den- snake [Elaphe obsolete]) were the dominant preda- 'sity•or bird abundance can be higher near edges tors of songbird nests in old-field habitats in cen- • (Strelke and Dickson 1980.; Kroodsma 1982, 1987; tral Missouri. Black rat snake activity and foraging Morgan and Gates 1982; Noss 1991); territories may be clustered along field-forest ecotones dur- can be distributed eciually among edge and inte- ing the songbird breeding season (Weatherhead riot (King etal. 1996); or pairing success can be and Charland 1985, Durner and Gates 1993). We lower near edges (Van Horn et al. 1995). Birds can only speculate why nest predation was greater might have preferred or avoided distance-to-edge >40 rn from edge; perhaps some shrubland preda- categories berause of their proximity to the edge tors avoid edges or nests are more visible at these or because of differences in vegetation structure; locations. Evidence of edge effects from previous , however, we did •not compare vegetation struc- studies is mixed. The greatest proportion of stud- ture among distance-to-edge categories, ies reporting edge effects are for forest habitats Nest predation levels were within' the range of adjacent to farmland; only a small proportion of other studies of shrubland birds in central Mis- studies have reported edge or area effects for birds soufi (Burhans and Thompson 1999), southern in open habitats (reviewed by Andr6n 1995). j. Wildl. Manage. 65(4):2001 EDGE EFFECTS AND ECOLOGICAL TRAPS • Woodwardet al. 673

Table2. Nestpredationmodelsthatdifferby the numberof between nest-site preference and predation _ . , - .distance-to-edgecategoriesfor5 shrublandsongbirdsin Mis- (Table 1). While ecological traps were originally souri,.USA, 1997-1999. _Modelsare ranked within each hypothesized for habitat edges (Gates and Gyse] (AIC);speciesmodelsin ascendiwith lower0gorderAICbyandAkaike'sz_,lCandInformationa greaterCriterionAkaike 1978), the best-documented examples for song-

weight (w)have more substantialsupport, birds are agricultural habitats affected by grazing, !1__ • mowing, or tillage (Best 1986, Bollinger and ....!_...." I _ I | Model.edge -2Logex # model Gavin 1992, Purcell and Verner 1998). ,,: categories - Likelihoodparameters AIC AAIC w No obvious explanation exists for the similarity ___ "++_ or differences we observed in nest-site preference _71-ii). Indigobunting or DPR relative to distance to edge. For example, , , Nbne " -456.0 1 -454.0 0.0 0.530 prairie warblers and yellow-breasted chats had <40, >40 -455.9 2 -451.9 2.1 0.185 the most similar patterns in DPR, yet were among

21--40,<_20+• >40 -455.1 2 -451.1 2.9 0.124 the most different species in nest characteristics • _<20,>20 -455.0 2 -451.0 3.0 0.118 and nest placement. Prairie warbler nests are rel-

<_20,21-40,'>40 -454.9 3 -448.9 5.1 0.041 atively small and usually placed in the top of + + ,, Yellow-breastedchat saplings (Nolan 1976), while yellow-breasted chat _' .++.+ . . None + -382.8 '1 -380.8 0.0 0.649 nests are medium-sized and are usually located in , <20, >20 -382.8 2 -378.8 2.0 0.239 a thick shrub or shrub patch (Petrides 1938). . .:::.. . ., <40,>40. -379.7 2 -375.7 5.1 0.050 ._ 21-40,<__20+>40 -379.6 2 -375.6 5.2 0.048 MANAGEMENT IMPLICATIONS • <_20,21-40, >40 -378.8 3 -372.8 8.0 0.011 We should not assume the generality of the tra-

Fieldslharrow ditional model of edge effects in which nest pre- • _:L? None -213.8 1 -211.8 0.0 0.519 dation decreases monotonically with distance to _+._-- <_40,>40 -213.7 2 -209.7 2.1 0.181 edge or that patterns are similar among species. _<20,>20 -213.3 2 -209.3 2.5 0.148 Landscape-, habitat-, and species-level factors 21--40,<20+ >40 -212.7 2 -208.7 3.1 0.110 affect nest success (Donovan et al. 1997, Thomp- . ....-: <__20,21--40,>40 -212.7 3 -206.7 5.1 0.040 son et al. 2002). Specifically, we cannot assume Prairiewarbler predators affect shrubland birds the same as for- None ,-185.4 1 -183.4 0.0 0.619 est birds. We need to better understand the _<40,>40 -185.2. 2 -181.2 2.2 0.206 predators and predation in shrubland habitats to <_20,>20 -183.4 2 -179.4 4.0 0.083 accurately assess their impacts on nest success. _, 21-40,<_20+>40 -183.1 2 -179.1 4.3 0.072 Predator assemblages and activity patterns in ___20,21-40, >40 -182.4 3 -176.4 7.0 0.018 these habitats may differ from those of forests Northern cardinal and grasslands. , ._' One focus of avian conservation efforts on the None 107.2 1 109.2 0.0 0.700 breeding grounds should be to manage areas for ,4 / _<40,>40 106.9 2 110.9 1.7 0.299 high-quality habitat where birds encounter low Allspecies levels of nest predation. We suggest that this None -1,348.0 1 -1,346.0 0.0 0.536 management goal would require multiple strate- ' <_20,>20 , -1,348.0 2 -1,344.0 2.0 0.197 gies to benefit the shrubland bird community. " • 21-40,<_.20+>40 -1,347.0 2 -1,343.0 3.0 0.119 Indigo buntings select for and experience low " _<40,>40 -1,347. 0 2 -1,343.0 3.0 0.119 levels of nest predation in edges of shrubland • , ___221-40,0,. >40 -1,346.0 3 -1,340.0 6.0 0.026 habitats. Indigo buntings were more abundant at + the pasture-edge sites than yellow-breasted chats or prairie warblers (A. D. Fink, University of Mis- • . souri, unpublished data) and utilize small habitat Nosignificant evidence of ecological traps exist- patches (Annand and Thompson 1997). Thus, ed. The only significant relationships between they can potentially benefit from edge and small .7 nest predation and habitat preference were in and large habitat patches. Species such as the the opposite direction predicted by the ecologi- prairie warbler and yellow-breasted chat, however,

cal trap hypothesis. Some species, however, pre- may suffer high levels of nest predation in close 0 ferred a single distance-to-edge category over proximity to edges. These species did not breed another with a lower DPR; this resulted in posi- in the pasture-edge sites (A. D. Fink, University of tive (but nonsignificant) rank correlation Missouri, unpublished data) and do not use very

ml n ..... • . •

•. • ... 674 EDGE EF/FECTS AND ECOLOGICAL TRAPS • Woodward et al. J. Wildl. Manage. 65(4):2001 \\

small habitat patches (Annand and Thompson ability along a transmission-line corridor in an 1997). These species will benefit more from man- oak-hickory forest region. Wildlife Monographs 82. agement that creates, larger shrubland patches. DONOVAN,T. M., P. W. JONES, E. M. ANNANO,ANDE R. THOMPSON, III. 1997. Variation in local-scale edge Habitat patch size is affected by the choice of sil- effects: mechanisms and landscape context. Ecology ..

-byviculturalhabitatother (Askinsmethods,methods 1998,theusedThompsonusetoof manageprescribedand shrublandDeGraaffire, or _, ecological78:2064-2075.ANDtrapF. R. hypothesis:THOMPSON,aIII.habitat2001.andModelingdemograph-the '_i_ii:_i_.i__ii__ / ic sensitivity analysis for a migrant songbird. Ecolog- '_

2001go buntings), These remainpatterns commonalso may acrossexplain theirwhy rangeindi- ical Applications, _, J. 11:871-882.FAABORG,ANDJ. R. PROBST. 1995. ' __'_ ' ___ '_'_ ...... and prairie warblers and yellow-breasted chats Reproductive success of migratory birds in habitat %'i_:_....: 0 are regional or national conservation priorities sources and sinks. Conservation Biology _ _ * 9:1380-1395. ' _ , (Askins 2000, Pashleyet al. 2000). DURNER,G. M., ANDJ. E. GATES. 1993. Spatial ecology _ AGKNOWLED(3MENT$ of black rat snakes on Remington Farms, Maryland. .:_;./_,_!_: . . Journal of Wildlife Management 57:812-826. We thank the U.S. Forest Service North Central GATES,J. E., ANDL. W. GYSEL. 1978. Avian nest disper- _i, _:_ii:!_ , , " Research Station for funding our project. The sion and fledging success in field-forest ecotones. _ _ii ...... - Ecology 59:871-883 ..... " " , USFWS Region 3, the Rolla-Houston Ranger Dis- HANSSON,L. 1983. Bird numbers across edges between _ :_:__'!"_ trict of the Mark Twain National Forest, and the mature conifer forest and clearcuts in Sweden. Ornis .,

al support. We also thank D. Burhans, J. Faab0rg, HEISEY,D. M., ANDT. K. FULLER. 1985. Evaluation of sur- ::_ z,:_i:.....• . University of Missouri-Columbia provided addition- vivalScandinavicaand 14:97-103. _!-'_...... z,'_.:_, • and M. Ryan for reviewing drafts of this manuscript, cause-specific mortality rates t_sing teleme- try data. Journal of Wildlife Management 49:668-674.

HILDI_N,O. 1965. Habitat selection in birds. Annales i__, _: _ " " LITEFIA]'URE CITED Zoologici Fennici 2:53-75. :_.v_?,_,_'_:,!:', ' "ALLDREDGE, J. R., ANDJ. T. RATTI. 1986. Comparison of JAMES, E C. 1971. Ordinations of habitat relationships ,__. _:,_ some statistical techniques for analysis of resource among breeding birds. Wilson Bulletin 83:215-236. __:_ ;__!_ :

50:157-165.selection. Journal of' Wildlife Management JOHNSON,and broodR. G.,parasitismANDS. A.ofTEMPLE.tallgrass 1990.prairieNestbirds.predationJour- ::;::°__i'L_: :.. ANDERSON, D. R., K. P. BURNHAM,ANDW. L. THOMPSON. nal of Wildlife Management 54:106-111. - 2000. Null hypothesis testing: problems, prevalence, KING, D. I., C. R. GRIVVEN,ANDR. M. DEGRAA_. 1996. and an alternative. Journal of Wildlife Management Effects of clearcutting on habitat use and reproduc- * .. 64:912-923. tire success of the ovenbird in forested landscapes. " ANoRi_N,H. 1995. Effects of landscape composition on Conservation Biology 10:1380-1386. predation rates at habitat edges. Pages 225-255 in L. KROODSMA,R. L. 1982. Edge effect on breeding forest . I1_, Hansson, L. Fahrig, and G. Merriam, editors. Mosaic birds along a power-line corridor. Journal of Applied landscapes and ecological processes. Chapman & Ecology 19:361-370. Hall, London, United Kingdom. . 1987. Edge effect on breeding birds along _. ANN)kND, E. M., ANDE R. THOMPSON, III. 1997. Forest power-line corridors in east Tennessee. American ' " / bird response to regeneration practices in central Midland Naturalist 118:275-283. hardwood forests. Journal of Wildlife Management LANYON,S. M., ANDC. E THOMPSON. 1986. Site fidelity ., 4 '/ 61:159-171. and habitat quality as determinants of settlement pat- j ASKINS,R.A. 1998. Restoring forest disturbances to sus- tern in male painted buntings. Condor 88:206-210. tain populations of shrubland birds. Restoration & MARTIN,T. E., ANDG. R. GEUPEL. 1993. Nest monitor- Management Notes 16:166-173. ing plots: methods for locating nests and monitoring • . 2000. RestOring North America's birds: lessons success. Journal of Field Ornithology 64:507-519. from landscape ecology. Yale University Press, New , C. PAINE, C.J. CONWAY, W. M. HOCHACHKA,P. Haven, Connecticut, USA.. ALLEN,ANDW. JENKINS. 1997. BBIRD field protocol: BEST, L. B. -1986. Conservation tillage: ecological traps breeding biology research and monitoring database. , ' for nesfingbirds? Wildlife Society Bulletin 14:308-317. Montana Cooperative Wildlife Research Unit, Uni- BOLLINGER,E. K., AND.T.A. GAVIN. 1992. Eastern bobo- versity of Montana, Missoula, USA. http://pica.wru. link populations: ecology and conservation in an agri- umt.edu/BBIRD/protocol/protocol.htm cultural landscape: Pages 497-508 inJ. M. Hagan, III 1VIAYFIELD, H. 1961. Nesting success calculated from c and D.M. Johnston, editors. Ecology and conserva- exposure. Wilson Bulletin 73:255-261. tion of Neotrbpical migrant landbirds. Smithsonian . 1975. Suggestions for calculating nest success. Institutiofl Press, Washington, D.C., USA. Wilson Bulletin 87:456-466. "_ BURHANS,D. E., ANDE R. THOMPSON,III. 1999. Habitat MORGAN, I_ A., ANDJ. E. GATES. 1982. Bird population * " " patch size arid nesting success of yellow-breasted patterns in forest edge and strip vegetation at Rem- chats. Wi'lson Bulletin 111:210-215. ington Farms, Maryland. Journal of Wildlife Man- BURNHAM, K. P., AND D. R. ANDERSON.' 1998. Model agement 46:933-944. selection and inference: a practical information-theo- NEU, C. W., C. R. BYERS,ANDJ. M. PEEK. 1974. A tech- retic approach. Springer-Verlag, New York, USA. nique for analysis of utilization-availability data. CHASKO,G.C., ANDJ. E. GATES. 1982. Avian habitat suit- Journal of Wildlife Management 38:541-545.

__ . , - . • • 0. " ¢" , _ r'- J. Wildl. Manage, 65(4):2001 EDGE EFFECTS AND ECOLOGICAL TRAPS • Woodward et al. 675 I

NOLAN, V. 1976. The ecology and behavior of the of habitat-interior bird populations in fragmented prairie warbler Dendroica discolor. Ornithological landscapes. Conservation Biology 2:340-347. Monographs 26. Allen Press, Lawrence, Kansas, USA. THOMPSON, E R., III, ANDR. M. DEGRAAF. 2001. Con- Noss, R. E 1991. Effects of edge and internal patchi- servation approaches for woody, early successional ness on avian habitat use in an old-growth Florida communities in the eastern United States. Wildlife hammock. Natural Areas Journal 11:34-47. Society Bulletin 28:483-494. PASHLEY,D. N., C.J. BEARDMORE,J. A. FITZGERALD,R.P. _, W. DIJAK,ANDD. E. BURHANS.1999. Video iden- FORD,W. C. HUNTER,M. S. MORISON,ANDK. V. ROSEN- tification of predators at songbird nests in old fields.

BERG.land birds2000of, thePartnersUnited inStates.flight: AmericanconservationBirdofCon-the Auk 11, T.6:259-264.M. DONOVAN,R. M. DEGRAm, J. FAABORG,AND ____!;. servancy, The Plains, Virginia, USA. S.K. ROBINSON.2002. A multi-scale perspective of the .... ;_¢i_..... PAT-ON,P. W. C. 1994. The effect of edge on avian nest effects of forest fragmentation on birds in eastern , ' success: how strong is the evidence? Conservation forests. Studies in Avian Biology: in press. Biology 8:17-26. " VANHORN, M. A., R. M. GENTRY,ANDJ. FAABORG. 1995. PETRIDES, G.A. 1938. A life history study of the yellow- Patterns of ovenbird (Seiurus aurocapiUus) pairing suc- : :: ' ,, breasted chat. Wilson Bulletin 50:184-189. cess in Missouri forest tracts. Auk 112:98-106. _..... _ _:: PURCELL,K. L., ANDJ. VERNER. 1998. Density and repro- VANHORNE, B. 1983. Density as a misleading indicator -_ ductive success of California towhees. Conservation of habitat quality. Journal of Wildlife Management . " • Biology 12:442-450. 47:893-901. , • . , , RALP_ C.J., G. R. GEUPEL, P.'PYLE, T. E. MARTIN,AND VICKERYE, D., M. L. HUNTER, ANDJ. v. WELTS. 1992. Is D. E DESANTE. 1993. Handbook of field methods for density an indicator of breeding success? Auk _ _. -. monitoring landbirds. U.S. Forest Service General 109:706--710. _"_'::: .... " " Technic:al Report PSW-GTR-144. WEATHERHEAD,P.j., ANDM. B. CHARLAND. 1985. Habi- -__i_ , RATrI, J. T., ANDK. P. REESE. 1988. Preliminary test of tat selection in an Ontario population of the snake, __ the ecological trap hypothesis. Journal of Wildlife Elaphe obsolete. Journal of Herpetology 19:12-19. 13_ ....._ . Management 52:484--491. WHITE, G.C. 1983. Numerical°estimation of survival __"+_'_'__ ::: .: " ROBINSON, S. K., E R. THOMPSON, III, T. M. DONOVAN, rates from band recovery and biotelemetry data. _:,: _,_:: . n. R. WHITEHEAD,ANDJ. FAABORG.1995. Regional for- Journal of Wildlife Management 47:716-728. _\_:.:_!_ " est fragmentation and the nesting success of migrato- ANDR. A. GARRO'rr. 1990. Analysis of wildlife _,_ ...... ' , ,._;, _:._ ry birds. Science 267:1987-1990. radio-tracking data. Academic Press, San Diego, Cal .... i_;i_.., STRELKE,W. K., ANDJ. G. DICKSON. 1980. Effect of for- ifornia, USA. est clear-cut edge on breeding birds in east Texas. WOODWARD, A.A. 2000. Habitat and edge effects on ' :" *...... '_ ' Journal of Wildlife Management 44:559-567. shrubland songbirds. Thesis, University of Missouri, SUAREZ,A.'V., K. S. PFENNING,ANDS. K. ROBINSON. 1997. Columbia, USA. Nesting success of a disturbance-dependent songbird . . on different kinds of edges. Conservation Biology Received 16 May 2000. 11:928-935. Accepted 16 May 2001. TEMPLE, S. A., ANDR.J. GARY. 1988. Modeling dynamics Associate Editor: Sullivan. _"