Schizocosa Ocreata (Hentz), and Anti-Predator Responses to Avian Cues

UNIVERSITY OF CINCINNATI

Date:______

I, ______, hereby submit this work as part of the requirements for the degree of: in:

It is entitled:

This work and its defense approved by:

Chair: ______

The impact of avian predation on the brush-legged wolf spider, Schizocosa ocreata (Hentz), and anti-predator responses to avian cues.

A thesis submitted to the

Division of Research and Advanced Studies Of the University of Cincinnati

In partial fulfillment of the requirements for the degree of

MASTER’S OF SCIENCE (M.S.)

In the department of Biological Sciences of the McMicken College of Arts and Sciences

2007

Anne K. Lohrey

B.A. Miami University, 2003

Committee:

Dr. George W. Uetz, Chair Dr. Kenneth Petren Dr. Ann Rypstra

Abstract

This research aimed to quantify the potential for avian predation on Schizocosa ocreata wolf spiders in the field and its impact on spider behavior. In a field study, enclosures that excluded birds had a higher proportion of spiders remaining at the end of the experiment than enclosures that allowed birds access. Additionally, observational data confirmed that some bird species seen active at the study site eat spiders presented in feeding trials. These data suggest that bird predation impacts survival of S. ocreata in the field. In the laboratory, I tested spiders‘ recognition of and behavioral responses to sensory cues indicating the presence of avian predators. Courting male S. ocreata responded to avian acoustic stimuli (bird calls) with anti- predator behavior, which supports the hypothesis that bird predation limits survival of S. ocreata and may be an important selective factor on the evolution of behavior in this species of wolf spider.

Acknowledgements

I would like to first thank my advisor, Dr. George W. Uetz, for his guidance throughout

this project. He has challenged me to become a better writer, presenter and thinker through this

experience. My committee members, Dr. Ken Petren and Dr. Ann Rypstra, were instrumental in

my success as well. They were always available and helped guide me through this process with great ideas to improve my project and make it more cohesive.

Thank you to my fellow graduate students, E. Galbraith, J. Gibson, S. Gordon, J. Johns,

B. Moskalik and J. Rutledge for being such great sounding boards and providing much needed

comic relief. I’d also like to thank the many undergraduate students who helped make this

research possible, especially J. Allen, I. Huang, M. Skelton, J. Smith and A. Stein.

My family also deserves much gratitude for supporting me through this endeavor. They

always offered a listening ear for the difficult times and helped me celebrate my successes. My

parents instilled in me, by example, a sense of integrity, a strong work ethic and impressed on me

the value of wisdom as well as knowledge.

Finally, I would like to thank my best friend and partner in life, Jeremy Gibson, who has

been unwavering in his support and encouragement.

iii

Table of Contents

Abstract i Acknowledgements iii List of Tables and Figures 2

General Introduction 4 Study Organism 4 Objectives and Hypotheses 6

Chapter Page

I. Potential for avian predation on Schizocosa ocreata (Hentz) wolf spiders (Araneae: Lycosidae) 12 Abstract 13 Introduction 13 Methods 16 Results 18 Discussion 20 References 23

II. Recognition of and response to avian predator cues in Schizocosa ocreata (Hentz) wolf spiders (Araneae: Lycosidae) 31 Abstract 32 Introduction 32 Methods 35 Results 38 Discussion 39 References 43

Conclusions and Future Directions 52 References 55

Appendix: Distance over which S. ocreata can be detected visually by birds in the field 56

List of Tables and Figures

Tables

Table 1.1. Ground foraging bird species observed at the field site during both anecdotal observations and timed focal observations (9 days; 15 min./day).

Table 1.2. Mean proportion of spiders remaining at the end of the experiment for each treatment.

Table 1.3. Two-way ANOVA of proportion of spiders remaining at the final census point.

Table 1.4. Two-way repeated measures ANOVA of the proportion of spiders remaining at each census point (duration).

Figures

Figure 1.1. Overlap in duration of S. ocreata breeding season, breeding season of Ohio birds and the enclosure study.

Figure 1.2. Mean proportion of spiders remaining at the end of the experiment for each treatment. N = 19 (Uncovered), N=17 (Covered).

Figure 1.3. Mean proportion of spiders remaining at each census point (duration). N=10 each.

Figure 2.1. Percentage of each behavior (locomotion, tap, stop, groom) following the stimulus (a. acoustic, b. visual, c. seismic, d. control) for each type of cue (N=10 per treatment group).

Figure 2.2. Average latency to return to courtship after presentation of each type of stimulus N=10 (Seismic), N=9 (Acoustic), N=9 (Visual), N=9 (Control).

Figure 2.3. Preliminary results from 2006. Percentage of spiders given each stimulus that responded with anti-predator behavior (N=12 per treatment group).

Figure 2.4. Percentage of spiders given each stimulus that responded with anti-predator behavior. N=21(Carolina Wren, Northern Cardinal, House Finch), N=16(Katydid), N=19(White Noise).

Figure 2.5. Percentage of spiders given each stimulus type (Bird Call, Non-threatening Sound) that responded with anti-predator behavior. N=63 (Bird Calls), N=35 (Non-threatening Sounds).

Figure 2.6. Average latency to return to courtship after presentation of stimulus (in seconds). N=19 (Carolina Wren), N=21 (Northern Cardinal), N=18 (House Finch), N=16 (Katydid), N=20 (White Noise).

Figure 2.7. Average latency to return to courtship after presentation of stimulus (in seconds). N=58 (Bird Calls), N=36 (Non-threatening Sounds).

Figure 2.8. Spectrum analysis for Katydid call compared to bird calls (House Finch and Northern Cardinal). Note that the frequency scale varies between the Katydid call (a) and the bird calls (b and c).

Figure 3.1. Two-dimensional representation of the average distance to the first visual obstruction from a point on the leaf litter, measured in two sites: Cincinnati Nature Center (a) and New Richmond, Ohio (b). Measurements for the New Richmond site (spring, 2007) were taken four times (May 12, 15, 22 and 20) over the breeding season.

General Introduction

Elaborate male courtship signals and displays have often been explained by sexual

selection, since such traits may increase conspicuousness of males to females and/or serve as

indicators of male quality, thereby increasing mating success (Andersson, 1994; Johnstone,

1995). However, such signals may incur predation costs, as elaborate male traits make the trait-

bearer more conspicuous to predators as well as to females (Zuk & Kolluru, 1998; Haynes &

Yeargan, 1999; Kotiaho, 2001). The respective benefits and costs of sexual and natural selection

can result in a trade-off between them (Tuttle & Ryan, 1981; Endler, 1992; Andersson, 1994;

Zuk & Kolluru, 1998; Basolo & Wagner, 2004; Husak et al, 2006). For example, male

Calopteryx damselflies with increased melanization of wing patches, a sexually selected trait,

suffer higher mortality due to predation (Svensson & Friberg, 2007). Likewise, bright body

coloration in male guppies (Poecilia reticulata) increases male mating success, but brighter

males incur greater direct fitness costs due to predation (Godin & McDonough, 2003). Female

Hygrolycosa rubrofasciata wolf spiders prefer males with higher courtship drumming rates;

however, such males are subject to increased risk of predation based on drumming rate (Kotiaho

et al, 1998, Lindstrom et al, 2006).

Study organism

Schizocosa ocreata (Hentz), a wolf spider commonly found in the leaf litter of eastern

deciduous forests (Cady, 1984), has a spring breeding season. The mating system of this species

has been described as scramble competition polygyny and females are unlikely to mate with more than one male (Norton & Uetz, 2005). Males mature in late March or early April (about two weeks prior to females) and become increasingly active on the surface of the leaf litter until

the end of the breeding season. In mid-summer, eggsacs hatch and spiderlings overwinter to

mature the next spring, completing the life cycle.

During courtship, males engage in a complex multi-modal display consisting of both

seismic and visual components upon detection of female dragline silk and associated chemical

cues (Stratton & Uetz, 1981, 1983, 1986; Scheffer et al., 1996; Uetz, 2000; Uetz & Roberts,

2002). Seismic communication consists of both substrate-borne stridulation produced in the

tibio-tarsal joint and percussion of the abdomen and chelicerae against the substrate. Some

attributes of the seismic signal have been found to influence female receptivity (Gibson & Uetz,

in press). In addition, visual communication consists of active leg-waving displays of the first

pair of legs. Associated tufts of bristles on the tibiae of legs I may serve as a decoration,

increasing male mating success (Scheffer et al, 1996; Hebets & Uetz, 2000; Uetz, 2000; Uetz &

Roberts, 2002; Delaney et al, in press)

Leg tufts, while serving to make male courtship displays more conspicuous and/or attractive to females, also increase detection by visually-hunting predators such as other spider

species, anurans and/or avian predators with which S. ocreata occur (Wise & Chen, 1999a,b;

Pruden & Uetz, 2004; Roberts et al, 2006). Digitally manipulated S. ocreata video images have

been used to demonstrate that larger leg tufts elicit a faster predatory response by a jumping

spider (Phiddipus clarus), another wolf spider (Hogna helluo) and a vertebrate predator, the

American toad (Bufo americanus) (Pruden & Uetz, 2004; Roberts et al, 2006; Roberts & Uetz,

unpubl.).

Reflectance measurements have shown that S. ocreata leg tufts as well as lateral parts of

the prosoma and opisthosoma contrast highly with the spectral qualities of the leaf litter

background (Clark, Roberts and Uetz, unpubl.). Since males are highly active on the surface of

the leaf litter, they are very visually conspicuous during the breeding season. Given the

conspicuousness of this display, questions arise about the impact of predation by animals that rely largely on acute vision to find prey. How much does bird predation impact S. ocreata

survival in the field during the breeding season and how likely are S. ocreata to be detected

visually on the leaf litter? If birds are important predators, how do S. ocreata respond to cues

that indicate the presence of a bird predator?

Objectives and Hypotheses

The goal of this study is to gain a better understanding of the importance of avian predation on S. ocreata wolf spiders. Both field and laboratory data were collected to answer

this question. The research outlined in Chapter I investigates the potential for avian predation on

spiders in the field and its impact on spider survival. If birds are important predators of S.

ocreata in the field, as predicted, anti-predator responses to sensory cues representing an avian

predator may have evolved. In Chapter II, behavioral responses of S. ocreata to a variety of cues

are examined (focusing on responses to avian acoustic cues).

Chapter I: Potential for avian predation on Schizocosa ocreata (Hentz) wolf spiders (Araneae: Lycosidae)

Birds are known to be highly dependent upon the visual sensory mode when foraging

(Hodos, 1993) and thus could have an important impact on spider survival based on visual characters, especially since leg tufts contrast highly with the leaf litter background (Clark,

Roberts and Uetz, unpubl.). Additionally, birds are likely to be provisioning nestlings with arthropod prey during the breeding season of S. ocreata, increasing the risk of predation during

the time at which males are actively courting females and are most conspicuous. Several species

of ground-foraging, insectivorous birds co-occur with S. ocreata in Eastern deciduous forests

(De Graaf, 1985; Haggerty & Morton, 1995).

Bird predation has been documented for some spider species (Askenmo et al, 1977;

Riechert & Hedrick, 1990; Gunnarsson, 1996) and it seems likely that ground-foraging birds

would prey on S. ocreata. While one study suggests no impact of vertebrate predation on a

mixed population of Schizocosa wolf spiders (Wise & Chen, 1999b), it was conducted over the

entire life history of the spiders. Currently, there are no studies focusing specifically on bird

predation on S. ocreata during the breeding season, the window of time throughout which

spiders, especially males, are most active and conspicuous. This study aims to examine the

potential for avian predation on S. ocreata in the field during the breeding season.

To gain an understanding of the potential impact of bird predation on S. ocreata, two types of data were collected: 1) observations of bird foraging activity and 2) survival

measurements of spiders in field enclosures either allowing or denying birds access. The

observations determined whether ground-foraging species observed preying on spiders were

active and foraging in the study area, while the enclosure experiments provided quantitative data

on the impact of bird predation on survival of S. ocreata. If birds are important predators of S.

ocreata, field enclosures allowing birds will contain fewer spiders than enclosures excluding

them.

Chapter II: Recognition of and response to avian predator cues in Schizocosa ocreata (Hentz) wolf spiders (Araneae: Lycosidae)

Other studies have demonstrated a variety of behavioral responses in lycosids (reduction

of activity, avoidance) to predator cues (usually chemical) which serve to decrease the risk of

predation (Persons & Rypstra, 2001; Persons et al, 2001; Taylor et al, 2005). If predation risk

7 from birds is high (investigated in Chapter I) this could select for behavioral recognition of sensory cues (including, but not limited to acoustic cues) associated with an avian predator. If this is the case, then spiders presented with sensory cues indicating the presence of an avian predator should exhibit behavioral recognition and avoidance responses distinct from responses to other stimuli. The hypothesis that spiders exhibit anti-predator responses to various types of sensory stimuli representing a potential avian predator (seismic, visual and acoustic) was tested.

Further, the hypothesis that spiders respond with anti-predator behavior when presented with avian acoustic sensory cues was tested using audio playback.

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Chapter I

Potential for avian predation on Schizocosa ocreata (Hentz) wolf spiders

(Araneae: Lycosidae)

Anne K. Lohrey and George W. Uetz

Department of Biological Sciences

University of Cincinnati

P.O. Box 210006

Cincinnati, OH 45221-0006

Abstract

The fitness benefits of conspicuous male signals (increased mating success) may be

balanced by the cost of increased predation risk. Male Schizocosa ocreata (Hentz) wolf spiders,

which have a visually conspicuous courtship display and associated sexual characters, may be at

increased risk for predation by visual predators, including birds, during the spring breeding season. This study investigated the risk of predation by birds on adult male S. ocreata during the

breeding season, using field enclosures that either allowed access to foraging birds or excluded

them. Enclosures allowing birds access lost a significantly higher proportion of spiders than

exclosures, suggesting that birds impact survival of S. ocreata males. In focal observations and

ad lib observations conducted at the field site, a number of ground-foraging birds were seen

active and foraging. In feeding trials, some of the species seen in the field site during survey

periods were observed preying on S. ocreata males in preference to mealworms. Taken together,

these data and observations suggest that bird predation impacts survival of S. ocreata males in the field, especially during the breeding season.

Introduction

The benefits of signals, including those used in courtship communication to increase the conspicuousness of the sender to the receiver, may come at the cost of attracting the unwanted

attention of predators (Andersson, 1994; Zuk & Kolluru, 1998; Haynes & Yeargan, 1999;

Kotiaho, 2001). When sexual selection favors individuals with traits of greater magnitude, but

natural selection from predation reduces the fitness of individuals with more conspicuous traits, a

trade-off results between them (Tuttle & Ryan, 1981; Endler, 1992; Andersson, 1994; Zuk &

Kolluru, 1998; Basolo & Wagner, 2004; Husak et al, 2006). Research on the costs and benefits

of sexual signaling in male guppies (Poecilia reticulata) showed that although brighter body

coloration increased mating success, brighter males incurred greater direct fitness costs due to

predation (Godin & McDonough, 2003). Svensson and Friberg (2007) found that higher levels

of melanization on wing patches in male Calopteryx damselflies increased mating success but

also increased the risk of predation. Additionally, predation on populations of C. virgo and C.

splendens lead to reduction of wing melanization patches and changes in melanin distribution.

Similar research has been conducted with Hygrolycosa rubrofasciata wolf spiders, demonstrating that while females preferred males with higher courtship drumming rates, such males were at increased risk of predation by lizards and birds (Kotiaho et al, 1998, Lindstrom et al, 2006).

Many laboratory studies of courtship and mating communication in the brush-legged

wolf spider, Schizocosa ocreata, have yielded knowledge of the reproductive behavior of this

species as well as the selection pressures guiding the evolution of its communication system.

However, the impact of some potential predators on the survival of S. ocreata in the field is not

clear.

S. ocreata has a multi-modal courtship display including both seismic (substrate-borne

stridulation) and visual components (Stratton & Uetz, 1981, 1983, 1986; Scheffer et al., 1996;

Uetz, 2000; Uetz & Roberts, 2002). Some attributes of the seismic signal affect mating success

(Gibson & Uetz, in press). The visual mode consists of active leg-waving displays and associated tufts of bristles on the first pair of legs, which may serve to increase detectability

(Scheffer et al, 1996). These leg tufts are a condition-indicating trait important for female mate choice, with females preferring males with larger leg tufts (Uetz et al., 2002; Uetz & Roberts,

2002).

Clark, Roberts and Uetz (unpubl.) have examined the reflectance of different body parts and whole-body views of S. ocreata and found that leg tufts as well as a lateral view of the prosoma and opisthosoma contrast highly with the spectral qualities of leaf litter. Since male S. ocreata contrast highly with the leaf litter background and are active on the leaf litter surface

(Roberts, Rector, Clark & Uetz, unpubl.), it is likely that they are very visually conspicuous during the breeding season. This conspicuousness makes them more vulnerable to visual predators such as other species of wolf spiders, jumping spiders and toads. In previous research, variation in leg tufts on digitally-manipulated S. ocreata video images affected predatory responses of wolf spiders (Hogna helluo) and jumping spiders (Phiddipus clarus) as well as a visually-oriented vertebrate predator, the American toad (Bufo americanus) (Pruden & Uetz,

2004; Roberts et al, 2006). If levels of predation during the breeding season of S. ocreata are high, it could influence the evolution of sexual characters and displays.

Birds are known to be highly visual predators (Hodos, 1993) and most ground-foraging bird species that co-occur with S. ocreata in eastern deciduous forests have a spring breeding season that overlaps with the breeding season of S. ocreata (DeGraaf et al, 1985; Haggerty &

Morton, 1995; Skinner, 2003). During this time, adult birds are foraging to feed both themselves and their offspring, particularly with high-energy prey such as arthropods (Robinson & Holmes,

1982; Savory, 1989; Moreby, 2004). At the same time, male S. ocreata undergo their final molt to maturity, developing tufts of bristles on their first pair of legs, and actively begin searching the leaf litter for females.

It is probable that bird predation on S. ocreata during the spring breeding season significantly impacts survival. Previous work has demonstrated bird predation on a variety of spider species, but not specifically during the breeding season (Askenmo et al, 1977; Riechert &

Hedrick, 1990; Gunnarsson, 1996). A study done by Wise and Chen (1999b) using field

enclosures showed no significant impact of vertebrate predation on spider survival in a mixed-

species population of Schizocosa wolf spiders. However, this study ran throughout the entire life

history of the spiders instead of focusing on the breeding season. As a result, significant

predation during the breeding season might not have been obvious because the impact could be

masked by other factors causing mortality throughout the season.

The goal of this study was to gain an understanding of the potential for avian predation

on S. ocreata during the breeding season through a combination of field studies including avian

foraging observations, prey preference trials at bird feeding stations and a field study that tracked the survival of spiders in enclosures that allow birds access versus those that prevent access.

Methods

Avian activity and foraging observations

Information on avian foraging activity was recorded during the breeding season of S.

ocreata at the location of the field enclosures on private property near New Richmond, Clermont

County, Ohio (39˚ 0’55.37” N; 84˚ 15’31.89”W). Both anecdotal observations and timed focal

observations were recorded. There were nine observation days with observation periods 15

min./day, occurring between 0900-1100 and 1400-1600 hours, the time of day during which

spiders are known to be most active (Uetz & Roberts, unpubl.). Information recorded included:

species, location (inside or outside of enclosure), position (in tree, on ground), height above

ground (if applicable), time spent on the ground, sex (if determinable) and vocalizations

produced.

Additionally, a live male S. ocreata and a mealworm were simultaneously presented to

birds foraging at a feeder to observe predatory behavior. The prey were placed in separate glass

fingerbowls and presented at ground level beneath a feeding station at the field site in New

Richmond between 0800 and 1100 hours. There were 21 preference trials and the locations of

the spider and mealworm were alternated. After the first attack and/or capture, the identity of the

prey taken was recorded (spider or mealworm), time of capture was recorded and the appropriate

prey item replaced so that the observation could continue. This study allowed verification that

species seen foraging at the field site would prey on live spiders and furthermore allowed

comparison of preference for spider prey with seed and mealworms.

Field enclosure exclusion study

This study was conducted in the deciduous forest habitat of S. ocreata during the spring

breeding season on private property near New Richmond, Clermont County, Ohio (39˚ 0’55.37”

N; 84˚ 15’31.89”W) in Spring 2006 and 2007. The breeding season of birds in Ohio is generally from late March or early April until September or October (Haggerty & Morton, 1995; Skinner,

2003; Leston & Rodewald, 2006), so the breeding period of S. ocreata and the duration of this study fall within that range (Figure 1.1). Twenty circular, 4m2 enclosures of galvanized

aluminum flashing were constructed and buried approximately 2-3 cm in the soil. Leaf litter was

left intact inside the enclosures to ensure natural conditions. All spiders were removed from

enclosed areas prior to the start of the experiment. Field-caught S. ocreata males were then

added to the enclosures at a density determined from previous research (5 male spiders / m2 = 20 male spiders in each enclosure) (Roberts, Rector, Clark & Uetz, unpubl.). Inner and outer edges of enclosures were lined with Vaseline® to prevent spiders from entering or leaving. Finally,

enclosures were either covered with bird netting to prevent access by birds, or left uncovered (10

of each, randomly chosen within blocks).

It was not possible to start all enclosure trials in one day, so they were stocked with

spiders in pairs (one covered and one uncovered) to avoid seasonal and day effects. Spiders

remained in enclosures from five to 21 days and were censused at approximately five day intervals. The last census day for each enclosure was considered the end point census and was used to compare mean proportion of spiders remaining at the end of the experiment for the two treatments. Censusing was conducted by walking through the enclosures for ten minutes and collecting all spiders seen. In 2006 additional leaf litter sifting was done to capture any remaining spiders. The initial census by walk-through searching was deemed sufficient, since only one spider was captured in the additional litter sifting, and was subsequently used. Data analysis included two-way repeated measures ANOVA on arcsine transformed proportion of spiders remaining in enclosures, including treatment and year as factors. Additionally, a post- hoc paired t-test on the difference in proportion (arcsine transformed) of spiders remaining by treatment was used, since the individual covered and uncovered enclosures were paired spatially and temporally.

Results

Avian activity and foraging observations

Seven species of ground-foraging birds were seen actively foraging in the study area

during both ad lib and timed focal observations (Table 1.1). In the preference trials presenting

both a spider and a mealworm, first attacks by Tufted Titmice were made on the spider 18 times

out of 21 trials (X2 = 21.429; df = 42; p < 0.0001), and it took on average about nine minutes

(8.95 ± 2.12 min.) from the start of the trial to the attack. In this study only Tufted Titmice

visited the feeding station and attacked spiders, although we anecdotally observed the following

species preying on live S. ocreata males as well: House Sparrow (5 events recorded) and

Northern Cardinal (1 event recorded).

Field enclosure exclusion study

Data for the bird exclusion study were obtained in both Spring 2006 (Uncovered, N =4;

Covered, N = 3) and Spring 2007 (Uncovered, N = 15; Covered, N = 14) and analyzed using a

two-way ANOVA with year and treatment (covered; uncovered) as factors. There were effects

of year (F1,1 = 5.4123; p = 0.0378) and experimental treatment (F1,1 = 7.6001; p = 0.0304).

Covered enclosures had a higher proportion of S. ocreata remaining at the end of the experiment

(census point) (43.2%) than uncovered enclosures (33.4%) (Tables 1.2, 1.3; Figure 1.2). A post-

hoc paired t-test on the proportion of spiders remaining (arcsine transformed) at the end of the

experiment produced a similar result (t = 2.3206; p = 0.0338). In a repeated measures ANOVA

on arcsine transformed proportion of spiders remaining, there was a treatment effect, with

covered enclosures containing more spiders than uncovered enclosures at each census point (F1,25

= 6.766; p = 0.0154), but no effect of census day on proportion of spiders remaining (F2,26 =

1.1083; p = 0.3452) (Table 1.4; Figure 1.3). Two data points were excluded from the analysis because in one, a large predatory wolf spider was found inside the enclosure and very few male

S. ocreata remained and in the other, a branch fell on the aluminum flashing (allowing spiders to escape).

Discussion

Over the course of the spring breeding season of S. ocreata, field enclosures allowing

birds access lost a significantly higher proportion (23% more) of male S. ocreata wolf spiders than covered enclosures, suggesting that bird predation has an impact on survival of S. ocreata.

This result is in contrast with a study conducted by Wise and Chen (1999b), which found no impact of vertebrate predation on survival of spiders. The key difference is that study measured survival of a mixed group of Schizocosa wolf spiders over the entire life history. High levels of predation on males during the relatively short breeding season could be masked in a study that looked at survival over the entire life history, and did not discriminate sexes. Given their high activity levels during the spring breeding season (Roberts, Rector, Clark & Uetz, unpubl.) and their high contrast with the leaf litter background (Clark, Roberts & Uetz, unpubl.), males are probably at the greatest risk of predation by visual predators during this specific “window” of their life history.

Generally, the distance from the leaf litter surface to the first visual obstruction in the

subcanopy is between four and eight meters (Appendix). This suggests that it is reasonable to

assume that a ground-foraging bird perched in the subcanopy would be able to see a spider on

the leaf litter. Several of the ground-foraging species familiar to Eastern deciduous forests were

seen active and foraging in the field site (DeGraaf et al, 1985; Haggerty & Morton, 1995),

including most notably, Wild Turkeys, American Robins and Northern Cardinals. Tufted

Titmice, which were observed active in the field site, were also recorded preying on live male S.

ocreata in feeding trials at bird feeding stations. Tufted Titmice prefer spiders as prey over

mealworms and are very quick and dexterous in their attack, suggesting that spiders are a part of

their natural diet. Roberts (pers. comm.) has also noted that a captive Northern Cardinal was

observed attacking and consuming escaped spiders in the laboratory on numerous occasions.

Though more spiders were lost in uncovered enclosures, there were losses in covered

enclosures as well. Some level of mortality is expected due to other predators (wasps,

centipedes, other spider species, etc.) (Wise and Chen, 1999a) as well as intra-specific

aggression (pers. obs. – one male consuming another). Presumably, the level of such mortality

was equal in all enclosures, with the primary difference being bird access. On a few occasions, a

large predatory wolf spider was found inside an enclosure on a census day and was removed, but

those enclosures were not included in the final analysis. Though we carefully lined the

enclosures with Vaseline® to prevent escape, it is possible that spiders under duress ran over the

Vaseline®. During one census period a spider was observed running over the Vaseline® to escape when pursued. Such loss of spiders could still be related to predation attempts if the spider was chased over the edge of the flashing by a bird predator.

High levels of predation during the breeding season of S. ocreata would be likely to impact selection on sexual signals and displays. During the spring breeding season of S. ocreata, birds are provisioning their nestlings with diets rich in arthropod prey, including spiders

(Robinson and Holmes, 1982; Savory, 1989; Moreby, 2004). Since male S. ocreata have a very conspicuous visual courtship display in terms of pigmentation of the legs and leg movements, they may be at increased risk for predation by visual predators. Although such conspicuous displays can increase mating success, selection for more conspicuous and exaggerated traits may be balanced by natural selection against these traits due to increased predation (Andersson, 1994;

Zuk & Kolluru, 1998; Haynes & Yeargan, 1999; Kotiaho, 2001).

Acknowledgements

This research was supported by the National Science Foundation (IBN 0239164 to

G.W.U.) and the University of Cincinnati Research Council (to A.K.L.). We thank the

Cincinnati Nature Center for allowing us to collect spiders and conduct avian foraging observations on their property. Additional thanks to J. Gibson, I. Huang, J. Johns and J.

Rutledge (for their assistance in building the enclosures and for helping to collect the spiders that were used to stock the enclosures), K. Uetz (for use of the field site), and K. Petren and A.

Rypstra for editorial comments and statistical advice.