Behavioral Stuff and Sexual Dimorphism in Yellow-Billed Cuckoos

University of Nevada, Reno

Sexual Dimorphism, Detection Probability, Home Range, and Parental Care in the Yellow-billed Cuckoo.

A dissertation submitted in partial fulfillment of the Requirements for the degree of Doctor of Philosophy in Ecology, Evolution and Conservation Biology

Mary Murrelet Halterman

Dr. Lew Oring/Dissertation Advisor

May, 2009

ABSTRACT

The biology of many species of conservation interest is poorly understood. Often, little is known apart from population estimates. Yellow-billed Cuckoos (Coccyzus americanus) are a neotropical migrant, and due to loss of riparian breeding habitat, are of great conservation concern in the western United States. Little is known about their basic biology. In this study I looked at sexual dimorphism, responsiveness to call playback, home range size, and parental care.

Determining sex of a study organism is fundamental to understanding almost every aspect of their biology and management. Although there has been speculation about methods of sexing adult cuckoos using measurements, vocalizations, and extent of white in the tail, we found the only reliable way to sex cuckoos utilized genetic markers.

Females gave the ―coo‖ call, considered an advertisement call, significantly more than males.

Although there have been extensive cuckoo surveys done in the western United

States, there are no data on responsiveness or detectability using call playback surveys.

We tested the standard call playback methodology with 18 radio marked adult cuckoos.

Response rate during call playback tests averaged 59.5%, and was higher for males

(72.7%, n=10) than females (40%, n=8). Detection rates were lower than response rates, averaging 32.4% overall, and were higher for males (43.2%, n=10) than females (16.7%, n=8). The low responsiveness and detectability of cuckoos may be influenced by their large home ranges. We monitored 28 cuckoos equipped with radio transmitters on the

San Pedro Riparian National Conservation Area during 2001-2005. Average home range

ii estimates were 95% KDE - 39 ha, 75% KDE - 17 ha, and 50% KDE 7.5 ha. There were large variances for all home range estimates, and females had significantly smaller home ranges than males. This may partially account for lower detectability of females.

Cuckoo researchers have observed small clutch sizes, rapid development of young, and a third adult helping to raise young, but there are no previous studies of parental care with banded, known sex Yellow-billed Cuckoos. We followed 28 adult cuckoos with transmitters and placed video cameras on four nests. Although both parents constructed nests, incubated eggs, and cared for young, males did all nighttime incubation, provided the majority of food to nestlings, and all care to fledglings.

Additionally, we confirmed the presence of a third adult providing care to nestlings.

Occasionally during the nestling period females appeared to abandon a viable nest and initiate a nest with another male. Males may have larger home ranges in order to locate females, who may call to attract second males. This male may assist with the first nest effort, then leave with the female for a subsequent nest. These observations present a pattern of male-dominated parental care, and Yellow-billed Cuckoos appear to be facultatively serially polyandrous.

iii

DEDICATION

To my parents, Carol and Joseph, for always supporting my endeavors, and for allowing me to pursue this strange career I‘ve chosen.

My Grandpa in Indiana was probably is responsible for my love

of birds, and Grandma Halterman was the strongest person I have ever known.

She taught me that a person can overcome anything.

ACKNOWLEDGEMENTS

A dissertation is a mind-bogglingly huge project, and far, far bigger than I realized when I started. Without the support and encouragement of fellow students

Juliana Bosi de Almeida, Meeghan Gray, and Angela White, and my advisor Lew Oring,

I would never have been able to get through the last year of crouching in front of my computer late into the night, to emerge into the sunlight of finishing my dissertation. I also had statistical, logistical, and moral support from fellow grads Alex Hartman and

Patrick Lemmons.

A special thanks to Barbara Raulston, who trusted that all the funding she worked to secure would eventually result in a worthwhile body of work. I would like to thank

Greg Clune and John Swett for providing logistical support and the US Bureau of

Reclamation and Southern Nevada Water District for providing financial support for this project. Thanks to Jack Whetstone and the Sierra Vista BLM office for logistical support and access to the Riparian Conservation Area and to Gray Hawk Ranch for access to their property. Additional thanks to Dr. Kathleen Blair and Dick Gilbert of the U.S.D.I. Fish and Wildlife Service, BWRNWR for their assistance. Thanks to the personnel of the

Southern Sierra Research Station for the flexibility and support to get through this huge undertaking.

Thanks to my entire committee, Dr. Michael Collopy, Dr, Catherine Fowler, Dr,

Mary Peacock, and Dr. Jim Sedinger for their editorial assistance and willingness to return comments quickly and change dates frequently. Lew and Kay Oring provided logistical support in addition to moral and editorial support. The Ecology, Evolution, and

Conservation program at UNR provided critically important financial support. I had

v unendingly cheerful support from the NRES office staff, Kerrie Medieros, Heidi

McConnell, and Ronald Rocky.

A special thanks to three hardworking and dedicated biologist who began as field assistants, but became cuckoo experts during their 4 years of work on the project -

Shannon McNeil, Eli Rose, and Diane Tracy. They have the sense of humor and tolerance for frustration required for working with cuckoos, and they all stepped up to the challenges of managing field crews and data when I could not be there. Also, many thanks to my hardworking field assistants for invaluable assistance during this project.

My time in Reno would not have been so pleasant if not for many friends who helped out numerous times during my stay here. Franko and Cynthia Ferris opened their hearts and homes to me, and helped me adjust to returning to school after many years away. The entire agility community of Reno helped keep me sane during this process, and Patrick and Cynthia Kennedy allowed me to stay with them, and have been great and supportive friends.

Thanks to my martial arts friends, including everyone at High Sierra Jujitsu, and

Larry and David at Ridgecrest Kung Fu for providing physical activity, and forcing me to use a very different part of my brain.

Although my dogs haven‘t provided much in the way of logistical support, they kept me sane during this entire process. Between forcing me to go walkies (and get away from the computer), and leading me to agility out of self-defense, I was able to maintain some balance in life, as well as meet new friends.

Thanks to my entire family, who have always been happy to see me, though I usually just showed up in time for the big meals! I love you all.

TABLE OF CONTENTS ABSTRACT ...... i DEDICATION ...... iii ACKNOWLEDGEMENTS...... iv TABLE OF CONTENTS ...... vi LIST OF TABLES ...... viii LIST OF FIGURES ...... xi GENERAL INTRODUCTION ...... 1 LITERATURE CITED ...... 4 Chapter 1. Sexing Yellow-billed Cuckoos ...... 6 ABSTRACT ...... 7 INTRODUCTION ...... 8 METHODS ...... 12 RESULTS ...... 15 DISCUSSION ...... 17 CONCLUSION ...... 20 ACKNOWLEDGMENTS ...... 21 LITERATURE CITED ...... 22 TABLES and FIGURES ...... 27 Chapter 2. Response Rate and Detection Probability of Yellow-Billed Cuckoos in Arizona ...... 32 ABSTRACT ...... 33 INTRODUCTION ...... 34 METHODS ...... 39 RESULTS ...... 43 DISCUSSION ...... 46 MANAGEMENT IMPLICATIONS ...... 50 ACKNOWLEDGMENTS ...... 51 LITERATURE CITED ...... 51 TABLES and FIGURES ...... 55 Chapter 3. Home Range, Site Fidelity, and Double-Brooding of Yellow-Billed Cuckoos on the San Pedro Riparian National Conservation Area, 2001-2005 and Implications for Management...... 66

vii

ABSTRACT ...... 67 INTRODUCTION ...... 68 METHODS ...... 72 RESULTS ...... 75 DISCUSSION ...... 78 MANAGEMENT IMPLICATIONS ...... 83 ACKNOWLEDGMENTS ...... 85 LITERATURE CITED ...... 85 TABLES and FIGURES ...... 92 Chapter 4. Parental Care in the Yellow-billed Cuckoo...... 104 ABSTRACT ...... 105 INTRODUCTION ...... 106 METHODS ...... 108 RESULTS ...... 110 DISCUSSION ...... 114 ACKNOWLEDGMENTS ...... 118 LITERATURE CITED ...... 119 TABLES and FIGURES ...... 124 GENERAL DISCUSSION ...... 132 LITERATURE CITED ...... 134

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LIST OF TABLES

Chapter 1.

Table 1. Mean measurements of male and female Yellow-billed Cuckoos captured on the San Pedro Riparian Conservation Area, 2002-2005…. .29

Table 2. Discriminant funtion models for male and female Yellow-billed Cuckoos captured on the San Pedro RNCA, 2001-2005. (n = 13 females, 27 males)…………………………………………………………………………..30

Table 3. Percentage of Yellow-billed Cuckoo call types detected during radiotelemetry observations on the SPRNCA (2003 - 2005), and percentage detected during surveys…………………………………………………………...31

Chapter 2.

Table 1. Number of yellow-billed cuckoos captured by year, sex, and mating status on the San Pedro River AZ, 2004-2005, and the response and detection rates during call-playback trials………….……………………...... 56

Table 2. Type of response to call-playback trials with marked yellow-billed cuckoos on the San Pedro River, AZ, 2004-2005………………………….……..57

Table 3. Models for estimating response rates of marked yellow-billed cuckoos using model selection during the first call-playback test on the San Pedro River AZ, 2004-05 (n=18)……………………………………………...... 58

Table 4. Models for estimating detection rates of marked yellow-billed cuckoos using model selection during the first call-playback test on the San Pedro River AZ, 2004-05 (n=18)………………………………….……..….59

Table 5. Models for estimating response rates of marked yellow-billed cuckoos using model selection model selection based on ΔAICc scores less than 4 during call-playback tests 1-4 on the San Pedro River AZ, 2004-05 (n=44)…………………………………………………………………………..…60

Table 6. Models for estimating detection rates of marked yellow-billed cuckoos using model selection model selection based on ΔAICc scores less than 4 during call-playback tests 1-4 on the San Pedro River AZ, 2004-05 (n=44)…………………………………………………………………....61

Table 7. ΔAICc values for DOBSERV models for independent- observer approach for yellow-billed cuckoos surveyed on the San Pedro River AZ, 2005…………………………………………………………..…62

Table 8. Detection probabilities for males, females, and all cuckoos from call-playback tests (n = 44) and double observer surveys (n = 16) for yellow-billed cuckoos on the San Pedro River AZ, 2004-05………………...... 64

Table 9. Number of surveys required to determine yellow-billed cuckoo absence from a site, using detection probabilities determined by double observer and call-playback trials, San Pedro River AZ, 2005 (N = 40)……..……65

Chapter 3.

Table 1. Home range (in hectares) derived by different means for Yellow-billed Cuckoos observed on the San Pedro RNCA, 2002- 2005. Means+ SD, Sample sizes (N) and ranges are given……………………….93

Table 2. Models for estimating home range of marked Yellow-billed Cuckoos using model selection based on ΔAICc scores for 95% MCP models on the San Pedro RNCA, 2002-2005 (n=28)…………………………..…95 .. Table 3. Models for estimating home range of marked Yellow-billed Cuckoos using model selection based on ΔAICc scores for 95% KDE models on the San Pedro RNCA, 2002-2005 (n=28)…………………………..…96

Table 4. Models for estimating home range of marked Yellow-billed Cuckoos using model selection based on ΔAICc scores for 75% KDE models on the San Pedro RNCA, 2002-2005 (n=28)……………………………..97

Table 5. Models for estimating home range of marked Yellow-billed Cuckoos using model selection based on ΔAICc scores for 50% KDE models on the San Pedro RNCA, 2002-2005 (n=28)…………………………….98

Chapter 4.

Table 1. Summary of observations at three video-monitored Yellow- billed Cuckoo nests on SPRNCA 2005……………………………………….....125

Table 2. Nest attendance and prey delivery at three Yellow-billed Cuckoo video-monitored nests on the SPRNCA 2005…………………..…...…126

Table 3. Size of prey items delivered to three Yellow-billed Cuckoo nests on SPRNCA 2005…………………………………………………...... 127

Table 4. Daily food delivery to video-monitored Yellow-billed Cuckoo nests on SPRNCA 2005………………………………………………...128

Table 5. Average measurements of five Yellow-billed Cuckoo nestlings, SPRNCA 2005………………………………………………...... 129

LIST OF FIGURES Chapter 1

Figure 1. Proportion of each call type given by male and female Yellow-billed Cuckoos on the San Pedro RNCA, 2002-2005……………...…28

Chapter 2

Figure 1. Probability of detection for male and female yellow-billed cuckoos during call-playback tests on the San Pedro River, 2004- 2005 (n=40)…………………………………………………………………....63

Chapter 3

Figure 1. Comparison of average home range estimates for Yellow- billed Cuckoos on the San Pedro RNCA, 2003-2005…………………………94

Figure 2. Home range for Female 2-2005, San Pedro RNCA, Summer 2005……………………………………………………………….....99

Figure 3. Weekly 95% KDE home range estimates for eight Yellow-billed Cuckoos on the San Pedro RNCA , 2002-2005………………100

Figure 4. Home range size for Yellow-billed Cuckoos on the San Pedro RNCA, 2002-2005, by number of points used to determine home range…………………………………………………...... 101

Figure 5. Overlapping home ranges of five individual Yellow-billed Cuckoos on the San Pedro RNCA, 2004………………………………...…..102

Figure 6. Weekly changes in home range use by Yellow-billed Cuckoo Female 1-2002 on the San Pedro RNCA, 2002……………………..103

Chapter 4

Figure 1. Morphological measurements of five nestling Yellow- billed Cuckoos on SPRNCA 2005…………………………………………...130

Figure 2. Changes in prey delivery rates by male and female Yellow-billed Cuckoos on SPRNCA 2005…………………………...... 131

GENERAL INTRODUCTION

The order Cuculiformes is an ancient line of birds which, like many groups, originated in Gondwana (Ericson et al. 2003). A recent phylogenetic analysis shows them to be most closely related to Gruiformes (Rails) (Hackett et. al. 2008). The order contains 141 widely distributed species, though most are tropical (Payne 2005).

Cuckoos are a diverse group, but they share several common features. Although most species eat insects, the larger species eat a wide range of prey including reptiles, birds, and mammals (Payne 2005). Most have a relatively long, graduated tail, often with white spots on the end of the outer rectrices. All have zygodactyl feet in which the fourth toe is rotated forward, resulting in two toes forward and two back.

Yellow-billed Cuckoos (Coccyzus americanus) are neotropical migrants, spending summers in North America and Mexico, and wintering in South America (Hughes 1999).

They are commonly found throughout the eastern United States and in low numbers in the western U.S. (Hughes 1999). Western populations are restricted to riparian habitats.

In most western states riparian habitat has declined in historic times by at least 95%

(Gaines and Laymon 1984). Like many western riparian obligates, this species experienced dramatic population declines paralleling historic habitat loss (Hughes 1999,

Gaines and Laymon 1984, Laymon and Halterman 1985). This decline has resulted in interest by state and federal agencies and private conservation organizations in preserving the vastly reduced western population, currently a candidate for federal endangered status.

Yellow-billed Cuckoos average 60 grams, and are about 250 mm long. They are sexually monomorphic, cryptic, and move slowly through the forest. Cuckoos begin arriving in Arizona in late May and in California in late May-early June (Hughes 1999).

Nesting activities usually take place between late June and late July, but can begin as early as late May, and continue to late September (Hughes 1999). Nest building takes one to two days, incubation begins as soon as the first egg is laid, and lasts 11 days (Hughes

1999). Clutch size averages just over two eggs, ranging up to four (Laymon et al. 1997).

Young hatch asynchronously and are fed large food items such as katydids, tree frogs, large caterpillars and cicadas (Laymon et al. 1997, Halterman 2000). After fledging at five to seven days of age, young are dependent on adults for at least three weeks

(Laymon and Halterman 1985).

I chose to study Yellow-billed Cuckoos for several reasons. They are a poorly known species of conservation concern. There are many unresolved basic issues relative to sexual dimorphism, vocalizations, responsiveness, probability of detection, home range, and parental care. This study was an attempt to resolve some of these issues.

Working with this species is complicated by their low visibility, infrequent vocalizations, and low response rate to call playback.

Study Site

I worked on the San Pedro Riparian National Conservation Area (SPRNCA) in southeast Arizona. This site, southeast of Tucson, Arizona, is managed by the Bureau of

Land Management for conservation. The SPRNCA is the largest protected riparian area in Arizona, and one of the largest in the southwest. A statewide survey for Yellow-billed

Cuckoos in Arizona in 1999 had more detections at SPRNCA than any other site

(Corman and Magill 2000), making it an ideal location for this study.

The 57,000 acre conservation area is primarily composed of Chihuahuan desert vegetation. A riparian corridor follows 40 miles of the upper San Pedro River between the Mexican border and St. David, AZ. I worked on a 30 mile stretch of the river. The riparian corridor consists of a narrow band of cottonwood (Populus fremontii) and willow

(Salix sp.) bordered by occasionally extensive mesquite (Prosopsis sp.) upland.

Catching Cuckoos

Most of the questions I hoped to answer required capturing and marking adult cuckoos. One of the biggest challenges was devising a method to catch cuckoos. These birds have large home ranges and do not respond aggressively to call playback. During the first years of the project I experimented with methods for catching cuckoos.

The first year of the study I used a dead mounted Screech Owl (Otus asio) placed near an active cuckoo nest and surrounded by mist nets. I hoped that adults would be caught while mobbing the decoy. This was attempted at nine nests in 2001. I caught two adults, but one had to be chased into the net, and the other flew into the net while responding to a survey tape. I also used a Great Horned Owl (Bubo virginianus) decoy near a nest on one occasion. Adult cuckoos flew to the top of the nearest trees and gave alarm calls, indicating that this method probably would not be effective.

During the next four years I developed a method that resulted in relative success, with one adult cuckoo captured for every two days of effort. I caught adult cuckoos using mist nets while playing a variety of recorded vocalizations. I placed a total of four

60mm nets, ranging from 6m to 12m in length, in a ‗V‘ by a low mesquite or willow.

The doubled nets were 6m high. Two speakers were placed in the tree below the level of the nets and a variety of cuckoo calls were played. When cuckoos dropped below the level of the nets, two biologists jumped up yelling, startling the cuckoo and usually flushing it into the net. I added the last modification after observing numerous slow- flying cuckoos bouncing out of the net. I began capture efforts just after dawn, and if no cuckoos showed interest after 45 minutes, I moved to another site. I typically relocated two to three times each morning, and ceased attempts when the temperature exceeded

300C. This target netting technique is modified from methods currently used to capture

Willow Flycatchers (Empidonax traillii) (Sogge et al. 2001).

Using this method I was able to capture and band 52 adult cuckoos. Twenty-four of the birds either left the area or lost their transmitters within a few days of banding.

Most of my results are based on observations of the remaining 28 birds.

LITERATURE CITED

Corman, T.E. and R.T.Magill. 2000. Western Yellow-billed Cuckoo in Arizona: 1998 and 1999 survey report. Nongame and Endangered Wildlife Program Technical Report 150. Arizona Game and Fish Department, Phoenix, AZ.

Ericson, P.G.P., M. Irestedt, U.S. Johansson. 2003. Evolution, biogeography, and patterns of diversification in passerine birds. Journal of Avian Biology 34: 3-15.

Gaines, D. and S.A. Laymon. 1984. Decline, status and preservation of the Yellow- billed Cuckoo in California. Western Birds 15:49-80.

Hackett, S.H., R.T. Kimball, S. Reddy, R.C.K. Bowie, E.L. Braun, M.J. Braun, J.L. Chojnowski, W.A. Cox, K. Han, J. Harshman, C.J. Huddleston, B.D. Marks, K.J. Miglia, W.S. Moore, F.H. Sheldon, D.W. Steadman, C.C. Witt, and T. Yuri. 2008. A phylogenetic study of birds reveals their evolutionary history. Science 320: 1763-1767.

Halterman, M.D. 2000. Population status of the Yellow-Billed Cuckoo at the Bill Williams River NWR, Alamo Dam, Arizona, and Southern Nevada: Summer 2000. Report to the Bureau of Reclamation, Lower Colorado River Division.

Hughes, J.M. 1999. Yellow-billed Cuckoo (Coccyzus americanus). In The Birds of North America, No. 148 (A. Poole and F. Gill, eds.). The Birds of North America, Inc. Philadelphia, PA.

Laymon, S.A. and M.D. Halterman. 1985. Can the western subspecies of the Yellow- billed Cuckoo be saved from extinction? Western Birds 18: 19-25.

Laymon, S.A., P.L Williams, and M.D. Halterman. 1997. Breeding status of the Yellow- billed Cuckoo in the South Fork Kern River Valley, Kern County, California: Summary Report 1985-1996. Prepared for USDA Forest Service, Sequoia National Forest, Cannell Meadow Ranger District. Challenge Cost-share Grant #92-5-13.

Payne, R.B. 2005. The Cuckoos. Oxford University Press. Oxford, UK.

Sogge, M.K., J.C. Owen, E.H. Paxton, S.M. Landgridge, and T.J. Koronkiewicz. 2001. A targeted mist net capture technique for the Willow Flycatcher. Western Birds 32:167-172.

Chapter 1. Sexing Yellow-billed Cuckoos

Murrelet Halterman1

Program in Ecology, Evolution, and Conservation Biology

University of Nevada, Reno

Reno NV 89557

Lewis Oring

Natural Resources and Environmental Science

1000 Valley Rd.

University of Nevada, Reno

Reno, Nevada

Barbara Raulston LC8224

U.S. Bureau of Reclamation

P.O. Box 61470

Boulder City NV 89006-1470

1Murrelet Halterman P.O. Box 1316 Weldon CA 93283 (760) 417-0765 [email protected]

ABSTRACT

Current literature cites vocalizations and extent of white in the tail as viable methods for sexing adult Yellow-billed Cuckoos (Coccyzus americanus). We examined vocalizations, morphology (tail spots and measurements with discriminant function analysis), and sex-specific DNA markers as methods for accurately sexing Yellow-billed

Cuckoos. We used data from 52 adult cuckoos captured between 2001 and 2005 on the

San Pedro Riparian National Conservation Area, Arizona. Of the 52 samples, 49 were assigned sex based on DNA samples. There were no significant differences between sexes in vocalizations, tail spot patterns, or body measurements. The best function from the discriminant function analysis accurately classified 85% of males, but only 69% of females. There was a high degree of overlap in measurements between sexes, and no reliable method of morphologically sexing cuckoos emerged. There is no practical way to sex unbanded Yellow-billed Cuckoos in the field, and only sex-specific DNA markers can be used to reliably sex cuckoos. Increased interest by state, federal, and private conservation agencies in western populations of Yellow-billed Cuckoos has heightened the need for a better understanding of life history parameters of this species. Most of these questions can only be answered by intense population-level studies of marked, known-sex individuals.

Key words: Sexual dimorphism, Coccyzus americanus, sex determination, DNA analysis,

DFA, vocalizations

INTRODUCTION

Sexual dimorphism in birds is sometimes correlated with mating system, food partitioning, differential parental investment, individual quality, mate choice, intrasexual competition, role differentiation, or sperm competition (Emlen and Oring 1977, Price

1998, Dunn et al. 2001, Badyaev and Hill 2003, Delph 2005, Krüger 2005). The significance of dimorphism has been of interest since Darwin (1871), and is proposed to result from differential selection pressures between the sexes. These pressures may result from sexual or natural selection (Lande 1980, Price 1998, Badyaev and Hill 2003). Many bird species (e.g. Andean Cock-of-the-rock, Rupicola peruvianus; Ridgely et al. 2001) exhibit obvious sexual dimorphism in plumage. Moreover, birds exhibit substantial sexual dimorphism in size (e.g. Sage Grouse, Centrocercus urophasianus, male twice as large as female, Schroeder et al. 1999), vocalizations (e.g. most Parulidae warblers), and behavior (e.g. Buff-breasted Sandpiper, Tryngites subruficollis, males form loose leks;

Lanctot and Laredo 1994). In some species there are only subtle visible differences between sexes (e.g. bill length in the Long-billed Curlew, Numenius americanus, Dugger and Dugger 2002; eye color in Bushtits, Psaltriparus minimus, Sloane 2001). In others it is essentially impossible to determine sex in the field or even in the hand.

Distinguishing sex in monomorphic species is essential to understanding differences in behavior, vocalizations, and responsiveness. This need is especially acute in small populations where skewed sex ratios may have great impact on conservation strategies. This issue has at times been urgent, such as with the Kakapo (Strigops habroptilus), a large, flightless, and highly endangered parrot from New Zealand. In this species a supplemental feeding program resulted in a male bias in offspring produced

(Clout et al. 2002), thus complicating recovery efforts. Sex ratio also became an issue with the extinct Dusky Seaside Sparrow (Ammodramus maritimus nigrescens). Here intensive conservation efforts via captive breeding began when the population dwindled to five individuals; all of those captured turned out to be males (Zink and Kale 1995).

Morphometrics has proven useful in sexing a number of apparently sexually monomorphic species such as Dunlin (Calidris alpina; Meissner 2005), Black-legged

Kittiwake (Rissa tridactyla; Jodice et al. 2000), Dovekie (Alle alle; Jakubas and

Wojczulanis 2007), Red-tailed Hawks (Buteo jamaicensis; Donohue and Dufty 2006), and Pohnpei Micronesian Kingfishers (Halcyon cinnamomina reichenbachii; Kesler et al.

2006). Such studies used morphometric variables in a discriminant function analysis

(DFA) to sex individuals. DFA uses a weighted combination of predictors to assign individuals to one of two classes; in this case two sexes (Sharma 1996).

Recent advances in DNA sexing technology have made it possible to sex many avian species (Griffiths et al. 1998, Fridolfsson and Ellegren 1999), greatly enhancing studies of avian biology. Hundreds of species of birds from a wide variety of taxa have been correctly sexed genetically (confirmed with known-sex samples; Fridolfsson and

Ellegren 1999, Wang et al. 2007). Female birds are heterogametic, with the CHD-Z gene found in both sexes and the CHD-W gene found only in females. Polymerase Chain

Reaction (PCR) is used to amplify CHD genes found on sex chromosomes, and gel electrophoresis of PCR products results in two bands for females and a single band for males (Griffiths et al. 1998). This technique allows accurate sexing as well as testing of less expensive and less invasive techniques utilizing morphometric measurements, behavior, or vocalizations.

Yellow-billed Cuckoos (Coccyzus americanus) are a neotropical migrant found commonly throughout the eastern United States and in extremely low numbers in the western United States (Hughes 1999). Cuckoo populations in the western US have declined dramatically over the last 100 years (Gaines and Laymon 1984, Halterman et al.

2001). This decline has prompted increased interest in monitoring western populations by local, state, and federal agencies, as well as private conservation organizations.

Knowing the sex of individuals detected in the field is essential to interpretation of data on population size, home range, mating system, parental care, detection probability, and site fidelity, yet this species is sexually monomorphic (Hughes 1999, Pyle and Howell

1997). In view of the steep decline in western Yellow-billed Cuckoo populations, developing methods to sex these monomorphic birds is a high priority.

A number of avian taxa have proven difficult to sex using standard genetic techniques. For example, Ito et al. (2003) were only able to sex two out of eight species of falcons. E. Paxton (pers com) attempted to determine the sex of Yellow-billed

Cuckoos in 1999 using tissue samples collected from five museum specimens. He followed the techniques of Fridolfson and Ellegren (1999) using the CHD gene of non- ratite birds, but this resulted in multiple bands indicating multiple priming sites, and failed to identify the known-sex samples. He then tried two other universal sexing techniques (Griffiths et al. 1998, Kahn et al. 1998) with similar results. A separate attempt which repeated the same standard techniques on known-sex specimens resulted in a similar lack of positive results (R. Fleischer pers comm.). These attempts indicate that it may be difficult to genetically sex Yellow-billed Cuckoos. Recent advances in genetic sexing of birds, however, justify revisiting this issue.

Information about the behavior and vocalizations of male and female cuckoos is available primarily in unpublished government reports (Laymon 1998, Bennett and

Keinath 2001, Furtek and Thomlinson 2005). This information occasionally is found in peer-reviewed literature (Laymon and Halterman 1985, Hughes 1999, Laymon and

Williams 1999, Sibley 2001). Hughes (1999) states that males primarily give the

―Kowlp‖ call, described as a series of ―kuk-kuk-kuk-kuk‖ notes followed by ―kow-kow- kow‖ notes. Females are said to primarily give the ―Knocker‖ call, described as a series of ―kow-kow-kow‖ calls. There are several soft calls typically given near a nest, including a series of soft ―kow‖ notes and an alarm call, described as a repetitive wooden knocking call. A fairly common ―coo‖ call, consisting of a series of soft dove-like ―coo‖ notes, was assumed by Hughes (1999) to be given primarily by unmated males. If this is true it would be possible to assign sex to birds detected on surveys, determine sex ratio in the population, and begin to answer other questions about the information conveyed by vocalizations. There has never been a study of banded, known-sex birds to confirm these assumptions, and there is no description in published accounts of how sex was assigned.

Yellow-billed Cuckoos have large white spots on the underside of the outer rectrices. It has been suggested that cuckoos can be sexed based on size and pattern of these white spots (Suckerling and Greenwald 1998). If true, this would provide a means of accurately sexing cuckoos in the field. However, no test for sex differences in tail coloration has been done with individuals of verified sex.

Because female Yellow-billed Cuckoos are slightly larger than males (based on collections, Pyle and Howell 1997), it may be possible to use DFA to develop a function that will accurately sex individual cuckoos. It is worthwhile to explore discriminant

12 function analysis as an alternative to molecular sexing, because not all researchers take blood, feather, or tissue samples. If the technique proves effective it could be used to sex birds captured and monitored in the past. However, the use of morphometric sexing with

Yellow-billed Cuckoos must be verified with known-sex individuals.

Our objectives were to:

1. Determine if current DNA-based genetic sexing techniques work with

Yellow-billed Cuckoos;

2. Determine if Yellow-billed cuckoos exhibit sexual dimorphism in

vocalizations;

3. Determine if tail-spot characteristics can be used to sex cuckoos;

4. Determine if morphological measurements and DFA can be used to

develop a function to sex Yellow-billed Cuckoos.

Study Area The study took place from June-September, 2002 to 2005 on the San Pedro River, southeast of Tucson, Arizona. Our study site was on a 40 km stretch of the river within the Bureau of Land Management‘s San Pedro Riparian National Conservation Area. The river channel is lined with cottonwood (Populus fremontii) and willow (Salix sp.), with mesquite (Prosopsis sp.) and netleaf hackberry (Celtis laevigata) common on the upper floodplain.

METHODS We caught adult cuckoos using a species-specific targeted mist net technique, modified from methods used to capture Willow Flycatchers (Empidonax traillii; Sogge et al. 2001). After capture, each cuckoo was banded with a USGS metal band and a unique

13 color combination using 3 Darvic® color bands. A Holohil Ltd. BD-2 transmitter, weighing 1.95 gms (slightly less than 3% of the adult‘s body weight), was attached to the bird‘s central rectrices using dental floss (Bray and Corner 1972, Pitts 1995, Woolnough et al. 2004).

We collected blood and feather samples for genetic analysis. Blood was taken using either a radial or femoral vein puncture technique with blood suspended in lysis buffer and frozen. All samples were sent to Avian Biotech International (ABI) in Florida for genetic sexing. Results provided by ABI were compared to marked birds that we had tentatively sexed behaviorally.

Each bird was followed every two days until the transmitter failed or the bird left the area. When the radio-tagged bird was visible, all behaviors (e.g. sitting, flying, foraging, incubating, etc.), vocalizations, and prey items captured were documented.

During banding and telemetry we attempted to sex individuals using a combination of size and behavior. The sole purpose was to calibrate genetics results, not to develop an alternate method of sexing cuckoos. Birds with relatively large wing, tail, and weight measurements compared to published averages (Pyle and Howell 1997) were classed as females, while small birds were classed as males. We also determined sex using observations of copulations and nighttime incubation (performed by males in other species of cuckoos) (Payne 2005).

Recently published accounts of cuckoo vocalizations describe four main calls:

―kowlp‖, ―knocker‖, ―coo‖, and an alarm call (Hughes 1999). However, we have not found that contact calls can be readily categorized as ‗kowlp‘ or ‗knocker‘ calls but fit a general category of contact calls comprised of differing numbers of ‗kuk‘ notes followed

14 by differing numbers of ‗kow‘ notes. We categorized each contact call heard into one of six general types based on the proportion of kuk and kow notes: 1. kuks only, 2. more kuks than kows, 3. equal numbers of kuks and kows, 4. fewer kuks than kows, 5. kows only, 6. an alternating mix of kuks and kows. We examined vocalizations of genetically sexed cuckoos for patterns in call type given. We assumed that calls given during telemetry were representative of background calling rates, and not influenced by observer presence.

We measured wing chord and tail length to the nearest mm using a stainless steel machinist‘s rule with a brass stop. We measured mass to the nearest 0.5g using a

Pesola® 100g spring scale, and tarsus length, culmen length and depth to the nearest

0.1mm using dial calipers. Due to concerns regarding measurement errors between individuals (Yezerinac et al. 1992), one researcher measured 49 of the 52 cuckoos.

Photos were taken of the ventral side of the tail of cuckoos captured in 2004 and

2005. These photos were examined to determine extent and pattern of the white spots on the underside of the rectrices. Because these characteristics are intended for field identification of sexes, precise extent of white spots was of less interest than overall impression and quickly observed characteristics. Three characteristics were measured: 1. extent of individual white tail spots, with each spot covering less than or more than 50% of the rectrix, 2. upper tail spots touching, and 3. lower tail spots touching.

Statistical Analysis

We used two-sample T-tests (assuming unequal variances) to assess differences in morphological measurements and vocalizations of male and female cuckoos. We used vocalizations/hour to adjust for uneven sample size. We used stepwise discriminant

15 function analysis to determine if cuckoos could be sexed by morphological measurements, and logistic regression to fit a combination of morphological measurements to the sex of birds in the sample. The model then was tested against the data to determine its ability to accurately sex individual cuckoos. We analyzed the data using SAS ver. 8 (SAS Institute 2002).

RESULTS Genetic Sexing

We collected blood and feather samples from 52 adult Yellow-billed Cuckoos between 2001 and 2005. Based on behavioral observations and measurements we tentatively assigned sex for 24 individuals. We did not consider this an alternative to genetic sexing, simply a means of confirming the accuracy of genetic results. We sent blood samples from five of these birds to ABI labs in Florida using Permacode® blood collection cards. These blood and feather samples resulted in clear separation of two bands for females and a single band for males. Genetic results for the five birds agreed with our tentative sex identification. ABI subsequently assigned a sex to 49 of the 52 individuals in our sample: 34 males and 15 females plus 3 unknowns. All samples below were sexed genetically.

Vocalizations

A total of 52 cuckoos were captured during 2001-2005. Sixteen of these birds moved out the study area immediately after banding; the remaining 36 (ten females, 26 males) were observed for 853 hours over 338 days. The 36 birds gave a total of 1118 vocalizations during observations. No vocalizations were given exclusively by one sex, although some calls were given predominantly by one sex (Figure 1). Males gave call

16 types three (even kuk and kow) and four (less kuk than kow) significantly more often than females (call 3: t-test = 2.2, p < 0.05, N = 32; call 4: t-test = -2.64, p < 0.001, N =

32). Females gave call type six, the ‗coo‘ call, significantly more frequently than males

(t-test = -5.31, p < 0.001, N = 36). Two call types regularly given during telemetry, the soft kow and soft alarm call, were never detected during surveys. Because both sexes gave each call type, vocalizations are not practical as a means of differentiating sexes of unbanded cuckoos in the field. Although the two call types together might allow differentiation, this would only be feasible using repeat observation of uniquely marked individuals. This is not a practical means of sexing given the difficulty of capturing and marking cuckoos.

Tail Spot Patterns

We compared tail spot patterns of eight females and 12 males. Three of the females had extensive white in the tail vs. seven of the males. The top tail spots touched for one male and one female. The lower tail spots touched in most birds of both sexes.

Because these three characteristics overlapped between the sexes they cannot be used to differentiate sexes in the field.

Morphometric Analyses

Complete measurements and genetically-determined sex data were collected for a total of 40 cuckoos – 13 females and 27 males. We excluded seven second-year (SY) birds from the analyses because their mean measurements were smaller than after second- year (ASY) birds (Table 1). There were no significant difference in any measurements between ASY males and ASY females (Table 1). Sex differences in wing chord, weight, and tail length approached significance, but all measurements overlapped between sexes.

We used data from 40 ASY cuckoos to build a number of discriminant function models.

These models incorporated wing chord, bill length, bill depth, tarsus, tail, and weight measurements. None of the models performed well, classifying between 61% and 77% of females correctly, and between 74% and 84% of males correctly (Table 2). There was a large degree of overlap in all measurements, possibly a result of our small sample size.

We did not consider these models to be sufficiently accurate to pursue cutting scores

(minimum and maximum numbers to separate males and females).

DISCUSSION

Genetically based sexing has been used successfully on a range of sexually monomorphic bird species of conservation interest (e.g , Whooping Crane, Grus

Americana, Duan and Fuerst 2001; Takahe, Porphyrio mantelli, Eason et al. 2001; and

Scarlet Macaw, Ara macao, Nader et al. 1999, Baker and Piersma 1999; Shealer and

Cleary 2007, Wang et al. 2007). Unbanded cuckoos cannot be sexed based on vocalizations, tail spot characteristics, or morphology. Long-term observation of marked individuals and genetically based sexing appear to be the only reliable means for sexing

Yellow-billed Cuckoos.

Although both sexes gave all vocalization types, there were statistically significant differences in proportion of several vocalizations given by males and females.

These results cannot be used to differentiate sex of unmarked cuckoos in the field, however. The proportion of calls given by each sex could potentially be used to determine sex ratio of responding cuckoos, if calls given on surveys are in the same proportions as during telemetry (Table 3). The coo call previously has been reported as given primarily by unmated males (Hughes 1999, Suckerling and Greenwald. 1998), but

18 these observations were not based on marked known-sex individuals. This vocalization was given predominantly by females, both mated and unmated. The mates of four marked males cooed, while marked females‘ mates did not, further confirming the coo call as a predominately female vocalization.

There were no significant differences in morphological measurements between males and females (Table 1). The largest females and smallest males fell outside the range of overlap (Table 1). Wing chord showed the greatest difference between the sexes, with 33% of males having wings smaller than the wing chord of the smallest female (wing chord = 145mm), and 46% of females having wings larger than the wing length of the largest male (wing chord = 152). Contrary to grey literature accounts

(Suckerling and Greenwald 1998) there was no clear pattern in the extent and overlap of white spots on the underside of the tail, making this an unsuitable characteristic for sexing cuckoos in the field.

Discriminant function analysis was unreliable at sexing Yellow-billed Cuckoos.

Although accuracy with males was acceptable (85%), it misclassified 31% of females as males. This tool shows some potential, and with additional data could be a useful tool for sexing cuckoos in the hand. Capturing cuckoos is time and energy intensive. Any means of sexing cuckoos using morphology or repeat vocalization will be hindered by the difficulty of catching birds. Genetically sexing cuckoos is inexpensive (approx. $20).

We recommend any researcher who captures a cuckoo take blood or feather samples for genetic sexing.

Sexing based on copulation is accurate, but is of limited use because it is rarely observed. Additionally, Yellow-billed Cuckoos practice reverse mounting (Halterman

2006), where the female mounts the male. This can clearly result in incorrect identification of the sex of an individual. Groove-billed Anis (Crotophaga sulcirostris), another member of Cuculidae, also have been observed to reverse mount (Bowen 2002).

This behavior may be common in other cuckoos, but few species have been well studied.

Previous studies have reported behavior and numbers of male and female cuckoos detected based on unreported sexing techniques (Laymon et al. 1997, Halterman et al.

2001). Because there is no reliable means of sexing unbanded cuckoos in the field, sexual differences in behavior (e.g. philopatry, desertion, movement, and density- dependant behavior) can only be obtained from individually marked and genetically sexed cuckoos.

It is extremely difficult to capture Yellow-billed Cuckoos. During the last four years of this study, with an experienced crew, an average of two field days were required to capture each cuckoo. While not prohibitively expensive to sex individuals, it is very time-consuming to capture them. The use of molecular sexing undoubtedly will only be of value to individual and population-level studies, where banded birds are followed, and behavioral observations take place which can be linked to individuals of known sex.

Because of strong interest in this species by numerous state, federal and private conservation entities, this effort will be worthwhile to facilitate research on mating systems, primary sex ratio, movement patterns, and habitat selection.

More than twice as many males as females were captured during this study. It is possible our capture technique was skewed toward attracting males, and because a number of the radio-tagged birds left the area immediately after capture, we may have caught a disproportionately large number of transients. It may be that vocalizations we

20 used to lure cuckoos were conveying different information to males and females. Thus, it is not possible to obtain a population sex ratio from this skewed sample.

The majority of Cuculiformes species for which there is information show sexual dimorphism in body size (87%; Payne 2005). Plumage dimorphism is found only in old- world parasitic cuckoos (Payne 2005, Payne in del Hoyo 1997). The majority of species exhibit female-biased (female larger than male) body size dimorphism (57%), with 30% of species male-biased, and 13% of equal size. The variation is unrelated to parasitism, but may be related to new vs. old world subfamily representatives. In the old world nesting Cuculinae, for example, 67% of species show male-biased size dimorphism (N =

9), while in New World representatives 76% of species (N = 13) show female-biased size dimorphism. The most uniform group is the coucals (Centropodinae), with all but one species showing strong female-biased dimorphism in mass (89%, N = 18). This is a poorly studied group in which at least one species, the African Black Coucal (Centropus grillii), exhibits classical polyandry (Goyman et al. 2004).

CONCLUSION

There is currently a great deal of interest in cuckoo populations in the western

United States. Little research recently conducted examines basic natural history of this species. Social and mating systems of cuckoos are varied and complex. Without knowing sex of birds in a population it is difficult, if not impossible, to understand important life history parameters that directly impact population levels. These include sex differences in home range, territoriality, dispersal, site fidelity, divorce and mate switching rates, and parental care differences. Although DFA shows promise as a means

21 of sexing Yellow-billed Cuckoos, genetic sexing should be considered the best means for determining sex of individuals.

ACKNOWLEDGMENTS

Thanks to G. Clune, and J. Swett for providing logistical support. Thanks to B.

Childress, Dr. K. Blair, D. Gilbert, R. Tollofson, and J. Whetstone for their assistance.

Thanks to Gray Hawk Ranch for access to their property. Thanks to A. Hartman and J.

Bosi De Almeida for statistical assistance. Funding was provided by the U.S. Bureau of

Reclamation and Southern Nevada Water District. Logistical support was provided by the BLM San Pedro Field Office, the Bill Williams River NWR, and the Audubon

Society‘s Kern River Preserve. Many thanks to the many field assistants who assisted with data collection.

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TABLES and FIGURES

Figure 1. Proportion of each call type given by male and female Yellow-

billed Cuckoos on the San Pedro RNCA, 2002-2005.

* indicates significant t-test

0.25

0.2 * 0.15

0.1 * *

0.05 Proportion of all calls recordedof calls (%)all Proportion

Vocalization type

Female Males 29

Table 1. Mean measurements of male and female Yellow-billed Cuckoos captured on the San Pedro Riparian Conservation Area, 2002-2005. Means ± SD, Sample sizes (N) and ranges are given. t-test comparisons are between ASY males and ASY females.

Measurement ASY Female t-test* ASY Male SY female SY male

Weight (gms) 66.6 ± 6.7 (13) t = 1.46; p = 0.081 61.4 ± 5.2 (27) 55 ± 12.72 (2) 64.3 ± 9.32 (5)

46 - 80 50 - 73 46-64 54.5 - 75

Wing Chord 151.2 ± 5.0 (13) t = 1.56; p = 0.067 145.7 ± 3.4 (29) 146.5 ± 2.1 (2) 143.4 ± 5.03 (5) (mm) 145-164 139-152 145-148 136-149

Bill Length 20.6 ± 1.5 (13) t = 0.49; p = 0.32 20.2 ± 1.3 (28) 20.2 ± 0.98 (2) 20.5 ± 2.00 (5) (mm) 18.1 - 23.1 16.6 - 23.3 19.5 - 20.9 18.3 - 23

Bill Depth 9.1 ± 0.13 (13) t = 0.41; p = 0.34 8.9 ± 0.5 (28) 8.95 ± 0.35 (2) 8.9 ± 0.51 (5) (mm) 8.5 - 9.9 7.9-10.1 8.7- 92 8.3 - 9.4

Tarsus (mm) 31.64 ± 1.6 t = 0.62; 31.0 ± 1.8 (28) 30.45 ± 0.91 (2) 28.6 ± 4.33 (5) (13) p = 0.27

28.5 - 34.6 27.9 - 36 29.8 - 31.1 21.3 - 32.6

Tail (mm) 152.9 ± 8.8 t = 1.58; 146.3 ± 9.9 (29) 143 ± 1.41 (2) 142.4 ± 4.56 (5) (13) p = 0.062

140 - 173 126 - 168 142- 144 135 - 147 *t-test assuming unequal variance 30

Table 2. Discriminant funtion models for male and female Yellow-billed Cuckoos captured on the San Pedro RNCA, 2001-2005. (n = 13 females, 27 males).

% Correctly Classified Females Males Wilk's Model Variables included in model Lambda F #variables DF P

1 Wing, Tars, BillLength, 69% 78% 0.60970201 3.52 6 5 0.0084 BillDepth, Tail, Weight

2 Wing, Tars, BillDepth, Tail, 69% 85% 0.61275953 4.3 5 4 0.004 Weight

Wing, BillDepth, Tail, 69% 81% 3 Weight 0.6145919 5.49 4 3 0.0015

4 Wing, Tars, Tail, Weight 61% 85% 0.64197434 4.88 4 3 0.0031

5 Wing, Tail, Weight 61% 85% 0.64262652 6.67 3 2 0.0011

6 Wing, Weight 69% 85% 0.67636183 8.85 2 1 0.0007

7 Wing, Tail 77% 74% 0.68882067 8.36 2 1 0.001 31

Table 3. Percentage of Yellow-billed Cuckoo call types detected during radiotelemetry observations on the SPRNCA (2003 - 2005), and percentage detected during surveys.

Year surveyed

Vocalization type Telemetry 2003 2004 2005

1 16.2% 21.5% 22.3% 14.7%

2 21.4% 25.9% 30.0 % 40.5%

3 18.0% 23.5% 23.1% 21.8%

4 9.0% 15.1% 8.5% 9.1%

5 13.1% 4.1% 7.3% 7.1%

6 5.0% 6.4% 6.9% 2.8%

8 6.2% 2.3% 1.9% 2.4%

9 2.2% 1.2% 0.4%

13 8.9% 0.8%

Total calls 1118 375 297 259

Chapter 2. Response Rate and Detection Probability of

Yellow-Billed Cuckoos in Arizona

Murrelet Halterman1

Program in Ecology, Evolution, and Conservation Biology

University of Nevada, Reno

Reno, NV 89557

Lewis Oring

Natural Resources and Environmental Science

1000 Valley Rd.

University of Nevada, Reno

Reno, Nevada 89512

1Murrelet Halterman P.O. Box 1316 Weldon, CA (760) 417-0765 [email protected]

ABSTRACT

Understanding population status of declining species is central to effective management. Avian population estimates are typically based on surveys, however, if detectability is unknown, accurate assessment of status is challenging, and appropriate management is difficult. Little is known of detection rates of yellow-billed cuckoos, a species of management concern in the western United States. In 2004 and 2005, we captured and banded cuckoos on the San Pedro Riparian National Conservation Area, and equipped them with radio transmitters. We conducted a test of the standard call playback methodology with 18 marked birds. In 2005 we also conducted double-observer surveys.

Response rate during call playback tests averaged 59.5%, and was higher for males

(72.7%, n=10) than females (40%, n=8). Detection rates were lower than response rates, averaging 32.4% overall, and were higher for males (43.2%, n=10) than females (16.7%, n=8). Results from the double-observer tests indicated a much higher probability of detection for two surveyors (89.5%) than for a single surveyor (36%-57%). We recommend doubling detections from a single survey by two (a 50% detection probability) to estimate populations in habitats similar to the San Pedro RNCA. Survey results will likely detect less than half the population, be male biased, and will detect more mated than unmated cuckoos. Caution must be used when applying these results to other study sites and habitats, however, because we still know little of the effects of habitat, population density, patch size, or breeding status on response and detection rates.

INTRODUCTION

Government agencies often must monitor and estimate populations of declining species. Estimates are frequently based on surveys with little or no knowledge of factors affecting detection probability. Detection probability can be affected by observer, weather conditions, reproductive phenology, habitat, time of day, and individual responsiveness. Because surveys are of such importance in species conservation, they must be sufficiently accurate to allow credible population estimates (Emlen 1977). By determining the efficacy of current survey methods, we can improve population estimates, and better monitor populations.

Effective monitoring of most species requires a population estimate. A basic model for estimating population size is given by:

E(n i) = i N i (1) where (n i) = count of animals detected at a point i, i = probability of detection at point i,

N i = population size at a point i (Lancia et al. 1994). The assumptions of this model are:

1. a linear relationship between the count and population size, and 2. constant detectability over time and space (Lancia et al. 1994, Pollock et al. 2002, Bart et al.

2004). While it is difficult, if not impossible, to determine the relationship between counts and population size, it is possible to test detectability of known-location birds.

Playback of a species‘ vocalizations to increase probability of detection by eliciting a response (―call playback‖) is commonly used in surveys for rare or secretive birds such as clapper rails (Rallus longirostris) and willow flycatchers (Empidonax traillii) (Johnson et al. 1981, Sogge et al. 1997, Conway and Simon 2003). Response to playback depends on a variety of factors, including time of day, weather, breeding stage,

35 density, sex and age of individual, and proximity to playback (Kroodsma 1982,

Kroodsma 1986, Slater 2004). Effectiveness of playback must be tested with each species.

Yellow-billed cuckoos (Coccyzus americanus) are neotropical migrants found commonly throughout the eastern United States, and in low numbers in the western U.S.

(Hughes 1999). Cuckoo populations in the western U.S. have declined dramatically over the last 100 years (Gaines and Laymon 1984, Halterman et al. 2001). This decline has resulted in increased interest by state and federal agencies as well as private conservation organizations in monitoring western populations. Because cuckoos exhibit little territoriality, have large overlapping home ranges, and are quiet and secretive birds, it is difficult to get accurate population estimates (Laymon et al. 1997, Hughes 1999,

Halterman et al. 2007). Call playback is typically used to survey for this species, but the efficacy of this method is unknown.

Researchers generally have assumed that all cuckoos respond during surveys and show no decline in response rate over time. Detection probability is likely substantially lower than 100% (Emlen 1977, Thompson 2002, Bächler and Liechti 2007), which could be due to lack of response, observer error, or both. Changes in responsiveness over time will affect population estimates. A decline in responsiveness within a season could be due to habituation or change in breeding status. A highly variable response rate may be due to random responsiveness by cuckoos. In this paper we determine responsiveness and probability of detection of yellow-billed cuckoos using call playback with known- location birds. We also examine an alternative method of estimating detection

36 probability that does not require the costly and time-consuming process of capturing adult cuckoos.

Current Survey Methodology

A standardized survey methodology and data forms for yellow-billed cuckoos were developed in 1998 (Laymon 1998) and have been modified several times since

(Halterman et al. 2007). The methodology and data forms were developed through collaboration of the Southern Sierra Research Station, Arizona Department of Game and

Fish, and the United States Geological Survey - Colorado Plateau Field Station in

Flagstaff, AZ. This standardized method requires four complete playback surveys at each site during the field season (June-September). Sequential surveys are spaced 12 to 20 days apart and take place between 0530 and 1200. Call playback, described by Johnson et al. (1981) and Gaines and Laymon (1984), is used for all surveys. Surveyors wait at the survey point for a 1-minute listening period. This is followed by broadcasting the cuckoos' contact call (the "kowlp" call) once a minute for 5 minutes using a portable CD player with a handheld detached speaker. Five seconds of calling is followed by 55 seconds of listening.

Stops are made every 100 meters along the edge of, or within, riparian habitat, with the distances determined by GPS unit or pacing. Each time a cuckoo is detected the time of detection and type of vocalization is recorded. Locations are recorded using GPS and plotted as UTM coordinates on USGS quad maps. Birds are identified as either mated or mating status unknown based on observed behaviors. Mated behaviors include carrying nesting material, copulation, or the presence of a mate or nest. Playback stops as

37 soon as a cuckoo is detected and the surveyor moves 300m from that detection point before resuming the survey.

Assumptions

The current cuckoo survey method makes three major assumptions: 1. all cuckoos within 100m respond to a broadcast call; 2. individuals do not move more than

300m in response to a broadcast call; 3. surveyors detect all cuckoos that call within

100m. The efficacy of this widely used technique has not been tested. By determining probability of detection for yellow-billed cuckoos we can make more accurate estimates of local population size.

The first and second assumptions about a cuckoo‘s responsiveness can be measured using call playback with known location individuals. When individuals are equipped with radio transmitters, the response probability can be compared to background call rates to determine effectiveness of eliciting a response using call playback.

The third assumption can be tested using two different methods to estimate detection probability. The first estimate is calculated from the percentage of known location cuckoos that respond during a survey and are detected by a surveyor. In the second method (Double Observer) two observers survey the same route to estimate detection probability (Nichols et al. 2000, Forcey et al. 2006). The number of cuckoos detected by each surveyor is used to estimate detection probabilities.

The Double Observer method requires two surveyors working together on a point count (Nichols et al. 2000). The primary observer records detections and shares these detections with the secondary observer. The secondary observer records the primary

38 observer‘s detections plus additional birds not detected by the primary observer. Because we were using call playback on a species with a low response rate, we modified this technique so the second surveyor begins the route an hour after the first. We calculated detection probabilities based on equations from Nichols et al. (2000) for double observer data, modified for two independent observers:

pˆ 1 = (x11 x 22 - x 12 x 21) / (x 11 x 22 + x 22 x 21) (2)

pˆ 2 = (x11 x 22 - x 12 x 21) / (x 11 x 22 + x 11 x 12) (3)

pˆ = 1 – (x12 x 21 / x 22 x 11) (4) where pˆ 1 estimates detection probability by the first observer, pˆ 2 estimates detection probability for the second observer, and pˆ is the overall probability of detection. The value of xij is the number of cuckoos detected by surveyor i (i = 1, 2) when observer j was the first surveyor (j = 1, 2). The number of cuckoos detected by the first surveyor is x11, and x12 is the number of birds seen by surveyor one that were missed by observer two.

Objectives

1. Determine the responsiveness of marked cuckoos to determine the effectiveness

of survey techniques;

2. Determine if cuckoos habituate to a broadcast vocalization;

3. Determine the responsiveness of marked cuckoos 300 m or more from a broadcast

vocalization;

4. Determine detection probability with marked, known-location cuckoos;

5. Determine detection probability of cuckoos using double-observer surveys.

Study Area

The study took place during summers of 2004 and 2005 on the San Pedro River, southeast of Tucson, AZ. This site has one of the largest populations of yellow-billed cuckoos in the western United States (Corman and Magill 2000). Our study site was a 40 km stretch of the river within the BLM‘s San Pedro Riparian National Conservation

Area. The river channel was lined with a band of cottonwood (Populus fremontii) and willow (Salix sp.) that varied from 10 m to 500 m in width. Mesquite (Prosopsis sp.) and netleaf hackberry (Celtis laevigata) were common, varying from small, scattered plants to dense stands of large trees (>10 m tall) more than 1 km in width.

METHODS

We caught adult cuckoos in areas where multiple cuckoos had recently been detected. We placed a total of four 60-mm mist nets, ranging from 6 to 12 meters in length, in a ‗V‘ by a low mesquite or willow. The doubled nets are 6 m high. One person played a variety of cuckoo calls using two CD players connected by 15 m wires to two speakers placed 1 meter high in the mesquite or willow. Capture efforts typically began just after dawn. If no cuckoos displayed interest after approximately 45 minutes, we moved nets to another site. We typically relocated 2-3 times each morning, ceasing attempts when temperatures exceeded 300C. This target netting technique was modified from methods used to capture willow flycatchers (Empidonax traillii) (Sogge et al. 2001).

After capture we banded each cuckoo with a USGS metal band and a unique color combination using 3 Darvic® color bands. We attached a Holohill Ltd. BD-2 transmitter, weighing 1.95 gms (slightly less than 3% of the adult‘s body weight), to the bird‘s central rectrices using dental floss (Bray and Corner 1972, Kenward 1987, Pitts 1995,

Woolnough et al. 2004). The BD-2 had a 10-20 week life and an approximate ground range of 1 km.

We collected blood and feather samples for genetic analysis. We collected blood using either radial or femoral vein puncture and measured wing chord, tarsus length, tail length, culmen length and depth, and mass.

We followed all birds with transmitters every 2 days for 2-3 hours/day while the signal was detectable. When the bird was visible, we documented all behaviors (sitting, flying, foraging, incubating, etc.), vocalizations, and prey captures. We determined location by either visual detection or triangulation. We did not monitor birds during heavy rain or lightning storms.

Call Playback Testing

We tested cuckoos equipped with radio transmitters using call playback to determine response and detection rates. Testing began 2-3 days after banding, and was repeated every 4 days until the transmitter failed or the bird left the area. Two people conducted this single blind test. One person (―observer‖) directed the surveyor to within

100m of the focal cuckoo, and watched this bird throughout the test. The second person

(―surveyor‖) played the survey ―kowlp‖ call once a minute for five minutes, or until they detected the focal bird (following the standard survey methodology). The observer could not inform the surveyor if the bird called or moved, but the surveyor could ask if a call heard was from the focal bird. Whether or not the focal bird was detected, the surveyor moved 300m and repeated the process. Vocal response and movement were recorded separately by each person. Tests were conducted between 0800 and 1000, and not conducted if it was raining or wind exceeded 15mph.

For each test, we recorded trial number and breeding status. For each trial, responses were categorized as: 1. did not respond, 2. called, but did not fly toward the researcher, 3. flew toward researcher, but did not call, 4. called and flew toward researcher, and 5. flew away from the researcher.

Double Observer Trials

Two observers surveyed the same route on the same day. The first surveyor began one hour before the second surveyor, and the two did not communicate about the position of cuckoos detected. Any sightings within 300m on the same day were assumed to be the same bird. This was a basic assumption of the survey method, and was supported by telemetry data (Halterman 2006). This approach provided an estimate of the percentage of cuckoos present but not detected by both a single surveyor and two surveyors working together. We calculated detection probabilities for each observer independently as well as for both using these data. This method was used on 16 of 55 surveys conducted in 2005.

Statistical Analysis

For all analyses we used only data from known-sex birds. The first analyses used only data from the first call playback test (n = 18) to avoid psuedoreplication (Hurlburt

1984, Kroodsma et al. 2001). The dependant variable was either responded (yes/no) or detected (yes/no). The independent variables were: sex, cuckoo responded (yes/no),

Julian date, time, response type (1. did not respond, 2. called, 3. flew closer, 4. called and flew closer, 5. flew away), mating status, if the bird was nesting at time of test, distance from surveyor, and play number (one through five times the recorded vocalization was played). The independent variables ―responded‖ and ―response type‖ were not included

42 when ―responded‖ was the dependant variable, nor were they used in the same analyses.

We used PROC GLM (SAS institute 2003) to generate residual sum of squares. These were used to calculate AIC values for each set of models. In the second analysis we used a repeated measures analysis on known-sex birds with 4 tests (n = 11). We used

PROC GENMOD (SAS institute 2003) to generate log likelihood. These were used to calculate AIC values for each set of models. The same independent variables were used with addition of test number (1-4). We only considered models with three main effects to avoid overfitting.

We built and evaluated models from the call playback data following the information theoretic approach to rank candidate models (Burnham and Anderson 2002).

Akaike Information Criterion weights corrected for small sample size (AICc) were used to address model selection uncertainty (Burnham and Anderson 2002). Those models with the smallest AICc values are considered to be closest to reality. All models were compared to calculate ΔAIC, and models with ΔAIC < 2 were considered to have substantial support, those with ΔAIC > 2 but less than 4 had some support, and those with

ΔAIC > 4 had little support. We used model weights (wi) to determine the most parsimonious model explaining response and detection of marked yellow-billed cuckoos.

We used multi-model inference or model averaging to calculate weighted averages of variables in top models.

We analyzed the double observer survey data using formulae from Nichols et al.

(2000) and DOBSERV (Hines 2000). We used eqs 2, 3, and 4 (above) to calculate detection probabilities. We compared models using the Akaike Information Criterion with small-sample bias adjustment (AICc) computed by program DOBSERV, and

43 selected the model with the lowest AICc. We only considered the models P(.,.), which assumed constant detection probabilities for all species and observers, and P(.,i) which assumed constant detection probability for species but different probabilities for observers. The other models generated by DOBSERV assume that multiple species are being considered. Finally, we used detection probabilities to estimate the minimum number of surveys required to determine that cuckoos are not present in an area with a given level of confidence (Pellet and Schmidt 2005):

Nmin = log (1-desired confidence interval) / log (1-detection probability). (5)

RESULTS

Call Playback Trials

The average background calling rate of marked cuckoos was 1.1 calls/hour (n =

18, from 115 hours of telemetry observation). Call playback increased this rate to 10 calls per hour. During playback testing, cuckoo response rate was 59%, and detection rate was 32% (Table 1). Male response rate was 70% while female response rate was

16% (Table 1). Only males responded by both calling and flying closer; these were detected 85% of the time (Table 2). Forty-two percent of responses occurred in the waiting period after the first contact call was played.

There were nine candidate models with ΔAIC > 4 for cuckoo responses during the first call playback test. These included sex, nest, mating status, and time (Table 3). All models with ΔAICc < 2 included sex, and three included time. Model averaged parameter estimates suggest that mated birds (0.67 ± 0.34), those with nests (0.66 ± 0.45), and females (0.65 ± 0.46) in this sample are less likely to respond during call playback than unmated males. These results also indicate cuckoos were more likely to respond

44 during surveys conducted earlier in the morning. Confidence intervals (C.I.) for sex, time, and nest did not overlap zero, lending support to these results. The 95% C.I. for mated birds did include zero, indicating very low precision.

Models predicting detection using data from the first trial included response, mating status, time of survey, and distance to surveyor (Table 4). Only three of the models had ΔAICc less than four. Response and mated were in each of these models, and the model with these parameters had the highest weight of 0.35. Model averaged parameter estimates indicate that response (0.73 ± 0.40) has a strong negative effect on detection. This seems counterintuitive, because only cuckoos that responded were detected. This effect may be driven by both the small sample size and the relatively large number of cuckoos that responded but were not detected. The parameter estimate indicates that mating status (0.39 ± 0.46) had a positive effect on detection. The previous analysis indicated that mated birds were less likely to respond, but it is possible they respond in such a way (calling) as to be more detectable. The 95% C.I. for these parameters did not overlap zero.

Analysis of response to a series of four call playback tests resulted in ten candidate models with ΔAICc < 4 (Table 5). Seven of these top models contained mating status, and five contained sex. The weights for the top three models ranged from 0.12 to

0.19, indicating that although there is support for these models, no single model explained response of cuckoos over four repeat trials. Based on model averaged parameter estimates response appears to decrease for mated (0.85 ± 0.01) and nesting birds (0.84 ± 0.0002), and females (0.811 ± 0.01) when compared to unmated males. The

95% C.I. did not overlap zero for these parameters. The 95% C.I. for time and trial

45 number overlapped zero, indicating little support for inclusion of these variables in the models.

Sex was the only parameter in the set of top models for detection with four tests

(Table 6). Mated, nest, and distance were also in the top models (ΔAICc < 4). Model averaged parameter estimates suggest that females are detected less than males (0.80 ±

0.26) and nesting birds are detected more than those not nesting (0.60 ± 0.27). The 95%

C.I. overlapped zero for all parameters, indicating weak support for these models. The limited support may be due to the small samples sizes.

A total of 72 tests were conducted with 18 cuckoos at both 100m and 300m. Only two birds responded to call playback at a distance of 300m. Neither of these cuckoos was detected by the observer at this distance.

Double Observer Test

We compared two models from program DOBSERV and found the P(.,.) model was the most parsimonious (Table 7). This had a model weight of 0.72, suggesting that there was no difference in detection probabilities between the four observers conducting these surveys, though power is limited due to small sample size. We next calculated overall and primary vs. secondary observer detection probabilities using formulae from

Nichols et al. (2000) and compared these with probabilities from Program DOBSERV, raw call playback data and data used in the different models (Table 8). Detection probabilities were similar from raw data and data used in call playback models. We found higher probabilities for first observers (57%) than second observers (36%). The overall probability of detection with two observers calculated using Program DOBSERV were slightly higher (89%) than that calculated from equation 4 (80.7%).

Presence/Absence Surveys

Using the double observer method, a minimum of four surveys/season is required to determine with 95% confidence that cuckoos are absent from a site (Table 9). This assumes a single observer survey with a probability of detection of 57%. Twice as many single observer surveys are required to achieve the same level of confidence that cuckoos are absent using the 32% detection probability from the raw data.

DISCUSSION

Yellow-billed cuckoos are elusive and vocalize infrequently. Somershoe et al.

(2006) calculated a detection probability of 22% for yellow-billed cuckoos using program

DISTANCE with point count data in Mississippi. Background calling rates in our study indicate a probability of detection without call playback of approximately 10%. Call playback increases probability of detection to between 22.5% (from call-playback tests) to 57% (double observer test).

Yellow-billed cuckoos have a relatively low response rate during call playback tests. Although the use of playback increases the probability that a cuckoo will vocalize during a survey, the response rate for all trials was only 59%. Detection rate for all trials was even lower (32%), due in part to the type of response. Cuckoos that called were twice as likely to be detected as those that flew closer but did not call (Table 2). The double observer method increases the probability of detection. The use of two observers resulted in a substantially higher detection probability ( pˆ = 89.5%) compared to a single observer ( 1 = 57%, 2 = 36%). These surveys were conducted on some of the highest relative density routes on the SPRNCA. We recommend repeating this approach in areas with different habitat types and densities of cuckoos to assess their effectiveness in

47 detecting cuckoos. This technique is useful for comparing detection rates in different habitats because it does not require banded birds.

Cuckoos do not appear to habituate to a broadcast vocalization. Response rates appear to be more affected by sex and mating status than by repeated exposure to survey calls. Response rate and type was different for males and females, with males calling more frequently as well as flying closer to the surveyor and calling (Table 2). Females either called or flew in, but did not do both. The increased probability of detection of males is likely due to their response, because probability of detection is higher when a cuckoo is closer (Figure 1). Mated birds are more responsive than unmated ones, highlighting the importance of surveys being conducted later in the season when cuckoos are more likely to be mated and therefore more responsive.

The assumption that cuckoos do not respond from a distance of 300m appears to be functionally valid because response rate at a distance of 300m was less than 5%, with a 1% detection rate. This distance can therefore be used with confidence to separate individuals on a given day. A cuckoo will occasionally follow a surveyor over 300m, but this only appears to happen in sparse habitat (M Halterman, unpublished data). It is typically obvious when this occurs, and it is unlikely that a cuckoo will be counted twice under these circumstances.

Distance from observer appears to influence detectability (Table 4 and 6).

Schieck (1997) found that birds with call frequencies less than 2.5 kHz were always detected at 100m. The two most common calls of yellow-billed cuckoos (contact and coo) are in the 0.5 to 2 mHz range. In both the single trial and four trials models, distance from the observer had a weak influence on detectability. The 95% C.I. for the

48 model averaged parameter estimates overlapped zero, indicating weak support for inclusion of this variable in the model and indicating that further tests of detection distance need to be conducted.

The only factor affecting detection that we addressed was distance from observer.

Schieck (1997) used recorded vocalizations with nine avian species in a variety of aspen- dominated forest types to determine the effect of vegetation on detection. He found that vegetation type and height of the bird had a strong influence on detection. He concluded that although a correction factor could potentially be calculated for each species in each habitat type, doing so is nearly logistically impossible. Because we are working with a single species in a more limited range of habitats, such corrections may be worth pursuing for cuckoos. Such a test would be done in at least three habitats where cuckoos are commonly surveyed: Cottonwood/Willow; Mesquite/Hackberry; and mixed native/exotic. This test could be conducted using a surveyor and an observer with speakers placed at set intervals, and calls played at random times to determine detection rates.

Implications of Probability of Detection

Yellow-billed cuckoos showed a 40-70% response rate to call playback surveys, detection probabilities ranging from 22-57%, and little responsiveness to a distant surveyor. These low response and detection rates can negatively affect presence/absence surveys, population estimates, and long-term demographic studies. Attempts to accurately determine population size are complicated by financial and logistical considerations.

Despite this uncertainty, we feel that our findings can be applied to survey results to estimate cuckoo populations. We recommend using a double observer approach when feasible to increase probability of detection. When this is not feasible, we recommend applying a detection probability of 50% to survey results. In large continuous riparian patches we recommend doubling the number of detections from a single survey visit to estimate population. In smaller patches, such as isolated riparian restoration sites, we recommend using the number of detections during a single survey visit. Our work was conducted in extensive, continuous riparian habitat, and further research is required to determine detection probability in small discrete patches.

It is important to conduct multiple surveys at each site. Cuckoos frequently move great distances within an area, both before and between nesting attempts (Halterman per obs). Detecting cuckoos during multiple survey visits may indicate breeding activity.

Single detections early or late in the season may indicate migratory stopovers.

In this paper we have provided a means to correct for one source of bias in population estimation, detection probability. We have not addressed issues of precision in the data, varying probability estimates, and the applicability of these estimates to cuckoo populations in different locations, at differing population densities, and at different times in the breeding season. Additionally, further study is needed to determine the influence of time, location, population density, and breeding status on response and detection rates.

MANAGEMENT IMPLICATIONS

1. Population estimates can be conditionally calculated in habitats similar to the San

Pedro RNCA for single surveys using a conservative 50% detection probability.

Before this detection probability is applied to other habitats and populations,

however, additional research needs to be conducted in other habitats and with

other populations to determine the best estimate of detection. Also, this

probability of detection may change through the season, and will be male-biased.

2. Intrinsic and extrinsic factors, such as time of day, nesting cycles, weather, and

population density may affect detection probability. Because there is also

seasonal fluctuation in vocalization rate, multiple surveys need to be conducted to

determine population levels and monitor population trends and habitat use

patterns over time.

3. Detection probabilities may be density-dependant. Data from this project relates

only to a high-density population, and care should be exercised when applying

these results to medium and low density sites.

ACKNOWLEDGMENTS

We thank G. Clune, B. Raulston, and J. Swett for providing logistical support and the US Bureau of Reclamation and Southern Nevada Water District for providing financial support for this project. Thanks to Dr. K.Blair and D. Gilbert of the U.S.D.I.

Fish and Wildlife Service, BWRNWR for their assistance. Thanks to J. Whetstone and the Sierra Vista BLM office for logistical support and access to the Riparian

Conservation Area. Thanks to Gray Hawk Ranch for access to their property. Thanks to

J. Sedinger for editorial assistance and A. Hartman for statistical assistance. Thanks to dozens of hardworking field assistants for invaluable assistance.

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TABLES and FIGURES

Table 1. Number of yellow-billed cuckoos captured by year, sex, and mating status on the San Pedro River AZ, 2004-2005, and the response and detection rates during call-playback trials.

Responded Detected Total captured Total Total

Sex 2004 2005 mated Trials Total Percent Total Percent

Male 7 3 6 (of 10) 44 32 72.7% 19 43.2%

Female 4 4 6 (of 8) 30 12 40.0% 5 16.7%

Total 11 7 12 74 44 59.5% 24 32.4%

Table 2. Type of response to call-playback trials with marked yellow-billed cuckoos on the San Pedro River, AZ, 2004-2005 (n = 74 trials with 18 individuals). Bird response to call-playback was recorded by the observer.

Type of response

Type of response Called Flew Closer Called&Flew In No Response

Responded 27% 18% 16% 35% Detected 14.9% 5.4% 12.2% 0.0%

Female response (n=30) 20% 20% 0% 53% Male response (n = 44) 32% 16% 27% 23%

Table 3. Models for estimating response rates of marked yellow-billed cuckoos using model selection based on ΔAICc scores less than 4 during the first call- playback test on the San Pedro River AZ, 2004-05 (n=18). Columns are the number of estimated parameters (k), the difference between the best model and the other models corrected for small sample size (ΔAICc), model likelihood (L), and model weight (wi).

Model k ΔAICc L wi

Nest Sex Time 4 0.00 1.00 0.21 Sex Mated Time 4 1.27 0.53 0.11 Sex Time 3 1.63 0.44 0.10 Sex 2 1.76 0.41 0.09 Nest Time 3 2.25 0.33 0.07 Sex Mated 3 2.25 0.33 0.07 Time 2 2.44 0.30 0.06 Mated Time 3 3.04 0.22 0.05 Sex Nest 3 3.39 0.18 0.04 Mated 2 3.55 0.17 0.04 59

Table 4. Models for estimating detection rates of marked yellow-billed cuckoos using model selection based on ΔAICc scores less than 4 during the first call- playback test on the San Pedro River AZ, 2004-05 (n=18). Columns are the number of estimated parameters (k), the difference between the best model and the other models corrected for small sample size (ΔAICc), model likelihood (L), and model weight (wi).

Model k ΔAICc L wi

Response Mated 3 0.00 1.00 0.35 Reponse Mated Time 4 0.56 0.76 0.27 Response Mated Distance 4 1.38 0.50 0.18 Response Time 3 4.69 0.10 0.03

Table 5. Models for estimating response rates of marked yellow-billed cuckoos using model selection model selection based on ΔAICc scores less than 4 during call-playback tests 1-4 on the San Pedro River AZ, 2004-05 (n=44). Columns are the number of estimated parameters (k), the difference between the best model and the other models corrected for small sample size (ΔAICc), model likelihood (L), and model weight (wi).

Model k ΔAICc L wi

Mated Sex 3 0.00 1.00 0.19 Mated Nest Sex 4 0.57 0.75 0.14 Mated Trial 3 0.84 0.66 0.12 Mated Sex Time 4 1.36 0.51 0.10 Mated Nest Sex Time 5 2.06 0.36 0.07 Nest Trial 3 2.96 0.23 0.04 Mated Nest 3 3.09 0.21 0.04 Mated 2 3.37 0.19 0.04 Sex Trial 3 3.49 0.17 0.03 Sex Nest 3 3.83 0.15 0.03 Sex Nest Time 4 4.03 0.13 0.03

Table 6. Models for estimating detection rates of marked yellow-billed cuckoos using model selection model selection based on ΔAICc scores less than 4 during call-playback tests 1-4 on the San Pedro River AZ, 2004-05 (n=44). Columns are the number of estimated parameters (k), the difference between the best model and the other models corrected for small sample size (ΔAICc), model likelihood (L), and model weight (wi).

Model k ΔAICc L wi Sex Mated 3 0.00 1.00 0.27 Sex 2 0.10 0.95 0.26 Sex Nest 3 0.96 0.62 0.17 Mated Sex Nest 4 1.37 0.51 0.14 Distance 2 3.67 0.16 0.04 No Effect 1 4.40 0.11 0.03

Table 7. ΔAICc values for DOBSERV models for independent- observer approach for yellow-billed cuckoos surveyed on the San Pedro River AZ, 2005.

Model k ΔAICc AICc weights

P(.,.) 3 0.00 0.73

P(.,I) 3 1.98 0.27

0.9 0.8 0.7 0.6 0.5 Male 0.4 Female 0.3 0.2 Probability Detectionof Probability 0.1 0 20 30 40 50 60 70 80 90 100

Distance (m)

Figure 1. Probability of detection for male and female yellow-billed cuckoos during call-playback tests on the San Pedro River, 2004-2005 (n=40).

Male Female Overall

Raw data 42.5% 16.7% 32.4%

1-trial models 33.3% 25.0% 27.8% 4-trial models 33.3% 6.3% 22.5% Double observer - surveyor 1 57.0% Double observer - surveyor 2 36.0% Double Observer - hand calculation - Overall 80.7% Double observer - DOBSERV 89.5%

Double observer surveys Call-playback method test four surveyor 1 raw data one-trial trial Detection Probability 0.57 0.32 0.28 0.23

Percent confidence desired

70% 1 3 4 5 80% 2 4 5 6 90% 3 6 7 9 95% 4 8 9 12

Chapter 3. Home Range, Site Fidelity, and Double-Brooding of

Yellow-Billed Cuckoos on the San Pedro Riparian National

Conservation Area, 2001-2005 and Implications for Management.

Murrelet Halterman1

Program in Ecology, Evolution, and Conservation Biology

University of Nevada - Reno

Reno NV 89557

Lewis Oring

Natural Resources and Environmental Science

1000 Valley Rd.

University of Nevada – Reno

Reno, Nevada

1Murrelet Halterman Southern Sierra Research Station P.O. Box 1316 Weldon, CA (760) 417-0765 [email protected]

ABSTRACT

State and federal agencies and private conservation organizations in the western

United States are concerned with management of diminishing Yellow-billed Cuckoo populations. This includes restoration of riparian habitat in addition to management of existing habitat. There is limited information on home range size in the Yellow-billed

Cuckoo, yet this is crucial and basic information required for management. We monitored 28 cuckoos equipped with radio transmitters on the San Pedro Riparian

National Conservation Area during 2001-2005. Each bird was monitored for at least one week. Home ranges were calculated using both 95% minimum convex polygon (MCP) and kernel density estimator (KDE) methods at 50%, 75%, and 95% probability.

Average home range estimates were MCP - 51 ha, 95% KDE - 39 ha, 75% KDE - 17 ha, and 50% KDE 7.5 ha. There were large variances for all home range estimates. There was no significant difference in home range size for nesting or non-nesting, or mated or unmated cuckoos. Males and females had significantly different home ranges sizes, with female home ranges estimated to be 60% smaller than those of males for all three KDE estimates. Cuckoos showed limited site fidelity during this study. Double-brooded cuckoos moved significantly farther to renest if their first nest was unsuccessful.

INTRODUCTION

Most animal populations are spatially structured due to availability of resources such as food, mates, nest sites, or wintering sites (Burt 1943, Worton 1989, Adams 2001,

Lopez-Sepulcre and Kokko 2005). The concept of home range (HR) has been used widely to describe aspects of this structure and can be used to designate breeding range, foraging areas, and/or wintering areas (Burt 1943, Worton 1989). The home range concept is frequently applied to studies of habitat selection, animal movement, energetics, and space use as predicted by allometry, guild type, and other aspects of life history theory (Silva et al. 1997, Ottaviani el at. 2006). Knowing a species‘ home range size, as well as its site fidelity, is fundamental when modeling territoriality, population regulation, optimal habitat use (Both and Visser 2003, Prasad and Borges 2006), and for conservation planning (Franzreb 2006, Germano 2007, Sharpe and Goldingay 2007).

Home range is typically estimated as the probability of an individual occurring in an area during a given time period (Kenward 2001). Two commonly used estimators of home range size are minimum convex polygon (MCP) (Mohr 1947), and kernal density estimates (KDE) (Worton 1989). With MCP, a minimum area containing 95% of location points from an individual is plotted, with a polygon fitted using a frequency distribution of activity of the animal within the range.

Silverman (1986) described KDEs as producing a density estimate directly from the location points, uninfluenced by effects of grid size and placement. The kernel method places a selected probability density (95%, 75%, and 50%) around each observation point in the sample (Seaman and Powell 1996). The total area contained in this probability density is then summed for the HR estimate. Hemson et al. (2005) state

69 that KDEs have several advantages over MCP because they accommodate multiple centers of activity, do not rely on outlying points to define the perimeter, and because outliers have a lower probability density, KDE excludes largely unused areas.

Several potential issues with accuracy of HR estimation are number of points collected per animal (Hansteen et al. 1997, Seaman et al. 1999, Barg et al. 2005, Börger et al. 2006a) and serial autocorrelation of data (Otis and White 1999, Feiberg 2007, De

Solla et al. 1999). A review of HR studies by Börger et al. (2006b) found that the greatest variation in HR estimates was explained by individual or study area, rather than number of points taken. They found KDE to be less biased than MCP. They additionally found that although precision and accuracy increased with a sample size larger than 10 points/individual, the contribution to total variation in estimates of home range size for individuals was minimal.

All home range data are autocorrelated to some extent, because an animal‘s location during one measurement interval will inevitably impact its location during the next measurement interval. De Solla et al. (1999) found that accuracy of home range estimates improved with shorter time intervals in spite of increased autocorrelation. They did not find that serial independence of observations was required for kernel density estimates.

Laver and Kelly (2008) reviewed different home range estimators and studies using these estimators. They found that many studies failed to use the appropriate HR estimator, failed to report sample size or address serial autocorrelation, and made inappropriate comparison to other studies. They made recommendations for implementing and reporting future home range studies which included reporting software

70 used and range of values in the dataset. These recommendations and different HR estimators are designed to ensure the least biased and most accurate estimate given available data, and improve understanding of estimate limitations.

Home range estimates are required for appropriate management of most species.

Where a species spends its time is often affected by breeding stage and sex. An individual should use the smallest space possible to minimize energy expenditure while gathering resources (Badyaev et al. 1996). Accurate knowledge of a species‘ HR assists efforts at habitat restoration, determination of population size, and description of habitat requirements.

Home range size describes a species habitat use on a patch scale, while natal and post-breeding movement addresses habitat use on a landscape scale, the foundation of metapopulation dynamics (Hanksi and Gilpin 1997). This movement may be affected by a number of factors, including population size, resource availability, and prior reproductive success (Pulliam 1988, Greenwood 1980, Hoover 2003). Movement can be determined by marking a large number of individuals and determining their rates of dispersal and philopatry. Dispersal rates are poorly understood in most species, primarily due to the difficulty of adequately covering a sufficiently large geographic area

(Greenwood and Harvey 1982, Winkler et al. 2004).

Site fidelity, the return of birds to a natal or breeding site, typically is determined by uniquely marking individuals in multiple populations and recording their return in subsequent years (Greenwood and Harvey 1982). Although site fidelity and movement are important components of management for species of conservation concern, they are

71 poorly understood, and often difficult to quantify with elusive, rare, or hard-to catch species.

Many species of neotropical migrants are capable of producing multiple successful nests per season, a phenomenon known as double or triple-brooding.

Numerous studies have related multiple broods to productivity (Gonzalez-Solis et al.

1999, Holmes et al. 1992), but fewer have examined its influence on home range size and site fidelity (Friesen et al. 2000, Hoover 2003, Kershner et al. 2004, Nagy and Holmes

2005, Paxton et al. 2007). Some species produce a second nest within the same home range/territory, while others move to a new territory before a subsequent nest is initiated.

Freisen et al. (2000) examined double-brooding in Wood Thrush (Hylocichla mustelina), and found that outcome of the first nest had no significant effect on distance moved to the subsequent nest. Kershner et al. (2004) also found no significant difference between successful and unsuccessful nesters in movement between nests in Eastern Meadowlarks

(Sturnella magna). Paxton et al. (2007) found that Southwestern Willow Flycatchers

(Empidonax traillii extimus) occasionally switched territories before initiating a second nest. If an individual moves for each nesting effort, this could significantly increase size of home range required for each breeding pair. Additionally, distance to a subsequent nest may differ depending on outcome of the previous nest.

Populations of Yellow-billed Cuckoos (Coccyzus americanus) west of the

Continental Divide have experienced sharp declines over the last 100 years (Gaines and

Laymon 1984, Hughes 1999), and are of conservation interest in most western states.

Cuckoos in the western U.S. are riparian specialists, and their decline is directly linked to massive loss of riparian habitat. Millions of dollars will be spent on surveys and habitat

72 restoration in the next decade, yet little is known of home range, habitat requirements, or site fidelity. Yellow-billed Cuckoos are a secretive neotropical migrant that vocalizes infrequently, exhibits little territoriality, and occurs in large patches of structurally complex habitat (Hughes 1999). Although home ranges appear to be large, the only home ranges measured with radiotelemetry are MCP estimates of 17 ha from two unsexed adults on the South Fork Kern River in 1985 (Laymon and Halterman 1985). It is unknown if home range size is influenced by sex, breeding status, or nesting status.

Nothing is known of site fidelity. Yellow-billed Cuckoos are not synchronous nesters, and regularly produce second and third broods (Hughes 1999). It is unknown how this behavior affects home range size. Without greater knowledge of home range and habitat use during the breeding season it is difficult to manage riparian habitat for cuckoos.

METHODS

Study Site

Research was conducted on the BLM‘s San Pedro National Riparian Conservation

Area (SPRNCA) in Southeastern Arizona from June-September 2001-2005. The river channel is lined with cottonwood (Populus fremontii) and willow (Salix sp.), with mesquite (Prosopsis sp.) and netleaf hackberry (Celtis laevigata) common on the upper floodplain. The floodplain vegetation varies in width from 50-1000m.

Additional data on cuckoos are presented from two other sites. The South Fork

Kern River in southern California is a 536 ha riparian preserve managed by National

Audubon Society for conservation. The Bill Williams River National Wildlife Refuge contains 518 hectares of riparian habitat in western Arizona, and is managed by the

USFWS for conservation.

Telemetry

We captured 52 adult cuckoos from 2001-2005 using a targeted mist net technique, modified from methods used to capture Willow Flycatchers (Empidonax traillii) (Sogge et al. 2001). After capture we weighed and measured each bird. It was then banded with a USGS metal band plus three uniquely combined Darvic® color bands. Next, blood and feather samples were collected for genetic sexing. Finally, we attached a Holohill Ltd. BD-2g transmitter, weighing 1.95 gms (slightly less than 3% of adult body weight), to the bird‘s central rectrices using dental floss (Bray and Corner

1972, Pitts 1995, Woolnough et al. 2004).

We followed banded birds every two days until the transmitter failed or the bird left the area. A hand-held telemetry receiver and Yagi antennae were used to locate cuckoos. When the radio-tagged bird was visible we recorded all behaviors (sitting, flying, foraging, incubating, etc.), vocalizations, and prey captures. We also recorded

UTMs using a handheld Garmin GPS unit every hour during observation, typically resulting in three UTMs per observation session. Because visual detection of cuckoos was possible for most of the observation period, no triangulation was required to ascertain location.

Home Range Analysis

Width of kernel must be determined prior to estimating the density of kernels used when estimating home range. Width of kernel is determined using a smoothing parameter or bandwidth. Width of kernel determines the scale of detail, so a narrow kernel shows small-scale detail of the data, while a wide kernel shows general shape of the distribution (Seaman and Powell 1996, Blundell et al. 2001). Kernel size can be

74 either fixed at a predetermined level or adaptive, which is dependent on the point density.

Seaman and Powell (1996) found that a fixed kernel estimator with a least squares cross validation, used to select the smoothing parameter, gave the least biased area estimate.

We used Program Biotas version 1.03 to calculate home ranges for 95% minimum convex polygon and 95%, 75%, and 50% fixed-kernal density estimators (BiotasTM

2004). KDE was calculated using a least squares cross-validation (Seaman and Powell

1996). We used two-sample t-tests assuming unequal variance to examine differences in mean home range between sexes, mated and unmated, and nesting vs. non-nesting cuckoos. There were insufficient data to test differences between years, between second year and after second year birds, or nesting vs. fledgling care periods for nesting birds.

There were not sufficient data to examine home range overlap for mated pairs, as there were only two mated pairs in the sample. We analyzed weekly changes in home range data for a subset of individuals to determine if our limited data set approached an asymptote during the observation period.

To determine the influence of different variables on observed home range results, we evaluated models following the information theoretic approach to rank candidate models (Burnham and Anderson 2002). We used Akaike Information Criterion weights corrected for small sample size (AICc) to address model selection uncertainty (Burnham and Anderson 2002). Models with the smallest AICc values are considered to be closest to reality. We used model weights (wi) to determine the most parsimonious model explaining home range of marked Yellow-billed Cuckoos.

We did four analyses, one for each home range estimator, with the following independent variables: sex, mated, nesting, and year. We used PROC GLM (SAS

Institute 2003) to generate residual sum of squares. These were used to calculate AIC values for each set of models.

Site Fidelity

During the five years of this study we attempted to visually examine all cuckoos detected for bands. W recorded retuning birds‘ locations to determine territory fidelity

(return within 300m of banding/nesting site) and site fidelity (return to the drainage where banded).

Movement Between Nests

Double-brooded cuckoos were observed a number of times during research on the

South Fork Kern River in CA (1992), San Pedro RNCA, AZ (2001-2005), and Lower

Colorado River, AZ (2008). Nests were identified as second broods by either presence of banded or telemetered adults, or by timing and proximity to another nest (<100m). We measured distance between nests using either a 50m tape or a handheld GPS unit. We used a t-test with unequal variances to test for differences in distance to second nest between successful and unsuccessful first nests. A nest was defined as successful if at least one fledgling was produced. Three cuckoos in the sample had more than two nests in one season. We included only the first two nests for each bird in our analysis to avoid psuedoreplication (Hurlbert 1984).

RESULTS

We captured 52 cuckoos between 2001 and 2005. We followed 28 of these for at least one week. Twenty-four cuckoos (excluded from analyses) left within two days after banding, lost the transmitter within a few days of banding, or had insufficient data points

(fewer than 10) to estimate their home range size.

Cuckoos were observed for a total of 524 hours, with an average observation time of 23 hours per bird (range 7-60 hours). This represents 243 separate days of observation, with an average of 11 days per bird (range 4 to 25 days). We collected 10 to

72 UTM locations per bird, and used an average of 29 points to form each home range estimate.

Home ranges were highly variable among individuals regardless of sex, mating status, or nesting status (Table 1). Males and unmated birds both had larger home ranges than females and mated birds respectively (Figure 1), but HR size differed significantly between sexes only for KDE estimators (Table 1). Female home ranges were less than half the size of male home ranges for all KDE estimates. The average 95% MCP home range size for cuckoos on the SPRNCA was 51 ha (Table 1). The average 95% kernel

KDE home range size was 38.6 ha. Home range sizes for nesting and non-nesting birds were similar (Figure 1, Table 1).

There was a single supported model for the 95% MCP, 95% KDE, and 50% KDE home range estimates (Table 2, 3, and 4). Mating status and sex had a strong influence on home range size for the first two estimates, while only mating status had an influence on 50% KDE. The top four models for 75% KDE analysis all had year as a parameter

(Table 5). Models 2-4 had mated, nest, and sex as parameters.

A typical HR for a female cuckoo with a nest is shown in Figure 2 (n=38 points).

The 95% MCP (55 ha) shows the range of areas covered, while the 50% KDE (10 ha) shows core areas of activity (foraging and nesting). The 95% KDE (61 ha) includes extensive grassy areas between points. The 75% kernel (23 ha) may be a better

77 representation of her foraging area, with the 95% kernel showing occasional forays from the nest. Several unused areas reflect the San Pedro River or grassy areas.

One individual had the most points (n=72) and the largest 95% MCP home range

(208 ha) in this study. Male 4-2004 initiated four nests, though none were successful.

He covered a large area, but most of the 95% MCP is open grassy fields where cuckoos spend little time. There was an order of magnitude difference between MCP and 95%

KDE (23 ha).

Site Fidelity

We resighted five of 52 adult cuckoos banded from 2001-2005. There were insufficient resights to allow statistical analysis of data. This low return rate may be partially due to the difficulty of seeing bands on a perching cuckoo. In 2005 we documented how often we were able to examine a cuckoo‘s legs for bands. We only had

20% success with cuckoos detected on surveys, and about 40% for cuckoos detected while nest searching (Halterman 2006).

Movement Between Nests

Sample size for this analysis was limited due to the difficulty of finding cuckoos with two or more nests. A total of 27 nests were located for 12 cuckoos. Ten birds were banded, and two were identified by timing their close proximity to a prior nesting attempt in the same season. Two birds had three or more nests in a single season. For these individuals we excluded the third and fourth nests to avoid pseudoreplication (Hurlbert

1984).

Average distance renesting cuckoos moved following nest failure was 697 meters

(range 478-1000m, n = 3), while the average moved after a successful nest was 131

78 meters (range 27-263m, n = 9). Although our sample size is very small, there was a significant difference for movement between nests dependant on outcome of the first nest

(t = 2.76, p < 0.05, n = 12).

DISCUSSION

Intraspecific variation in space use is poorly understood, and typically is described, rather than explained (Börger et al. 2006a). It is particularly difficult to explain space use in Yellow-billed Cuckoos because of huge variation in home range size among individuals. Breeding cuckoos occupy large overlapping home ranges, they exhibit little territoriality, and home ranges appear to be flexible. They seem to shift use areas within home range during a season, perhaps dependant on resource availability or nesting habitat. Male 4-2004 shifted core area with each of four nest attempts during nearly two months of observation. These home range shifts resulted in a huge 95% MCP home range (208 ha), and while 95% KDE was only 23 ha, access to a larger habitat patch may be an important consideration for both cuckoos and land managers.

The minimum number of locations generally required to reach asymptote home range estimates is 50 (Otis and White 1999). Due to transmitter failure we were seldom able to obtain more than 40 locations for any individual, and averaged 29 locations per bird. There were insufficient points to calculate the asymptote at which home range size stabilized. In order to determine if home range estimates from our data approached asymptote we grouped sightings cumulatively by week (approximately 10 locations/week) for eight individuals with at least four weeks of observation (Figure 3).

All birds were mated. Four birds, one male and three females, appeared to reach asymptote after three weeks of observation. These birds were either incubating eggs or

79 feeding nestlings. The other four, two males and two females, continued to increase home range throughout the four weeks of observation. The females both renested during telemetry, moving several hundred meters for second nests. Males were feeding fledglings, which are capable of moving great distances after fledging. These adults were apparently following their young, and an analysis of weekly home range size might reveal quite a different pattern.

We see a similar result by using data for all 28 cuckoos, summed by total points collected for each individual (Figure 4). Although 95% MCP continues to increase with each increase in locations, the three KDE appear to stabilize between 30 and 40 points.

The conflicting pattern of MCP and KDE is explained by the calculation methods. A few outlier points may increase MCP, but if these areas are not regularly used, there will not be a concomitant increase in KDE home range.

Home ranges of females are about 40% percent as large as male home ranges.

This difference could be associated with sexually selected foraging patterns (Holmes

1986, Mills 2005) or by mating system (Emlen and Oring 1977), but there were insufficient prey capture observations to determine if observed HR size difference was due to differences in foraging patterns. Mated birds had smaller home ranges than unmated ones, but not significantly so. Yellow-billed Cuckoos are probably monogamous, serially monogamous, or both (Halterman pers obs). Males may be seeking EPCs in a larger home range, or they may be prospecting for mates for subsequent nesting attempts.

Makarieva et al. (2005) predicted that home range size and population density should scale isometrically with body size. They examined 33 species of avian predators

80 with known home ranges. The only species close to Yellow-billed Cuckoos in size was the Great Grey Shrike (Lanius excubitor). This species had a reported MCP home range of 65 ha (Yousef et al. 1991). The somewhat smaller Scarlet Tanager (Piranga olivacea)

(weight 30-38 gms) used a much smaller home range of just under 6 ha (95% KDE)

(Vega Rivera et al. 2003). Average HR size for cuckoos in this study fell between those of these othe two species, although there was great variation in home range size. Many cuckoos on the SPRNCA renested following both successful and unsuccessful nesting attempts. These subsequent nests were sometimes hundreds of meters away from previous nests (Halterman per obs), resulting in large MCP and 95% KDE.

Use of space by animals is determined by many factors and varies spatially and temporally for most species (Levin 1992). Breeding home ranges measured in this study do not appear to be used exclusively by a single pair of cuckoos. Rather there is a great deal of home range overlap, at least in some locations and in some years. Some species of birds exhibit a range of behaviors dependant on resource availability and population density (Both and Visser 2003). We do not know if cuckoo‘s apparent lack of territoriality is due to an abundance of food, low population densities, or some other factor (Newton 1992).

In 2004 we monitored a number of individuals using overlapping areas. One group of five individuals, plus several other unbanded cuckoos, often were seen within

100m of each other (Figure 5-a). The 95% MCP for the group was 75ha. Another group of three individuals monitored in 2004 also showed a great deal of home range overlap

(Figure 5-b).

Area use by individuals shifts during the breeding season. We radiotracked

Female 1-02 for seven weeks. During this time she initiated three successful nests and had a 95% MCP of 28 ha. Figure 6 gives a visual representation of her shifting home range use over time. Each multicolored oval represents a 50% and 75% frequency ellipse based on single week‘s results. This female shifted her center of activity through time, and with each successive brood.

There is a fairly extensive literature on renesting, and many single-brooded species move substantial distances after failure of their first nest (Greenwood and Harvey

1982, Catlin and Rosenberg 2008). The opposite pattern has been observed in Hooded

Warblers (Wilsonia citrina), with second nests closer to the site of a failed nest than a successful one (Howlett and Stuchbury 1997). This has also been observed in Eastern

Meadowlarks (Sturnella magna) and Bobolink (Dolichonyx oryzivorus) (Perlut et al.

2006, Kershner et al. 2004). There is limited data on the spatial relationship of multi- brooded species to the first nest, but limited published accounts indicate that many species move further after a successful nest than after an unsuccessful one, possibly to avoid noisy fledglings (Howlett and Stuchbury 1997).

Between-year site fidelity may be influenced by nest success the previous year

(Greenwood 1980, Paradis et al. 1998, Gonzalez-Solis et al. 1999, Hoover 2003, Paxton et al. 2007). Our five resights were all close to their banding location, and all successfully nested the year they were banded. Two males were banded in 2001; one was resighted in 2004 and the other in 2005; each was only 25m from where they were banded years before. The three other resights, two males (banded in 2003) and a female

(banded in 2004), were each seen the following year several km from their banding site.

The female was resighted again a third year, several km from where she nested the previous year.

Determining factors affecting site fidelity requires a thorough knowledge of age- specific mortality rate, age-specific reproductive success, habitat stability, and availability of food resources, mates, and suitable breeding areas (Newton 1998). The low return rate during this study may simply indicate that cuckoos are highly mobile, but other factors may be involved such as detectability, mortality, highly variable food resources, and scarcity of mates.

Yellow-billed Cuckoos on the SPRNCA appear to be regularly double-brooded, and occasionally triple brooded, based on behavior and timing of nests. Little work has been done on movement between broods for multi-brooded species. Most work has been done on renesting following failure of the first nest. The few published studies of double- brooded species found that distance to the second nest was either not significantly different for successful vs. unsuccessful females or females moved farther after a successful nest than an unsuccessful one (Howlett and Stutchbury 1997). An exception to this was found among female Dickcissels (Spiza americana) moving over 10 km from their first, unsuccessful, nest (Walk et al. 2004).

There are several limitations of this study. We captured a larger number of males than females (19 males vs. 9 females). It is possible that the comparison of home range size by sex is biased. Additionally, observation periods were fairly short for each bird, leading to a greater probability of autocorrelation. We may underestimate home ranges due to the small samples sizes during a short period of time. There were insufficient data to determine if males move farther than females on individual flights. These data are

83 limited to cuckoos that responded strongly enough to playback vocalizations to be captured. This may not be a representative data set, and the data set is skewed toward males and mated birds. This is to be expected, because males and mated birds had a higher rate of responsiveness (Halterman, Chapter 2).

Yellow-billed Cuckoos at this study site were not regularly detected on surveys until late June, and breeding in some years did not begin until late July (Halterman 2006).

Cuckoos at other western locations appear to typically single brood (Laymon et al. 1997).

The breeding season for cuckoos in southeastern Arizona appears to be prolonged, however, and in most years conditions are apparently right for producing multiple broods.

With our limited data set for 12 individuals apparent nest success was high for first nests

(75%) and moderate for second nests (58%). In spite of this relatively high success rate, there does not appear to be a strong correlation between nest success and site fidelity in this population. Cuckoos seem to be a highly mobile species, with little territoriality or site fidelity and large home ranges that shift throughout the breeding season. Appropriate management of this species in the western U.S. requires additional information on their movement and home range size in other locations.

MANAGEMENT IMPLICATIONS

There is currently heightened interest in appropriate management of Yellow- billed Cuckoos in the western United States. The Lower Colorado River Multi-Species

Conservation Plan (http://www.lcrmscp.gov/index.html) requires creation and maintenance of 1631 ha (4030 acres) of riparian habitat aimed specifically at providing breeding habitat for Yellow-billed Cuckoos. The number of breeding pairs this would accommodate is unknown. To successfully provide restored habitat for Yellow-billed

Cuckoos, we need to better understand habitat requirements of mated and nesting cuckoos. The small 3ha (50% KDE) core home range for females is not likely to encompass sufficient habitat for a pair of cuckoos to successfully raise young. A better home range goal for restoration is the average for mated cuckoos of 14.3 ha (75% KDE) or 31.5 ha (95% KDE). Many studies use 95% KDE as the estimate of choice, and 31.5 ha should contain most nesting and foraging habitat. Smaller core areas should be restored for breeding habitat, with larger areas provided for foraging.

The findings of this study should be compared with those of other cuckoo populations. There is currently a great deal of resources being spent on cuckoo surveys and habitat restoration in California and Arizona. A better understanding of home range size and habitat utilization will help guide riparian restoration efforts aimed at increasing cuckoo populations.

ACKNOWLEDGMENTS

Thanks to G. Clune, B. Raulston, and J. Swett for providing logistical support and the U.S. Bureau of Reclamation and Southern Nevada Water District for providing financial support for this project. Thanks to Dr. K.Blair and D. Gilbert of the U.S.D.I.

Fish and Wildlife Service, BWRNWR for their assistance. Thanks to J. Whetstone and the BLM‘s Sierra Vista Field Office for logistical support and access to the Riparian

Conservation Area. Thanks to Gray Hawk Ranch for access to their property. Thanks to

A. Hartman for statistical assistance. Thanks to Eli Rose, Shannon McNeil, and Diane

Tracy for their help in the field, managing data and crews. Many thanks to many excellent and dedicated field assistants for their hard work.

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TABLES and FIGURES

Table 1. Home range (in hectares) derived by different means for Yellow-billed Cuckoos observed on the San Pedro RNCA, 2002-2005. Means+ SD, Sample sizes (N) and ranges are given.

MCP 95% Kernal 75% Kernal 50% Kernal Male 52.9 ha ± 11.7 48.6 ± 45.5 ha 21.1 ± 21.9 ha 9.4 ± 55.4 ha (16) (16) (16) (16)

Male range 43.5 - 208.5 ha 2.6 - 158.1 ha 0.5 - 81.2 ha 0.1 - 44.5 ha

t-test* t = -0.17, p = t = -2.33; p = t = -1.87; p = t = -1.955, p = 0.432 0.0146 0.037 0.0326

Female 46.9 ± 3.7 ha 15.8 ± 21.7 ha 8.9 ± 9.1 ha 3 ± 8.0 ha (7) (7) (7) (7) Female range 1.2 - 225.3 ha 1.4 to 161.9 0.5 - 22.8 ha 0.2 - 10.6 ha

Nest 64.7 ± 73.2 ha 37.2 ± 33.3 ha 16.8 ± 13.9 ha 6.8 ± 6.9 ha (13) (13) (13) (13)

Nest range 8.3 - 225.2 ha 1.6 - 104.9 ha 0.5 - 43.9 ha 0.1 - 22.8 ha

t-test* t = -1.30; p = t = 0.168; p = t = 0.1355; p = t = 0.268; p = 0.104 0.434 0.447 0.396

No nest 33.2 ± 41.7 ha 40.5 ± 53.4 ha 18.1 ± 26.0 ha 8.2 ± 14.0 ha (10) (10) (10) (10)

No nest range 12.3 - 118.6 ha 1.4 - 15.8 ha 0.5 - 81.2 0.2 - 44.5 ha

Mated 54.6 ± 69.2 ha 31.5 ± 32.3 ha 14.3 ± 13.6 ha 5.8 ± 6.5 ha (16) (16) (16) (16)

Mated range 2.1 - 225.3 1.4 - 104.9 0.5 - 43.9 0.1 - 22.8 t-test* t = 0.47; p = t = -0.98; p = t = 0.88; p = t = -0.84; p = 0.322 0.176 0.203 0.215 Unmated 42.9 ± 46.6 ha 54.8 ± 58.8 ha (7) 24.5 ± 29.2 ha 11.1 ± 16.1 ha (7) (7) (7) Unmated range 1.2 - 118.6 4.6 - 158.1 1.2 - 81.2 0.4 - 44.5 OVERALL 51.1 ± 62.4 ha 38.6 ± 42.2 (23) 17.4 ± 19.6 7.5 ± 10.3 (23) (23) (23)

Range 1.2 - 225.3 1.5 - 158.1 0.5 - 81.2 0.1 - 44.5 *t-test assuming unequal variance

Figure 1. Comparison of average home range estimates for Yellow-billed Cuckoos on the San Pedro RNCA, 2003-2005. 70

50 Male 40 Female Nest 30 No nest Mated 20 Unmated

0 MCP 95% Kernal 75% Kernal 50% Kernal

Table 2. Models for estimating home range of marked Yellow-billed Cuckoos using model selection based on ΔAICc scores for 95% MCP models on the San Pedro RNCA, 2002-2005 (n=28). Columns are the number of estimated parameters (k), the difference between the best model and the other models corrected for small sample size (ΔAICc), model likelihood (L), and model weight (wi).

Model k ΔAICc L wi

Mated Sex 3 0.00 1.00 1.00 Year Sex 2 48.24 0.00 0.00 Year 2 48.80 0.00 0.00 Sex Nest 2 49.40 0.00 0.00 Nest 2 49.58 0.00 0.00 Noeffect 1 50.37 0.00 0.00 Nest Mated 3 50.62 0.00 0.00 Mated 2 50.92 0.00 0.00 Sex 2 51.38 0.00 0.00

Table 3. Models for estimating home range of marked Yellow-billed Cuckoos using model selection based on ΔAICc scores for 95% KDE models on the San Pedro RNCA, 2002-2005 (n=28). Columns are the number of estimated parameters (k), the difference between the best model and other models corrected for small sample size (ΔAICc), model likelihood (L), and model weight (wi).

Model k ΔAICc L wi

Mated Sex 3 0.00 1.00 1.00 Year 2 24.26 0.00 0.00 Year Sex 3 24.94 0.00 0.00 Sex 2 29.73 0.00 0.00 Mated 2 29.77 0.00 0.00 Nest Mated 3 30.47 0.00 0.00 Noeffect 1 30.47 0.00 0.00

Table 4. Models for estimating home range of marked Yellow-billed Cuckoos using model selection based on ΔAICc scores for 75% KDE models on the San Pedro RNCA, 2002-2005 (n=28). Columns are the number of estimated parameters (k), the difference between the best model and the other models corrected for small sample size (ΔAICc), model likelihood (L), and model weight (wi).

Model k ΔAICc L wi

Year 2 0.00 1.00 0.35

Year Mated 3 0.59 0.74 0.26 Year Sex 3 1.23 0.54 0.19 Year Nest 3 1.25 0.54 0.19 Mated 2 4.96 0.08 0.03 Mated Sex 3 5.60 0.06 0.02 NoEffect 1 5.33 0.07 0.02

Table 5. Models for estimating home range of marked Yellow-billed Cuckoos using model selection based on ΔAICc scores for 50% KDE models on the San Pedro RNCA, 2002-2005 (n=28). Columns are the number of estimated parameters (k), the difference between the best model and the other models corrected for small sample size (ΔAICc), model likelihood (L), and model weight (wi).

Model k ΔAICc L wi

Mated 4 0.00 1.00 1.00

Year Sex 3 36.50 0.00 0.00 Year 3 36.61 0.00 0.00 Mated Sex 2 38.48 0.00 0.00 Nest Mated 3 40.12 0.00 0.00

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Figure 3. Weekly 95% KDE home range estimates for eight Yellow-billed Cuckoos on the San Pedro RNCA , 2002-2005. Fem 1-02

50 Fem 1-03 45

40 Fem 1-04 35

30 Fem 2-04

25 Fem 1-05 Hectares 20

15 Male 1-03 10

5 Male 1-04

0 Male 2-04 1 2 3 4 Week of observation

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Figure 4. Home range size for Yellow-billed Cuckoos on the San Pedro RNCA, 2002-2005, by number of points used to determine home range.

120

100

mcp 60 kernal95 40 kernal75

Average Home range (ha) range Home Average kernal50 20

0 10 to 19 20 to 29 30 to 39 40 to 49 Number of points

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Figure 5. Overlapping home ranges of five individual Yellow-billed Cuckoos on the San Pedro RNCA, 2004.

500 m

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Figure 6. Weekly changes in home range use by Yellow-billed Cuckoo Female 1-2002 on the San Pedro RNCA, 2002. Weeks 5 and 7 are not visible.

Week 3 Week 1 Week 2 Week 6

Week 4

Week 8 500 meters

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Chapter 4. Parental Care in the Yellow-billed Cuckoo.

Murrelet Halterman1

Program in Ecology, Evolution, and Conservation Biology

University of Nevada, Reno

Reno NV 89557

Lewis Oring

Natural Resources and Environmental Science

1000 Valley Rd.

University of Nevada, Reno

Reno, Nevada 89512

1Murrelet Halterman Southern Sierra Research Station P.O. Box 1316 Weldon, CA (760) 417-0765 [email protected]

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ABSTRACT

Birds in the order Cuculifomes have the widest range of parental care systems known among avian orders, with obligate brood parasites, communal nesters, and monogamous and polyandrous species. Little is known of the nesting biology or parental care of Yellow-billed Cuckoos. They are known to be biparental, but the relative contribution of each sex to the nesting effort is unknown (Hughes 1999). We followed

28 adult cuckoos with transmitters and placed video cameras on four nests in southeastern Arizona from 2001-2005. Both males and females constructed nests and eggs were laid within 24 hours of nest initiation. Males did all nighttime incubation and females did the majority of daytime incubation. Females decreased food deliveries on days five and six, and stopped feeding on day seven (fledging). We observed one incidence of infanticide. In this study we observed a pattern of male-dominated parental care. Males provided the majority of incubation and provisioning to nestlings and all care to fledglings. Occasionally during the nestling period, females appeared to abandon a viable nest and initiate a nest with another male. The second male may assist with the first nest effort, and be tolerated by the primary male as a secondary food provisioner.

Infanticide may be a strategy of the second male to reduce the female‘s commitment.

Yellow-billed Cuckoos appear to be facultatively serially polyandrous.

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INTRODUCTION

Parental care in birds takes a wide variety of forms (Emlen and Oring 1977). For example, in many species of passerines such as North American warblers (Parulidae), males defend a territory and help care for nestlings, but females incubate alone (Ehrlich et al. 1988). In other passerines, such as Common Raven (Corvus corax), males assist with both incubation and feeding of young. Although biparental care is often associated with monogamy, it occurs in polygamous species, where either individual males help at more than one nest (Cockburn 2006, Paxton et al. 2007) or where females are associated with more than one nest as in facultative polyandry (Weibe 2007).

In both monogamous and polygynous species, males may desert their mates after breeding. Female-only parental care is at its extreme in lekking species where males are simply sperm donors and are not even aware of the location of nests, e.g. Greater Sage

Grouse (Centrocercus urophasianus) and Greater Prairie Chicken (Tympanuchus cupido)

(Höglund and Alatalo 1995). On the other hand, male-only parental care is at its greatest extreme in nearly all ratites, and in polyandrous species such as the seven species of jacanas and three species of phalaropes (Oring 1986). Recently it has been found that a cuckoo, the African Black Coucal (Centropus grillii) too is typified by classical polyandry and exclusive male incubation (Goymann et al. 2004, 2005).

With the recent discovery of cuckoo polyandry, it can be claimed that cuckoos

(Cuculiformes) have perhaps the greatest range of parental care of any avian order.

Although biparental care is dominant in the order, 38% (of 141 species) are obligate brood parasites (Payne 2005). The best known of these are the Common Cuckoo

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(Cuculus canorus, Davies and Brooke 1988, Wolfgang et al. 2002) and Great Spotted

Cuckoo, (Clamator glandarius, Soler et al. 2003). In one genus (Crotophaga) communal breeding is the rule; as mentioned above, at least one species has been shown to exhibit classical polyandry (Payne 2005).

The Yellow-billed Cuckoo is a North American species whose western populations have declined substantially in the recent past (Laymon and Halterman 1987).

Today, much of its former range is devoid of cuckoos, with small remnant populations limited to the riparian zones along a few western rivers, e.g. Sacramento, Bill Williams,

San Pedro, and middle Rio Grande (Hughes 1999). Because of its status as a candidate for Federal Endangered Species status (USFWS 2002) the necessity for discerning fundamental aspects of its breeding biology is widely recognized (Laymon 1998, Hughes

1999, Halterman et al. 2001). Though the species is believed to be monogamous with biparental care (Hamilton and Hamilton 1965, Laymon 1980, Potter 1980, Laymon et al.

1997), extensive observations of marked individuals are lacking.

During the course of our initial studies (see Chapters 1-3), observations of varying numbers of adults at nests, small clutch (average 2) coupled with extremely rapid development (which may be unique among birds) and what appears to be rapid sequential nesting of females, indicated that a study of Yellow-billed Cuckoo parental care might prove central to understanding this declining species. Additionally, such a study may make a major contribution to the understanding of avian development in general. To this end we initiated an attempt to follow known individuals through the nesting cycle via radio telemetry, and to study parenting behavior in detail through the use of video cameras at the nest. Because of the extreme difficulty in capturing Yellow-billed

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Cuckoos our data are limited and yet they indicate that further study of cuckoo parental behavior may reveal fascinating insights into avian breeding biology.

METHODS

Study Site

Research was conducted on BLM‘s San Pedro National Riparian Conservation

Telemetry

We captured 52 adult cuckoos using a targeted mist net technique, modified from methods used to capture Willow Flycatchers (Empidonax traillii) (Sogge et al. 2001).

After capture we weighed, measured, and banded each cuckoo with a USGS metal band and a unique color combination using 3 Darvic® color bands, and collected blood and feather samples for genetic sexing. We attached a Holohill Ltd. BD-2g transmitter, weighing 1.95 gms (slightly less than 3% of adult body weight), to the bird‘s central rectrices using dental floss (Bray and Corner 1972, Pitts 1995, Woolnough et al. 2004).

We located banded birds every two days until transmitters failed or birds left the area. A hand-held telemetry receiver and Yagi antennae were used to locate cuckoos.

When the radio-tagged bird was visible we recorded all behaviors (sitting, flying, foraging, incubating, etc.), vocalizations, prey captures, and nest locations.

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Nest Searching and Monitoring

We searched for nests of unbanded birds using several methods. When a cuckoo was detected during a survey, the surveyor moved back about 100m and searched every tree for nests (Martin and Geupol 1993). Alternatively two to three people worked together, triangulating on vocalizations of nesting cuckoos. Approximately 30% of nests were located by following telemetered birds.

For each nest we determined, when possible, number of eggs, number of nestlings, and apparent nest success. We did not flush adults from nests to monitor nest contents. Cuckoos on the Bill Williams River NWR have abandoned nests as a result of human activity (Halterman 2000), and we did not wish to affect nest outcome by our activity. We were therefore only able to calculate apparent nest success rather than

Mayfield nest success (Mayfield 1975). This latter method calculates exposure days, and resolves the bias of finding more nests in later stages of incubation or feeding nestling.

In 2005 we weighed and measured nestlings at three nests until fledge, and for 1-2 days afterward when possible. Nestlings were processed within ½ hour after sunrise. We measured wing chord and tail length to the nearest mm using a stopped wing rule, and mass to the nearest 0.5g using a Pesola® 30g spring scale. We measured total tarsus length, culmen length and depth to the nearest 0.1mm using dial calipers. Total disturbance lasted approximately 10 minutes. Nests were active between late July and early September.

In 2005 we placed video cameras on four active cuckoo nests. We used a

Fuhrman Diversified black and white time lapse video system. This system is composed of a small video camera placed within 1m of the nest, and connected by 18m of cable to a

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VCR. The system is powered by a deep-cycle marine battery. Tapes and batteries were changed every 24 hours. Each eight hour tape recorded 24 hours of nest activity. These systems were set up one day after finding the nest. Set up took about 20 minutes. We monitored the nest after set-up was complete, and removed the camera if no adults returned within 1 hour.

Video tapes were reviewed and all activity noted. Each nest had one banded adult, and when possible we noted which adult attended the nest. We noted nest exchanges, time spent incubating and brooding, and prey deliveries. For prey delivered, we attempted to determine order (Orthoptera, Lepidoptera, etc.) and prey size compared to adult bill size. This measurement is inexact, but gives a general idea of changes in prey size during nestling provisioning and the relative contribution of adults.

RESULTS

We found ten nests on SPRNCA in 2005, and seven were successful. We used video cameras to monitor four nests. One was abandoned two days after video observation began. We found the banded female‘s transmitter near a Gray Hawk (Asturina nitida) nest, and suspect she was eaten. We recorded 45 days (984 hours) of video on three successful nests (Table 1).

Nest Initiation

We were able to follow 28 of 52 captured cuckoos for at least one week. Many had nests, but only three were observed during nest construction. Both males and females helped construct nests, with males bringing twigs to the female who positioned them. Eggs were laid within 24 hours of the start of nest building.

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Incubation

We observed incubation at two nests (nests 6 and 8) for a total of eight days, and brooding young at nests 6, 8, and 10 for a total of 23 days. Both adults incubated eggs and brought nesting material. Males spent more total time incubating (average 13.8 hours/day vs. ♀ = 7.3 hrs/day), due to nighttime incubation (Table 2). Females spent more time on the nest during the day (average 7.3 hours/day vs ♂ = 2 hrs/day) (Table 2).

Daytime incubation bouts typically lasted about 2 hours, but ranged from 20 minutes to

4.5 hours. Nighttime incubation lasted between 11.5 and 14.5 hours. At nests six and eight, males incubated or brooded every night. At nest ten the male incubated/brooded seven nights while the female brooded three nights.

The length of time each adult incubated varied among nests, with as few as four exchanges in a day to as many as twelve. There was an average of one nest exchange every 1.5 hours. Adults brought a twig to add to the nest 90% of the time when they exchanged. Nest attendance was compensatory, with one adult replacing the other within

1-2 minutes of departure from the nest. We were unable to see approaching adults on video tapes. We know, from hundreds of hours of nest observation from blinds, that approaching adults typically call from near the nest (Halterman 2000). The adult on the nest may respond vocally, then it leaves and the replacement approaches the nest. Nests in this study were never unattended for more than 10 minutes during incubation and the first four days of nestling care.

Nestling Care

Both adults fed and brooded the young, but males provided twice as many food items as females (Table 2). Males fed more small food items (28.3%) than females

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(15.7%) (Table 3). Females may have compensated for their lower feeding rate with larger food items, feeding 53% large food items compared to males‘ 42% large food items (Table 3). Although this is a small sample, both females exhibited this pattern.

There was, however, some variation in daily food delivery. On day 1 (hatch) the female at nest 8 delivered 70% of food items while the female from nest 6 only delivered 14% of food items. All three females decreased feedings on the sixth day, and did not feed on the seventh day, when young fledged (Table 4).

Yellow-billed Cuckoos have a very low feeding rate, with total daily food deliveries ranging from 9.3 to 16.3 food items (Table 4). Daily food items per nestling ranged from a low of 5.6 food item/day to a high of 9.8 items per nestling on day 6, just before fledging.

We were unable to identify many of the prey items delivered to the nest. Small items were particularly challenging, but included beetles and spiders. Medium sized food items consisted of grasshoppers (order Orthoptera), cicadas (Diceroprocta sp.) and caterpillars (order Lepidoptera). Large food items included big caterpillars of sphinx moths (family Sphingidae) and swallowtail butterflies (family Papilionidae), large katydids (family Tettigoniidae), grasshoppers, and cicadas, and tree lizards (Urosaurus sp.). Tree lizards are one of the most impressive prey items, because they weigh 4 grams and are fed to nestlings weighing as little as 20 grams.

Nestling Growth

Yellow-billed Cuckoos begin incubation as soon as the first egg is laid (Hughes

1999). Consequently hatching is asynchronous, and thus young of different ages are in the nest. All six eggs in this study hatched at night. Nestlings weighed about 10 gms the

113 first morning after hatching, and gained an average of 4.5gms/day for the first 4 days, tripling their weight (Table 5). The greatest gain in 24 hours was by nestling #1 at nest 6, gaining 9 gms from day four to day five. Weight gain stops after 5 days, but wing and tail feathers continue to grow quickly, averaging 4mm/day (Table 5, Figure 1). These limited data show no trend for second nestlings to receive fewer food items or to have a slower growth rate. We were only able to measure nestlings for seven days. We do not know the rate of growth post-fledging or at what age young achieve adult weight.

Because we lacked measurements for most of the growth period we could not calculate growth rates using Ricklefs or Gompertz equations (Stark and Ricklefs 1998).

Fledgling Care

We observed eight cuckoos with transmitters during the fledgling care period.

Three females were followed for a total of 60 days post fledging (range 2-40 days), and one female, observed 18 days post fledgling, fed fledglings for two days. The other females never fed fledglings. Five males were followed for a total of 73 days (range 8-23 days) and fed fledglings for all 73 days. Clearly males take on essentially all care just before fledging, and continue this care until the young are independent. In 2005 we placed transmitters on two eight day old cuckoos. One lost the transmitter, and the other was followed for 8 days post fledging. It moved a total of 150 meters during this time.

The adult was silent unless we approached the fledgling.

Parental Care

Both sexes contributed to incubation. Males incubate more total hours, but females spent more time incubating during the day. Males provided twice as much food to nestlings as females, and apparently provided all care after day six.

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Two females, one in 2002 and one in 2004, retained transmitters following a successful nest. These two females left prior to fledging, and the male raised the young with no female assistance. Both females re-nested within several days of leaving the first nest. The first female‘s second nest was unsuccessful. The second female had a total of three successful nests. She left the first nest seven days post-hatch. She initiated a second nest and left it four days post-hatch, prior to fledging. She then initiated a third nest, and was still feeding nestlings when her transmitter failed. All three nests were successful, and we observed adults caring for nestlings and fledglings at the first two nests after the female left. The two subsequent nests were initiated while the male cared for dependant young from the previous nest.

Infanticide

Three adults were observed caring for young at nest 6: one banded female and two unbanded birds. The third adult was only observed incubating once, but provided

27% of food items to nestlings. When the two oldest nestlings were three days old, a recent hatchling was observed in the nest. This nestling did not receive any food during 8 hours of observation. At 1436 in the afternoon an unbanded adult approached the nest and fed one of the older nestlings. It then picked up, dropped, then picked up and flew away with the youngest nestling, which was less than 18 hours old. This is the first video record of infanticide in Yellow-billed Cuckoos.

DISCUSSION

This study revealed a pattern of male-dominated parental care in this population of Yellow-billed Cuckoos. Males provided the majority of incubation, the majority of food to nestlings, and were the only care-givers for fledglings. Females shared in

115 incubation and provided a steady supply of food during the first four days post-hatch, though they provided less food than males. Beyond four days post-hatch, there was a sharp decrease in feeding by females (Figure 2).

A greater contribution to incubation by males has been documented in numerous sex-reversed species (females larger and/or more colorful than males). Yellow-billed

Cuckoos, however, are sexually monomorphic (Pyle and Howell 1997). At three nests subjected to detailed video-monitoring, males provided more incubation than females.

The division of labor hypothesis (Andersson 2005) predicts that the demands of egg- laying on females results in males contributing more to the nesting effort. The demands on female Yellow-billed Cuckoos incurred from producing a two-egg clutch are unknown.

Feeding rates varied among nests, but averaged fewer than 10 food items/nestling/day (Table 4). This is far fewer feedings than is normal for passerines

(Ehrlich et al. 1998). Most food items were large - grasshoppers, caterpillars, and lizards.

Nestlings grew rapidly, and reached fledging weight in four days. The large, high calorie food items post-hatch likely are responsible for this rapid growth rate. Nestlings stop gaining weight on the fifth day, two days before leaving the nest.

It has been observed that approximately 30% of Yellow-billed Cuckoos nests have three adults feeding nestlings (Laymon et al. 1997, Halterman 2000). One of our three video monitored nests had three adults provisioning young. Observation of second males, lack of female contribution to fledging care, and observation of females initiating nests while young from the previous nest still required care, suggests that female cuckoos, on occasion, are serially polyandrous. Female cuckoos may be maximizing

116 reproduction by leaving their current nest as soon as young are old enough for males to provide all care. Second males may be tolerated by primary males because they provide a significant number of feedings to young. Unfortunately lack of a substantial banded population relegates observation of this fascinating female behavior to speculation.

Siblicide is fairly common in birds. Many species of eagles, for example, regularly lay two eggs, but usually fledge just one chick (Mock et al.1990). Infanticide, however, is much less common, and has only been studied in colonial nesting swallows

(Møller 2004), House Sparrow (Passer domesticus, Viega 2003), polyandrous Pheasant- tailed Jacana (Hydrophasianus chirurgus, Chen et al. 2008), communally nesting Guira

Cuckoos (Guira guira, Macedo and Melo 1999) and Acorn Woodpeckers (Melanerpes formicivorus, Koenig et al. 1995). In all species but the Guira Cuckoo this behavior involves removal of eggs. Infanticide has been observed in Yellow-billed Cuckoos several times, involving removal of the youngest nestling (Hamilton and Hamilton 1965,

Laymon et al. 1997). Our video of a parental adult removing a nestling confirms this behavior. This was observed at a nest with three adults in attendance. We do not know the genetic relationship of adults and nestlings. If the youngest nestling was removed by a second male, this behavior may have expedited the female‘s moving on to another nest.

Maurer (2008) speculates that males of Pheasant Coucals (Centropus phasianus) are able to provide all incubation and the majority of nestling care since males can incubate in short bursts during the day. Females of this species provide just over 20% of feedings to nestlings, and were observed with only half of fledgling groups. Ralph

(1975) observed Dwarf Cuckoos (Coccyzus pumilus) in Colombia, and found that although biparental care was the norm, one of four banded females was polyandrous. A

117 proportion of Yellow-billed Cuckoos may practice serial polyandry, with females providing parental care but leaving before young are independent in order to re-nest with another male.

Yellow-billed Cuckoos show a pattern of extremely rapid reproduction. There are several possible ultimate causes for this pattern. This species may have historically experienced very high predation rates (e.g. Bosque and Bosque 1995, Martin 1995,

Fontaine et al. 2007, Eggers et al. 2008), they may specialize in exploiting resources available for very brief periods of time (Koenig and Liebhold 2005), and/or females maximize individual productivity by producing multiple nests in a season (e.g. Houston et al. 2005, Johnstone and Hinde 2006). Apparent nest success in our population was high – exceeding 70%, as has been found in other western studies (Laymon et al. 1997,

Halterman 2000). Western cuckoos have clutches averaging just 2.5 (Laymon et al.

1997, Halterman 2000, 2006). By contrast, eastern populations of Yellow-billed

Cuckoos tend to have larger clutch sizes (average 3.75, Wilson 1999) and nest success less than 35% (Wilson 1999, Best and Stauffer 1980, Brunjes 1988).

Despite a paucity of marked birds, a number of observations taken together inexorably indicate male dominated care. These include multiple observations of second males at nests, early cessation of female feeding coupled with female departure from the nest site, females with up to three nests per season, and observation of infanticide – seemingly by second males at the nest. All these behaviors are indicative of facultative serial polyandry by female cuckoos. The opportunity for this mode of reproduction is maximized by small clutch size, asynchronous hatching, brief incubation period, and extremely short nestling periods. This system appears especially well positioned to

118 exploit the seasonal monsoon rains which cuckoos at the study site await prior to the onset of nesting.

ACKNOWLEDGMENTS

Fish and Wildlife Service, BWRNWR for their assistance. Thanks to J. Whetstone and the BLM‘s Sierra Vista Field Office for logistical support and access to the Riparian

Conservation Area. Thanks to Gray Hawk Ranch for access to their property. Thanks to

A. Hartman for statistical assistance. Thanks to Eli Rose, Shannon McNeil, and Diane

Tracy for their help in the field managing data and crews. Many thanks to many excellent and dedicated field assistants for their hard work.

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TABLES and FIGURES

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Table 1. Summary of observations at three video-monitored Yellow-billed Cuckoo nests on SPRNCA 2005.

# food Nest number Sex of banded # adults present # # eggs # young Hours items adult at nest eggs hatched fledged observation delivered 6 Female 3 3 3 2 312 134 8 Female 2 2 2 1 384 142 10 Male 2 2 1 1 288 74

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Table 2. Nest attendance and prey delivery at three Yellow-billed Cuckoo video-monitored nests on the SPRNCA 2005.

Avg. % total incubation Food Food No. days time Avg. hours daytime deliveries deliveries recorded incubating incubation only (n) (%) Nest 6-Female 3 24% 5.3 5.3 40 30% Nest 6 - Male 3 75% 15.4 3.1 58 43% Nest 6 - 3rd Adult 1 1% 1.0 1.0 36 27% Nest 8 - Female 5 40% 8.6 8.6 40 28% Nest 8 - Male 5 60% 12.9 0.9 102 72% Nest 10 - Female 1 - - - 21 28% Nest 10 - Male 1 - - - 53 72%

Male mean 65% 13.8 2 101 29%

Female mean 35% 7.3 7.0 249 71%

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Table 3. Size of prey items delivered to three Yellow-billed Cuckoo nests on SPRNCA 2005.

Prey size Male total Male % Female total Female %

Small 45 28% 14 16% Medium 48 30% 28 31% Large 66 42% 47 53%

Total 159 64.1% 89 35.9%

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Table 4. Daily food delivery to video-monitored Yellow-billed Cuckoo nests on SPRNCA 2005.

Nest number # nestlings 1 (hatch) 2 3 4 5 6 7 (fledge) Total

Nest 6 2 14 16 18 21 22 20 6 117

Nest 8 2 10 11 14 12 10 17 17 91

Nest 10 1 4 10 7 14 11 12 11 69

Average per nest 9.3 12.3 13.0 15.7 14.3 16.3 11.3 92.3 feeds/hour 0.26 0.34 0.36 0.44 0.40 0.45 0.31 0.37 feeds/day/nestling 5.6 7.4 7.8 9.4 8.6 9.8 6.8 7.9

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Table 5. Average measurements of five Yellow-billed Cuckoo nestlings, SPRNCA 2005.

Weight Age (gms) Wing (mm) Tail (mm) Bill length (mm)

1 9.9 ± 3.1 14.6 ± 4.0 1.6 ± 1.8 4.5 ± 0.38

2 14.2 ± 2.5 19.1 ± 3.5 2.3 ± 2.6 5.7 ± 0.48

3 18.3 ± 4.1 24.1 ± 4.3 4.7 ± 2.8 5.8 ± 0.91

4 22.6 ± 4.9 32.2 ± 4.9 10.2 ± 2.8 7.7 ± 0.85

5 27.98 ± 3.6 37 ± 5.1 14.6 ± 3.6 8.6 ± 0.75

6 29.7 ± 3.4 45.2 ± 3.6 20.5 ± 4.4 9.3 ± 0.43

7 29.3 ± 1.5 49.7 ± 3.7 29.0 ± 4.4 9.4 ± 0.30

8 29 ± 3.3 54.6 ± 4.6 35.2 ± 6.9 9.8 ± 0.25

Adult Female 64.6 ± 5.1 149.5 ± 3.7 154 ± 9.5 20.5 ± 1.4

Adult Male 59.3 ± 5.6 145.9 ± 3.0 152.7 ± 7.1 20.3 ± 0.7

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Figure 1. Morphological measurements of five nestling Yellow-billed Cuckoos on SPRNCA 2005.

50 weight

bill length 40 tarsus 30 wing

20 tail

Measurements or mm) (grams Measurements 10

0 1 2 3 4 5 6 7 8 9 10 -10 Age of neslings (days)

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Figure 2. Changes in prey delivery rates by male and female Yellow-billed Cuckoos on SPRNCA 2005.

100% 90% 80% 70% 60% 50% Male 40% Female 30% 20%

10% Percent of total prey deliveriesprey total of Percent 0% 1 2 3 4 5 6 7 (hatch) (fledge) Age of nestlings

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GENERAL DISCUSSION

In this study we looked at responsiveness and sexual dimorphism of Yellow- billed Cuckoos, as well as a number of aspects of the breeding biology. Because of sharp population declines in the west, this species is of great conservation interest. A better understanding of this species will help guide future management efforts.

Sexual dimorphism in birds takes a variety of forms, including sexual differences in size, plumage, behavior, and/or vocalizations (Ridgely et al. 2001, Schroeder et al.

1999, Lanctot and Laredo 1994). I examined vocalizations, morphology, and DNA from cuckoos captured during this study. The use of genetic markers was the only reliable way to distinguish between male and female cuckoos.

Accurate estimation of numbers of animals is necessary for monitoring population trends and effective management (Lancia et al. 1994, Emlen 1977). Knowing the effectiveness of standard survey methods allows better estimation of populations. I found the current survey method for cuckoos detected between 23%-57% of the population present in a given area. Males responded more than females, and unmated cuckoos responded more than mated cuckoos.

I used radio telemetry to follow 28 cuckoos for at least one week during 2002-

2005 field seasons. I used these data to calculate cuckoo home ranges, but these must be considered preliminary estimates due to the small sample size and small number of locations. Individual females used between 5 ha and 15 ha, while male home ranges varied from 10 ha to 35 ha, depending on the estimator used.

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Parental care in birds takes a wide variety of forms (Emlen and Oring 1977).

Yellow-billed Cuckoos are known to be biparental, but relative contribution of each sex to the nesting effort is unknown (Hughes 1999). By following cuckoos with transmitters and placing video cameras on nests I was able to add to the current knowledge base.

Both males and females constructed nests and eggs were laid within 24 hours of nest initiation. Males did all nighttime incubation and females did the majority of daytime incubation. Eggs hatched after 11 days of incubation, and young fledged at seven days of age.

Both parents fed the young, but males delivered twice as many food items as females. Females fed a larger proportion of large food items than males. Females decreased food deliveries on days five and six, and stopped feeding on day seven

(fledging). Males provided essentially all care to fledglings. Two females initiated a second nest before young fledged from their first nests. I observed one incidence of infanticide at a nest where three adults fed nestlings.

In this study I observed a pattern of male-dominated parental care. Males provided the majority of incubation, food to nestlings, and all care to fledglings. Under some circumstances females abandoned one nest and initiated another with a second male. The second male sometimes assisted with the first nest effort, and was tolerated by the primary male as a junior food provider. Infanticide may be a strategy of the second male to reduce the female‘s commitment to her first nest, thus promoting the likelihood of her availability to nest with a second male. Yellow-billed Cuckoos appeared to be facultatively serially polyandrous.

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In this study I found that genetics was the best way to sex cuckoos. Other asserted methods were problematic. Cuckoos responded less than half the time to call- playback, and had large but variable home ranges. They expressed a fascinating parental care system in which males sometimes divided care with a second male, and females routinely ceased care at a very early stage (six days post-hatch). Females appeared to maximize reproductive potential by increasing the number of nests in a season while reducing investment in each nest. This strategy may drive their reproductive system with small clutch sizes, rapid development and fledging of young, and male-dominated parental care. Yellow-billed Cuckoos are a poorly known species of great conservation interest. Population assessment requires expanded studies on habitat use, responsiveness in different habitats, basic biology, and mating systems.

LITERATURE CITED

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Emlen, S.T. and L.W. Oring. 1977. Ecology, sexual selection and the evolution of mating systems: Science 197: 215–223.

Hughes, J.M. 1999. Yellow-billed Cuckoo (Coccyzus americanus). In The Birds of North America, No. 148 (A. Poole and F. Gill, eds.). The Birds of North America, Inc. Philadelphia, PA.

Lancia, R.A., J.D. Nichols, and K.H. Pollock. 1994. Estimating the number of animals in wildlife populations: Pages 215–253 In Research and Management Techniques for Wildlife and Habitats, 5th ed. (T. A. Bookhout, Ed.). The Wildlife Society, Bethesda, Maryland.

Lanctot, R.B. and C.D. Laredo. 1994. Buff-breasted Sandpiper (Tryngites subruficollis). In The Birds of North America Online (A. Poole and F. Gill, eds.). The Birds of North America, Inc. Philadelphia, PA.

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Ridgely, R.S., P.F. Greenfield, and F.B. Gill. 2001. Birds of Ecuador Field Guide. Cornell University Press. 880 pages.

Schroeder, M.A., J.R. Young, and C.E. Braun. 1999. Greater Sage-Grouse (Centrocercus urophasianus), In The Birds of North America (A. Poole and F. Gill, eds.). The Birds of North America, Inc. Philadelphia, PA.