THE SOCIAL SYSTEM OF THE GREEN

DOUGLAS C. GAYOU • Divisionof BiologicalSciences, 105 TuckerHall, Universityof Missouri, Columbia, Missouri 65211 USA

ABSTRACT.--Acces$otybirds were absent at the nests of Green Jays (Cyanocoraxyncas). However, young stayedin the family flock for one year. After the young from the following year fledged,the 1-yr-old young were forced from their natal territory by the breeding male. These young either dispersed into adjacent habitat or became floaters within their former territories until, possibly,a breeding position opened up in a family flock. The yearlings provided a significant amount of territorial defense, which freed the breedersof much of the energeticcosts inflicted on them by the stringent territoriality required in south Texas habitat. I proposethat southTexas Green Jaysrepresent an early stagein the evolutionarysequence of development of cooperativebreeding as a responseto environmental factors.The reten- tion of young on the natal territory without helping at the nest representsan evolutionary early step,heretofore only hypothesized,that may lead to a more complexcooperative system that includes helpers at the nest. Received3 September1985, accepted 28 January1986.

NEW World Jays possessa wide variety of of the Texas population of Green Jaysare an- socialorganizations and breeding systemsthat ecdotal,and information on breeding biology range from territoriality by breeding pairs in in North America consistsprimarily of nest lo- the (Cyanocittacristata; Hardy 1961); cation,height, and compositionand clutch size through highly cooperativebreeding systems (Merrill 1878, Sennett 1878, Bendire 1895, Sut- in the Gray-breasted(Mexican) Jay ( ton et al. 1950). ultramarina;Brown 1963, 1970), the I report here on detailed field observations (Cyanocoraxdickeyi; Crossin 1967), and the Flor- of the 'ssocial system and discussthe ida Scrub Jay (Aphelocomacoerulescens; Wool- evolution of helping behavior and territoriali- fenden 1975);to colonialismin the ty in the North American population. I also (Gymnorhinuscyanocephalus; Balda and Bateman comparethe socialsystems of the two disjunct 1972). The neotropical Green Jay ( Green Jay populations. yncas)has been most intensively studied in Co- lombia, South America where it occurs in METHODS AND MATERIALS groups of 3-9 individuals that defend stable territories all year (Alvarez 1975). Breeding is I studiedGreen Jaysat SantaAria National Wildlife cooperative,with membersof the group help- Refuge(NWR) locatedapproximately 12 km south of ing to feed and care for the young. Juvenile Alamo, Hidalgo Co., Texason the Rio GrandeRiver. The area is semiarid, with a mean annual rainfall of Green Jaysdo not disperseimmediately from 45 cm. Most of the precipitationoccurs in late spring the parental group but stay as helpers at the and early autumn. Autumn precipitation occasion- nestfor a minimum of one additionalbreeding ally is enhancedby the movementof a low-pressure season. center onshoreand into the Rio Grande Valley. The There is no published information on the so- mean temperaturein winter is 15.5øC,spring 20.5øC, cial system of the North American population summer 28øC, and autumn 27øC. The lowest recorded of the Green Jay,which occursfrom just north temperatureis -9øC and the highest43øC (Fleetwood of the Rio Grande River in southeast Texas 1973). south to north-central Honduras (Meyer de The refuge consistsof about 900 ha coveredmostly Schauensee 1966). References to the behavior by evergreen,dry subtropicalforest. All land adja- cent to the refuge has been cleared for agriculture and is subjectto intense aerial spraying of insecti- cides and herbicides. Thus, Santa Ana NWR has been • Presentaddress: 2307 Ridgefield, Columbia,Mis- an island of natural habitat for 30-40 yr. The most souri 65203 USA. common trees are elm (Celtis spp. and Ulmus crasi-

540 The Auk 103:540-547. July 1986 July1986] TexasGreen Jay Social System 541 folia), ebony (Pithecellobiumfiexicaule), anaqua (Ehretia flying in the open resultsin heavy useof travel anacua),mesquite (varieties of Prosopisjulifiora), hui- corridorsof dense vegetation. sache(Acacia farnesiana), and retama (Parkinsoniaacu- Three reports on Green Jay age at Santa Ana leata). Beneath the canopy is a dense understory of NWR exist. The first (Kennard 1975) gave the shrubsand thorny vines. age of an AHY Green Jay banded at SantaAna A total of 2,850 h of observations was made from NWR as 9 yr, 9 months at death. On 15 June April 1981 through June 1984. I followed three flocks of jays for the majority of time and observed one 1982,I live-trapped an AHY jay that was band- ed on 30 November 1972 at the same location. other flock only occasionally.Hereafter, the study flockswill be referred to as Ray's Group, Handicap This extended the minimum lifespan to 10 Group, Blue Group, and Willow Lake Group. As of yr, 0 months.This jay, releasedunharmed, has March 1984 a total of 133 after-hatching-year (AHY) not been resighted since. Finally, Clapp et al. Green Jayshas been banded within the refuge. Each (1983) discovereda SantaAna Green Jay record bird received one numbered metal USF&WS band extending the age record to 10 yr, 8 months. and up to four plastic colored leg bands. The plastic Theseage recordswere of Green Jaysbanded bands were cemented with Duco Cement and none and recaptured within the confines of this were lost during the study period. small refuge. As of late 1985, it was unknown The jays were captured in potter traps baited with bird seed. Each jay was banded, measured, and whether a significantnumber of banded jays weighed using a 300-g Pesolaspring scale.Each jay had ventured outsideof the refugeboundaries. was then released within 10 m of the capture point. Only one recordof dispersalbeyond the refuge I sexedGreen Jaysby mating behavior becauseI could exists.A female (banded 8 January 1982) was not discern any sexual differencesin plumage, size, found dead on 24 February 1983 south of Rey- or other characteristics.Sexing via laparotomieswas nosa,, Mexico, 15 km west of Santa not attempted becauseof Alvarez's (1975) lack of suc- Ana NWR. cess with this method. Groupcomposition.--In south Texas, Green Jays Nine nests were located during the study period, lived in a family group that remained stable and the majority of time was spent observing nests from one breeding seasonto the end of the of Ray's Group and the Handicap Group. Observa- tions commenced when a nest was located and con- next. In the winter and spring a family group tinued until all young fledged. In 1981, 6-h nest ob- consistedof the monogamousbreeding adult servation periods were conducted for Ray's Group male and female and all surviving offspring after the young had hatched. In 1982 and 1983, 4-h from the previous year's reproductive effort. observationperiods per nest were conductedand were During and after the breeding season,the rotated for the study nests so that observationsin- family group size increasedby the addition of cluded some morning and afternoon study periods the young producedduring the current year's for all nests until young fledged. After the young reproductiveeffort. At this time the group size fledged,observations continued on a similar rotating basis for 2-3 weeks. peaked.Several weeks after the young fledged, the yearling jayswere driven out of their natal RESULTS territory by the adult breeding male. The fam- ily group size was then reduced to just the Generalobservations.--Green Jays were con- breedingpair and the currentyear's young. This spicuousand scoldedloudly during the entire group size is maintained until the next breed- year except for the spring and summer breed- ing season(Figs. 1 and 2, Table 1). ing season,when they became secretive and During the winter, the family group usually difficult to locate. At this time the adults and foragedtogether (>76%, n = 142).In the spring young rarely scolded or called when alarmed when the breeding pair was building the nest, but, rather, silently moved away. laying ,etc., the yearlingsspent almost all Adult Green Jaystended to avoid flying in of their time foraging together within the pa- open spaces.In 5 yr of observations,I saw only rental territory yet having little contactwith 5 jays fly 30-200 m in the open, and all 5 were the breeders. The breeding male and female juveniles. Adult Green Jays preferred to fly foraged within 100 m of the nest during this short distancesin dense understory until they time (>90%, n = 78). The yearlings joined in a arrived at their destination.When flying in the "greeting" behavior with the adult pair in the open, Green Jays had an undulating, wood- morning and at dusk before separating. pecker-like flight. The apparent avoidance of After the current year's young fledged, the 542 DOUGLASC. GAYOU [Auk, Vol. 103

Fig. 1. Composition of Ray's Group study flock, Fig. 2. Compositionof Handicap Group study 1981-1983.In the age classificationused in this study, flock, 1981-1983. by winter those individuals initially placed in the "juvenile" categorybecome "yearlings." territorial year-round, but exhibited a higher degree of territorial defense behavior during breeding male spent increasingamounts of time the spring and summer breeding season.The with the yearlings foraging and moving about territory boundarieswere defined through ob- the entire territory and only occasionallyre- servationsof daily group movements and of joined the femaleduring the day. The breeding numerousboundary disputesbetween adjacent female foragedalone at this time and provided family groups. Territorial boundariesfor the prey for the dependent fledglings with- four groupsusually coincidedwith topograph- out help from other family group members.An ic features such as lakes, field boundaries, and increase in agonistic behavior between the roads(Fig. 3). breeding male and the yearlings was first no- TexasGreen Jay territory size averaged 16.2 ticed4-10 daysafter fledging.Eventually, year- ha (Table 2). The territories supported4-9 in- lings were banishedfrom the family flock by dividuals in a family group as well as one or the breedingmale, a processthat took 3-5 weeks more other jays that were not family members. and sometimesincluded fighting and grap- The four study flock territories were locatedin pling between the breeding male and one or an area of the refuge dominated by mesquite more of the yearlingsof the family flock. The and ebony ,which I considerexcellent yearlings usually remained together for 3-6 Green Jay habitat. weeksnear the periphery of the natal territory, Family groupsvigorously defended their ter- but avoided the breeding male. ritories at all times. I observed 27 territorial en- By winter, someyearling jays had dispersed countersbetween Ray's Group and either the into areasadjacent to their natal territory. It is Handicap Group or the Blue Group. The en- not known how far they dispersed,but obser- counterslasted from 5.5 min to slightly more vations revealed that some apparently became than 42 min (mean = 22 min). A typical terri- floaters and remained close to the area in which torial encounter began when 1-3 intruders flew they were hatched. In spring 1984, a banded into a group'sterritory while calling very loud- female (hatchedby Ray'sGroup in 1982) was ly. The first member of the family flock to re- observedfeeding three fledglings in the Hand- spond, if the intrusion was near the nest area, icap Group territory, where she had previously usuallywas the breedingmale. He would alight been observedalone or with other jays. This on a branch within 0.5 m of the intruder and suggeststhat a female can spend at least one face the other bird. Both would call con- year as a floater before being incorporatedinto stantly while performing stereotypeddisplays a group'sbreeding structure. characteristicof this territorial behavior (Gay- Territorialbehavior.--Green Jays in Texaswere ou 1984).Only twice did I observethe breeding July1986] TexasGreen Jay Social System 543

TABLE1. Green Jay family group compositionone week postfledging.a

1981 1982 1983

B Y F B Y F B Y F

Ray'sGroup 2 2 2 2 2 4 2 4 3 Handicap Group 2 3 2 2 2 3 2 3 4 Willow Lake Group 2 3 2 Blue Group 2 2 3 2 3 3 breeders,Y = yearlings,F = fledglings. male face an intruder alone. In all other re- corded observations,yearling members of the group whose territory was being invaded also participated in the defense behavior. They ex- hibited the same calls and postures as the breedingmale. The breedingfemale rarely par- ticipated,and usually only if an intruder came near the nest. She normally watched from an adjacenttree, always arrived last at a particular territorial encounter, and was the first to de- part. Eventuallythe intrudersbroke off the en- counter and flew away calling loudly. The breeding male continued to call loudly from the tree tops on the edge of his territory for some minutes after the intruders had left (mean time = 11 min, max = 23 min, n = 22). The yearlingsquieted quickly and usuallyflew away several minutes before the breeding male re- sumed his prior activities. In 20 of 31 (65%)territorial encountersamong all groups,yearlings detected the intrudersfirst. The breeding pair arrived very quickly if the intrusion was near the nest, but not at all if the event occurredat a distant periphery from the nestarea. In two instancesI observedyearlings from Ray's Group respondto an incursionby a member of the Willow Lake Group at the southern edge of Willow Lake. The intruder was driven off without the breeding male or female'sparticipation. In 19 of 27 territorial encounters between Ray's Group and the other groups, all calling a territory only if it made itself conspicuousby and displaying occurred in and around one calling frequently or perching near a family open areawhere territoriesof three study flocks group member. At this time the floater was met. Whether this area was consistentlyused chasedwithout the typicalterritorial encounter as a display arena for territorial encountersis display behavior becausethe floater did not re- unknown, but these preliminary observations spond and withdrew immediately. Generally, suggestthat Green Jayspreferred to display in floatersforaged in a particular territory with- open areas during these encounters. I have out being chasedif they remained inconspic- never observed a territorial encounter in dense uous and quiet. vegetation. Although territories are defended year- A solitary floaterjay was pursuedoutside of round, vigorous territorial defense became ev- 544 DOUGLASC. G^¾OU [Auk,VoL 103

TABLE2. GreenJay family groupterritory size (ha), 1981-1983.Group sizes are given in parentheses.

1981 1982 1983 Mean Ray'sGroup 13.6 (6) 18.6 (8) 15.9 (9) 16.0 (7.7) Handicap Group 18.6 (7) 14.9 (7) 15.8 (9) 16.4 (7.7) Willow Lake Group 16.1 (?) 16.3 (?) 16.3 (7) 16.2 (7.0)

ident during March and April. The entire fam- rangelack helpers at the nest.In contrast,Green ily group joined in maintaining the territorial Jaysin Colombiahave helpersat the nest (A1- boundaries. This group behavior involved varez 1975).The biology of these two popula- moving along the territory boundaries while tions apparently share several features. The calling loudly. During thesefamily group pa- mating behaviors(Gayou 1984) are like the de- trols, especially in the breeding season,there scriptionsprovided by Alvarez (1975), and var- were always several territorial encountersbe- ious aspectsof foraging ecology, mating calls, tween family groupsof adjacentterritories that and reproductivebehavior also share many consistedof stereotypedbehaviors and calling. characteristics.Other similarities are apparent After such an encounter,the family group's in yearly family group stability:the number of displaybehaviors and calling were maintained family group membersin both populationsre- at a higher level of intensity for a period of mained constantfrom one breeding seasonto time. Family groupswere more likely to patrol the next. Although Alvafez (1975) did not dis- areas of their territories subject to frequent in- cussthe ultimate fate of the one-year-oldCo- cursionsby other jays. During patrol periods lombianGreen Jays at the beginningof the next mating behaviorsoccurred frequently between year'sbreeding season, he describeda system the breeding male and female. After nesting whereby new groups sometimesformed dur- began, the yearlings continued to move about ing the current breeding seasonthat enabled the group territory and intercept and drive young to becomemembers of thesenew groups. away any intruding jays. South Texas Green Jaysare driven from their Absenceof nest helpersat Green Jay nests.- parental groups a few weeks after the current During approximately 73 h of observing nest- year's young have fledged. lings and fledglings over 4 yr, I observedonly The differencesthat occurare of major sig- the parentsfeed the young (Gayou1984). Nine nificance and provide a divergence between nestswere locatedduring the studyperiod, and what was previously thought to be identical the majority of time was spent observingnests allopatric populations(Hardy 1961). The most of Ray'sGroup and the Handicap Group. significantdifference between the populations During nesting, the yearling family group is in socialsystems. South Texas Green Jays have members approached the nest only in the an extended interaction between parents and morning to call and display with the breeders young but do not employ helpers at the nest for severalminutes. The yearlingsflew off and during any stageof the reproductivecycle. Co- usually did not return to the nest area until lombia Green Jays have a year-round fixed dusk,when there wasanother short displaype- compositionflock and utilize helpersat the nest. riod. Breederswere never observedto prevent In addition, breeding Colombian female jays a yearling group member from approachinga provide a minimal amount of food items once nest. Even after the young had fledged and the young are fledged (Alvafez 1975). South might beg from all family group membersdur- Texasbreeding femalesappear to fill the op- ing these "greeting" periods, only the breed- positerole in caringfor the young becausethey ing femaleresponded. No attemptto bring food provide almost 100%of the food items for their to a nestor fledgedyoung by any bandedyear- fledged young (Gayou 1984). ling was observed. Theevolution of groupterritoriality.--Given that DISCUSSION both populationsof Green Jaysshow somede- gree of group territoriality, I hypothesizethat Basedon my observationsat the Santa Ana both face some amount of habitat saturation, Refuge,Green Jays at the northernlimit of their with the more severe situation occurring in July1986] TexasGreen JaySocial System 545

Brown Jays

Mexican Jays Blue Jays Florida ScrubJays WesternScrub Jays SouthTexas GreenJays SouthAmerican Green Jay• NO HIGHLY COOPERATIVE COOPERATrVE EVOLUTIONARY CONTINUUM OF JAY SOCIAL SYSTEMS BREEDING BREEDING

NEST

HELPING

EXCELLENT POOR DISPERSAL OPPORTUNITIES

BREEDING EXTENDED ADULTS FAMILY FLOCK SIZE FAMILY ONLy

NONE • I YEAR LENGTH OF RETENTIONOF YOUNG

Fig. 4. Hypotheticalstatus ofsouth Texas Green Jays on the evolutionary continuum ofjay social systems.

South America. Alvarez (1975) found that C. as,helpers should increase the ultimatenum- yncasmove in smallflocks in a widevariety of berof young fledged from a nestby being able habitatsranging from grasslandsto densesec- to locatemore food over a given time interval. ondaryforests. Each flock is a discretesocial In fact,flocks with the highestsurvivorship of unit that defends a stable territory the entire fledgedyoung had the mosthelpers (Alvarez year.The boundaries of theflock territory are 1975).South American Green Jays also may re- defendedby all members,and aggressionoc- main within a flock if the alternative to dis- cursfrequently between members of different persalwill resultin a significantincrease in flocksduring territorial encounters. The flocks mortality.Although Alvarez (1975) presented donot dissolve during the breeding season, and no dataon dispersalor mortalityas a resultof onlyone pair breeds in eachflock. In addition, dispersal,his dataindicate an apparentlysig- Alvarez found that a flock of Green Jays may nificanttrend of youngjays to remainwithin divideto producetwo separateflocks with ad- a flockas helpers for at leastone, and perhaps jacentterritories. This behavior seems similar several,years. Thus, selection would reinforce to FloridaScrub Jay territory splitting by relat- thehelping aspect of thesocial system of these ed offspringof the parentsin a particularter- jays,but such selection might not occur in south ritory,and suggests that South American Green Texas. Jaysmay be undersimilar habitat constraints The situationappears less extreme in south asFlorida Scrub Jays. Yet the questionof when Texas.There must be somecost to dispersalor groupterritories evolved for this population youngGreen Jays would leavesooner, and remainsa matterfor speculation.Because South yearlingsmust provide some benefit in terri- AmericanGreen Jays are somewhatdependent torial defense.Yet, south TexasGreen Jaysseem on occasionalsuperabundant resources, selec- to be able to disperseinto marginalhabitat or tion pressureswould seemto favor a system to become floaters within their former territo- whereby a flock could locate temporary re- ries. A floater would retain the benefits of its sourcesquickly so as to exploit them to the full- high-qualitynatal territory and could quickly estpossible extent (Alvarez 1975). Additional fill an openingin an adjacentflock as an ex- flockmembers would help a grouplocate such perienced,older bird if the timebetween open- resources(Krebs et al. 1983).If food in Colom- ingsin breedingpositions in sucha saturated bia is lessabundant, more patchily distributed, habitatwere short. Preliminary observations of and shows less seasonalvariation than in Tex- southTexas Green Jays showed that breeding 546 DOUGLASC. GAYOU [Auk, Vol. 103 positionsbecame available in Ray'sGroup after aids the parentsreciprocally. Retention of the three years and in the Handicap Group after young in the natal territory without helping at two years (Gayou 1984). the nestmay be an importantevolutionary step Becauseyearling south Texas Green Jaysdo that leadsto a more complexcooperative sys- not provide help directly to siblings, they do tem that includeshelpers at the nest (Fig. 4). not gain breeding experience, their potential Thus, the socialsystem used by south Texas socialbonds are limited, and they have limited Green Jays represents a first example of this effecton the successof closelyrelated kin. Even early stage in the evolution of cooperative so, some trade-off of costs and benefits exists, breeding. associatedwith the territory defense behavior that probably benefits the breedersby freeing ACKNOWLEDGMENTS them (especiallythe males)of someof the costs This researchwas done in partial fulfillment of the inflictedby the stringentterritoriality required requirementsfor the Doctor of Philosophydegree at in south Texas. the Division of Biological Sciences,University of Insufficient information exists on sex ratios Missouri, Columbia, Missouri. I thank John Faaborg to draw conclusionsabout mate availability as and Glenn Woolfenden for their commentsand sug- a cause for reducing the amount of dispersal gestionsduring the preparationof this manuscript.I among south Texas jays. A last consideration am deeply indebted to the entire staff of SantaAna for dispersal,that of dealing with an unpre- National Wildlife Refuge, who made my research dictableor harshenvironment, is probablynot there productiveand enjoyable.I alsothank the Frank M. Chapman Fund of the American Museum of Nat- very important for south Texas Green Jays.Ob- ural History and the TexasOrnithological Societyfor servationssuggest that the high degreeof hab- their financial support. itat saturation of jays in south Texas does not change dramatically through the year, as it LITERATURE CITED might in an unpredictable environment. Oc- casional cold or hurricanes may cause some ALVAREZ,H. 1975. The social systemof the Green mortality, but theseare rare events. Jay in Colombia.Living Bird 14: 5-44. [•ALDA,R. P., & G. C. gATEMAN.1972. The breeding Evolutionof jay socialsystems.--The social sys- biologyof the Pinyon Jay.Living Bird 11: 5-42. tems employed by various jay species range BENDIRE,C.E. 1895. Life histories of North Ameri- from the most simple to the most highly co- can birds. U.S. Natl. Mus. Spec.Bull. 3. operativesystem. It hasbeen hypothesizedthat BROWN,J.L. 1963. Socialorganization and behavior at one stagein the evolutionary sequence,the of the . Condor 65: 126-153. breedersof a particular speciesbegan to allow 1970. Cooperative breeding and altruistic the young to remain within the territory for an behavior in the Mexican Jay Aphelocomaultra- additional time period (Brown 1974, 1978; marina. Anim. Behav. 18: 366-378. Ricklefs 1975; Gaston 1978; Emlen 1982a, b). ß 1974. Alternative routesto socialityin jays-- Once young were permitted to remain on the with a theory for the evolution of altruism and communalbreeding. Amer. Zool. 14: 63-80. natal territory, they developedhelping behav- ß 1978. Avian communal breeding systems. ior as a method of increasingtheir overall fit- Ann. Rev. Ecol. Syst. 9: 421-422. ness. They gained reproductive experience, CLAPP, R. [•., M. K. KLIMKIEWICZ, & A. G. FUTCHER. helped raisesiblings, located resources, and de- 1983. Longevity records of North American tected predators.The parents tolerated this be- birds: Columbidae through Paridae.J. Field Or- havior becausethe young could not disperse, nithol. 54: 123-137. perhapsbecause of the lack of suitable habitat CROSSIN,R. $. 1967. The breeding biology of the in which to disperseand survive. Tufted Jay. Proc. Western Found. Vert. Zool. 1: I propose that south Texas Green Jays ex- 265-297. emplify an early stage in the evolutionary se- EMLEN,$. T. 1982a. The evolution of helping be- havior I. An ecologicalconstraints model. Amer. quence of development of cooperative breed- Natur. 119: 29-39. ing as one responseto environmental factors. --. 1982b. The evolutionof helping II. The role Although southTexas Green Jayspermit young of behavioral conflict. Amer. Natur. 119: 40-53. to remain on a territory even though the young FLEETWOOD,R.J. 1973. Plants of Santa Ana National do not act as nest helpers, the territorial de- Wildlife Refuge. Washington, D.C., U.S. Dept. fensebehavior of the young birds undoubtedly Interior, Fish Wildl. Serv. July1986] TexasGreen Jay Social System 547

GASTON,A. J. 1978. The evolution of group terri- the vicinity of Fort Brown,Texas, from February torial behaviorand cooperativebreeding. Amer. 1876 to June 1878. Proc. U.S. Natl. Mus. 1: 118- Natur. 112: 1091-1100. 173. GA¾OV,D.C. 1984. The behavioralecology of Texas MEYERDE SCHAUENSEE, R. 1966. The speciesof birds GreenJays (Cyanocorax yncas). Unpublished Ph.D. of South Americaand their distribution. Wynne- dissertation, Columbia, Univ. Missouri. wood, Pennsylvania,Livingston Publ. Co. FIARD¾,J.W. 1961. Studiesin behaviorand phylog- RICKLEFS,R.E. 1975. The evolution of co-operative eny of certainNew World jays(Garrulinae). Univ. breeding in birds. Ibis 117: 531-534. Kansas Sci. Bull. 42: 13-149. SENNETT,G. B. 1878. Notes on the ornithology of KENNARD,J. I-I. 1975. Longevity recordsof North the lower Rio Grande of Texas from observations Americanbirds. Bird-Banding456: 55-73. madeduring the seasonof 1877.Bull. U.S. Geol. KREBS,J. R., D. W. STEPHENS,& W. J. SUTHERLAND. Geogr. Surv. Territory 4: 1-66. 1983. Perspectivesin optimalforaging. Pp. 165- SUTTON, G. M., R. B. LEA, & E. P. EDWARDS. 1950. 216 in Perspectivesin ornithology(A. H. Brush Noteson the rangesand breedinghabits of cer- and G. A. Clark,Jr., Eds.). New York, Cambridge tain Mexican birds. Bird-Banding21: 45-59. Univ. Press. WOOLFENDEN,G.E. 1975. Florida ScrubJay helpers MERRILL,J. C. 1878. Notes on the ornithology of at the nest. Auk 92: 1-15. southernTexas, being a observedin