Breeding Biology of the Black-Headed Grosbeak in Northern Utah

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Breeding biology of the black-headed grosbeak in northern Utah

Article in Western Birds · January 1983

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Gary Ritchison Eastern Kentucky University

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The user has requested enhancement of the downloaded file. BREEDING BIOLOGY OF THE BLACK-HEADED GROSBEAK IN NORTHERN UTAH

GARY RITCHISON, Departmentof Biology,Utah State University,UMC 53, Logan Utah 84322 (presentaddress: Department of BiologicalSciences, Eastern Kentucky University,Richmond, Kentucky 40475)

Althoughthe Black-headedGrosbeak (Pheucticus melanocephalus) is a common breeding bird in many parts of western North America, little is known aboutits breeding biology. Apart from a few anecdotalreports (Bent 1968), information on the breeding biology of this speciescomes from a singlestudy performed in California(Weston 1947). The objectiveof the presentstudy was to examinethe breedingbiology of a populationof Black- headed Grosbeaks in northern Utah.

STUDY AREA

The study was conducted at Malibu-Guinavah Forest Camp (Cache Na- tionalForest), 10 km eastof Logan,Cache County, Utah. The area,at 1500 m elevation,is locatedon the fiat bottom of Logan Canyon, with the Logan River cuttingdiagonally across the easternsection. The vegetationis discon- tinuouswoodland, which is characterizedby a heavygrowth of grassesin the open areas and a dense understory of wild rose (Rosa woodsii), Blue Elderberry ($ambucus coerulea), hawthorn (Crataegus rivularis), Chokecherry(Prunus virginiana), and SierraWillow ($alix wolfii). The domi- nant trees in the area are Box Elder (Acer negundo), Dusky Willow ($alix melanopsis),and River Birch (BetulafontinaIls). Numerous Mountain Alder (Alnustenuifolia) can be found alongthe streambanks with occasionalNar- rowleaf Cottonwood (Populus angustifolia)and Green Ash (Fraxinus lanceolata)dispersed over the area. Becauseof recreationalimprovements by U.S. Forest Servicepersonnel, the canopy is discontinuous.

METHODS

I made field observationsalmost daily from 1 April through 31 Augustin 1977 and 1978 at the Malibu-GuinavahForest Camp. Approximately850 hourswere spentobserving birds or nestsand observationswere equallydis- tributedthroughout the day. Territorialboundaries were delimitedby plotting on a map thoselocations where intraspecificaggressive behavior occurred. If a part of a territorycould not be determinedby observationof boundary disputes,the outermostpoints of utilizationwere connectedby straightlines to form a polygon of maximum size. Hatching dates were obtained by inspectingthe nests.When this was impossible,these dateswere estimated within 1 or 2 days on the basisof the behavior of the adults. In all cases, eitherfiedging was observed,or young known to have been in the nestthe previousday were seen in nearby trees or shrubsa day later. Thirty-one adults (24 males and 7 females)were capturedand marked with combina- tionsof coloredleg bands, numberedaluminum bands, and felt pens. In ad- dition, 21 nestswere located, and colored and aluminum bandswere placed Western Birds: 14:159-167, 1983 159 BLACK-HEADED GROSBEAK BREEDING BIOLOGY

on 20 nestlings. Observations at such nests were made with 7x 35 binocularsat distancesof 4-8 m, usingnatural vegetation as a "blind." A stopwatchwas used to time the activitiesof breedingadults.

RESULTS AND DISCUSSION

The firstbirds arrived in the studyarea duringthe first 2 weeksin May. AlthoughWeston (1947) reportedthat males arrive about 6 daysbefore the females,my observationsindicated that many of the firstbirds to arrivewere alreadypaired. Grosbeakscontinued to move into and throughthe area for the next 2 weeks or longer. Bandingreturns suggested that the firstbirds in the study area were often those that nestedin the area the previousyear. These birds, however, did not always remain in the study area. Six birds bandedin 1977 were observedin the studyarea early in the 1978 breeding season;two of thesepreviously banded birds (one male and one female) re- mained to nest in the study area. Because many birds arrived already paired, observationsof courtship behavior were limited. Weston (1947:55) stated that "the only type of displayseen was a nuptialflight," i.e., the male utteredloud songsfrom someexposed perch near a femaleand then suddenlyflew out, performinga song-flightin the air abovethe female. My observationsindicated that such song-flightswere not utilizedsolely for courtship.On severaloccasions males were observedperforming song-flights during "singing duels" with neighbor- ing males.

The Pair Bond

Duringthe earlypart of the breedingseason (before nesting began), paired birdsforaged together within their territories. Females usually followed as the males moved through the territory feeding and singing. Paired birds sometimesfed asclose together as several centimeters, or morecommonly in differentparts of the same tree or bush or in adjacenttrees or bushes. Vocalizationsgiven by the birdsas they moved throughtheir territoriesin- cludedchip and wheetcalls. Chip callswere givenby both sexesand appearedto functionas locationcalls. Wheet calls were given only when a bird was moving, e.g., when flying a short distancefrom bush to bush or when flyingfrom the nestafter incubatingthe eggs. As statedabove, males often sang as they foraged.Such song apparently serveda territorialfunction and wasprobably used by the femalein maintain- ing contactwith the male. Femalesinfrequently sang while foragingnear the male (Weston1947; pers.obs.). Female song has also been reported in the Rose-breastedGrosbeak (Pheucticusludovicianus; Ivor 1944a, Dunham 1965). Such songmay play some role in pair-bondmaintenance.

Territorial Behavior

In the Black-headedGrosbeak, singing by the male appearsto be the most importantfactor in acquiringand retaininga territory.However, singingby itselfis apparentlynot sufficientto maintaina territory.Early in the breeding 160 BLACK-HEADED GROSBEAK BREEDING BIOLOGY

seasonagonistic encounters involving chasing and even physicalcontact occurred. Nearly all chasesinvolved males, although several female-female chaseswere observed.On three occasionsfemales were observedchasing males. No instancesof actualphysical contact were noted in thesefemale- female or female-male encounters. Weston (1947:56), however, describeda conflictbetween mated pairsin apparentdefense of their respectiveterritories in which the females were more aggressivethan the males. The females "repeatedlypostured and flew at eachother, and at each attack,loud songs, calls, and soundsof bodily contact could be heard." Weston reported no other instancesof female song in territorial encounters. I observedtwo instancesof singingby females in such situations.On one occasion,a female chaseda male and, upon landing,sang one loud song. On anotheroccasion a female appearedto engagein a briefsinging duel with a neighboringmale. Following territory establishment,Black-headed Grosbeaksbecame pro- gressivelyless aggressive.This change in behavior was quantified in two ways. First, male singingrates tended to decline as the seasonprogressed (Figure 1). A second indicator of this decline was the distributionof intraspecificagonistic encounters (chases or actualphysical encounters). Figure 2 summarizesthis distributionfor the 1977 and 1978 breedingseasons. It is

222 16•1• I % • •Red I I --• Guinavah I .,.....,,,...,.., Riverside

I % •-4•-w•, Black11978l z12O]I, \ ..-- cs28

"', !

...... h /

•..... ,•,m•m,•a•,,•-•"• •' ..... T ...... T ...... T .... firming' younghatch you•the leave•st TIME IN DAYS

Figure 1. Singing rates of selectedmale Black-headedGrosbeaks during the 1977 and 1978 breeding seasons.

161 BLACK-HEADED GROSBEAK BREEDING BIOLOGY

apparent that after egg-layingbegan there was a substantialdrop in the number of encountersand, later, such agonisticbehavior disappeared altogether.In the daysprior to and immediatelyafter the youngleft the nest, males and femalesresponded weakly, if at all, to the presenceof other grosbeaks. Similar behavior has been reported in the Rose-breasted Grosbeak (Dunham 1964). Territoriesin the studyarea averagedabout 2.7 ha (n -- 12, range: 1.9 - 3.9). Previous investigatorsof the Black-headed Grosbeak have not in- dicated territory sizes. However, Dunham (1964, 1965) found that the averagesize of 20 Rose-breastedGrosbeak territories was 0.8 ha (range:0.3 1.8).

Nest site selection and nest construction

Nestingusually occurred in deciduousbushes and trees, usually at a heightof 2-7 m above the ground (n = 21, • = 4.1). Weston (1947) listedheight recordsfor 163 nestsand foundthe averageto be about3 m aboveground. The nest is bulky and looselyconstructed, and composedof slendertwigs, plant stems,and rootlets. Nestswere generallybuilt by the female. Weston (1947:60) reportedthat he had "never seena male carryingnesting material nor in any way aid in the actualconstruction of the nest."However, Finley (1907) mentionedseeing a male grosbeakcarrying a twig in his beak. On severaloccasions I observed

TimeCdays)

Figure2. Distributionof intraspecificagonistic encounters (chases and/or actualphysical encounters)among male and female Black-headedGrosbeaks (day 0 = firstegg laid). 162 BLACK-HEADED GROSBEAK BREEDING BIOLOGY malesassisting in nestconstruction. In all pairsobserved, however, most of the constructionwas performedby the female. Constructionof neststook from 3-4 dayswith mostof the buildingoccur- ring in the morning.Visits to the nestbecame less frequent and more ir- regularas the day progressed,and in the afternoonnests were sometimes visitedwithout any nestingmaterial. During the finalstages of construction, femalesspent less time placingnew materialin the nestand, instead,spent more time readjustingmaterial already there (Weston1947; pers.obs.). Followingthe completionof thenest there was a periodof 2-5 daysbefore the firstegg was laid. The eggswere laid at intervalsof approximately24 hours, and the usualset consistedof two to four eggs(R -- 2.8, n = 14). Weston (1947) indicatedthat the averageclutch consisted of 3.3 eggs(n -- 192).

Incubation

Both sexesincubated during the day (Head 1902, 1904; Weston 1947; pers. obs.), while the female incubatedat night (Weston 1947; pers. obs.). Duringthe day, eggswere incubated about 97% of the time, about41% of the time by malesand 56% by females.The averagelength of eachincuba- tionperiod for t0 maleswas about 35 minutes(range: 2.5 to tOO)and for t0 females,about 51 minutes (range: tt to 130). Both sexeswere surprisinglyvocal on and aroundthe nest. Malesfre- quentlysang while incubating.At timesthis song appeared to be in response to the singingof neighboringmales; i.e., a male that was quietlyincubating wouldbegin to singupon hearing a neighboringmale sing. At othertimes the male'ssinging appeared to be a signalto the female.When a male'speriod of incubationwas due to end he oftenbegan to sing.Generally, the femaleap- peared at the nest within a few seconds. Whereasincubating males often sangto inform the female of their ap- parentintention to leavethe nest,incubating females appeared to conveythe sameinformation with chip calls.Males generally returned to the nestwithin a few secondsupon hearingtheir incubatingmate's call note. On many occasionsa male or femaleapproached the nestand found its matequietly incubating. At thesetimes, the approachingbird frequently uttered chip callsor sang.The incubatingbird, upon hearingits mate, would then leave the nest (usuallyafter utteringseveral chip calls).Rose-breasted Grosbeaksalso behave in this manner when changingplaces on the nest (Ivor t944a,b; Allen 1916). As mentionedpreviously, when grosbeaksflew fromthe nestthey nearlyalways uttered one or morewheet calls. Such calls apparentlyinformed the mate that the bird on the nest was leavingand resultedin fasterchange-overs. Rarely were nestsleft uncoveredfor more than a few seconds (• = 9.7sec, n = 74). The incubationperiod ranged from 12-14 days,with mosteggs hatching at 13 days. Eggsin a clutchusually hatched on the sameday, and in no case were more than 2 daysrequired for the hatchingof all eggsin a clutch.

163 BLACK-HEADED GROSBEAK BREEDING BIOLOGY

Parental Care

During the first few days post-hatchingadults maintainedthe same "schedules"as whenincubating. Both adults fed and broodedthe young, and theirbehavior when changingplaces on the nestwas similar to that during incubation,with one significantdifference. During incubation an ap- proachingfemale usually uttered chip calls to inform the male of her presencebut duringthe broodingperiod females were more likely to sing (Figure3). After fiedging,such songs were usedby femalesto maintaincontact with the young (Ritchison1983). Malesand females contributed equally to thefeeding of theyoung throughoutthe nestling period. And, surprisingly,the number of feedingtrips to the nestwas found to remainrather constant throughout that period (Figure 4). However,later in the nestlingperiod adults appeared to bringlarger food items,and they frequently brought more than one itemper trip to the nest. Asthe young developed both parents spent progressively longer periods off the nest.By the 7th day post-hatchingthe parentsbrooded much less con- stantly,although the young were still covered a goodpart of thetime (Figure 5).

42 47

. • • •.GUINAVAH ...... RIVER =.16 ...... i&"

. • I

/%//' /I/ I I I I I I I I '1 I I I I I I I I I I I I I I I I I I I I I I I 1st you• •g •9 la• •tch fled• Time

Figure3. Singingrates of selectedfemale Black-headed Grosbeaks during the 1977 and 1978 breedingseasons. 164 BLACK-HEADED GROSBEAK BREEDING BIOLOGY

On the 8th day the eyes of the young beganto open, and by the 9th day they were usuallywide open. At this stagethe young were broodedinfre- quently, the time spentbrooding being dependenton the weather (Weston 1947; pers. obs.). Adults approachingthe nest to feed the young usually vocalized,uttering either chip calls or songs.Upon the arrivalof an adultat the nest, young grosbeaksimmediately began to utter beggingcalls. At times younggrosbeaks responded to the chipcalls of theirparents and begancalling before the adults arrived at the nest. Young grosbeaksleft the nest as early as the 9th day post-hatching, although departure at 10-14 days post-hatchingwas more common (• = 11.5, n = 21). After leavingthe nestthe youngscattered among the shrubs nearthe nest,perching on low branches.During the firstfew daysafter leaving the nest,the youngwere ratherquiet. As the fledglingsare unableto fly at this time, they remainedwithin a restrictedarea and the adultsappeared to have little trouble locating and feeding them (Weston 1947; pers. obs.). If, however, an adult was unableto locatea young bird, it would beginto utter chip calls and songs. Upon hearing their parents' vocalizations,young grosbeaksresponded by utteringphee-oo and hunger-distresscalls. In this manner the parentsand young were able to maintaincontact. Afterthe youngattained flight (approximately 15 dayspost-hatching) main- taining contact betweenparents and young became more difficult.When parentshad food for the youngbut were unsureof the locationof the young, the parents uttered chip calls or, more frequently, songs. Upon hearing a

ß ß Total

eo 4, e• trips/nestling•.

' I ' I ' I • I ' I I 2 4 6 8 10 12 Days post-hatching

Figure4. Averagenumber of feedingtrips made by pairsof Black-headedGrosbeaks (n --8) throughoutthe nestlingperiod.

165 BLACK-HEADED GROSBEAK BREEDING BIOLOGY

parent sing, a young grosbeakwould fly to within a few metersor lessof the adult and, if not fed immediately,would begin calling. At thisstage (2-3 weekspost-hatching), family groups no longerremained within their territories.Because of this wandering, it was difficultto observe specificfamily groupsover long periodsand, therefore,the durationof such groupsremains unknown. Weston (1947) reported seeingyoung grosbeaks beingfed by adultsin earlyAugust, but he was unableto determinethe actual lengthof the dependentperiod. In the Rose-breastedGrosbeak, Watts (1935) and Dunham (1965) reportedthat adultscontinued to feed the youngafter they had moltedinto their firstwinter plumage in at leastsome cases, and the family groupsremained together until migration.Ivor (1944a,b), however, reported adult Rose-breastedGrosbeaks striking young on the bill after feedingthem, beginning27 daysafter hatching.He suggestedthat thismay have beena weaningprocedure, the "adultsstill reacting to beggingwith food, but to the adult appearanceof the young with aggression." Since males appeared to leave the nesting area before the females or young, laterin the seasonfamily groups consisted solely of femalesand their

50 - -100

30-

[ •at nest

\ i•off nest

10-

I I I I I 2 4 6 8 10 Days post-hatching

Figure5. Averageamount of time spenton and off the nestby pairsof Black-headedGrosbeaks (n = 8) throughoutthe nestlingperiod. 166 BLACK-HEADED GROSBEAK BREEDING BIOLOGY

young(Weston 1947; pers.obs.). Resident females and young began leaving the studyarea in earlyAugust, with the lastgroups leaving the studyarea in mid-tolate August.Transients were seen in the area into earlySeptember.

ACKNOWLEDGMENTS

I wishto thank Keith Dixon for his guidancethroughout this study.Also, thanks are extended to Jack Watson and Lee Jones for assistancein the field. Thisinvestigation was partially funded by grants from the FrankM. Chapman Fund of the American Museum of Natural History and from Sigma Xi.

LITERATURE CITED

Allen, F.H. 1916. A nestingof the Rose-breastedGrosbeak. Auk 33:53-56. Bent, A.C. 1968. Life historiesof North American cardinals,grosbeaks, buntings, towhees,finches, sparrows, and allies.U.S. Natl. Mus. Bull. 237. Dunham, D.W. 1964. Behavior of the Rose-breasted Grosbeak, Pheucticu$ ludoui- cianu$. Unpubl. Ph.D. thesis,Cornell Univ., Ithaca, NY. Dunham, D.W. 1965. Territorial and sexual behaviour in the Rose-breastedGros- beak, Pheucticusludovicianus. Z. Tierpsychol.22:438-451. Finley, W.L. 1907. Americanbirds studied and photographedfrom life. Scribner& Sons, New York. Head, A. 1902. A studyof the Black-headedGrosbeak. Condor 4:119-121. Head, A. 1904. Nestinghabits of the Black-headedGrosbeak. Condor 6:35-37. Ivor, HR. 1944a. Bird study and some semi-captive birds: the Rose-breasted Grosbeak. Wilson Bull. 56:91-104. Ivor, H.R. 1944b. Rose-breasted Grosbeak in semi-captivity. Aviculture 14:179-182. Ritchison,G. 1983. The functionof singingin femaleBlack-headed Grosbeaks: family-groupmaintenance. Auk 100:105-116. Watts, G.E. 1935. Life historyof the Rose-breastedGrosbeak. M.S. thesis,Cornell Univ., Ithaca, NY. Weston, J.G., Jr. 1947. Breedingbehavior of the Black-headedGrosbeak. Condor 49:54-73. Accepted 6 September 1982

Black-headed Grosbeak Sketch by Tim Manolis

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