REPRODUCTIVE BEHAVIOR OF WHITE-BREASTED NUTHATCHES II. COURTSHIP LAWRENCE KILHANI WroTE-BREASTEDNuthatches (Sitta carolinensis)are unusualamong northernhemisphere birds in their closepair bondsheld over most of the year as well as in their variedforms of courtship,which can reacha crescendoin midwinter.The presentreport on their behaviorincludes field observationsbegun in Bethesda,Maryland in 1952 but carried on for the mostpart in Lyme, New Hampshirebetween 1963 and 1970, as well as studiesof hand-raisedindividuals. I have been studying Red- breastedNuthatches (S. canadensis)similarly with an aim of eventually comparingthe behaviorof the two species. General accountsof White-breastedNuthatches are given by Tyler (1916) and Bent (1948), amongothers. While theseauthors describe somedisplays excellently, they omit othersand fail to accountfully for all that happensin courtship,which Thomson (1964) describesas covering "a widerange of activitiesof whichthe functionseems to lie in attracting a mate,maintaining the pair bond,and in facilitatingcopulation and parental activities." METtIODS OF STUDY Aviary studies.--I removedyoung in the pinfeatherstage from severalnests and raisedthem by hand. One pair of thesecarried out breedingbehavior, going as far as laying and incubatingeggs in 2 successiveyears. This handsraisedpair enabled me to seerepeatedly and at closerange much that helpedinterpret field observations. The birds were maintainedin an aviary 2 m square,3 m high, and built inside a greenhouse. Field studies.--I observed courtship behavior to best advantage by going into woods before dawn in winter months, often at temperaturesclose to OøF, and watchingthe roost holes (Kilham, 1971) in order to follow the activitiesof males in the first half hour of the day when, as Tyler (1916) notes, courtshipactivities may reach a peak. White-breastedNuthatches become recognizable individually when followed throughmost of the year. One male held the same territory for 2 and two others for 3 years. All retained the same mates throughout this time as couldbe checkedby head patterns (Figure 1) in which the distributionof gray and black differs between one individual and another. Retention of the same mates over successiveyears is also describedby Brackbill (1969) for S. carolinensisand by Lack (1945) for the EuropeanNuthatch (S. europaea);both authorsused color bands for identification. I operateda woodlandfeeding station over two successivewinters. Althoughthis enabled me to watch nuthatches at close range, the artificial abundance of food had a markedly disruptiveeffect on their behavior. Hence essentiallyall of the presentstudies were madein woodlandsaway from housesand feedingstations. 115 The Auk, 89: 115-129. January 1972 116 LAWRENCEKrZ•A•t [Auk, Vol. 89 Figure 1. Head patterns of individual female White-breasted Nuthatches, ranging from dull black to light gray with mixed types in between. White-breasted Nuthatches have a variety of vocalizationsassociated with court- ship (Table 1), and each of these can vary in the way it soundswith distance, as Tyler (1916) noted. Main displays associatedwith courtship were the following: INTIMATE NOTES The most frequent vocalizationsof White-breastedNuthatches are the low "hit-tuck" notesmembers of pairs exchangeas they travel through woods in fall and winter months. The vocalizations are seldom monoto- nous, for each bird makes a slightly different note from the other, as Thoreau (1962) noted, "Nuthatches are faintly answeringeach other, tit for tat, on different keys," his accountindicating their occasional antiphonalnature. Much of the answeringby the two birds is irregular, for one may be feeding while the other continuescalling alone. A fast rate of exchangesis 30 a minute,but this rate is seldommaintained. The term "intimate" is appropriate,as thesenotes reflect the closepair bond of a well-establishedpair. They doubtlessserve a numberof functions. One of theseseems to be location,for the two nuthatchesare frequently out of sightof eachother as they spiral about the trunks and branches of large trees; anotheris expressionof moodsas they changefrom minute to minute in relation to circumstances.The European Nuthatch (S. europaea) has equivalent"sie, sie" notes which LiShrl (1958) de- scribes as Stimm/uhlungslaut. Such notes may also have additional functions. Equilibrium is not always present between members of a pair, and the "kun," or "kun-uns" and "tchups" that may replace the usualnotes may be a way in which a male assertshis dominance. At the approachof actual nestingor during the early nestingperiod, femalesare generallysilent while males,hunting prey to feed them, may continueto make small notesthat can be surprisinglyvaried when they are away from their mates. January 1972] White-breastedNuthatch Courtship 117 TABLE 1 VOCALIZATIONS1 CONiNiONL¾ ASSOCL\TEDWITI• COURTSl•IIP IN THE Wl•ITE-BREASTED NUTHATCH Vocalization Purpose When used "•Vurp-wurp-wurp" Courtship song of male; associatedwith January to early (8-11 notesin back presented to female and bowing May, sporadic rapid series) display at full intensity. Numerous only at other variations at less intensity. May serve seasons as territorial song; location notes, etc. "Phee-oo" Expression of intense sexual emotion (1) February (male by male prior to and during pursuit only) to early flights, (2) by female immediately be- May fore and after coition. "Hit-tuck" and Serves (1) to maintain pair bond, (2) as Winter and early "tchup" location notes. "Tchup" conveysa mild spring primarily degree of excitement. "Kun," "ka-un," Expressesexcitement, the degree depending All months "kaan," etc. on whether the notes are single or given ("quank") in a rapid series and whether loud or soft. • A rapid "hn, hn, hn" or trill, commonly heard in late breeding season, is considered more related to agonistic than to courtship behavior and will be dealt with elsewhere. COURTSHIP SONG The song the male nuthatch singsin winter and spring has at least four variations, and while all may serve to advertise territory, their main function appearsto be courtship. Early morning rendezvoussong.--The finest and most prolonged singingof male White-breastedNuthatches may begin in January and last until early March, often at temperaturesbelow freezing when woods are deep in snow, and always in the first half hour after leaving the roost hole. The male is essentiallya lone bird at this time, for males and females roost at a distance from each other and may emerge from their holes at different times. Within minutes of leaving his roost hole in late winter, for example,Male B (MB), who had recently acquired his mate, would fly to the topmostbranch of one of the tallest oaks or maplesgrowing in an exposedposition at the edgeof a swamp. Resting at right anglesto his perch20 to 35 m abovethe ground,he sangflat- sounding"what, whats" in a rapid seriesof 8 to 11 notes lasting 2 seconds,followed by a rest periodof 3 secondsin whichhis body swayed slowlyin an arc of 45 degrees.His head and neck would then suddenly shootup (Figure 2) so that his body was almostvertical as he began again. In full performancehis body bowed down with each note, but at lesser intensities only his bill appeared to move from an upward 118 LAWRENCEK•L>tA•r [Auk, Vol. 89 Figure 2. A male White-breasted Nuthatch (A) shoots head and neck upward at start of courtship song, (B) then relapsesat end to resting position. position of 45ø at the start to a position slightly below the horizontal at the end. After 2 to 3 minutes of facing in one direction, MB would hop around to face the opposite way. A suddenchange, often noted after 5 to 10 minutes, was a shift from the dull "what" notes to musical "wurp, wurp, wurps." On nearly all such occasions I soon heard the first "kun" or "kun-un" notes of the female. She was usually at a distanceand in no hurry to arrive. When she did come to branchesbelow her mate, he would soon stop singing and join her, the two then foraging together and exchanging"hit-tuck" notes. Direct display to mate song.•Another pattern of singing the ren- dezvoussong was exemplifiedby Pair L in February 1966, when FL, on arriving to join her mate, took a perch below the level of his and about 3 m away. After swaying slowly from side to side for a time, shethen became motionless, as if held by his song. This latter beganwhen ML, stretchingupward into a vertical position, began bowing down with each "wurp" of his song, thus displaying in succession,as well describedby Bent (1948), first "the black of his crown and his rough raisedmane, then the blue gray of his back, then the variegatedpattern of his expandedtail, then perhaps at the end of his bow, a flash of ruddy brown." This ruddy brown in the vent region, although present January 1972] White-breasted Nuthatch Courtship 1 19 in both sexes,appears to be brighterin malesthan females.The complete attention that a female can give to such a performanceover a period of 6 to 8 minutes is extraordinary. After this time FL would become restlessand leave to forage; ML, like other males, would then stop singing. One doesnot encounterthis full intensityperformance with all males. In the winterof 1969,for example,I heardit quite regularlywith MB whohad acquireda mate the fall before,whereas in the followingyear, whenI likewisefollowed his activitiesfrom Januaryto March, I never witnesseda full performance.It seemspossible therefore that males matedfor a year and havingwell-established pair bondssing in a less prolongedfashion. During the first few