Natural History of the Nuttall Woodpecker at the Hastings Reservation

NATURAL HISTORY OF THE NUTTALL WOODPECKER AT THE HASTINGS RESERVATION

ALDEN H. MILLER Museum of Vertebrate Zoology University of California Berkeley, California 94720

AND CARL E. BOCK Biology Department University of Colorado Boulder, Colorado 80302

FOREWORD Stickel 1965; Davis 1965; Lawrence 1967; Den- Between 1954 and 1964, the late Alden H. Mil- nis 1969)) the ladder-backed Dendrocopos spe- ler involved himself at irregular intervals in a cies have received relatively less individual field study of the Nuttall Woodpecker (Den- attention. Ligon (1970) has recently reported drocopos nuttallii) at the Hastings Natural on a study of the Red-cockaded Woodpecker History Reservation, Monterey County, Cali- in Florida, while Short (in press) has studied fornia. I have attempted in this paper to pre- the systematics, ecology, and behavior of Den- sent the results of this study, based upon Mil- drocopos species, including the “ladder- lers’ partially analyzed data. I wish to thank backed” forms. John Davis for making available these data as Root (1967:346) proposed the term “eco- well as pertinent field notes of other observers logical guild‘ . . . for groups of species that at the reservation, Among the latter, G. A. exploit the same class of environmental re- Bartholomew, H. Hjersman, J. T. Marshall, sources in a similar way.” He pointed out (p. Jr., and especially T. Riney made extensive ob- 335) that “one advantage of the guild concept servations of local D. nuttullii. John Davis is that it focuses attention on all sympatric kindly read and criticized the original manu- species involved in a competitive interaction, script. Gene M. Christman prepared the illus- regardless of their taxonomic relationship.” tration (fig. 1) . There is also value to recognizing and com- CARL E. BOCK paring species ecologies within truly taxonomic guilds, whether in sympatry or not. This calls The Nuttall Woodpecker is one of a group of attention to processes of adaptive radiation “ladder-backed” Dendrocopos species ( VOOUS and the plasticity possible within a certain 1947), so-called because they exhibit trans- basic ecological pattern, or, in other words, verse black and white barring dorsally. In to the existing variations on a phylogenetic North America there are three such species, theme. North American Picidae appear to be similar in appearance and occupying closely among the better known and easily recognized complementary ranges. The Red-cockaded “taxonomic guilds,” and we hope that this Woodpecker (D. borealis) inhabits pine for- study will further an understanding of the ests of the southeastern United States (Bent group. 1939; Ligon 1970), occurring west to eastern Texas and Oklahoma (A.O.U. 1957). The THE STUDY AREA Ladder-backed Woodpecker (D. scalaris) is All field data were collected by means of direct ob- most typical of desert scrub, ranging from servation of Nuttall Woodpeckers on the Hastings Reservation. The reservation lies between 1500 and Texas, Oklahoma, and southern Colorado to 2750 ft elevation at the northern end of the Santa southeastern California and south through Lucia Mountains in Monterey County, California. Mexico and Central America to northeastern Rainfall, which averages 22 inches annually, falls al- Nicaragua. Dendrocopos nuttallii is largely most entirely between December and March, sum- endemic to California, where it is common in mers being hot and dry. mesic oak woodland and riparian situations There are three general habitat types utilized by Nuttall Woodpeckers on the Hastings Reservation. ( Bent 1939; Short, in press ) . North-facing slopes are covered by deciduous oak While the autecologies of many North Amer- woodland, largely blue oak (Quercus douglasii) and ican woodpeckers have been well studied valley oak (Q. lob&r). Exposed south-facing slopes (e.g., Howell 1952; Kilham 1958 and others; are covered with chaparral species, predominantly

[284j The Condor 74:284-294, 1972 THE NUTTALL WOODPECKER AT HASTINGS RESERVATION 285

TABLE 1. Plant species availability and utilization by foraging Nuttall Woodpeckers at the Hastings Reservation.

Minutes of utilization

Availability Total April-June July-Nov. Dec.-March

Plant species n % n % n % n % n %

Live oak 71 26.0 779 39.54 33 11.34 322 36.67 424 52.93 (Quercus agrifolia) Blue oak 68 24.9 504 25.58 191 65.63 80 9.11 233 29.09 (Quercus douglasii) Valley oak 57 20.9 338 17.16 50 17.18 240 27.33 48 5.99 ( Quercus Zobata) Oak subtotal 196 71.8 1621 82.28 274 94.16 642 73.11 765 88.01 Chamise 2 0.7 135 6.85 - - 65 7.40 70 8.74 ( Adenostomafasciculatum) Willow 31 11.4 95 4.82 15 5.15 77 8.77 3 0.37 ( Salir spp. ) Sycamore 9 3.3 53 2.69 - 0 40 4.56 13 1.62 ( Platanus racemosa ) Elderberry 2 0.7 6 0.30 - - 6 0.68 - - (Sambucus gluuca) Poison oak 2 0.7 3 0.15 - 0 1 0.11 2 0.25 (Rhus dioersiloba) Miscellaneous 31 11.4 57 3.00 2 0.69 47 5.46 8 1.00 ’

Totals 273 100.0 1970 100.00 291 100.00 878 100.00 801 100.00 chamise ( Adenostoma fasciculatum). Canyons and 1944; Short, in press). Chaparral is utilized, shaded areas support a mixed woodland, common but only where it is associated with larger trees species being live oak (Quercus agrifolia), western which can serve as nest/roost sites. Most field sycamore ( Platanus racemosa), big-leaf maple ( Acer macrophyllum), and California bay ( Umbellularia observers agree that Nuttall Woodpeckers califomica) . Impoltant brushy species in moister completely avoid pure coniferous forest (Beld- areas include willows (Salix spp.) and cream bush ing 1878; Dawson 1923; Grinnell and Miller (Holodiscus discolor). For a more complete descrip- 1944), although Short (in press) found birds tion of the Hastings Reservation, see Linsdale ( 1943). foraging in pinon pines (Pinus cemhroides) HABITAT UTILIZATION in the San Bernardino Mountains of southern Californa. GENERAL DISTRIBUTION AND HABITAT According to the American Ornithologists ’ HABITAT UTILIZATION AT THE HASTINGS RESERVATION Union Checklist ( 1957), the Nuttall Wood- pecker is “resident in California west of the Table 1 is a summary of plant species utilized deserts and the Sierra divide, from southern by Nuttall Woodpeckers at the Hastings Res- Humboldt and Sonoma counties and the head ervation, based upon 1970 minutes of direct of the Sacramento Valley south to northwest- observation of foraging birds. These data are ern Baja California.” Short (1965) has re- divided into three periods: the breeding sea- viewed possible records of D. nuttallii in Ore- son (April-June); the post-breeding dry sea- gon. It probably occurs there only very rarely. son (July-November); and the wet season Within its range the Nuttall Woodpecker (December-March). Included in table 1 are most typically occurs in oak woodland. Miller data on tree availability, based upon a strip ( 1951)) in analyzing the distribution of the census through the reservation about 100 yards birds of California, lists “oak woodland” as the wide and 0.5 mile long. Brushy species were primary habitat of Dendrocopos nuttallii and counted as “clumps” 30-50 ft across the crown, “riparian woodland” as a secondary habitat. rather than on the basis of trunks, in an at- Bendire (1895) likewise found the species tempt to make tree and brush “individuals” most abundant in oaks, but also in riparian equivalent. cottonwoods ( Populus), willows, sycamores, From table 1, it is obvious that oaks are the and the like. Where oaks are scarce, as in mainstay for foraging Nuttall Woodpeckers parts of southern California and Baja Califor- at the Hastings Reservation, both in terms of nia, Nuttall Woodpeckers are most abundant availability (71.8%) and selection ( 82.3%). in riparian situations (Grinnell and Miller However, there are important seasonal shifts 286 ALDEN H. MILLER AND CARL E. BOCK

TABLE 2. Nest tree preference of Nuttall Wood- sites were in dead trunks or limbs, indicating peckers, based upon literature references, unpublished again the preference for soft wood. field notes, and personal observations. The following data on nests were taken

Nest trees n % from the sources mentioned above: nest heights, 345 ft ( f = 17; n = 54); hole diam- Willow 11 19.3 eter, 1.53 inches (? = 2; n = 6); cavity Sycamore 10 17.5 depth 5-18 in (?= 11; 12= 12). Cottonwood 9 15.8 CONCLUSIONS Alder 7 12.3 Valley Oak 4 W. L. Dawson (1923) noted that it was easiest to predict where Dendrocopos nuttallii would Live Oak 2 Blue Oak 1 I1 22.8 not be found (e.g., pine forest), but that the most likely place to find the species is where Oak sp. 6 riparian vegetation is bordered by or mixed Elderberry 2 3.5 with oaks. We have found that Nuttall Wood- Laurel 2 3.5 peckers prefer oaks for foraging and riparian Fencepost 2 3.5 trees for nesting, which would make the situa- Maple 1 1.8 tion described by Dawson ideal habitat for the species. Total 57 100.0 FEEDING ECOLOGY in oak utilization. During the breeding season FOODS when deciduous species are newly leafed-out, The foods that Nuttall Woodpeckers con- birds foraged almost exclusively in oaks, par- sume are not seen readily at the time they are ticularly in the blue oak (table 1). This spe- eaten. The specific items that we have noted cies occurs in nearly pure stands on certain are mainly berries and fruits, but only because north-facing slopes; individual woodpeckers these can easily be identified as the wood- often ranged for hours, foraging particularly peckers work on them. Many hours of watch- on and around branchlets and leaves of the ing show that most of the effort is directed blue oaks. At other times of the year, Nuttall toward search for surface or subsurface insects Woodpeckers foraged predominantly in live in places where little or no edible plant ma- oaks (table 1 ), especially during the winter terial would be found (table 1). Our experi- and early spring when other trees are bare. ence in watching foraging is then fully in ac- The woodpeckers spent less time feeding in cord with Beals’ conclusion ( 1911), based oaks during the summer and fall than in other upon analysis of the contents of 53 stomachs, seasons. This is probably due to the avail- that about 80% of the food is animal matter. ability at this time of seeds and fruits of other Much dependence must be placed on Beals’ sorts of riparian and chaparral plants. Even original studies of the food habits of this spe- during the summer season, however, Dendroc- cies; only a few specific items have since been opos nuttallii continued to utilize oaks approxi- added to the record. mately in proportion to their availability (table Vegetable material. Fruit amounted to 1). 8.49%.in Beals’ analysis and was present in 15 individuals taken in summer and fall months; NEST SITES there was one occurrence in December. Fruits Short (in press) found Nuttall Woodpeckers of Rubus were found in two instances, but the in southern California nesting in willows, cot- principal fruit he detected was elderberry tonwoods, and sycamores. At Hastings Res- (Sambucus), a food source widely present in ervation, Dendrocopos nuttallii usually nested the range of the Nuttall Woodpecker. The in sycamores or willows. Table 2 is a summary seeds or berries of poison oak (Rhus diver- of literature references, unpublished field siloba) appear in the record often enough to notes, and personal observations of nests from indicate that they are sought and taken reg- throughout the species ’ range in California. ularly. While birds occasionally nest in oaks, they In a species that is confined very largely to seem to prefer soft-wooded species (table 2). oak woodland, it is strange that little attention This probably relates to the fact that the Nut- is given acorns. We have never seen Nuttall tall Woodpecker is not specialized to chisel into Woodpeckers pounding on acorns and they wood for insect food, but is more of a surface do not seem to be attracted by the stores of gleaning and probing species (see “Feeding the Acorn Woodpecker ( Melanerpes formiciv- Ecology”). In 45 of 48 recorded cases, nest orus) even though they commonly work over THE NUTTALL WOODPECKER AT HASTINGS RESERVATION 287 the limbs of the storage trees of that species. However, Beal did report acorn mast in five stomachs and this combined with poison oak \ seeds largely accounted for the 12% of vegetable material other than fruit. Emlen (1937) reported Nuttall Woodpeck- ers taking almonds at Davis, Solano County, California. Bock (1970) found Dendrocopos nuttullii attempting to rob the winter almond stores of Lewis Woodpeckers ( Asyndesmus Zewis) in the Livermore Valley, Alameda County, California. Nuttall Woodpeckers occasionally take sap, but never, so far as we know, develop a series of holes especially for this purpose as do sapsuckers (Sphyrupicus). On 21 October, a series of sapsucker holes had been made and were being used by a Yellow-bellied Sapsucker (S. varius) in a non-native birch at Hastings Reservation. Members of a pair of Nuttall Woodpeckers visited the sap workings and lapped up sap repeatedly. The sapsucker was dominant over the woodpeckers and drove them away on several occasions. On 10 July, an independent juvenile Nuttall Woodpecker spent half an hour feeding from sap oozes in a red willow (SaZix Zaevigata) at the reservation. Apparently there was an old injury which the woodpecker had developed by fresh peck- ing. The hole was not shaped as in sapsucker workings but consisted merely of an enlarge- FIGURE 1. Foraging posture of a Nuttall Wood- ment of a bark break that may have resulted pecker gleaning for surface and subsurface insects. from earlier rubbing together of the limbs. There are no sapsuckers in the area at this season and it was evident that the Nuttall oaks in which Nuttall Woodpeckers spend Woodpecker had torn away some cambium. much time (table 1). There was a continual flow of sap so that a Hemipterans follow beetles as the second drop reappeared every 5 sec. largest animal food category (14.7% of all Animal material. All identified items in this food). They probably are all taken on the category consisted of arthropods, and the surface or in the foliage, as are most of the beetles alone constituted 28% of the total diet lepidopterous caterpillars that constituted the reported in Beals’ analysis. Larvae of the third major animal food category (14.2% of Cerambycidae and Elateridae were the most all food). Ants are not much favored as food prominent elements. The first of these are in comparison with the degree to which they wood borers in the larval stage and their pres- are utilized by some other woodpeckers, ence reflects the work of the woodpeckers in notably flickers (Beal 1911). They constituted penetration of the bark of woody plants. Lar- but 8% of the food in Beals’ samples. val elaterids (click-beetles) may also occur in FORAGING METHODS AND TYPES rotten wood and it probably is here rather than in the ground that Nuttall Woodpeckers take Nuttall Woodpeckers possess the basic equip- ment of tail and feet common to woodpeckers them. Beal recorded considerable numbers of which permits scansorial activity, in more or small leaf beetles (Chrysomelidae) and sur- less vertical posture, on tree trunks and mised that these were taken from leaf sur- branches (see W. Bock and Miller 1959; faces; this seems highly probable in view of Spring 1965). However, the species uses this the extensive leaf scanning that we have seen stereotyped trunk climbing movement much the birds carry on. Beal also found weevils of less than its congeners, the Hairy (Dendroc- the genus Buluninus that feed on acorns, a opos villosus) and Downy Woodpeckers (D. type of prey likely to be encountered in the pubescens), and in turn is more versatile and 288 ALDEN H. MILLER AND CARL E. BOCK acrobatic. This difference may arise in part nique, superficial probing, gleaning, and scan- from the tangled, irregular growth form of the ning are in fact common in many woodpeck- tree branches and chaparral which the Nuttall ers, including other Dendrocopos (Short, in Woodpecker frequents. On the other hand, press), the Lewis Woodpecker (Bock 1970), the two other species, when foraging in these and Centurus species (Selander 1966). The same plant formations at the Hastings Reserva- ladder-backed Dendrocopos species appear tion, showed less of this diversified activity. unusual only insofar as they have minimized This diversity of foraging behavior is typi- subsurface excavation as a foraging technique fied by the following deviations from the usual in comparison with other members of the woodpecker program of upward hitching genus. along a surface, with the bill more or less hori- zontally directed at right angles to the sur- THE ANNUAL CYCLE face: (1) the woodpeckers seldom moved more DENSITY AND TERRITORIALITY than a foot or so without circling or working on another aspect of the trunk or branch; (2) they Lawrence (1967) distinguished between a frequently hopped across to adjoining sur- woodpecker “territory,” a small area near the faces of nearby limbs or trunks; (3) they often nest defended against all intruders regardless almost crept rather than hitched along a forag- of species, and a more flexible “range,” whose ing surface, assuming a rather humped pos- boundaries are not precise and which is de- ture, with the bill thrust ahead or somewhat fended only intraspecifically. Nuttall Wood- tangentially (fig. 1); (4) bark scaling and peckers aggressively protect their nest sites probing were much more common than hori- against many species (see “Interspecific Com- zontal, right-angle tapping; (5) birds hopped petition and Aggression”); in addition, per- freely into tangles of %-inch twigs, using the manent pairs occupy year-round “ranges.” tail not at all or only when an opposing sur- Figure 2 shows the ranges of seven pairs of face happened to be available; (6) scanning Dendrocopos nuttallii as occupied October surrounding leaf and twig clusters for surface 1954-July 1955 on the Hastings Reservation. insects occurred frequently; (7) birds often The boundaries are only approximations since hopped into small limbs and perched cross- the birds usually foraged in the central por- wise, with the tail thrust ventrally but not in tions of their ranges. However, it is apparent contact, as a balancer; (8) they crept through that the pairs centered their activities along foliage masses with no more than %-inch twig drainage patterns where both oaks and soft- support, fluttering and balancing with the wooded trees were available, each pair oc- wings; (9) they gathered fruits while climb- cupying an area approximately 0.5 miles along ing in foliage clusters or while hanging upside a stream bed. Only four conflicts, all involv- down, with or without a tail brace; and (10) ing males, were observed during 2800 bird- they occasionally pursued insects in the air, min of observation in 1954-55; each occurred tumbling out from or down through the foliage at or near a range boundary (fig. 2). in the process. A summary of all field observations at the This multiplicity of foraging methods defied Hastings Reservation indicates that most ag- classification or quantitative appraisal, for the gression between adult males occurs during shifts from one type to another or back to nor- the breeding season in the spring (table 3). mal woodpecker stance were complex and The lack of encounters observed during April highly irregular. Opportunism in food sources probably is due to the fact that the males are and response to local tree or brush configura- occupied with nest excavation and/or incubation, itself irregular, appear to dictate the next tion at this time and are not moving about move. Of the various foraging techniques em- much on their ranges. Encounters between ployed, trunk and limb gleaning and probing two males usually were preceded by a period and foliage and twig scanning were seen more of drumming back and forth across a range frequently than actual excavation or flycatch- boundary. The birds would then approach ing or sapsucking. and exchange loud, aggressive rattling and Short (in press) observed similar foraging sucking calls, accompanied by displays involv- behavior in Dendrocopos nuttallii in southern ing crest elevation, bill-pointing, and wing California and noted that the Ladder-backed extension and flicking similar to aggressive Woodpecker (D. scalaris) used an identical movements described for other Dendrocopos foraging repertoire. species (Lawrence 1967; Kilham 1969; Short, Although true excavation is considered a in press). Actual overt attack or at least chas- more “typical” woodpecker foraging tech- ing usually followed. THE NUTTALL WOODPECKER AT HASTINGS RESERVATION 289

TABLE 3. Aggressive encounters between Nuttall Woodpeckers at the Hastings Reservation.

Month Type of encounter J F M A M J J A S 0 N D

Male X male 117 6 1 1 1 Female x female 1 1 Adult x juvenile 2 6

male was twice observed driving off a juvenile, at the same time giving loud, aggressive sucking notes and wing extension displays. With the exception of these adult-juvenile encounters, which probably result in dispersal A. of the young, very little aggression occurred

\ between June and January (table 3); activity was low and restricted to the “range,” with the result that very little interpair contact was observed.

TIME OF BREEDING A summary of literature references, unpublished field notes, and personal observations indicates that Nuttall Woodpeckers have active nests between 25 March and 14 June (n = 46), the average egg date being 28 April. Of the 46 records, 37 fall between 12 April and FIGURE 2. Map of the Hastings Reservation, show- 6 May. ing the locations of Nuttall Woodpecker ranges in 1954-55. Dots represent the locations of observed Timing of nesting varied at the Hastings aggressive encounters between males; dashed lines Reservation, but incubation never was noted indicate approximate range boundaries; triangles rep- before the second week of April nor later than resent nest sites. Note that ranges occur along drain- the first week in May. One nest studied ex- ages and appear to be roughly 0.5 miles across. tensively in 1941 by T. Riney showed the following sequence: excavation, 4-16 April (13 Encounters between female Nuttall Wood- days) ; egg laying, 14-16 April (3 days) ; peckers were rare (table 3), and no male- incubation, 17-30 April ( 14 days); feeding female encounters were observed except, ob- young, 1 May-29 May (29 days), with the viously, between members of the same pair. first of three young fledging on 28 May and On 16 April 1956, Miller recorded the follow- the last on 29 May. ing interaction, which began with two females Bent (1939) reports an incubation period of drumming about 50 ft apart: about 14 days for Dendrocopos nuttallii and about 13 days for D. scalaris, while Ligon “Second female drums again and female number (1970) observed D. borealis incubating for 10 one gives a loud sucking aggression note. Female two comes to the tree of female one, alighting below about days, with fledging taking place 26-29 days 15 feet, and moves up to within 10 feet; sucking notes after hatching. Most woodpeckers apparently of loud type follow. Female two holds rigid with bill follow this pattern of incubating between 10 pointed straight up at other bird. Female one re- days and 2 weeks, and feeding nestlings for mains at drumming station and both freeze on guard, 3 or 4 weeks (e.g., Bent, op. cit.; Lawrence silently, for two minutes. Female two raises and spreads both wings, giving sucking notes, and moves up into 1967 ) . small branches; female one flies off down through the oaks 150 feet to the north.” PAIR RELATIONSHIPS Another sort of “territorial” aggression oc- Male-female contact. Nuttall Woodpeckers curs in late summer when adults become in- apparently were permanently paired and oc- tolerant of juveniles. Fledged young birds cupied the same ranges year-round. Per- often were seen following adults and giving manent pairing has been recorded for many begging “trill” notes. Such behavior was com- species of woodpeckers when they are resident, mon in early July 1955, but by the first week including Dendrocopos villosus (Lawrence of August the trilling had ceased and an adult 1967), D. puhescens (Kilham 1962; Lawrence, 290 ALDEN H. MILLER AND CARL E. BOCK

the nonbreeding season and also at the nest, they gave soft sucking or wheezing calls which were similar but less intense than the loud sucking notes which occurred during territorial encounters (see above). Lawrence (op. cit.) similarly recorded “mutual recognition or contact notes” which occurred when members of mated pairs met during the breeding season and which appear to be soft versions of her “aggressive-social notes.” She and Kilham (1962) have considered these contact notes as a form of greeting, expressing a close pair- FIGURE 3. Annual cycle of the Nuttall Wood- bond relationship and mutual tolerance. How- pecker at the Hastings Reservation (based upon ever, the similarity of these calls to the loud, 14,347 min of observation). The precise timing of breeding varied slightly from year to year (see text). aggressive calls suggests that they may in fact be an expression of hostility between sexes. Davis et al. (1963) noted that the chrrp-call op. cit.), D. alholarvatus (Robinson 1957), of the Western Flycatcher (Empidonar dif- Asyndesmus lewis (Bock 1970)) and Dryoco- ficilis) occurred both during aggressive en- pus pileatus (Kilham 1959). In all of these counters and also when pairs met at their species there is at least some contact outside nests. Similarly, the Lewis Woodpecker gives the breeding season, and often preliminary a “chatter-call” when defending winter mast courtship may begin as early as mid-winter. stores or nest sites against intruders, and also Although pairs of Nuttall Woodpeckers ap- during courtship (Bock 1970). Hinde (1966) peared to reside together permanently, they discussesthe basic ambivalence of pair relation- often roosted in widely separated cavities at ships in birds, noting the conflict between the reservation, and there was a marked an- courtship and threat. “Contact notes” such as nual fluctuation in the amount of actual con- those occurring in Dendrocopos nuttallii and tact (fig. 3). Following fledging during July other woodpeckers may have evolved as a and August, adults became very inactive and means for release of potentially dangerous in- inconspicuous, and they were almost always trapair hostility. solitary once adult-juvenile contact terminated. In late January or February, pair relation- Then gradually through the fall and winter ships among Nuttall Woodpeckers at the Hast- months males and females, which seemed by ings Reservation changed markedly. Both their locations to be pairs of the previous nest- sexes, but especially the males (fig. 3)) began ing season, spent increasing amounts of time to drum on their ranges. Pairs, but particu- foraging together, with courtship and pair- larly females, also gave a yipe note which usu- bond reinforcement reaching a peak in Feb- ually was in response to drumming. This ruary and March (fig. 3). This was followed reached a peak during March, but also was by periods of marked separation during which common during egg-laying following nest the males excavated nest sites. Pair contact excavation (fig. 3). Although the pair-bond increased somewhat for the remainder of the obviously was reinforced prior to nest excava- breeding season, when birds were copulating, tion, copulation did not begin until after con- incubating, and caring for the nestlings. struction was nearly completed. We observed Unfortunately, we have no data on pairing that females usually gave yipe notes prior to in first-year birds although it very likely oc- coition, perhaps as an invitation to the males. curs in February and March when established The following is a description of copulation pairs are most involved in courtship. between the male and female of pair 2 (fig. 2) Communication and courtship behavior. observed on 10 May 1955. The female flew to During the fall and winter, pairs of Nuttall a valley oak near the nest site and gave a yipe Woodpeckers often were “in touch” vocally, note. As the male appeared, the female as- exchanging check and multiple check calls sumed a horizontal position across a limb while foraging. These are probably equivalent about 1.5 inches in diameter; the male flew in to the “location calls” described by Lawrence silently and mounted the female. While copu- (1967) for Dendrocopos villosus and D. pub- lating, the female swung her tail sharply to escens. the right and the male kept his left wing ex- When paired male and female Nuttall tended, swinging over to the left side of the Woodpeckers came into close contact, both in female during the 20 set of contact. THE NUTTALL WOODPECKER AT HASTINGS RESERVATION 291

TABLE 4. Attentiveness of male and female Nuttall TABLE 6. Attentiveness of male and female Nuttall Woodpeckers during nest excavation (based upon Woodpeckers during incubation (based upon 4156 1222 min observation). min nest observation).

Attentive periods (min) inattentive periods Attentive periods (min) Inattentive periods

n f range % n f range % n f range % n c range %

Males 19 27.2 2-66 42.2 19 37.2 cl52 57.8 Males 50 48.5 l-115 59 47 35.8 l-79 41 Females 5 10.8 4-21 4.4 8 146.0 3-365 95.6 Females 34 45.2 5-79 37 36 72.6 5-189 63

NESTING BEHAVIOR tiveness of both sexes, and particularly the fe- Excavation. Nuttall Woodpeckers excavated male, increased sharply between the last day new nests each year; winter roosts were not of laying and the first days of incubation used, nor were old nest cavities. It is not clear (tables 5 and 6). During the incubation from our data which sex selects the site, but period, at least one adult was attentive at the approximately 20 hr of observation indicate nest for 95% of 4156 min nest observation. that males construct nests with very little as- Actual incubation occurred for 85%, the adults sistance from the females. Not only did fe- perching outside the cavity for the remainder males rarely visit three nest sites observed of their attentiveness. during construction (table 4), but when they The nestling period. Nuttall Woodpeckers did, it was not to assist in excavation. Males fed their young an average of 7.2 times per hr, were seen to drop wood chips from cavities based upon over 208 hr of observation of six 82 times, the females, never. In addition, the different nests on the Hastings Reservation. males began to roost in the cavities when they Females for the first time played an approxi- were near completion. mately equivalent role, feeding 3.8 times per Egg-laying and clutch size. Miller and hr as compared with 3.4 for males. Riney both observed nests during this period. Both sexes increased feeding rates during In both cases, copulation and egg-laying be- the fledging period. Overall rates increased gan in the last few days of nest construction. from an average of 4.8 per hr during the first The females began to spend more time at the week of nestling life, to 6.3 during mid-fledg- nests (table 5), usually copulating two or ing, to 9.4 during the fourth and last week. three times on successive mornings during lay- Hourly feeding rates generally were higher in ing. In addition, the females became more the morning than in the afternoon (table 7). involved in completion of the nest. In I385 Males brooded the young at night through min of observation the males dropped chips about the first 10 days of nestling life, after 44 times, the females, 20. which both parents roosted away from the A survey of literature references and un- nest. Males did 50.2% of the diurnal brooding published data indicates that clutch size var- ies as follows (n = 42) : 3 eggs, 2 records; 4 TABLE 7. Hourly variation in feeding rates of eggs, 19 records; 5 eggs, 16 records; 6 eggs, 5 Nuttall Woodpeckers. records. Incubation. The trend of increasing interest Total HOW n feedings Average/hr Rank in nest activities on the part of the female con- tinues during incubation. Riney made an ex- 5-6 14 161 11.50 1 tensive study of incubation behavior at a nest 6-7 21 209 9.95 2 on the reservation in 1941. As during construc- 7-8 16 114 7.13 5 tion, the male continued to play a predominant 8-9 22 176 8.00 3 role, incubating the eggs at night and a ma- 9-10 23 159 6.91 6 jority of the day (table 6). However, attcn- 10-11 22 162 7.36 4 11-12 21 136 6.48 11

TABLE 5. Attentiveness of male and female Nuttall 12-13 12 80 6.67 8 Woodpeckers during egg-laying (based upon 1385 13-14 18 97 5.39 13 min observation). 14-15 18 115 6.39 12 Attentive periods (min) Inattentive periods 15-16 16 105 6.56 9 n f range % n n range % 16-17 11 74 6.73 7 Males 28 22.9 l-92 46.3 27 27.5 l-79 53.7 17-18 9 43 4.78 14 Females 21 11.6 l-27 17.6 23 49.6 2-159 82.4 18-19 4 26 6.50 10 292 ALDEN H. MILLER AND CARL E. BOCK and the females, 49.8%. Young were brooded ject to marked daily variation “caused by the 70.4% of the daylight hours during the first impact of impromptu events connected with week, but this declined rapidly and occurred the relationship between the parents, their pre- not at all the last 2 weeks before fledging. occupation and relative industry, or the de- Males were observed removing feces from fense of territory.” In a species such as the nests on 63 occasions while the females did so Nuttall Woodpecker, which feeds to a con- on 24 visits to the nests. Nest sanitation does siderable degree by gleaning surface insects, not seem to be a major occupation of Nuttall fluctuations in food availability related to such Woodpeckers, as this represents only one things as weather and insect emergences very fecal mass removed per 144 min of nest ob- likely also have an effect upon feeding rates. servation. While birds we observed generally fed more Fledging. Riney observed two young Nut- in the morning hours than during mid-day, tall Woodpeckers leaving the nest which he there was no corresponding evening peak studied. At OS:51 on 28 May, the adult male (table 7). In addition, table 7 represents only flew to the nest and fed the young. Two min- the overall picture, which masks daily and utes later a juvenile, which had continued to hourly variations similar to those described beg vigorously with its head at the cavity en- by Lawrence. trance, left the nest tree and flew unsteadily to a living tree 25 yards away. This bird was INTERSPECIFIC COMPETITION heard calling all day and occasionally one of AND AGGRESSION the adults would feed it. The next morning Nuttall Woodpeckers interacted with a variety at 06:13 the male came in and gave part of of other species at the Hastings Reservation. its food to another nestling, and then hitched This included not only other woodpeckers but down the tree about 8 inches. This juvenile also, during the breeding season, a number of fell out of the cavity apparently in an attempt hole-nesting passerine species (table 8). The to reach the food in the males’ bill. The male frequency of encounters during the breeding immediately flew off, as the young bird season was far greater than at other times of landed on a limb 10 ft below the nest. Soon the year, suggesting that competition for nest thereafter the juvenile flew off in the direction sites is high. All of the interactions with pas- of the adult bird. serine species observed during the nesting pe- Juveniles remain with adults for some time riod took place at nests, often where the other after fledging, following them about and beg- birds were nesting or attempting to nest in old ging for food. The adults apparently remain woodpecker holes in the same trees. A good tolerant of these young through June and early example is the aggressive relationship which July, but become aggressive and drive them developed between a pair of Nuttall Wood- off in late July and August (table 3). peckers and a pair of Ash-throated Flycatchers Discussion. The Nuttall Woodpecker ap- (Myiarchus cinerascens) which nested in the pears similar to most picids insofar as the same partially dead sycamore. The flycatchers males perform most of the nest excavation, di- had taken over an old nest hole in the tree and urnal incubation, and nest sanitation, in addi- were reacting very aggressively toward the tion to incubating and brooding at night (see woodpeckers. This persisted throughout the Kendeigh 1952; Lawrence 1967). Feeding nesting cycle, the flycatchers being dominant young and diurnal brooding usually are ac- and pugnacious toward the woodpeckers. On tivities shared more nearly equally by the 25 occasions between 29 April and 28 May, sexes, and this appears to be true of Dendroc- one of the flycatchers chased a Nuttall Wood- opos nuttallii. pecker flying to or from the nest tree. In The overall average feeding rate (7.2/hr) five of these instances, the flycatcher actually is within the range of other species in the fam- attacked and grappled with the woodpecker ily (Kendeigh, op. cit.). There is some con- in flight. troversy over the significance of hourly varia- Similar aggressive situations were observed tion in feeding rates. Kendeigh noted that between Nuttall Woodpeckers and Plain Tit- birds are most active in the early morning and mice (Parus inornatus) and House Wrens evening, with the result that the adults may (Troglodytes aedon) sharing nesting trees, feed young more frequently at these times. except that here the woodpeckers were dom- Stickel ( 1965), for example, found this to be inant in nearly every encounter recorded. true for the Red-bellied Woodpecker (Cen- Interactions with other woodpeckers seemed turus carolinus) . However, Lawrence ( 1967: to be related to competition for food. Mac- 116) noted that such a bimodal pattern is sub- Roberts (1970) found that Acorn Woodpeckers THE NUTTALL WOODPECKER AT HASTINGS RESERVATION 293

TABLE 8. Aggressive interactions between Nuttall aggressive postures (bill-pointing) until the Woodpeckers and other species at the Hastings Reser- intruders flew off. vation. Our observations of intense interspecific ag-

Number of interactions gression related to nest sites are in decided

Jan.- Apr.- Jul.- contrast to those of Lawrence (1967:103) who Species Mar. Jun. Sept. found “the woodpeckers ’ attitude toward Acorn Woodpecker 4 - 1 other than their own species at this point in (Melanerpes formicivorus) the nesting cycle [incubation and feeding] is Downy Woodpecker 1 8 4 - remarkably lenient.” This difference may be ( Dendrocopos pubescens) due to a greater abundance of potential nest Hairy Woodpecker - 5 1 sites in Lawrences’ study area in a central ( Dendrocopos villosus ) Ontario mixed forest, as compared with the - - Sapsucker - 6 more xeric woodlands of the Hastings Res- ( Sphyrapicus varius ) ervation. Ash-throated Flycatcher - 32 4 ( Myiarchus cinerascens) SUMMARY Violet-green Swallow _ 5 - - Nuttall Woodpeckers (Dendrocopos nuttallii) ( Tachycineta thalassina) were studied at the Hastings Reservation, Scrub Jay 2 - 1 2 ( Aphelocoma coerulescens) Monterey County, California. Foraging oc- Plain Titmouse - 15 - 1 curred primarily in oaks, but pairs showed a ( Parzis inornatus ) preference for softer-wooded sycamores and House Wren - 19 - willows as nest sites. (Troglodytes aedon) -The birds employed a variety of foraging Western Bluebird - 4 - techniques, including trunk and limb gleaning (Sialia mexicana) and probing, foliage and twig scanning, fly- Misc. 1 6 2 2 catching, and sapsucking, as well as actual Totals 8 92 13 11 “classical” woodpecker excavation. Most foraging appears to be for surface and subsurface insects, although various fruits and berries, as at the Hastings Reservation maintain and de- well as sap, are taken in certain seasons. fend “sap trees,” and observed 71 interactions Permanent pairs occupied and defended between them and intruding Nuttall Wood- year-round ranges which were approximately peckers. We have observed six interactions 0.5 miles in diameter and which centered between Dendrocopos nuttallii and true sap- along drainage patterns. There was little intra- suckers ( Sphyrapicus varius) which took place pair contact in the summer following nest- at the sap trees of the latter (table 8). Nuttall ing, but during the fall and winter males and Woodpeckers apparently only rarely feed upon females spent increasing amounts of time to- acorns (see “Feeding Ecology”), but we have gether, with courtship and pair-bond rein- observed them being chased from Acorn forcement reaching a peak in February and Woodpecker storage trees on several occasions. March. They may simply have strayed there by Nesting occurred from mid-April to mid- chance. June. Incubation lasted about 14 days, fledg- Interactions with the ecologically similar ing, 29 days. Males excavated the nests and Downy Woodpecker took place both at forag- incubated and brooded the young at night, ing and nesting sites. On two occasions, a as well as performing most of the diurnal in- male Nuttall Woodpecker drove an intruding cubation and nest sanitation. The sexes shared Downy Woodpecker from its nest tree. On diurnal brooding and feeding activities. four other occasions, the two species met while Adults fed the young an average of 7.2 times both were foraging, each being dominant per hr. This feeding rate tended to be high- twice. Once a female Nuttall gave a loud ag- est in the morning hours and also increased gressive sucking note as it displaced a Downy generally during the nestling period. Adults foraging in a toyon (Photinia arbutifolia) were accompanied by fledged juveniles until bush. mid- July, at which time they became intolerant We once observed a Hairy Woodpecker sup- of the young and drove them off. planting a Nuttall Woodpecker in a valley oak. Many aggressive interactions occurred dur- Hairy Woodpeckers were recorded visiting ing the nesting season between Nuttall Wood- INuttall Woodpecker nest trees on four occa- peckers and several hole-nesting passerine spe- sions. The latter never reacted overtly toward cies as well as other woodpeckers, suggesting the larger species. but did maintain alert and a high level of competition for nest sites. 294 ALDEN H. MILLER AND CARL E. BOCK

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