Winter Food Habits of Grey-Beaded Green Woodpeckers Picus Canus

Tori, 28: 107-116, 1979.

Winter Food Habits of Grey-beaded Green Woodpeckers Picus canus

Shigeru MATSUOKA* and Kenji KOJIMA Instituteof AppliedZoology, Faculty of Agriculture, HokkaidoUniversity, Sapporo 060

ヤマゲラの冬期間の食性について

松岡茂*・小嶋研二北海道大学農学部応用動物学教室

Recently many studies on the foraging ecology of sympatric species of woodpeckers have been carried out in North America and Europe (STALLCUP,1968; WILLSON,1970; HOGSTAD,1971; KISIEL, 1972; and others). Many of them noted only the foraging height and diameter of trees, foraging manner, and tree species on which woodpeckers foraged but about the food taken by woodpeckers they have seldom mentioned. In the Tomakomai Experiment Forest of Hokkaido University, MATSUOKA (1977) also studied the foraging ecology of five sympatric species of woodpeckers by the same way mentioned above. But food habits of woodpeckers have also been researched by methods that shed light on the differences and overlaps of food taken by woodpeckers. One of them is an analysis of fecal droppings of woodpeckers. It is the purpose of this paper to make a contribution towards the description of the food habits of Grey-headed Green Woodpeckers by analyzing the fecal droppings left in their roost holes, and to document the relationship between the seasonal change of food taken by the woodpeckers and environmental factors.

STUDY AREAAND METHODS The Tomakomai Experiment Forest is located in the south-central part of Hokkaido, and belongs to Pan Mixed Forest Zone (for further information on the vegetation, see MATSUOKA,1979). Fecal droppings of Grey-headed Green Woodpeckers were collected from the nest boxes set on the Forest Observation Tower (Fig. 1). In many cases several fecal droppings were left in a box each morning and we called them "a sample of fecal droppings" (Fig. 2). From 20th October 1977 to 9th April 1978 we collected 150 samples for a male of the woodpecker, and 8 samples for a female in March 1978. The male woodpecker was ringed near the Forest Observation Tower on

* Present address: Upland Insect Pest Laboratory , Central Agricultural Experiment Station, Ministry of Agriculture,Forestry and Fisheries,Yatabe-machi,Tsukuba,Ibaraki 305.現所属:農林

水産省農事試験場畑作研究センター. 108 Shigeru MATSUOKA& Kenji KOJIMA [Tori 28 (4)

Table 1. Body parts of prey animals used to identify the prey and to estimate the number of prey.

7th February 1978 and thereafter the same individual utilized the Tower for roost. The female had been ringed when she roosted in a box of the Tower, and continued to utilize it. Each sample of droppings was preserved in a phial with 70 % alcohol solution, and later was put under a binocular microscope to examine the prey species and to count the number of prey individuals. Table 1 shows the body parts of prey animals used for identification of prey species and for counting the number of individuals. Undigested prey animals, which occasionally appeared in the droppings, were useful in identifying the prey. The only plant matter taken by the woodpeckers were fruits and berries; undigested seeds were helpful in identifying the species eaten.

RESULTS Some features of roost holes of Grey-headed Green Woodpeckers. In the Ex- periment Forest Grey-headed Green Woodpeckers usually roosted in their own nest holes, which were dug in the earlier breeding season, and also in the nest and roost holes of the other woodpecker species, i.e., Black, White-backed, and Great Spotted woodpeckers. But we have not observed that Grey-headed Green Woodpeckers dig their own roost holes (MATSUOKA,1977). Twenty-four nest boxes, 8 boxes a floor, are set on the four-storied Observation Tower. The male woodpecker roosted in a box on the third floor (18 m above the ground) for ninety-two percent of 150 nights. The female roosted in a box on the second floor (11 m) for eight nights. Although the diameter of the entrances of the boxes varied 2 to 15 cm, Grey-headed Green Woodpeckers used boxes with entrances of 6, 8, and 10 cm in diameter, and roosted most often in the boxes with entrance of 6 cm (93 % of roost nights). Food items taken by Grey-headed Woodpeckers. Table 2 summarizes the results of the dropping analysis for the male woodpecker. The results for the female are shown in the Appendix, as the number of samples is much smaller. We could identify the following food items: Insecta, Caulogastra (Araneida: spiders, genus Clubiona and unkown species), Epimorpha (Geophilomorpha: centipedes), and December 1979] Winter Food Habits of Grey-headed Green Woodpeckers 109

Fig. 1. The Forest Observation Tower. About 31 m in height. Arrow indicates a nest box set up in the second floor.

Fig. 2. A sample of fecal droppings (collected on the morning of 30th Nov. 1978). vegetable food. Insecta included Hymenoptera (three genera of ants and two species of ichneumon flies), Coleoptera (Temnochila japonica and species of family Curculionidae), Diptera (genus Drosophila and species of family Muscidae), and Dermaptera (Anechura japonica). 110 Shigeru MATSUOKA& Kenji KOJIMA [Tori 28 (4)

Table 2. Prey taken by the male Grey-headed Green Woodpecker.

* The figure indicates the total number of prey identified in that season, and that of parenthesis does the percentage of occurrence.

Seasonal changes of prey taken by Grey-headed Green Woodpecker. The results of the dropping analysis are arranged in the order of the subdivision of seasons in the Tomakomai Experiment Forest (MATSUOKA& MAEDA,in press) (Table 2). According to their subdivision, `Autumn' corresponds to the period from 21st Sep- tember to late October, `Early Winter' from 1st November to 10th December, 'Winter ' from 11th December to 31st January I , `Winter II' from 1st February to 10th March, and `Late Winter' from 11th March to 10th April. Food items that appeared in all the seasons concenred were Lasius niger, L.fuliginosus, Camponotus obscripes, Clubiona spp., and seeds of Rhus spp.. Lasius niger was especially favored in all seasons (80.9-99.5% of the total number of animal food). Seeds of Aralia elata were fre- quent in Autumn; as one fruit of Aralia elata includes 5 seeds on average, at least 121 fruits were taken by the woodpecker in Autumn. Seeds of Rhus spp. were also favored in Early Winter and Winter I. In Winter I a species of family Ichneumonidae were abundant in the droppings. December 1979] Winter Food Habits of Grey-headed Green Woodpeckers 111

Fig, 3. Seasonal changes of the mean number of prey per sample. A: Lasius niger, B: animal foods other than ants (dotted: Clubiona spp.), C: vegetable food (dotted: Rhus spp.).

Fig. 3 indicates the mean number of prey per sample of droppings in each seasonal subdivision in order to follow seasonal changes in the contents of the droppings. The ant Lasius niger decreased in Winter I, and more sharply in Winter II, but increased again in Late Winter. Animal foods other than ants were common in Winter I when Ichneumonidea appeared in large number. Vegetable food suddenly decreased in Winter II and did not increase thereafter. A similar tendency is recognized in the distribution of occurrence rate of prey (Fig. 4), but the high occurrence rate of Clubiona spp. in Winter II is conspicuous. Snow is most plentiful in Winter II at Tomakomai (MATSUOKA& MAEDA, op. cit.). To elucidate the effect of snow upon the prey of the woodpecker, Fig. 5 shows the mean number of Lasius niger per sample and snow depth for ten-day periods. In the normal year the depth of snow averages 30-40 cm from early February to early March. We had much snow in the winter of 1977-78, especially 112 Shigeru MATSUOKA& Kenji KOJIMA [Tori 28 (4)

Fig. 4. Seasonal changes of percentage of occurrence, i. e. (No. samples in which a species appeared / No. samples analyzed) *100.

in early and mid March of 1978. Lasius niger suddenly decreased in the droppings in early January of 1978 when minimum snow depth exceeded 10 cm. Only 1.3 to 2.4 individuals of ants on average were recorded per sample during the last February to mid March. But again many ants appeared in the droppings in early April, when minimum snow depth decreased to below 10 cm.

DISCUSSION Some questions of dropping analysis. The following points become subjects for discussion when we estimate the food habits of Grey-headed Green Woodpeckers by means of dropping analysis. First, do the remains of prey in droppings ac- curately reflect the food habits of the woodpecker or not? Analyses of stomach contents show that Grey-headed Green Woodpeckers prey upon large number of ants (YAMASHINA,1951; BLUME,1962) and the woodpeckers are observed attacking December 1979] Winter Food Habits of Grey-headed Green Woodpeckers 113

Fig. 5. Seasonal changes of snow depth (dotted) and the mean number of Lasius niger per sample for each 10-days. Vertical line represents the range between the maximum and minimum snow depth. the anthills frequently (Voous, 1960; DEMENT'EVet al., 1966). Although further study of stomach contents and forgaing behavior of the woodpeckers are necessary, food habits of the woodpeckers reported previously are similar to the results of this study. Secondly, do the contents of the droppings reflect the quantity of prey taken by the woodpeckers or not? In this study the heads of the ants were in relatively good condition. GRONLUNOet al. (1977) who analyzed the pellets of Great Grey Shrikes also counted the number of ant heads to estimate the number of individuals taken by the birds. Chelicerae of spiders and forewings (elytera) of beetles were useful for estimating the number of prey individuals. Vegetable food was easily calculated from the number of seeds. Although Great Spotted and White-backed woodpeckers regurgitate seeds as pellets when they swallow relatively large fruits (e.g., Magnolia obovata) (MATSUOKA,unpublished), we have not observed Grey-headed Green Woodpeckers regurgitating pellets. To estimate the food habits of the woodpeckers by dropping analysis, it is required that the countable remnants of prey certainly appear in the droppings, and the woodpeckers do not regurgitate the remnants as pellets. In relation to this, it appear that the contents of the droppings analyzed in this study do reflect the main food of Grey-headed Green Woodpeckers (i.e., ants). Thirdly, do the droppings collected in the roost hole represent the real food habits of the woodpeckers? This question will be clarified from the analysis of droppings collected every hour of a day, now proceeding in the Tomakomai Ex- periment Forest. The results of the present study at least indicate the food taken by Grey-headed Green Woodpecker just before roosting. Seasonal changes of prey taken by the Grey-headed Green Woodpecker. The 114 Shigeru MATSUOKA& Kenji KOJIMA [Tori 28 (4) number of ants which appeared in the droppings apparently changed seasonally, and it is suggested that the occurrence of ants in the droppings is strongly correlated with the snow depth (Figs. 3 and 5). IMAMURA(1975) who studied myrmecofauna in the Tomakomai Experiment Forest stated that Lasius niger was widely found in forest, bare land, etc., and nested in daed trees and logs, and in the earth under stones. The ant overwintered in a similar environment (IMAMURA,pers. com.). Therefore, as the snow depth increases, exploitation of such ants by the woodpeckers would be disturbed. The fact that the ants increased again as the snow melts sup- ports the point of view mentioned above. Most of the ant species that were identified in this study, including Lasius niger, inhabit dead trees, and snow probably limits their exploitation by the woodpeckers. But as Grey-headed Green Wood- peckers are sometimes observed foraging for ants (Camponotus obscripes) at the places where Black Woodpeckers (Dryocopus martius) foraged (MATSUOKA,1976), it is possible that such a behavior would reduce the effect of snowfall upon the resource utilization. In winter Black Woodpeckers could exploit ants in logs and dead trees under snow. They used to sweep away the snow on fallen logs, and reach the logs to forage (PYNNONEN,1939; MATSUOKA,1977), but we have not observed such behavior for Grey-headed Green Woodpeckers. The main foraging technique employed by Grey-headed Green Woodpeckers is "probing" and "glean- ing" and only in a few cases do they employ "pecking" and "hammering" techniques (MATSUOKA,1976, 1977). Such a specialization in foraging technique would limit the exploitation of ants during the snow season. When ants and vegetable food in the droppings decreased in Winter II, animal foods other than ants, especially spiders (Clubiona spp.), increased in number and occurrence rate. We observed Grey-headed Green Woodpeckers foraged Clubiona vigil under the bark of dead trees and we ourselves also collected many of them in similar places in winter. Probably the woodpeckers foraged this spider species in this way. Seasonal changes in the number of winter chambers of Clubiona spp., which also appeared in the droppings, were similar to the changes in the number of individuals of Clubiona. The increase of spiders in Winter II, we think, relates to the decrease of ants as a food resource.

ACKNOWLEDGEMENTS

We thank Dr. H. ABE who read the early draft, Mr. S. HIGASHI and Mr. S. IMAMURA who helped identification of ants, and Dr. K. ITOwho helped identification of seeds. We are indebted to Dr. K. ISHIGAKI and staff of the Tomakomai Experiment Forest for their help with many aspects of the research.

SUMMARY

Fecal droppings of Grey-headed Green Woodpeckers, which were left in roosting nest boxes, were collected and analyzed from 20th October 1977 to 9th April 1978. The nest boxes were set up on the Forest Observation Tower in the Tomakomai Experiment Forest of Hokkaido University. (1) Food items identified were insects, spiders, centipedes and plant food (seeds of trees). (2) Results of the dropping analysis were expressed according to the subdivision of seasons in the Experiment Forest. Lasius niger was favored from Autumn to Winter I, then decreased in December 1979] Winter Food Habits of Grey-headed Green Woodpeckers 115

Winter II, and increased in Late Winter again. (3) Many seeds of trees appeared in Autumn to Winter I but they decreased in Winter II and did nor increase thereafter. (4) Animal foods other than ants increased in Winter I; in Winter II only spiders increased. (5) We discussed the questions of analysis of droppings and the relation between the food habits of Grey-headed Green Woodpeckers and snow depth.

摘要

1977年10月20日から1978年4月9日まで,北海道大学苫小牧地方演習林で,ヤマゲラが寝ぐらに残したふんを採集し分析した,ヤマゲラが利用した寝ぐらは森林観測塔に設置されていた巣箱である.

(1) 同定できた餌品目は,動物では昆虫網,くもがた類,整形類,植物では樹木の種子であった. (2) ふん分析の結果を苫小牧演習林における季第区分に従って区分した. トビイロケアリはどの季節区分にも数多く出現した.しかし,厳冬IIには急に減少し,晩冬に再び増加した. (3) 樹木の種子は秋に特に多かったが,初冬,厳冬1まで多く出現した.しかし,厳冬II以降は急に減少し,再び増加することはなかった. (4) アリ以外の動物餌は,秋,初冬は少なかったが,厳冬1にはヒメバチが多数出現した.厳冬に数,頻度共に多く出現したのばクモだけであった. II (5) ふん分析の問題点について言及し,またヤマゲラの採餌生態,ふんに出現する食物(特にアリ類),環境要因との関係について論議した.

LITERATURE CITED

BLUME, D., 1962. Schwarzspecht, Grunspecht, Grauspecht. Wittenberg Lutherstadt, A. Ziemsen Verlag. DEMENT'EV,G. P., N. A. GLADKOV,S. E. PTUSHENKO,E. P. SPANGENBERG,& A. M. SUDILOVSKAYA, 1966. Birds of the Soviet Union, 1. Jersalem, Israel Program for Scientific Translation. (Translated from Russian.) GRONLUND,S., J. ITAMIES,& H. MIKKOLA,1970. On the food and feeding habits of the Great Grey Shrike Lanius excubitor in Finland. Ornis Fennica, 47: 167-171. HOGSTADT,O., 1971. Stratification in winter feeding of the Great Spotted Woodpecker Dendrocopos major and the Three-toed Woodpecker Picoides tridactylus. Orals Scand., 2: 143-146. IMAMURA,S., 1975. Myrmecofaunal survey at Hokkaido University Tomakomai Experiment Forest with some observations on a polydomous colony in Formica sanguinea (LATERILLE). Res. Bull. Coll. Exp. Forests, Hokkaido Univ., 32: 93-104. (In Japanese with English summary.) KISIEL, D. S., 1972. Foraging behavior of Dendrocopos vilksus and D. pubescens in eastern New York State. Condor, 74: 393-398. MATSUOKA,S., 1976. Autolycism in the foraging of the Grey-headed Green Woodpecker Picus canus. Tori, 25: 107-108. - 1977. On the ecological overlaps and differences among five sympatric species of woodpeckers, with special reference to their foraging ecology. Dr. Agric. Dissertation. Sapporo. Hokkiado University, (In Japanese with English summary.) - 1979. Ecological significance of the early breeding in White-backed Woodpeckers Den- drocopos leucotos. Tori, 28: 63-75. MATSUOKA,S., & Y. MAEDA,in press. The subdivision of seasons in the Tomakomai Experiment Forest of Hokkaido University. Enshurin Gyomu Shiryo, College Experiment Forest, Hokkai- do University. (In Japanese.) 116 Shigeru MATSUOKA& Kenji KOJIMA [Tori 28 (4)

PYNNONEN,A., 1939. Beitrage zur Kenntnis der Biologic Finnischer Spechte. I. Ann. Zool. Soc. Zool. Bot. Fenn. Vanamo, 7: 1-171. STALLCUP,P. L., 1968. Spatio-temporal relations of nuthatches and woodpeckers in ponderosa pine forest of Colorado. Ecology, 49: 831-843. Voous, K. H., 1960. Alfas of European Birds. London, Nelson. WILSON, M. F., 1970. Foraging behavior of some winter birds of deciduous woods. Condor, 72: 169-174. YAMASHINA,Y., 1941. A Natural History of the Japanese Birds, 2. Tokyo, Iwanami. (In Japa- nese.)

APPENDIX

Prey taken by the female Grey-headed Green Woodpecker (March 1978, Late Winter)

*Rice would be derived from feeders near the Forest Observation Tower .

(Received 15 September 1979)