Breeding Ecology of the Mississippi Kite in Arizona
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Condor85:200-207 0 The Cooper Ornithological Sowsty 1983 BREEDING ECOLOGY OF THE MISSISSIPPI KITE IN ARIZONA RICHARD L. GLINSKI AND ROBERT D. OHMART ABSTRACT. -The Mississippi Kite (Zctinia mississippiensis)recently has ex- tended its breeding range into the southwestern United States and was first re- corded nesting in Arizona in 1970. Approximately 25 regularly active nesting sites occur in Arizona in riparian forest-scrublandhabitat along the tributaries of the Gila River. Nesting habitat consisted of a structurally diverse (patchy) ar- rangement of cottonwood (Populusfiemontiz~trees and salt cedar (Tamarix chi- nensis)understory. Cicadas, the principal prey of the kites studied, were captured frequently (4 1% of all prey captures)by hawking from cottonwood percheswithin 150 m of nests. Vegetation patchinessfacilitated foraging and accounted for 7 1% of the variation in reproduction. Increased vegetation diversity in the more tra- ditional breeding areasof the Great Plains and in migration and wintering habitats may have enhanced foraging, reproduction, and survival of kites, and may help to explain the recent population increase. Most nest sites were distributed among four groups. No movement between groups was noted during any one nesting season.Most adult kites attempted to nest, but up to 52% of all nesting attempts failed during courtship and nest- building (44% of all failures), incubation (40%), and nestling (16%) stages.Re- productive successwas 0.60 fledglings per nesting attempt, similar to that esti- mated for kites in the Great Plains. Apparently, reproduction at a nest was not enhanced by close proximity to another active kite nest. The Mississippi Kite (Zctinia mississippiensis) (vegetation classification after Brown et al. nestsin North America from Florida and South 1979) along the Gila River and its tributaries. Carolina westward through the Great Plains Surveys of kites were begun in 1977 and were south of Nebraska and, recently, into Arizona, intensified in 1978, when we attempted to find New Mexico and Colorado. It has been re- every nesting effort in known and potential ported during spring and summer irregularly breedingareas. We visited known nestingareas from California to Massachusetts(Parker and beginningin early May when kites first arrived, Ogden 1979). Migration and wintering records and watched for aerial courtship displays from for the neotropical region are scarcebut show hillsides that bordered riparian nesting habi- that most individuals may winter in tropical tats. We then searchedriparian forestsfor nests. regions (Eisenmann 1963, Parker 1977). Individual kites were counted during initial Levy (1971) first recorded the Mississippi courtship display flights and throughout the Kite in southeasternArizona in 1970 and es- summer during communal foraging and pred- timated that as many as 10 pairs nested along ator-mobbing flights. On several occasionswe the lower San Pedro River. Observations of were able to count what we believed were all Mississippi Kites and possiblebreeding activ- of the individual kites occurring in a nesting ity along the Verde River in central Arizona group. These instances were often prompted during 1970 and 1973 were reported by John- by the presenceof other raptors, which caused son and Carothers (1976). In this paper we the kites to congregate and emit alarm cells, examine the breeding ecology of the Missis- as well as to soar and stoop at predators. Also, sippi Kite in Arizona and discussthe ecological communal hunting over the forest canopy dur- relationshipsthat influence the presenceof this ing midmorning and communal soaringduring speciesin the southwesternUnited States. windy periods preceding afternoon summer showersmade kites quite conspicuous. METHODS Individual kites were distinguishedby molt In 1976 we assessedMississippi Kite nesting pattern, sex, and age (adult or yearling). We distribution in Interior SouthwesternRiparian used hair dye on seven birds to mark rectrices (rivet-me) Deciduous Forest and Woodland or remiges (after Ellis and Ellis 1975). Kites MISSISSIPPI KITES IN ARIZONA 201 were in heavy molt of flight feathers during the sented as the percent of maximum theoretical nesting season, and distinctive molt patterns patchiness. were the best aid to individual recognition. Diet was documented mainly from obser- RESULTS AND DISCUSSION vations at nests. A total of 2,200 h was spent watching kites from blinds set up near nests DISTRIBUTION AND POPULATION SIZE (1,708 h) and overlooking nesting and for- From 1976 through 1979 we located 25 kite aging habitat (492 h). Most observations from nest sites in Arizona and believe this number blinds were made during whole-day periods representsthe present total nestingpopulation from 0.5 h before sunrise through 0.5 h after in the state. A nest site, or territory, consisted sunset. Blinds were usually in trees 30 to 40 of the space within at least 50 to 100 m from m from the nest. In one instance a 16-m scaf- an active nest and often contained several old folding tower was erected 10 m from a nest. nests used in previous years. Nest sites were In all cases the kites accepted the structures usually grouped, with nests spaced from 125 after a brief period of defensive calling and to 1,700 m (X = 550 m, SE = 8 1 m). Six sites stooping, and we believe our presencedid not were solitary during at least one year and were significantly alter normal behavior. We used more than 4 km from other sites.These remote binoculars, spotting scopes,and tape recorders sites were probably frequented by adjacent to observe and record nesting behavior. nestingbirds during extensive midday soaring Analysis of Mississippi Kite productivity flights. Therefore, we considered the isolated follows the methods and terminology outlined sites to be loosely associatedwith a group. by Postupalsky(1974). We visited most of the Generally, four groups of nest sites existed. active nests weekly. As a measure of nest site (We employ the word “group” rather than quality for use in regressionanalyses, we noted “colony” to describeaggregations of kite nests the number of weeks that a nest remained oc- after the strict interpretation of the two words cupied or active by attending kites. Thirteen as presented by Wilson [ 19751.) Two groups weeks were required for successfulreproduc- (SPl and SP2) on the San Pedro River oc- tion from initiation of courtship and nest curred along 14 km and 10 km, respectively, building through fledging. of narrow (< 1 km wide) mixed riparian forest- Kite nestsare relatively small structures,are scrubland, 594 to 792 m in elevation. They frequently lost to strong winds and predators, were separated by 27 km of riparian forest- and are easily overlooked by an observer. scrublandand had 10 nest siteseach. The third Nesting areas were intensively surveyed only group (G) was along 3 km of the Gila River in 1978, and we suspectthat we missed several in a narrow mixed riparian forest-scrubland, early nest failures in other years. No attempt 549 m in elevation. It was approximately 21 was made to correct calculations of reproduc- km from SP2 and had four nest sites.The fourth tive successby estimating the number of un- group (V) occurred along a 2-km reach of the discovered early nesting failures. Since kite Verde River in mixed riparian forest-scrub- neststhat successfullyfledged young were con- land, 457 m in elevation. It was 102 km from spicuously attended throughout the summer Group G (its nearest neighbor) and had one, by adults,we probably found all successfulnests or possibly two, nest sites. and thus can compare reproductive success The nestingactivity at each site varied year- basedon fledglingsper successfulnest in 1976, ly and many sites were neither active nor oc- 1977, and 1978. Nesting success,as shown by cupied every year. Of five sites monitored for the number of fledglings per total nesting at- four consecutive years, two were occupied all tempt, was based only on 1978 data. four years; two and one were occupied only Distances between grouped nests and for- three and one years, respectively. Of an ad- aging distances from nests were calculated ditional six sites studied for three years, four either by direct measurement or from scaled were occupied all three years, and two were aerial photographs.The species-specificfoliage occupied for only two years. Probably 15 to volume and structural horizontal patchiness 17 of the 25 known nest siteswere consistently (Z, after Anderson et al. 1978) of nesting site occupied during the four years of this study: vegetation were measured. At a total of 13 five to sevenin Group SP 1, nine in Group SP2, sampling sites within 150 m of the nest tree, and one in Group G. Group V was occupied the distance and speciesof the nearest vege- only in 1976 and 1977 and was the most in- tation were recorded at height layers of 0.2, consistently occupied nest site. 0.6, 1.5, 3.0, 5.0,6.0, 8.0, 9.0, 12.0, 15.0, 18.0, In 1978, becauseof our familiarity with Mis- and 21.0 m. Calculation of Z, was from the sissippi Kite nesting habits, we were able to volume of the layers sampled rather than from discover all individuals and nesting attempts point estimates of the total volume and is pre- and thus to associatethe total group popula- 202 RICHARD L. GLINSKI AND ROBERT D. OHMART tion with the total number of nestingattempts. days of the nestlingperiod, becausethe posture We found 25 pairs of adults at nest sites, 7 of adults while feeding hatchlings and the unpaired adults, and 13 yearlings. These cen- quickness of ingestion by the older nestlings susessuggested that the number of adult kites prevented a view of the prey. in each group closely reflected the number of Insects composed 95% of all identified prey nest sites in the group. This observation cor- and 85% of all prey deliveries. Probably most roboratesParker ’s (1974) conclusionthat adult of the unidentified prey specieswere insects.