Attentiveness and Time Budget of a Pair of Nesting Wood Storks

Transcription

1 University of Central Florida Retrospective Theses and Dissertations Masters Thesis (Open Access) Attentiveness and Time Budget of a Pair of Nesting Wood Storks Summer 198 E. Scott Clark University of Central Florida Find similar works at: University of Central Florida Libraries Part of the Biology Commons STARS Citation Clark, E. Scott, "Attentiveness and Time Budget of a Pair of Nesting Wood Storks" (198). Retrospective Theses and Dissertations This Masters Thesis (Open Access) is brought to you for free and open access by STARS. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of STARS. For more information, please contact lee.dotson@ucf.edu.

2 ATTENTIVENESS AND TIME BUDGET OF A PAIR OF NESTING WOOD STORKS BY E. SCOTT CLARK B.S., North Carolina State University, i THESIS Submitted in partial fulfillment of the requirements for the degree of Master of Science: Biology in the Graduate Studies Program of the College of Natural Sciences at :the University of Central Florida; Orlando, Florida Summer Quarter 198

3 ABSTRACT An instantaneous sampling system was used to quantify nest attentiveness and time budget of a pair of Wood Storks (Mycteria americana) nesting at the Moore Creek colony on Merritt Island National Wildlife Refuge in The amount of time devoted to various activities during each stage of the 4-month reproductive cycle was examined and differences between stages evaluated. During the incubation period an adult was constantly at the nest site and the birds shared equally in the incubation duties. During the first four weeks of the 8-week pre-flight nestling stage, an adult was with the chicks continuously, although the adults discontinued brooding after the first week. In the latter four weeks of the pre-flight stage and 4-week post-flight stage, the amount of time spent in the colony by the adults diminished until the parents only returned to the colony for several minutes per day to feed the young. The time devoted to incubation, brooding, nest maintenance, and sexual displays declined during the breeding season, while the time spent uloafing" and away from the colony increased. Nest defense, chick maintenance, and standing at the nest were maximal during the first half of the pre-flight stage.

4 ACKNOWLEDGMENT This study was supported in part by the National Aeronautics and Space Administration through contract NAS to the University of Central Florida, and was administered by Llewellyn M. Ehrhart, principal investigator of the threatened and endangered species aspect of the study. Thanks are due to my advisory committee members, Drs. L. M. Ehrhart, H. W. Kale, II, I. J. Stout, W. K. Taylor, and H.. Whittier, who provided comments and criticisms of the manuscript. Thanks are especially expressed to John C. Ogden of the National Audubon Society for comments and discussion, and Karen G. Clark for financial and moral support. iii

5 TABLE OF CONTENTS page In t r o.d uc t ion : Study Area ~ Methods Results General Breeding Biology Nest Attentiveness Incubation Pre-flight nestling stage Post-flight stage+ ---~ Time :Budget Aggression Chick maintenance Incubation and brooding Nest maintenance Standing at the nest Loafing in the colony Sexual displays Discussion Summary : Append~x ~ Literature Cited iv

6 INTRODUCTION The colonial breeding American Wood Stork (Mycteria americana Linnaeus) is a large conspicuous wading bird of the Florida wetlands and is the only member of the family Ciconiidae found in the United States. This specialized bird generally utilizes a non-visual myot?-ctile foraging method commonly referred to as 11 groping 11 (Kabl and Peacock 1963), and because feeding efficiency is related to prey concentration, the stork is extremely sensitive to seasonal oscillations in rainfall and water levels. As a result, the life cycle of the stork is highly synchronized with the environment (Kushlan et al. 1975, Browder 1978, Clark 1979). In this study, data were collected to quantify the nest attentiveness and time budget of a pair of nesting Wood Storks at an east-central Florida colony in 1977, and to determine how the breeding cycle of this species is adapted to a fluctuating wetland system. A significant aspect of a bird's ecology is the partitioning of the available tim,e and energy among various behaviors associated with maintenance and reproductive activities. In studies examining the optimization of time and energy budgets, the division of the effort between various activities must be known. This necessitates the construction of time budgets and the conversion of these budgets to energetics costs. This study, on the time budget of one pair of Wood Storks, provides a baseline for future study.

7 2 Time budget studies on breeding avian species are not new; however, it has only been in recent years that detailed studies have been. conducted (Orians 1961, Verner 1965, Col1ias and Collias 1967, Schartz and Zimmerman 1971, Enderson et al. 1972, Utter and LeFebvre 1973, Derksen 1977, Austin 1978, Jenkins 1978). No time budget studies on the order Ciconiiformes were found after an extensive literature search.

8 STUDY AREA This study was conducted in 1977 at the Moore Creek Wood Stork co.lony, which is located on two small islands (Fig. 1) in an impounded section of Banana Creek on the western side of Merritt Island, Brevard County, Florida (28 35' N, 8 42' W). The northernmost island is about 1 ha in area; the other, about 4 ha. White Mangrove (Laguncularia racemosa), ranging from 1.5 to 7. min height, covers both islands. Open brackish water 1 to 2 m deep surrounds the islands and frequently covers them to a depth of.5 m. Human disturbance at the colony is minimal because it is within a National Aeronautics and Space Administration restricted area on the Merritt Island National Wildlife Re fuge. Additional information on this colony can be found in Clark ( 1 979). 3

9 , BANANA CREEK ~......, , , , ,....., "'I ' , " ,...,....., , Figure 1. Nesting sites used by wading birds in the Moore Creek area, Islands 1 and 2 were used by Wood Storks.

10 METHODS Once a week during the 16-week nesting period the focal pair was observed from a blind at the edge of the colony from 6 to 2 hrs. To avoid observer influence, a nesting pair 3 m from the blind was selected for study (Fig. 2, nest 1125). Entry and exit from the blind were poss~ble without coming into the birds' view. Data were collected on this pair from the onset of incubation in the first week in April and continued until the last week of July. Observations were terminated when the two young reached independence and the adults abandoned the nest site. No data were collected in the third week of incubation, and only partial data were gathered in the first and third weeks of the pre-flight stage. During the 4-week incubation period, field notes were taken continuously and the various activities plotted over time. A ter hatching, the behavior of the adult birds was sampled by using a 3-sec. instantaneous sampling system (Altmann 1974) in addition to field notes. For this, an electronic metronome was used to mark 3 sec intervals, and one of 24 behavioral states was entered on a time sheet at each interval. The behavioral codes were analyzed in 3-min units to determine the percentage of time devoted to each activity and then pooled into 8 major groupings. The Students t-test and Wilcoxon (matched-pairs) signed-rank test (Siegel 1956) were the only statistical tests used. 5

11 <bo o oo ooo o o o o Figure 2. The locations of Wood Stork nests surrounding the observation blind on island #1 of the Moore Creek colony, Study nests are numbered. The focal pair occupied nest #25. '1 oo ~ )_/ 12 9 / - I / I / 7 8- I ~ o o -3-2 e o / / ;,o eo ooo o ooo )-4 26 /25 e I 33 / oo o o - ooo oo ojo oo I 5 l I I 1-s I 2 l meters

12 7 For analysis, the breeding cycle of :the storks was divided as follows: incubation period (weeks 1-4), pre-flight nestling stage (weeks 5-12), and post-flight stage (weeks 13-16). The pre-flight stage was further divided into early (weeks 5-8) and late (weeks 9-12) stages. The analysis of the nest attentiveness data was based on a 24-hour day starting at midnight; the time budget study was analyzed for daylight hours only. The focal pair was sexed by copulation position, and each bird identified by unique natural markings.

13 RESULTS General Breeding Biology The general breeding biology of the Wood Stork has been described in several popular periodicals (Sprunt and Kahl 196, Allen 1964, Kahl 197la) and scientific journals (Kahl 1964, 1972). The behavior of the storks at the Moore Creek colony does not appear to differ to any major extent from these published accounts. A brief description of the storks' breeding biology, which is based on the above publications and the author's observations, is helpful in understanding this study and is, therefore, included below. During the initial stages of breeding, the unmated storks gather in the taller mangrove trees where the aggressive males flap, intimidate, and supplant one another. Eventually the dominant male establishes himself and begins to advertise the potential nest site by displays, especially preening. One or more females are attracted to the male's displays and move to nearby limbs from which they approach the male in a submissive balancing and gaping display. Initially the male drives the females away, but in time a female is accepted. After she is accepted she becomes more aggressive an~ frequently gapples and nips at the male's bill. During the first few days after pair formation the bond between the pair is reinforced by mutual greeting displays and copulation occurs. The male leaves the nest site frequently to gather twigs and sticks from within the colony or surrounding dikes, and a nest, about one meter 8

14 9 in diameter and lined "vith leaves, is built in a few days. Several days after the initial copulations, the female begins to lay creamy w4ite eggs at one to two day intervals until a clutch of three or four eggs is completed. During the first week of the incubation period both birds remain near the colony, except for short trips made by the nonincubating bird to forage, drink, and gather additional nesting materials. Both birds brood and the eggs are never left unattended, although the nonbrooding adult spends less time in the colony as incubation progresses. After sitting for several hours, the brooding bird may stand up, stretch, preen, flap, rearrange nest sticks, pull twigs from branches around the nest, or turn the eggs with its bill before sitting again. Twigs and leaves are worked into the nest throughout the incubation period. The young begin to hatch asynchronously after 29 to 31 days of incubation, and the last chick to hatch generally starves unless food is plentiful. The newly-hatched storks are helpless and naked except for a few gray feathers on t.he wings. Within several days, however, they are covered with down. Parents brood the young during the first week after hatching, and during this time the young lie quietly in the nest except during feedings, at which time they sit up and vocalize. The parents regurgitate food onto the nest floor where it is taken up by the chicks. Initially the young are fed frequently, but the number of feedings declines as the breeding season progresses. When the nestlings are very young the parents regurgitate more food than the chicks can consume at one time. Adults reingest the excess fish, and regurgitate them several hours later. The adults also bring several pints of water in the throat which is drooled over the chicks or into their open bills. After the

15 1 chicks are a week old, the parents no longer brood them except during rain and at night. However, on hot days the chicks remain cool qy resting in the shade provided by the adult standing at the nest. A ter two weeks the young acquire a white wooly down and are more active. By the second week the begging posture of the chicks is well developed. When the feeding parent arrives at the nest the young drop on their tarsi, spread their wings to the wrist, and cock their tails. The head is nodded up and down and a braying note emitted. After a month the young are more alert and are left alone for short periods of time. By the sixth week the adults leave the chicks alone most of the day and night. At this time the chicks are capable of defending themselves, especially against neighboring adults which constantly pilfer nesting materials from one another. By their second month the young are well-feathered and begin to fly from nest to nest within the colony. As the young birds' flight abilities develop they fly to marshes within.5 km from the colony to "loaf" and forage. Because the young are not totally independent, they return to the colony during the middle of the day to be fed, and they roost there at night. The time spent in the colony by the parents gradually diminishes until the adults are returning to feed the chicks only two or three times a day. The young reach full independence in about 75 days. After the largest, and ostensibly the oldest chick leaves the colony, the smaller chicks receive more of the food and grow quickly until they reach independence. Nest Attentiveness Storks were very attentive at the nest with one, or both, of the parents remaining at the nest site until the chicks were several weeks

16 11 old. After that the time spent at the nest gradually diminished until the young were independent. A graphic presentation of the nest attentiveness of the focal pair during one 24 hour period each week is in Fig. 3. Although the birds were not continuously observed at night, the same bird noted at the nest in the late evening was always present in the early morning, and arrivals/departures were noted only during daylight hours. Most nest reliefs occurred between 8 and 11 hrs (43.6%) and 14 to 16 hrs (25.6%). The number of exchanges ranged from one to four per day, and averaged 1.9 for the entire breeding season. Although the longer visits were not timed from start to finish, it was conunon for a stork to remain at the nest site for 18 to 2 hours. One neighboring individual was observed at its nest from sunrise to sunset and probably remained the.night before and after - a nest attentive period of at least 34 hours. Incubation During the incubation period at least one member of the pair attended the nest site continuously while the mate, if present, stood on the nest rim or a nearby branch. The male remained at the nest site an average of 55.3% of the daylight hours; the female, 73.6%. In the first week the adults were present simultaneously 7.5% of the day; however, this declined ~o 1.1% by the fourth week. Pre-flight nestling stage During the first four weeks of the pre-flight nestling stage at least one adult attended the chicks continuously, and in the remaining four weeks of this stage the combined parental attentiveness declined gradually from 6.1% to.5% of the day. During the whole pre-flight

17 Figure 3. Nest attentiveness by a pair of Wood Storks at the Moore Creek colony during one 24 hour period each week of the breeding cycle in 1977.

18 E I :'ilil ::1:. :1 1:: fi :i.l i"l1ll :l i:':l:: llllili i ill1!'1:1 ~ ~~: ~ E = " z W E E K\-Q...,._ II ' N MALE ~ LLJ. J: ~ 1-5 <( w ~ ~. - r post- FLIGH T.. : REPRODUCT{. VE STA_GES INCUBATION P R E- F L I G H T

19 stage the male averaged 22.9% of its time in attendance,. while the female l3 averaged 16.2%. The time spent at the nest togeiher declined throughout this stage, and was.5% of the day. Post-flight stage In the post-flight stage of chick development the adults visited the colony only 1 to 22 min (mean= 1.1 min) per day to feed the chicks. The male was in the nest area an average of 1.2% of the day while the female averaged.2%. The pair was never observed together at the nest in this stage. Time Budget The time budget of the storks was divided into 8 major groupings: absent from the colony:. aggression, chick maintenance, incubation and brooding, loafing in the colony:. nest maintenance, sexual displays, and standing at the nest. A graphic presentation of the time budget during daylight hours is given in Fig. 4, and the time budget of the pair while at the nest is found in Fig. 5. daylight hours is given in Fig 6. A summary of the time budget during Data for these graphics are in Tables 1-6 of the Appendix. Aggression A high intensity Threat Display (Kahl 197lb) directed toward an intruder was regarded as an aggressive encounter. If the intruder did not retreat in response to the display, then the stork struck at it while Bill Clapping. Of 4 observed aggressive acts, 95% were directed at other storks, and the remaining 5% at Great Egrets (Casmerodius albus). The number of aggressive encounters increased from the start of incubation until the first week of the pre-flight stage and declined to

20 14 ~ 4 > Avgresslon > chick ~ ~ Mo intenance ~ "' :X: :X: "" 1- z... 2 &&.. ~ ~ &I. POST- FLIGHT INCUBATION PRE- FLI OHT REPRODUCTIVE STAGES REPRODUCTIVE STAGES too 3 > I ncubation > Loafing ~ lij Til Broodino :r ::r LL &&.. 1 ;f!. 2 II c:( '1&.1 ~ 2 PRE-FLIGHT POST-FLIGHT INCUBATION REPRODUCTIVE STAGES REPRODUCTIVE STAGES > N e sf > Sexual C( ~ 3 Displays I 1&.1 ::1: ::r "' u... &&.. ll ~ ~ POST- FLIGHT REPRODUCTIVE STAGES REPRODUCTIVE STAGES 1 1: 6 > in g > Total Time C( 78 ILl ::1:... ao... c:( of the. Ne-st 1 lij :X: LL && II ~ ~ POST-FLIGHT INCUII.ATION I"OIT- P'&.leHT R EPRODUCTJVE STAGES REPRODUCTIVE STAGES Figure 4. The percentage of daylight hours devoted to various activities by a nesting pair of Wood Storks.

21 Figure 5. The percentage of time at the nest devoted to various activities by a nesting pair of Wood Storks.

22 Figure 6. The total time budget of a nesting pair of Wood Storks during daylight hours, including time away from the colony.

23 '\ 2 STORK NOT IN THE COLONY w 15 ~ I- ~ 1 w z - ~ '{.) 5 AGGRESION CHICK MAINTENANCE MAINTENANCE I ~ oo:; 6 INCUBATION I POST-FLIGHT REPRODUCTIVE STAGES

24 17 zero by the seventh week. The amount of time devoted to aggressive actions was low, ranging from to 3.6% of daylight hours, and the maximum number of aggressive actions by the pair in one day was 24 (Fig. 7). There was no significant difference between the number of aggressive actions by the male and female (Wilcoxon signed-rank test, P::-.5). Chick maintenance Chick maintenance was defined as the time spent caring for the young from the time of hatching until the juveniles left the colony. This category included fee_ding, watering, preening, and shading the chicks with wing-spreads. Brooding and shading the young in normal standing postures were excluded and treated separately. Feeding the young was regarded as an important chick maintenance activity and examined in greater detail than other actions. During the first two weeks after hatching, the young were unable to consume all the food provided, and the parent re-ingested the remainder only to regurgitate it several minutes or hours later. The number of feedings varied from one to eight per day ~x=4.+1.9), with a general decline in the number of feedings as the chicks developed (Fig. 8). The exception to this decline was a slight increase in feedings during the third week of the post-flight stage. This increase was probably due to a shift in the foraging grounds from the St. Johns River, 25 to 5 km away, to the nearby marshes on Merritt Island. Except for the fourth and fifth week of the pre-flight stage, the number of feedings by the male exceeded that of the female, and this difference was significant (P<.5, Wilcoxon signed-rank test). The pair averaged 3.8 feedings per day (N=24), of

25 ,._, OJ (/).25 z - 2 r- I IJ...U O<t I 15 I a:: ww m~ ~ C/) ( ::)(/) zw a:: (.!) (.!) 5 <{ ' '..., [,'. WEEK: [}~] [}}j Jttd r~tej l}}] [\}] 7 8 MALE FEMALE TOTAL rit:i:1 lwil INCUB ATI.. ON PRE-FLIGHT REPRODUCTIVE STAGES POST-FLIGHT Figure 7. Aggressive encounters exhibited by a nesting pair of storks.

26 Figure 8. The number of times young were fed during the nestling period by a pair of Wood Storks. Data for the first and third week are based on partial data and pro-rated.

27 ... \. >- <( Q LL.. :: 8 6 w a.. :: w CJ) 4 (ll, (.!) :E z :::> z w w ll.. 2 MALE ~ FEMALE ~ TOTAL ~ Will WEEK: I I INCUBATION PRE- FLIGHT p S T- FLIGHT REPRODUCTIVE STAGES

28 Figure 9. The time, in hour intervals, and number of feedings by a nesting pair of Wood Storks. N (/) (.9 z - w w LL 8 6 MALE ~ FEMALE TOTAL a. LL 4 ::: w CD 2 ~ :J z 6 8,)>1!' ' 'if)))'! t===\'») L d)\\'1 J b'>'\'1 t=1 :<1 II- } T I M E (hrs)...

29 Figure 1. The temporal distribution of feedings by 11 Wood Stork pairs at the Moore Creek colony in N l-' (/) (!) z 4-3 w w IJ... :. 2 ll o.. :: w 1 (D ::E :::> z Q_.l jl I.-,-,-,-,-,-,.,,..,.,-,-,-, t fn n ] l'f ' "fffl 1,,,,,,,1 ( " 'fffff..-,-,-, n] p.,,,,,,j lj',',',.,.,,j,,.,,,,, f,,,,..,,j f " : : " ' 'i li'i'i'!'t' 'o'l J I- I I V I T I M E (hrs) 24

30 22 which the male was responsible for 6.5%. However, in a nearby nest (nest #2, Fig. 2) in which the chicks were fed at a comparable rate (mean=3.1, N=34), the male's share (51.6%) only slightly exceeded that of the female. Feedings occurred throughout the day (Fig. 9); however, most regurgitations were noted between 8 and 14 (78.6%) with a peak between 8 and 12 (54.8%). A similar temporal pattern was found for 238 feedings recorded at random from 11 other nests (Fig. 1). During the first two weeks the parent storks only nudged the young with their bills; however, allopreening was observed the third week when the chicks' feathers had grown enough for the adults to grasp and manipulate individual feathers. Parental allopreening was noted only during the third, fourth, and fifth weeks, and was directed to hard to reach areas (head, neck, and back). After the parents discontinued allopreening, the young continued to allopreen each other until they abandoned the colony. On hot days the adult storks brought the young water that was gathered below the nest or from surrounding impoundments. Three to seven minutes were required to collect water (x=4.5 min), and all watering visits were between 122 and 1527 hrs (N=6). After the first week the adults brooded the chicks only at night and during periods of rain. On hot days the chicks kept cool by remaining in the shade of an adult, and they appeared to move around in the nest until they found the shade. On some occasions the parent assumed fullor delta-wing spread postures (Kahl 197lc) to shade an. additional area; however, the members of this pair assumed such postures only one day (fifth week).

31 23 Incubation and brooding The focal pair covered the eggs an average of 89.3% of the time (Table 7), and the time incubating declined as the period progressed (Table 8). Nest relief occurred an average of 1.9 times per day, and the time off the eggs during nest relief averaged min (N=l3). The pair averaged min (N=l3) to initiate incubation after the mate stood, and this difference was not significant (t=.8, P>O.OS). During recess from incubation, but not during nest relief, the on-duty bird stood, stretched, preened, worked twigs into the nest, and rolled the eggs before re-settling. The average recess was min (N=SS), ranging from less than a minute to slightly more than 1 min with no significant difference (t=l.l4, P>O.OS) between the sexes (Table 9). The eggs were covered continuously from several seconds to 96 min ( , N=67) before the incubating bird stood. Although the male's sessions ( , N=28) averaged significantly longer than those of the female ( , N=39), the total incubation time was about equai because the female stood more often. Although a full day of quantitative data is not available for the first week after hatching, observations on other nests indicate the young are brooded most of the time. In the second week the young were brooded only at night, and during a brief period when an adult stork approached the nest aggressively and could not be driven away. After the second week the chicks were no longer covered, except for one half-hour during heavy rain in the fourth week. Nest maintenance The nest of the focal pair was well constructed by the time

32 Table 7. The percentage of daylight hours an incubating Wood Stork covered the eggs. Total N +' Sex Week 1 2 3* 4 Male Female Total * No data were gathered on week 3.

33 Table 8. Mean incubation session length (min) by a pair of Wood Storks during each week of the Sex Week Total Male Female i Total N ljl incubation period * 4 * No data were collected on week 3.

34 Table 9. The mean time (min) a pair of Wood Storks stood off the eggs during each week of the Total N (J\ incubation period. Time off during nest exchange is excluded. Sex Week 1 2 3* 4 Male ± Female Total *No data were ~ collected on week 3.

35 27 observations began, and was composed primarily of White Mangrove and Brazilian Pepper (Schinus terebinthifolius) twigs. In general, the male gathered nesting materials and brought them to the female for insertion; but if the female was absent, the male inserted the sticks alone. The male collected materials near the nest and dik~s surrounding Moore Creek, while the female only gathered twigs from White Mangroves near the nest. The male brought 9.2% of the sticks (N=41) that were added to the nest after egg laying and worked in 68.3% of the twigs. The majority of the repair or enlargement materials were incorporated into the nest during the pre-flight stage. Twigs were stolen from surrounding nests 19.5% of the time, and these thefts occurred after the third week of the nestling stage. The male performed 7 of 8 thefts observed; the only theft by the female was a long stick from a neighboring nest that she could reach from her own nest rim. The trips to gather nesting materials ranged from 2 sec to 15.5 min (mean=3.5 min, N=15), and most gathering occurred between 7 and 1 (63%, N=41). Twigs added to the nest were grasped in the center and worked into the nest by back and forth shoving, and once in place, the twigs were rearranged in a similar manner. the nest repair and enlargement. This activity accounted for about 98% of The remaining 2% consisted of "jackhammering", in which the open or closed mandibles were thrust into the nest floor with a rapid up-and-down motion. Standing at the nest Storks stood at the nest for long periods without performing any obvious actions other than comfort movements. The amount of time spent standing at the nest varied from to 64.5% of a bird's day, and up to

36 % of the time a bird was attentive to the nest. The time standing increased dramatically after the chicks hatched, and remained high halfway through the pre-flight stage, then gradually declined to zero the last week. Comfort movements, such as body shakes, head rubs and shakes, scratching, wing stretches, yawning, and preening accounted for 13.9% (male 12.2%, female 16.7%) of the time spent standing at the nest. Loafing in the colony Storks sometimes spent brief periods in the colony, but away from the nest. If no actions of interest (i.e., twig gathering, watering, or aggression) were noted, then it was assumed the bird was loafing. Loafing occurred in the latter half of the pre-flight stage and in the post-flight stage. A gradual increase in the number of loafing episodes was noted as the season progressed, but a maximum of only 2.4% of a bird's day was spent this way. Loafing periods ranged from several seconds to 1 min (mean= min, N=23) and the amount of time spent loafing by the male ( min, N=l7) was significantly higher (t=2.2 P<.5) than that of the female (1.1+.6, N=7). The number of loafing episodes by the male (N=16) was s.ignificantly higher than that of the female (N=7) (Wilcoxon s.igned-rank test, P<O. 5). During this time the female performed no obvious activities while the male preened 9.2% of the time. Sexual displays Sexual displays by the storks occurred frequently during courtship, but tapered off rapidly once the pair bond was established. Of seven displays described by Kahl (1972), only four were noted after egg laying. One incidence of Copulation Clattering and one of Flying Around was

37 29 noted; the former in the first week, and the latter in the second week of incubation. The Up-Down was the most frequently observed display and was noted up to the sixth week of the pre-flight stage. Swaying Twig-Grasping frequently followed the Up-Down, although the frequency decreased as the season progressed. The other sexual displays; Balancing Posture, Display Preening, and Gaping, may have occurred, but were of such reduced intensity that they were not considered as a definitive display.

38 DISCUSSION For a species to survive and maximize the production of young, the organism must effectively perform a variety of activities - all of which require time and an expenditure of energy. Natural selection has resulted in an optimal time budget for each species and will continue to maintain it. This is not to say that time and energy budgets are fixed, but that there are bounds within which an organism must remain in order to reproduce successfully. The Wood Stork is highly adapted to a fluctuating wetland system and grope-feeding and low-energy soaring are the major mechanisms involved in this adaptation. For the stork t.o forage efficiently and repr oduce successfully, high concentrations of prey in drying and ephemeral ponds, marshes, and channels are required, and frequently these concentrations are considerable distances from the breeding colonies. To conserve energy the storks utilize the kinetic energy in thermal air currents to gain altitude and then glide off to the foraging areas. Storks from Moore Creek were noted foragi_ng up to 5 km from the colony (Clark 198), and Ogden et al. (1978) found storks foraging 13 km from a south Florida colony. Relying on thermals for locomotion restricts the time and speed at which a bird can move. The arrival or departure of storks, including the focal pair, was only noted during daylight hours, and generally occurred in mid-morning and mid-afternoon. Such movements coincide with the formation of thermals in the morning and 3

39 31 their decline in the afternoon. The number of storks soaring above the Moore Creek colony on each half-hour reflected this pattern (Fi.g. 11), and was similar to that reported by Kahl (1964) at the Corkscrew Swamp Sanctuary. Although the storks have a shorter feeding day than do other ciconiiforms that use a flapping flight, the conspicuous white plumage and long range soaring ability of these very social foragers allows for an effectiv e exploitation of high eco~ogical densities of prey in areas of declining water levels. It appears the ability to concentrate on areas of high prey densities and to move long distances with a small expenditure of metabolic energy more than compensates for the shortened foraging time. The nest attentiveness and time budget of the stork would be e xpected to reflect the birds' adaptation to its environment and feeding behavior. During the initial week of the incubation period both the male and female stork s were frequently at the nest together, and this tendency probably helped to reinforce the pair bond. Sexual displays decreased after t h e fir st week as the pair bond had matured and the clutch was completed. By the second week, however, only one bird remained at the nest, while the other was presumably foraging. This allowed both adults to replenish body weight lost during courtship and to be in better physical condition for the nestling stage. During the incubation stage the predominate activity at the nest was crouching over the eggs. This is to be expected as avian eggs must be warmed and protected if the embryos are to develop properly. If the eggs are not kept at an optimal temperature, their development may be slowed or the embryo may perish (Kendeigh 194). Obviously, the longer the time an egg requires to

40 Figure 11. Numbers of Wood Storks soaring over the Moore Creek colony at half-hour intervals on 8 April w N (/) 25 :'::!: 2 :: LL.o ::(/) 15 w (D(!) ~z 1 :J za::: <( 5 (f) OJ...fl I..,...- a A T I M E (hrs) OJ- I 'f-

41 33 hatch the greater the chance of predation on both the parent and egg. As the incubation period progressed~ the time spent incubating declined while aggression and nest maintenance increased. This change was probably due to greater irritability and restlessness of the adults. In the first four weeks of the pre-flight nestling stage an adult was constantly at the nest to protect the young from predators and thermal stress. During the first several days of life~ the altricial chicks probably were unable to thermoregulate, and required brooding for warmth and protection from other environmental conditions; however, after a week the young were feathered and required brooding only during cool nights, early mornings, and rainy periods. In the heat of the day the young were shaded by the adults. During this stage the young grew rapidly, and by the fifth week, they were quite large and capable of f e ndi ng off most predators while demanding greater quantities of food. Kahl (1962) found captive chicks attained a plateau of maximum food intake (ca. 35 gms/nestling/day) from the.age of 23 to 45 days, and this period coincides with the time the adults be~an to leave the chicks alone. Once both adults were "freed" of protective duties at the nest, they foraged simultaneously and were able to supply more food to the young. By the end of the pre-flight stage, the adults began to spend a considerable amount of time away from the colony; however, the amount of time loafing in the colony increased. During the post-flight stage of chick development the time devoted to all activities, except loafing, declined. This is because the fledged young were free of the adults except for feeding. In many instances a significant difference occurred between the time

42 devoted to various activlties by the male and female, especially during 34 the last half of the breeding cycle. In almost all activities, except time away from the colony, the percentage of time devoted to the various activities by the male exceeded that of the female. In most cases the magnitude of this difference was small and probably would have no effect on the number of young reared. Additional studies on time and energy expenditures of breeding ciconiiforms are clearly needed. This is especially true for the environmentally sensitive Wood Stork. In examining the ecology and foraging strategies of the stork, time and energy budgets must be considered. This study on the time budget of a pair of breeding storks provides a base-line for future research, and could be used to approximate the breeding season energetics if energy data became available.

43 SUMMARY An instantaneous sampling system supplemented by field notes was used to quantify nest attentiveness and time budget of a pair of Wood Storks (Mycteria americana) nesting at the Moore Creek colony on Merritt Island National Wildlife Refuge (Brevard County, FL) in Because the Wood Stork is a highly specialized bird whose tactolocating feeding methods are adapted to a fluctuating wetland system, it requires high concentrations of prey during the breeding season. Frequently, these ephemeral wetlands are considerable distances from the colonies, and the storks must depend on thermal ~ updrafts to soar to or from the colony during mid-day hours. These time constraints are reflected in the nest attentiveness schedules and time budget of the storks. During the 4-week incubation period at least one adult constantly attended the nest, with both sexes sharing incubation duties equally. In the incubation and brooding phases, nest.reliefs generally occurred once or twice a day with a majority of the exchanges occurring in midto late- morning. After the first week of the pre-flight stage the adults discontinued brooding; however, an adult continuously remained with the young through the fourth week. During the remaining 8-weeks the amount of time spent in the colony diminished until the parents only returned to the colony several minutes per day to feed the volant young. The amount of time devoted to incubation, brooding, nest maintenance, and sexual displays declined during the breeding season, while the time 35

44 36 spent ''loafing" in the colony and away from the colony increased. The time spent in aggression level, chick maintenance, and standing at the nest peaked during the first half of the pre-flight stage. Time at the nest followed a similar trend during the incubation and pre-flight stages; however, chick maintenance, nest maintenance, and loafing in the colony increased dramatically in the post-flight stage.

45 APPENDIX 37

46 Table 1. Daylight activity ( r.) by a pair of Wood Storks during one day oi each week in the incubation, pre-flight, and post-flight nesting Absent from Colony M (.) F (1.) Aggression M (3.7) F o.o o.o. Chick Maintenance M.. -. (.6) F Incubation or Brooding M (25.)... o.o..... o.o. F o.o... o.o. Loafing in the Colony M. o.o -.. (.).2 o.o F Nest Maintenance M (o.o) F o.o o.o I Sexual Displays M (. ).2.3, F Standing M (7. 7) F w ex:> stages. A Nesting Stage Sex Incubation Pre-fliS:ht Post-flight la abased on 3.5 hours of observation.

47 Absent from Colony (1. ) Aggression.4 o (3.7) o.o Chick Maintenance.. - o.o (.6) Incubation or Brooding (25. ) 11.6 o.o 3.8. o.o o.o.... Loafing in the Colony.. -. (. ) Nest Maintenance (.) 1.1 G.B Sexual Displays (. ) o.o... o.o Standing (7~7) o.o w \. Table 2, Total daylight activity (%) by a pair of Wood Storks during each week of the :incubation, pre-flight, and post-flight nesting stage Percentages are the male and female combined. - Nesting Stage Incubation Pre-flight Post-flight la Based on 3.5 hours of observation I

48 Table 3. The percent of daylight hours devoted to various activities by a pair of Wood Storks during each reproductive stage. The total Incubation Pre-flight (tveel\ 1-4) Pre-flight (week 5-8) Post-flight Male Female Total Male Female Total Hale Female Total Male Female Total Absent from Colony Aggression Chick Maintenance Incubation or Brooding o.oo..... Loafing in the Colony Nest Maintenance Sexual Displays Standing ' values are the combined male and female percentages.

49 Table 4. Daylight activity at the nest (%) by a pair of Wood Storks during one day of each week in the incubation, pre-flight, and post-flight Sex Incubation Pre-flight Post-flight Aggression M (3.7 ) F o.o Chick Haintenance M.. -. (.6) F ~ Incubation or Brooding M (25.) o.o F o.o Loafing in the Colony M.. - o.o (.).4 o.o F o.o o.o Nest Maintenance M :- 6.2 (.) o.o F Sexual Displays M co:o) o.o F S,tanding M (7.7) F Time at the Nest(% of Da~ M 68, (1.) F ~ 1-' nesting stages, 8 Based on 3.5 hours of observation

50 Table 5. Total daylight activity at the nest (%) by a pair of Wood Storks during one day of each week of the incubation, pre-flight, and Incubation Pre-flight Post-flisht Aggression (3.7) Chick Maintenance.. -. (.6) ,5 I Incubation or Brooding (25.) Loafing in the Colony.. -. (.) Nest Maintenance (. ) Sexual Displays (.), ,... Standing (7.1) Time at the Nest (1.) (% of Day) p.. N post-flight nestling stages. Percentages are for the male and female combined. 8 Based on 3,5 hours of observation

51 Table 6. The percent of time at the nest devoted to various activities by a pair of Wood Storks during daylight hours in each reproductive stage. Incubation Pre-flight (week 1-4) Pre-flight (week 5-8) Post-flight Male Female Mean Male Female Mean Male Female Mean Male Female Mean Aggression Chick ~1aintenance j Incubation or Brooding o.o..... toafing in the Colony. o.o. >.1. > Nest Maintenance Sexual Displays Standing , Time at the Nest (% of Day) ~ VJ The total values are the combined male and female percentages.

52 LITERATURE CITED Allen, R. P Our only native stork,. the Wood Ibis. National Geographic 25: Altmann, J Observational study of behavior, sampling methods. Behavior 49; _ Austin, G. T. Auk 95: Daily time budget of the postnesting Verdin Barr, A. J., J. H. Goodnight, J. P. Sall, and J. T. Helwig A user's guide to SAS. SAS Institute Inc., Raleigh, N. C. 329 pp. Browder, J. A A modeling study of water, wetlands, and Wood Storks. Pages in A. Sprunt, J. Ogden, and S. Winckler, eds. Wading birds. National Audubon Society Research Report No. 7, New York. Clark, E. S Factors affecting the initiation and success of nesting in an east-central Florida Wood Stork colony. Proc. Colonial Waterbird Group. 2: Clark, E. S A continuation of base-line studies for enviromnentally monitoring space transportation systems - threatened and endangered species of KSC - avifauna. NASA Tech Reports. (in press). Collias, N. E., and E. C. Collias A quantitative analysis of breeding behavior in the African Village Weaverbird. Auk 84: Derksen, D. V A quantitative analysis of the incubation behavior of the Adelie Penguin. Auk 94: Enderson, J. H., S. A. Temple, and L. G. Swartz photographic records of nesting Peregrine Falcons. 12: Time lapse Living Bird Jenkins, M. A. fledging Gryfalcon nesting behavior from hatching to Auk 95: Kahl, M. P. Condor Bioenergetics of growth in nestling Wood Storks. 64:

53 Kahl, M. P Food ecology of the Wood Stork. (Mycteria americana) in Florida. Ecol. Monogr. 34: Kahl, M. P. 197la. The courtship of storks. Nat. Hist. 8: Kahl, M. P. 197lb. Social behavior and taxonomic relationships of the storks. Living Bird 1: Kahl, M. P. 197lc. Spread-wing postures and their possible functions in Ciconiidae. Auk 88: Kahl, M. P Comparative ethology of the Ciconiidae - the Wood Storks (genera Mycteria and Ibis). Ibis 114: Kahl, M. P., and L. J. Peacock The bill-snap reflex: a feeding mechanism in the American Wood Stork. Nature 199: Kendeigh, S. C Factors affecting length of incubation. Auk 57: Kushlan, J. A., J. C. Ogden, and A. L. Higer Relation of variation in water level and fish availability to Wood Stork reproduction in the southern Everglades, Florida. U. S. Geological Survey, Tallahassee, Florida. Openf~le Report e 56 pp. Ogden, J. C., J. A. Kushlan, and J. T. Tilmant The food habits and nesting success of Wood Storks in Everglades National Park in Natural Resources Report Number 16, National Park Service. 25 pp. Orians, G. H The ecology of blackbird social systems. Ecol. Monogr. 31: Schartz, R. L., and J. L. Zimmerman The time and energy budget of the male Dickcissel (Spiza americana). Condor 73: Siegl, S Nonparametric statistics for the behavioral sciences. McGraw-Hill, New York. 312 pp. Sprunt, A., and M.P. Kahl Our American stork. Audubon 62: 26-29, 234, 252. Utter, J. M., and E. A. LeFebvre Daily energy expenditure of Purple Martins (Progne subis) during the breeding season: Estimates using D2l8 and time budget methods. Ecology 54: Verner, J Time budget of the male Long-billed Marsh Wren during the breeding season. Condor 67: