ORNlTOWGIA NEOTROPICAL 6: 87-95, 1995 @ The Neotropical Ornithological Society DIET AND FLOCK SIZE OF SYMPATRIC PARROTS IN THE ATLANTIC FOREST OF BRAZIL Marco Aurélio Pizo 1, Isaac Simáo 1 & Mauro Galetti 2 1 Departamenlo de Zoologia I.B., Universidade Esladual de Campinas. CP 6109, 13083-970 Campinas, Sáo Paulo, Brasil. 2 Wildlife Research Group, Departmenl of Analomy, University of Cambridge. Cambridge CB2 3DY, U.K. Resumo. Paclmetros populacionais de psitacídeos neotropicais, tais como tamanhos de bando e abund~cia, podem ser influenciados pela disponibilidade de frutos como fonte de alimento. Os psitacídeos podem responder aos períodos de escassezde recursos alterando o tamanho dos bandos, mudando a dieta, ou mesmo movendo-se para outras áreas. Nós estudamos durante 3 anos a dieta, o tamanho de bando e ~ abund~cia de dois psitacídeos (pyrrhura frontalis e Brotogeris tirica) em uma área de Mata Atl~ntica no sudeste do Brasil. Também fornecemos algumas informa~oes sobre outras quatro espéciesmenos abundantes na área (F.°rpus xanthop!erygius, Pionus maxi. miliani, Piono~itta pileata e Triczaria mazachitacea). Os psitacídeos consumlram 40 espécles de plantas perten- centes a 21 famílias. As famílias mais bem representadas na dieta foram Cecropiaceae, Myrtaceae e Moraceae. Em geral, frutos carnosos foram mais consumidos 9ue frutos secos, e E frontalis consumiu mais flores que B. tirica. Considerando as esta~oesúmida (vedo) e seca(Inverno), B. tirica e E frontalis foram as únicas espéciesa apresen- tarem diferen~ inter-estacional no tamanho de bando. Enquanto os bandos de B. tirica foram menores na esta~o secaque na úmida, E frontalis apresentou o paddo inverso. Houve um marcado declínio na abund3-ficia dos pisita- cídeos durante a est~ao seca,indicando um possível deslocamento para outras áreas.Nós discutimos a possível in- fluencia da dieta e disponibilidade de recursos sobre o tamanho dos bandos, bem como sobre as flutua~oes popula- cionais observadas. Abstract. Population parameters of Neotropical p'acrots, such as flock size distribution and abundance, are likely to be influenced by the availability of fruits as food resources. Parrots may respond to periods of fruit scarcity by altering floc~ size, changing diet, or even dispersing to a n~ area. Here we repo~ results of a t~r~J:'ear .study on diet, flock SIze,and seasonal abundance of two parakeet Specles(pyrrhura frontaús and Broto~ens tInca) In the Atlantic forest of southeastern Brazil. We also provide information lor four other parrot speciestForpus xanthopte- rygius, Pionus maximiliani, Pionopsitta pileata, and Triczaria mazachitacea). We observed parrots eating 40 plant species,primarily fruits of Cecro~iaceae, Myrtaceae, and Moraceae. Fleshy fruits predominated over dry ones, and E frontalis ate a greater ..proportlon of flowers than did B. tirica. Considering wet (summer) and dry seasons (winter), B. tirica and E jrontalis were the only speciesto show significative inter-seasonal difference i~ mean flock size. Brotogeris tirica flocks were smalle~ in .the dry season than in the wet s~on, whereas E frontaús sho:wed the opposite tendency..A well-ma;rked declIne lt;1 p~rot abundanc~ occurred durl~g t~~ dry season, .suggestIng that parrots shifted habltats. We dlSCU$ the posslble lnfluence of dlet and food avaIlabI1lty on flock Slze, and suggest the influence of such factors on the seasonal population fluctuations observed. Accepted 17 July 1995. Key words: Atzantic forest, Brazil, Brotogeris tirica, diet, parrots, Psittacidae, Pyrrhura frontalis. INTRODUCTION A pressing issue for any conservation policy Neotropical parrots are ecologically a very im- is knowledge of population parameters such as portant group of birds because of their role as variation in flock size distribution and abundan- seed predators and the consequent impact they ce of the speciesof concern. In the case of "obli- can have on the structure of tropical forests gate frugivorous" birds such as parrots, popula- aanzen 1969, Galetti & Rodrigues 1992). Fur- tion parameters may be tightly linked to fruit thermore, parrots constitute a large fraction of availability, as has been demonstrated for other the bird biomass in many Neotropical forests fruit-eating birds (Snow 1962, Crome 1975, (Terborgh et al. 1990). Despite this biological Leighton & Leighton 1983, Levey 1988, Loiselle importance and the declining numbers of many & Blake 1991, Rivera-Milán 1992). The availabi- species due to habitat destruction and the pet lity of fruits likely varies in space and time (Fran- trade (see Beissinger & Snyder 1992), there is a kie et al. 1974, Hilty 1980, Morellato & Leitao- lack of knowledge regarding the ecology of most Filho 1992) and, together with other factors, neotropical parrots. may influence flock size by dictating the num- R7 PIZO ET AL ber of birds that can efficiently forage together unpaved roads that cross the study area per- (Chapman et al. 1989). forming aproximately 20 km. We observed Here we report on seasonal variability in parrots between 06:00 and 18:00 h, avoiding days flock size, diet, and abundance of two common, with heavy rains and wind which reduce census sympatric parakeet species (Brotogeris tirica and reliability (Karr 1981). Overall, about 533 and pyrrhura frontalis) in an area of Atlantic forest in 366 hours were spent walking in wet and dry southeastern Brazil. Additional information on seasons,respectively. four other less common speciesof parrots also is Diet. We recorded a feeding-bout whenever we provided. encountered parrots feeding. Thus, a single bout could represent one or more parrots feeding on .METHODS a plant species, irrespective of the length of time Study site. The study was carried out at Parque they fed. If the parrot ( or a flock) moved to Estadual Intervales, Ribeirao Grande, sao Paulo another food source, a new bout was recorded. State (24°16's, 48°25'W}, a 49000 ha reserve in This method emphasizes the diversity of items the Serra de Paranapiacaba mountains of south- ingested by parrots, but does not provide infor- eastern Brazil. The reserve ranges in elevation mation on the amount of each plant species from 60 m a.s.l. near the coast to 1100 m in the consumed. However, we used this method be- interior. Our study was carried out at an eleva- cause parrots usually flew away upon detecting tion of 700 m where the vegetation is composed the presence of the observer. Thus, our estimate of primary forest with trees reaching up 30 m, of a parrot's diet is basedon frequency of feeding- and patches of second growth vegetation near bouts (see Snyder et al. 1987, Galetti 1993). Whenever possible, plants eaten were collec- human settlements. Climate is generally wet, ted for further identification at the herbarium of with rain or fog ocurring in most days which led t4e Universidade Estadual de Campinas (UEC). Willis & Schuchmann (1993) to classify the vege- tation as a cloud forest. Annual precipitation is Flock sizesand abundance estimate. From August around 1600 rnrn, with a dry season from April 1990 to December 1991 we estimatedthe monthly to August (winter), when the temperature often abundance of parrot species in terms of number drops below 5 ° C and frosts may occur, and a of individuals detected per field time (289 h in wet season from September to March. Seasonal the wet seasonand 198 h in the dry season).Such variation in temperature is pronounced, ranging estimate was obtained by multiplying the average from a minimum mean temperature of 13.4 ° C encounter rate of each parrot species by their in winter to 21.6 ° C in summer. monthly mean flock size (see Terborgh et al. Six parrot species (Pisittacidae) occur at 1990). The average encounter rate was based on Parque Estadual Intervales: Reddish-bellied Para- number of flocks seen or only heard during keet (pyrrhura frontalis), Plain Parakeet (Broto- walks. Mean flock sizes were obtained by coun- geris tirica), Blue-winged Parrotlet (Forpus xan- ting only flocks effectively seen perched or thopterygius), Scaly-headed Parrot (Pionus maxi- f1ying overhead. We adopted this method to esti- miliani), Red-capped Parrot (Pionopsitta pileata), mate abundance becauseof the wandering habits and Blue-bellied Parrot (Triclaria malachitacea) of parrot flocks, and also becauseof the absence (scientific names follow De Schauensee 1970). of a complete trail system in the study area The former four species are among the most which makes density estimates unreliable. Be- common parrots within their ranges, the latter cause our goal was to detect general patterns of two are endemic to the Atlantic forest and are annual population fluctuations, we assume that considered threatened (Ridgely 1981, Collar et al. this procedure is sufficient. At 'parque Estadual Intervales, parrots were 1992). Data were collected from December 1989 to easily identified by their regularly emitted metal- December 1991, and from August 1992 to Ja- lic call-notes which are audible at great distances. nuary 1994 during monthly visits (4-10 days Thus, the abundance estimate suffers little in- each) to the reserve. Observations were con- fluence of factors such as hearing ability (Bart ducted while walking along several trails and 1985) and song attenuation (Waide & Narins 88 DIET ANO FWCK SIZE OF PARROTS 1988), that common1y affect accuracy in singing bouts). These four families together comprised bird surveys. 43.6% of the feeding-bouts. Fleshy fruits (i.e., di- Statistical Analysis. We used Chi2 test to com- spersed by animals) predominated over dry ones pare the diet of flowers and fruits between parrot (i.e., dispersed by wind or gravity; 76.6% and species. Kruskal-Wallis test was used to evaluate 23.4% ofthe fruits eaten, respectively), but fruits monthly variability in flock sizes, and Mann- were frequently eaten in an immature, green con- Whitney test with normal approximation stati- dition. pyrrhura frontalis for example, ate the en- stic (Snedecor & Cochran 1980) was used to com- dosperm of immature fruits of the palm Euterpe pare flock sizes between species and seasons.