Uiv. itnl. Orn.. Milimo, 51(1-2): 1*7-112. 15-VM981

MAURO FASOLA (*), PAOLO GALEOTTI (*), G I U S E P P E BOGLIANI (*)

& PIETRO NARDI (**)

F O O D O F N I G H T H E R O N (NYCTICORAX NYCTICORAX)

A N D L I T T L E E G R E T (EGRETTA GARZETTA) F E E D I N G I N R I C E F I E L D S

Summary. — In Northern Italy, the distribution of heronries seems related witn the abundance of rice fields. We studied the diet of Night Heron and Little Egret in a zone with abundant rice, in order to ascertain the extent to which the prey are taken in agricultural wet habitats (rice, irrigation canals) or elsewhere (rivers, mar­shes). We collected food regurgitated by the nestlings in the heronries, complementing the data in rice fields by direct observation of adult Night Herons feeding and by sampling the available prey.

The list of prey species (App. A) overlaps with the lists given in the literature. The diet of nesting Night Herons in our study area is largely based on Amphibia and Pisces (Fig. 1). The prey taken by Night Heron and Little Egret are largely the same: the Egret catches smaller prey, and particularly smaller fish and to a lesser extent adult frogs. Marked fluctuations in percentages of Amphibia, Pisces and Crustacea occurred in Night Heron's diet, in keeping with the times of greatest abundance of each type of prey (Figg. 2, 3). Differences in the frequency of each prey category between neighbouring heronries were detected (Fig. 4). In six zones of the Palearctic and Oriental regions, the most frequent prey of the Night Heron (those in excess of 30'/ in number) were: Amphibia (once, our data), Pisces (twice), Insecta (three times), Crustacea (once) (Tab. I). The observations on adult Night Herons feeding and the sampling of prey (Tab. II ) , show that Crustacea, tadpoles and Am­phibia are captured only in rice fields, frogs mainly in irrigation canals, and Pisces in canals, rivers, marshes. Anellida and tadpoles, small and rapidly digestible, are probably more important in the diet than can be seen from regurgitations. The prey definitely taken in rice fields reach a peak when the number of young Herons in the nests, and their food domands, are higher.

In conclusion, a tentative estimate of the percentage of food contributed by the wet agricultural habitat (rice and irrigation canals) is 60-70'/* in number and 30-60',/ in dry weight.

(*) Istituto di Zoologia dell'Universita, Piazza Botta, 27100 Pavia. (**) Istituto di Ecologia Animate ed Etologia dell'Universita, Piazza Botta,

27100 Pavia.

98 M . FASOLA, P. GALEOTTI, G. BOGLIANI & P. NARDI

Riassunto. — AlinuntuzioHc di Xitticora < (iarzi tut in i isuiu.

Nell'Italia settentrionale, la distribuzione delle garzaie sembra essere in relazione con l'abbondanza di risaie. Abbiamo percio studiato l'alimentazione della Nitticora e della Garzetta in una zona con abbondanti risaie, per accertare la proporzione di cibo raccolto in esse e nei canali adiacenti. Abbiamo effettuato raccolte di rigurgiti dei nidiacei (97 raccolte in quattro garzaie in tre anni, in totale 4838 prede di Nitticora e 228 di Garzetta), osservazioni di adulti in nutrizione (totale 115 osservazioni per 912 min.), campionamenti delle prede.

Le categorie di specie predate (App. A) si sovrappongono largamente con quelle trovate da altri autori. La dieta della Nitticora nella nostra area di studio e basata, sia considerando il numero che il peso secco delle prede, su Anfibi e Pesci (Fig. 1). Le specie predate da Nitticora e Garzetta sono in gran parte le stesse; la Garzetta cattura in genere specie di pesci di dimensioni minori, e meno rane adulte. Durante tre mesi, la dieta della Nitticora ha mostrato ampie variazioni delle categorie di prede (Figg. 2, 3), in particolare di Crostacei, Anfibi, Pesci; tali variazioni paiono seguire i cicli di abbondanza di ogni preda. Esistono dfferenze nella frequenza delle prede tra alcune garzaie, anche tra due distanti solo 3,5 km (Fig. 4). In diverse aree geografiche, la dieta della Nitticora e basata su diverse categorie di prede, a volte Pesci, altre volte Insetti, Anfibi, Crostacei (Tab. I) . Le osservazioni di Nitticore adulte in nutrizione in risaie (Tab. i l ) e i campionamenti con reti mostrano che Cro­stacei, girini e Anellidi sono catturati solo in risaia, che le rane sono catturate pre-valentemente nei canali d' irrigazione all' intorno, i pesci nei canali, nei fiumi e nelle paludi. L a percentuale di girini e Anellidi, prede piccole e facilmente digeribili, rile-vata nei rigurgiti e inferiore alia percentuale effettvamente catturata dagli adulti. Cio suggerisce che queste prede sono sottostimate nella dieta studiata mediante ana-lisi di rigurgiti. Le prede raccolte in risaia sono piu abbondanti nei periodi di mas-sima presenza dei nidiacei di Nitticora e Garzetta, e quindi di maggiore necessita di cibo.

In conclusione, i dati raccolti permettono di stimare che il cibo fornito dalle risaie e dai canali di irrigazione adiacenti e circa il 60-70' '< in numero e il 30-60'/ in peso secco della dieta dei nidiacei di Nitticora.

Ardeidae, like most other avian predators, are more or less genera-lists, and take different prey in relation to their availability in different habitats and zones. The food of many species of Ardeidae in various countries is known qualitatively and in some cases also quantitavely (CRAMP & SIMMONS 1978).

In Northern Italy, a dense population of nesting Night Herons (more than 10.000 pairs), and little Egrets (more than 2.000 pairs), is concentrated in a zone lacking extensive marshes but covered by abundant rice fields in which the Herons are frequently seen feeding (BARBIERI et al. 1979); the number and size of the heronries increases percentagewise proportionately to the surrounding land which is cultivated by rice (FASOLA & BARBIERI 1978). Therefore these agricultural habitats seem to be important feeding grounds for Ardeidae nesting in Northern Italy.

FOOD OF NIGHT HERON (NYCTICORAX NYCTICORAX) ETC. 99

The aims of this paper are to determine the diet of the Night Heron Nycticorax nycticorax and the Little Egret Egretta garzetta nesting in a zone of abundant rice fields, to identify temporal and local variations of the diet, to compare it with the diets in other countries, and to ascertain to what extent the prey are taken in wet agricultural habitat or elsewhere.

Diet was studied primarily in heronries from regurgitation of nest­lings, complementing the data in rice fields by direct observation of adults feeding and by sampling the available prey.

Nestling herons regurgitate when alarmed by predators or humans. This behaviour was explained as an antipredator device, to lure away predators from nestlings by causing them to consume the regurgitaded material instead of killing the nestling ( K U S H L A N 1978), or to make the nestlings lighter and more mobile in order to escape easily from pre­dators (OWEN 1955, VOISIN 1978). The first explanation is supported by-repeated observations of one Cathartes aura, a predator known to ki l l nestling herons, which forced nestlings of Ardea herodias to regurgitate and took the regurgitated food to its chicks ( T E M P L E 1969).

Nestlings of Night Herons and Little Egrets regurgitate readily only when about 15 to 30 days old (pers. obs.). At this age the diet of the nestlings is identical or very similar to that of the parents ( K U S H L A N 1978).

Study area and methods.

Food samples were obtained during reproductive seasons 1978, 1979, 1980, by collecting food regurgitated by the nestlings in four heronries (called below C. L. V. M.).

The heronries are located in a 15 km radius around Pavia (Fig. 4), and are surrounded by flat agricultural plain, 17% of which is covered by rice fields. These fields are flooded from May to August, the water depth being uniform (about 15 cm); rice is sown at the beginning of May, and the seedlings emerge above the water surface in the second half of May.

In the study area, other feeding habitats of the Ardeidae are the rivers (Po and Ticino), their small bordering marshes, and the irrigation canals more frequent near rice fields.

Collection of regurgitations was made twice a week, from 8 to 10 a.m., simultaneously in all the heronries.

Each collection lasted about l h ; we walked below the nests picking up regurgitated food, and searching with the greatest care the ground surrounding each item found, in order to minimize the risk of missing smaller ones.

100 M . FASOLA, P. GALEOTTI, G. BOGLIANI & P. NARDI

The species which regurgitated was identified. When possible, at each visit at least 50 prey items from at least 5 different broods were collected.

In all we made 97 collections in the four colonies in three years, from May 9th to August 10th, obtaining 4838 prey items of the Night Heron and 228 of the Little Egret.

Samples, preserved in alcohol, were later examined, identifying the species and counting the number of prey collected on each heronry. Frogs of the genus Rana and tadpoles which had been digested so much that identification was not possible, were assigned to Rana esculenta, because those identified (about 80% of the frogs and 20'/ the tadpoles found) all belonged to this species.

To calculate weights of the prey, we captured samples of each prey type, and of each size class for Rana esculenta and fish, in various habi­tats in the study area, and weighed them both fresh and dry (70h in oven at 70-C).

Observations of feeding adult Night Herons were performed by visit­ing a 15 km- zone between heronries L and V, comprising about 3 km-of rice fields. Each adult Night Heron encountered in rice fields and not scared by our presence, was observed with a 30 X 75 telescope, recording captured prey. Standard observations lasted 10 min. each but sometimes the bird was out of sight before this period had elapsed. 115 observations were retained for analysis (mean duration 7 min. 56 sec, total duration 912 min.), rather regularly distributed in each hour of daylight (5 a.m. to 8 p.m.) from May 13th to June 11th 1980.

Sampling of prey available to the herons was carried out in a number of rice fields, by sweeps of a long handled net.

Results and discussion.

Prey species.

The diet of nestling Night Herons in the study area (Fig. 1) is largely based on Amphibia and Pisces. Crustacea are important in num­ber, but not in weight. Anellida and tadpoles, however, are probably more important than was found from the analysis of regurgitated food, as suggested by the observations of feeding adults (see « Significance of rice fields as feeding habitats »).

A detailed list of prey species and numbers found in regurgitated material by Night Herons and Little Egrets (App. A), shows that Insecta are primarily aquatic larvae of Hydrophilidae and Dytiscidae; Crusta­cea are all Triops cancriformis, Amphibia almost all Rana esculmta\

FOOD OF NIGHT HERON (NYCTICORAX NYCTICORAX) ETC. 101

Pisces consist of almost every common species living around the study area. The few species of Pisces living around the study area, but not comprised in the list, live in fast running waters of major rivers (Rutihis pig us, Lenciscus souffia muticellns) or in the mud on the botton

Fig. 1. — Percentages in numbers (NO) and dry weight (DW), of categories of prey found in regurgitations of nestling Night Herons. Cumulative data for the four heronries and for years 1978 to 1980.

101' M . FA SOLA, P. GALEOTTI, G. BOGLIANI & P. NARDI

(Anguilla anguilla), or are rather scarce and local (Phoxinus phoxinus, Gambusia affinis holbrooki) (Nardi in press).

This list of prey species of the Night Heron is very similar to that given by MOLTONI (1936, 1948) for Northern Italy: even most insect speces are the same (e.g. Harpalus, Stenolophus, Gryllotalpa) and only Reptilia (Natrix) were missing in our sample.

A major qualitative difference in the trophic spectrum of the Night Heron and the Little Egret between our sample and data from other parts of their breeding range (HAFNER 1977, WOLFORD & BOAG 1971, M U K H E -R J E E 1971, VALVERDE 1955, 1956, A L L E N & MANGELS 1940, GROSS 1923) is the absence in our sample of Mollusca, Crustacea other than Triops, Aracnida, Reptilia, Aves and Anellida other than Lnmbvicus and Hirudo. This absence is not due to limited sampling, our sample being in fact larger than that of the publications quoted. Moreover, many species sub­stitute others of the same taxa.

The lengths of fish of the species more frequently regurgitated by nestling Night Herons were as follows.

Mean standard lenght in

cm

Standard deviation Range

No. individuals

Alburnus a. alborella 6.3 1.4 2.8-12 266 Carassius carassius and auratus 8 3.9 2.2-18 149 Rutihis ntbilio 7.3 1.6 5-12 97 Tinea tinea 12.2 3.8 2.5-19 60 Seardiniiis crytrophtahnus 12.3 3.8 2.5-19 54 Lepomis gibbosus 6.5 1.8 2.5-10.8 59 Cob it is taenia 6 1.4 2.5- 8.4 55

Differences in diets of the Night Heron and the Little Egret.

A comparison of the diet of the two species is difficult, because the sample of the Egret's prey is small. The range of prey species and taxa of the two birds largely overlap.

Overall, the Egret catches smaller prey than the Night Heron, and particularly smaller fish (more Alburnus a. alborella, less of other larger fish species) and less frogs than the Night Heron. Triops seems to be absent from the Egret's diet, but this may be due to the collection of regurgitated food of this species later in the season, when Triops were at the end of their abundance cycle (the Egret breeds 1-2 weeks later than the Night Heron).

FOOD OF NIGHT HERON (NYCTICORAX NYCTICORAX) E T C . 103

Conversely, HAFNER (1977) found Triops more frequently in food regurgitated by Egret than by other Ardeidae.

In the Camargue, an overlap in the diet of the two species was found by VALVERDE (1955, 1956), with the Egret taking only partially different and smaller preys (HAFNER 1977, VOISIN 1978).

Temporal variation in diet. The variation in the categories of prey in the diet of nestling Night

Herons during our sampling period is shown in Fig. 2. Fluctuations in the percentages of Amphibia and Pisces are small and are inversely

% no.

T I — —— 1 1 1 1 1 I ' 1 ' 1 1 1 1 1 1 1 V ' 1 1 1 1 1 1 1 L T 15 30 15 30 IS 30 10

may may June June Jul. Jul. aug.

ot her

Fig. 2. — Temporal variation of the main categories of prey in the diet of Night Heron nestlings. Cumulative data for the four heronries and the years 1978-1980, expressed as percentages in number of individuals of each prey category. Dates are split in periods of three days, or longer for early and late dates.

104 M. FASOLA, P. G A L E O T T I , G. BOGLIANI & P. NARDI

correlated; Crustacea are abundant, fluctuating widely only until the beginning of June; Insecta and « Others » remain rather constant. Life stages of Rana esculenta show marked temporal variations (Fig. 3) that follow their development from tadpoles to young frogs, while frogs more than 1 year old (« adults ») are preyed on mostly in the earlier and later parts of the period.

Seasonal variation in the food of Ardea cinerea (OWEN 1955) and of Ardeola ibis (SIEGFRIED 1971) was related to the behaviour and the life cycle of the different prey species. In our sample too, an increased presence of each prey in the diet coincides with periods of its greatest

% no.

l O O - i —

Fig . 3. — Temporal variations of life stages of Rana esculenta i n the diet of the Night Heron. I n « juven i l e s» we included individuals wi th body lenght < 30 mm, almost certainly born in the current year. Other details as in Fig . 3.

FOOD OF NIGHT HERON (NYCTICORAX NYCTICORAX) E T C . 1 05

abundance in aquatic habitats (pers. obs. and sampling with nets): Triops have population explosions in May and early June, Rana tadpoles are abundant in rice fields from the end of May, and juvenile Rana frogs from the middle of June.

For Ardea cinerea, OWEN (1960) concluded that the young are in the nest at the time of maximum availability of food. In our study area, the peak of Night Heron and Little Egret young in the nest (from June 1st to July 10th) coincides with the time when tadpoles and young frogs are available.

Year to year variations of the food in the same heronry may occur ( A L L E N & MANGELS 1940, VOISIN 1978), but we found no difference in our samples between 1978, 1979 and 1980.

Local variation.

The local variation of prey categories in the diet of the Night Heron is shown in Fig. 4. The differences between the heronries in the fre-

Fig. 4. — Location of the four heronries sampled, and inter-heronry differences in frequencies of the main categories of prey of the Night Heron. > greater frequency in heronry to the left; < in heronry to the r igh t ; A Amphibia; P Pisces; C Crustacea; I Insecta. Differences tested by x"» p < 0.01.

106 M . FA SOLA, P. G A L E O T T I , G. BOGLIANI & P. NARDI

quency of each prey category were those which turned out to be signifi­cant when tested by f on 2 x 2 contingency tables, taking the heronries two by two and one prey category at a time against all the others. For each pair of heronries we consider only prey sampled on the same date in both, so as to eliminate the effect of the temporal variation of the prey, utilizing all samples from 1978 to 1980.

Variations of the main prey categories occur in some of the heron­ries, even in a pair which were only 3.5 km apart, and may be related to the availability of different feeding habitats in the feeding range of each heronry. Pisces are more abundant in the diet of nestlings in heronry V, the one nearest to the rivers; Crustacea are more abundant in C and L, which are surrounded by rice fields; differences in Anphibia and Insecta do not follow a recognisable pattern.

Local variation of food, related to the availability of different feed­ing habitats, was also found in Ardeidae by OWEN (1955) in Ardea cinerea and by VOISIN (1978) in Egretta garzetta.

Regional variation.

In six zones of the Paleartic and Oriental regions prey of the Night Heron more frequent than 30% in numbers (Tab. I) were Amphibia (once, our data), Pisces (twice), Insecta (three times), Crustacea (once). Mo­reover this abundance of Crustacea (VALVERDE 1955, 1956) is probably due to the collection of regurgitations only in days of high presence of Triops. Other data, expressed in percentage of occurrence and not com­parable with those in Table I , suggest that in zones of North America, the diet was occasionally based largely on birds (WOLFORD & BOAG 1971), mammals ( A L L E N & MANGELS 1940) and fish (HOFFMAN 1978).

Therefore, the diet of the Night Heron is highly variable, and is based on different types of prey in the different zones of its range, as suggested by JENNI (1973) for Ardeola ibis (but the data were probably biased because samples from various colonies were collected on different dates, without taking into account possible temporal variations of prey).

The existence of marked temporal, local and regional variations in the food of Ardeidae indicate that intra- or interspecific comparison of diets must be based on large sampes, collected during extended and coin­cident periods.

Significance of rice fields as feeding habitats.

The diet of the Night Heron's nestlings is compared in Table I I with the prey taken by the adults in rice fields and the availability of the prey. We consider only regurgitations collected during the period

T A B L E I . — Comparison of the diet of the Night Heron in different countries. Prey expressed in percentage of numbers of individuals of each taxa.

Italy (1)

No. prey 4838

France (2)

Camargue No. prey 625

France (3)

Camargue No. prey 620

Ungary (4)

No. prey 747

U.R.S.S. (5)

Volga delta

India (6)

Gange delta No. prey 373

Japan (7)

No. stomachs 11

Anellida 0.9 0.3 9.3 Mollusca 2 0.2 18.7 Crustacea 13.3 0.8 46.1 ) 11.8 + Aracnida 0.3 0.3 1.1 + Insecta 4.3 73.1 30.3 67 14.2 28.4 Picses 20.8 24.3 15 10.4 75.6 18.7 56 Amphibia 60.3 1.5 6.9 17 5.2 25.4 9.8 Reptilia 0.7 0.7 2.4 Aves 0.1 Mammalia 0.3 0.3 0.8 +

(1) Our data. (2) From Hafner (1977). (3) Calculated by us from Valverde (1956). (4) Calculated by us from Vasvari (1935-1938).

(5) From Skokova (1960) in Voisin (1978). (6) Calculated by us from Mukherjee (1971). (7) From Kosugi (1960) in Voisin (1978).

10S M . FASOLA, P. GALEOTTI, G. BOGLIANI & P. NARDI

in which we made direct observations of the adults feeding. The diffe­rences in the percentages of prey indicate to what extent the nestlings' diet is based on food collected in rice fields and on that collected in the other available aquatic habitats (irrigation canals, rivers, marshes).

TABLE I I . — Comparison of percentages in number of items of different prey, taken by adult Night Herons feeding in rice fields, regurgitated by nestlings, and of

presence of the prey in rice fields.

Presence rank: + + + high, + + medium, + low, 0 obsent.

rA no. prey of adults feeding in rice fields

'/< no. prey in nestlings

regurgitations

Presence in rice fields

Anellida 42 Crustacea (Triops cancriformis) 31 Tadpoles (Rana esculenta) 23 Amphibia ad. 4 Fish 0 Others 0

4 23 4

41

+ + + + + + + + +

+ + 0

+

Total no. prey 599 1064

Higher percentages in the first column suggest that Anellida, Cru­stacea ad tadpoles are captured mainly (or only) in rice fields. Moreover Triops and Rana esculenta tadpoles are very scarce, or absent, from other aquatic habitats in the study area; Anellida (Lumbricus) may be taken only when rice fields are flooded and the worms come to the sur­face of the ground, as we noted during observations of Night Herons feeding, so these prey are captured only in rice fields.

Higher percentages in the second colum indicate that adult Amphibia (almost all Rana esculenta) are taken mostly outside rice. They are espe­cially numerous in irrigation canals from which they move into rice for reproduction; they are also present in the small marshes bordering rivers.

The differences in the percentages of Anellida and tadpoles between the columns in Table I I are higher than the difference in Crustacea, sug­gesting that the first two prey (and especially Anellida, whose difference is higher) are more important in the diet of the nestlings than may be

FOOD OF NIGHT HERON (NYCTICORAX NYCTICORAX) E T C . 109

appreciated from regurgitations. These are in fact the most rapidly dige­stible of all the categories of prey.

The occurence of Ardeidae in rice fields for feeding was studied by HAFNER (1977) and VOISIN (1978) in the Camargue, concluding that rice is a less important feeding ground than marshes and logoons.

In our study area rice should contribute to about 55% in numbers and 11% in dry weight of the prey regurgitated by Night Heron nest­lings from the middle of May to the middle of June, i f only Anellida, Crustacea and tadpoles and few other Amphibia are preyed on in this habitat. But Anellida and tadpoles are under — represented in the diet studied through regurgitation, and their percentages are probably higher; adult frogs, and fish living in standing and low running waters, that con­stitute about 8 / 1 0 of all fish taken, are probably captured in the vast network of irrigation canals that surround the rice fields, and less in the little marshes bordering rivers.

In conclusion, our data do not give us a precise calculation of the percentage of food contributed by the agricultural wet habitat (rice fields and irrigation canals) to the diet of the Night Heron, but a tenta­tive estimate is 60 to 70% in number and 30 to 60% in dry weight. The prey definitely taken in rice reach a peak from the end of May to the end of July, when the number of young Herons in the nests, and their food demands, are higher.

Acknowledgments. — Thanks are due to F . Barbieri, M. Ghidini and C. Prigioni for help in fieldwork, to A. Pozzi for identification of Amphibia, to E . Balestrazzi for identification of Insecta, and to S. Jayakar for correction of the manuscript.

no M . FASOLA, P. GALEOTTI, G. BOGLIANI & P. NARDI

A P P E N D I X A.

Cumulative numbers of individuals of each prey species found in nestlings' regurgitations, i n four heronries, from 1978 to 1980.

Insecta are adults, i f not otherwise stated.

Class, Order, Family, Genus, Species No. prey

Nycticorax Egretta nycticorax garzetta

TURBELLARIA Planaria sp.

OLIGOCHAETA Lombricus terrestris

HIRUNDINEA Hirudo medicinalis

CRUSTACEA Notostraca Triops cancriformis

INSECTA indeterminated

Odonata Sympetrum depressiusculum Lestes sponsa

Ortoptera Gryllotalpa gryllotalpa

Hemiptera indeterminated Notonecta glauca

Hymenoptera Apis sp.

Coleoptera indeterminated

Carabidae Stenolophus discophorus Stenolophus teutonus Amara sp. Harpalus sp. Diachromus germanus

Dytiscidae indeterminated indeterminated larvae

Hydrophilidae Hydrophilus piceus larvae

Elateridae indeterminated

Curculionidae indeterminated

Diptera indeterminated larvae

PISCES indeterminated

Salmonidae Salmo sp. Salmo gairdneri

Esocidae Esox lucius

Cyprinidae indeterminated Rutilus rubilio Leuciscus cephalus cabeda

38

6

642

5

1

6

1 1

1 8 2 1

1 34

115

1

1

21

18 2 1

1

15 116 26

40

FOOD OF NIGHT HERON (NYCTICORAX NYCTICORAX) ETC. I l l

(segue Appendix A)

No. prey Class, Order, Family, Genus, Species Nycticorax Egretta

nycticorax garzetta

Tinea tinea 7 1 1 Scardinius erythrophthalmus 67 Alburnus a. alborella 3 0 4 53 Chondrostoma soetta 1 4 Chondrostoma toxostoma 38 1 Gobio gobio 2 Barbus barbus plebejus 3 Carassius carassius 140 Carassius auratus 3 4 Cyprinus carpio 1 8

Cobitidae Cobitis taenia 52 3

Ictaluridae Ictalurus melas 8

Percidae Perca fluviatilis 5

Centrarchidae Lepomis gibbosus 64 5 Micropterus salmoides 2

Gobidae Padogobius martensi 5 1

A M P H I B I A Salamandridae Triturus cristatus 8

Ranidae Rana esculenta adults 1047 1 0 Rana esculenta larvae 1862 105

Hylidae Hyla arborea 3

M A M M A L I A indeterminated 2

Soricidae Sorex araneus 2

Microtidae indeterminated 1 Arvicola terrestris 3

Pity my s savii 1

Muridae Mus musculus 1 Micromys minutus 4 Apodemus sp. 1 Apodemus flavicollis 1

Total 4838 2 2 8

112 M . FASOLA, P. GALEOTTI, G. BOGLIANI & P. NARDI

R E F E R E N C E S

A L L E N R. P. & MANGELS F. P., 1940 - Studies of the nesting behavior of the Black Crowned Night Heron - Proc. Linn. Soc. N.Y., 50-51: 1-28.

BARBIERI F., FASOLA M . , PRIGIONI V. & BOGLIANI G., 1979 - Le garzaie dell 'Italia Nord-occidentale, 1978 - Avocetta, 3: 3-28.

CRAMP S. & S I M M ONS K. E. L . (Eds.), 1978 - The Birds of the Western Paleartic -Oxford Univ. Press, Vol. I .

FASOLA M . & BARBIERI F., 1978 - Factors affecting the distribution of heronries i n Northern I ta ly - Ibis, 120: 537-540.

GROSS A . O., 1923 - The Black Crowned Night Heron (Nycticorax nycticorax naevius) of Sandy Neck - Auk, 40: 1-30.

HAFNER H. , 1977 - Contribution a l'etude ecologique de quatre especes de herons (Egretta garzetta L., Ardeola ralloides Scop., Ardeola ibis L . , Nycticorax nycticorax L.) pendant leur nidification en Camargue - These Universite Toulouse, 183 + X L I X pp.

HOFFMAN R. D., 1978 - The diets of Herons and Egrets in Southwestern Lake Erie -I n : SPRUNT A . et al., « Wading birds ». National Audubon Society: 365-369.

J E N N I D. A . , 1973 - Regional variation in the food of nestling Cattle Egrets - Auk, 90: 268-280.

KOSUGI A., 1960 - On the food habits of some herons - Miscel, Yamashina Inst. Orn., 15: 89-98.

K U S H L A N J . A., 1978 - Feeding Ecology of Wading Birds. I n SPRUNT A. et al., « Wading Birds ». National Audubon Society: 249-297.

MOLTONI E., 1936 - Le garzaie in I tal ia . Riv. ital. Orn., 6: 109-148, 211-269. MOLTONI E., 1948 - L'alimentazione degli Ardeidae in Ital ia - Riv. ital. Orn., 18: 87-93. M U K H E R J E E A. J., 1971 - Food habits of water birds of the Sundaraban, 24-Parganas

District, West Bengala India. I I - Bombay Nat. Hist. Soc, 68: 37-64. NARDI P., La distribuzione della fauna i t t ica in provincia di Pavia - Boll. Pesca Piscic.

Idrobiol. ( i n press). OWEN D. F., 1955 - The food of the Heron Ardea cinerea in the breeding season -

Ibis, 97: 276-295. OWEN D. F., 1960 - The nesting success of the Heron Ardea cinerea in relation to

the availability of food - Proc. zool. Soc. London, 133: 597-616. SIEGFRIED W. R., 1971 - The food of the. Cattle Egret - J. anim. Ecol., 8: 447-468. SKOKOVA N . N . , 1960 - (Regime du Heron bihoreau dans le delta de la Volga) - Orni-

thologia, 3: 396-404 ( in russian). T E M P L E S. A., 1969 - A case of Turkey Vulture piracy on Great Blue Herons - Wilson

Bull, 81 : 94. VALVERDE J . A. , 1955, 1956 - Essai sur l 'Aigrette garzette (Egretta g. garzetta) en

France - Alauda, 23: 147-171, 254-279 and 24: 1-36. VASVARI M . , 1935, 1938 - Die Ernahrungsoekologie des Nachtreihers und Rallenreihers

- Aquila, 1935, 1938: 556-613. V O I S I N C , 1978 - Util isation des zones humides du delta rhodanien per les Ardeides -

Oiseau Revue Jr. Orn., 48: 217-261, 329-380. WOLFORD J . W. & BOAG D. A., 1971 - Food habits of Black Crowned Night Heron in

Southern Alabama - Auk, 88: 435-437.