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Breeding Season Diet and Prey Selection of the (Falco novaeseelandiae) in a Plantation Forest Author(s): Richard Seaton, Noel Hyde, John D. Holland, Edward O. Minot, and Brian P. Springett Source: Journal of Raptor Research, 42(4):256-264. 2008. Published By: The Raptor Research Foundation DOI: 10.3356/JRR-07-50.1 URL: http://www.bioone.org/doi/full/10.3356/JRR-07-50.1

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BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. J. Raptor Res. 42(4):256–264 E 2008 The Raptor Research Foundation, Inc.

BREEDING SEASON DIET AND PREY SELECTION OF THE (FALCO NOVAESEELANDIAE)INA PLANTATION FOREST

RICHARD SEATON Institute of Natural Resources, Massey University, Private Bag 11-222, Palmerston North, New Zealand

NOEL HYDE Wingspan of Prey Trust, P.O. Box 993, Rotorua, New Zealand

JOHN D. HOLLAND,EDWARD O. MINOT,1 AND BRIAN P. SPRINGETT Institute of Natural Resources, Massey University, Private Bag 11-222, Palmerston North, New Zealand

ABSTRACT.—We studied the diet of the endemic New Zealand Falcon (Falco novaeseelandiae) in a pine plantation forest by identifying occurring in pellets and prey remains collected from 37 nest sites during the 2003 and 2004 breeding seasons. We assessed species abundance along transects in differ- ent-aged pine stands and along stand edges. Diet and prey abundance were compared to determine whether birds were taken disproportionately or in proportion to their abundance in the environment. Birds composed the greatest proportion of the diet, 84% by frequency and 74% by biomass. Common Chaffinches ( coelebs) were taken most frequently, but Eurasian Blackbirds (Turdus merula) and European rabbits (Oryctolagus cuniculus) contributed more by biomass, although rabbits were not recorded at every nest site. Bird density increased significantly with stand age but was highest along stand edges. Chaffinches were the most abundant species and taken in proportion to their availability. Species that occurred in open habitat (e.g., Yellowhammers [Emberiza citrinella]) or were of medium size (e.g., black- birds) were taken more than expected based on their availability. Very small species (e.g., Grey Gerygone [Gerygone igata]) were taken in lower proportions than expected from their abundance. Proportions of bird species preyed upon were correlated most closely with bird species abundance in young pine stands (P 5 0.02, r 2 5 0.52). In a pine plantation habitat, New Zealand took primarily the more abundant species, those intermediate in size (16–160 g), and those frequenting open habitat.

KEY WORDS: New Zealand Falcon; Falco novaeseelandiae; diet; plantation; prey.

DIETA Y SELECCIO´ N DE PRESAS DURANTE LA E´ POCA REPRODUCTIVA EN FALCO NOVAESEELAN- DIAE EN UNA PLANTACIO´ N FORESTAL

RESUMEN.—Estudiamos la dieta del halco´n ende´mico de Nueva Zelanda (Falco novaeseelandiae) en una plantacio´n forestal de pinos (principalmente Pinus radiata) mediante la identificacio´n de especies encon- tradas en egagro´pilas y restos de presas recolectados en 37 nidos durante las e´pocas reproductivas de 2003 y 2004. Evaluamos la abundancia de especies de aves a lo largo de transectos ubicados dentro de rodales de pino de diferentes edades y a lo largo de bordes de rodales. La dieta y la abundancia de las presas fueron comparadas para determinar si las aves fueron consumidas desproporcionadamente o en proporcio´n a su abundancia en el ambiente. Las aves representaron la mayor parte de la dieta: el 84% de acuerdo a la frecuencia y el 74% de acuerdo a la biomasa. Fringilla coelebs fue la especie ma´s frecuentemente consumida, pero Turdus merula y los conejos Oryctolagus cuniculus contribuyeron ma´s en te´rminos de biomasa, aunque los conejos no se encontraron en todos los sitios de anidacio´n. La densidad de aves aumento´ significati- vamente con la edad de los rodales, pero fue ma´xima a lo largo de los bordes de los rodales. La especie F. coelebs fue la ma´s abundante, y estas aves fueron consumidas en proporcio´n a su disponibilidad. Las especies de aves que eran de ambientes abiertos (e.g., Emberiza citrinella) o que eran de taman˜o mediano (e.g., Turdus) fueron consumidas ma´s de lo esperado de acuerdo a su disponibilidad. Las especies de taman˜o

1 Present address: Ecology Building PN624, Massey University, Palmerston North, New Zealand; email address: e.minot@ massey.ac.nz

256 DECEMBER 2008 DIET OF THE NEW ZEALAND FALCON 257

muy pequen˜o (e.g., Gerygone igata) fueron consumidas en proporciones menores a las esperadas de acuerdo a su abundancia. Las proporciones de especies de aves consumidas se correlacionaron ma´s cercanamente con la abundancia de las especies en rodales de pinos jo´venes (P 5 0.02, r 2 5 0.52). En un ambiente de plantaciones de pinos, Falco novaeseelandiae se alimento´ principalmente de las especies ma´s abundantes, de las de taman˜o intermedio (16–160 g) y de las que frecuentaban ambientes abiertos. [Traduccio´n del equipo editorial]

The endemic New Zealand Falcon (Falco novaesee- scape and which prey species contribute the most to landiae) exists in three ecologically distinct forms: the diet, is therefore key to the effective conserva- bush, eastern, and southern (Fox 1977). They breed tion of raptor species. in a variety of habitat types, from rough pasture and We here describe the diet of New Zealand Falcons tussock lands to beech ( spp.) and podo- in an exotic pine plantation. We address three fun- carp (Podocarpacae) forests (Fox 1977). Recently, the damental questions about the distribution of prey bush form of the species, which traditionally inhab- species in the diet. (1) Are prey species in the diet its the indigenous forests of the of New taken in proportion to their abundance in the en- Zealand (Fox 1977, Barea et al. 1997), has been vironment? (2) Are prey of certain sizes taken more discovered breeding in exotic pine plantations frequently than would be expected based on their (Stewart and Hyde 2004). The New Zealand Falcon abundance? (3) Does the preferred habitat of the is classified as threatened by the New Zealand De- prey affect the likelihood that it appears in the diet partment of Conservation. The bush form, which is of the falcons? the focus of this study, is classified as ‘nationally vulnerable’ (Hitchmough et al. 2007). This increase STUDY AREA AND METHODS in their range has significant implications for the Study Area. The study was conducted in the cen- conservation of the species. Very little is known of tral plateau of the North Island of New Zealand in the biology of the New Zealand Falcon in its forest Kaingaroa pine plantation (Fig. 1). Kaingaroa For- habitat (Fox 1977, Barea et al. 1997). The diet of est is situated on the Kaingaroa Plateau, immediate- nestling New Zealand Falcons in indigenous forest ly west of the Te Urewera mountain ranges, between has been described (Barea et al. 1999), yet quanti- the cities of Rotorua to the north and Taupo to the fied studies of their diet in exotic forests are lacking. south. Mean monthly temperatures range from 6– The New Zealand Falcon is primarily a bird-catch- 16uC and mean monthly rainfall ranges from 108– ing falcon (Fitzgerald 1965, Fox 1977, Lawrence 153 mm. Kaingaroa Forest is the largest plantation and Gay 1991, Barea 1995, Stewart and Hyde forest in the southern hemisphere and comprises a 2004). They are also known to take reptiles, mam- single 180 000-ha block of primarily radiata pine mals, and (Buller 1888, Fitzgerald 1965, Fox (Pinus radiata). This plantation is bordered by dairy 1977), although and reptiles were not re- farms and indigenous podocarp forest to the east corded in the diet of nestlings in indigenous forest and dairy farms to the west. Smaller pine planta- (Barea et al. 1999). They will take a wide range of tions adjoin Kaingaroa Forest at the northern and prey sizes, from insects to prey up to six times their southern boundaries. In New Zealand, stands of ra- body mass, including Ring-necked Pheasants, (Pha- diata pine mature between 25 and 35 yr old and are sianus colchicus) and European hares (Lepus euro- generally felled at this time. The pine trees are har- paeus; Fox 1977, Hyde and Seaton in press). vested in discrete blocks or compartments that are Predators generally take prey species either op- approximately 1 km2, creating a mosaic of different- portunistically, i.e., in proportion to their relative aged pine stands. abundances, or because of their relative profitability Pellets and Prey Remains. Falcon pellets and prey (Jaksic 1989). Some raptor species take most prey remains were collected from nest scrapes and adja- opportunistically (Sodhi and Oliphant 1993, Joy et cent plucking posts over two breeding seasons, Sep- al. 1994, Figueroa and Corales 2005), whereas oth- tember to March 2003 and September to March ers feed more selectively (Steenhof and Kochert 2004. Pellets were dried and dissected using a dis- 1988, Quinn and Cresswell 2004). Prey abundance secting microscope. The feather and bone remains is often a limiting factor in the breeding density and were identified using a reference collection. Using reproductive success of raptors (Newton 1979). Un- either pellets or prey remains alone causes bias in derstanding how prey densities vary over the land- prey estimation (Mersmann et al. 1992, Real 1996, 258 SEATON ET AL.VOL. 42, NO.4

Figure 1. Map of Kaingaroa pine plantation illustrating its location in New Zealand, and compartment structure of the forest.

Redpath et al. 2001); to reduce this bias, the num- masses as the mean masses of actual prey items tak- ber of individuals of each prey species taken was en by New Zealand Falcons in Fox (1977). calculated based on pellet and prey remains com- masses were estimated to the nearest 0.5 g. Biomass bined (Fox 1977). Pellets were assumed to contain of unidentified prey items recorded in the diet was one individual of the bird species identified within estimated as the mean mass of that taxonomic it, unless several pellets were collected from a nest group. containing the combined remains of a single large Bird Abundance. The assessment of prey availabil- prey item within them such as a Ring-necked Pheas- ity was restricted to bird species because previous ant, or rabbit (Oryctolagus cuniculus). In the latter studies have shown that birds constitute the greatest instance the combined pellets were assumed to rep- proportion of the New Zealand Falcon diet (Fitzger- resent one individual of that species (Fox 1977). ald 1965, Fox 1977, Lawrence and Gay 1991, Barea The biomass of each species was taken as the mean 1995, Stewart and Hyde 2004). To assess the rela- adult mass (from Heather and Robertson 1996), tionship between falcon diet and prey abundance, except for larger prey items such as European hares. we conducted surveys along transects to estimate For these species, falcons may select only smaller avian prey abundance in Kaingaroa Forest. Our individuals (Fox 1977). Thus, to reduce the overes- transects were established in four representative hab- timation of the mass of prey, we estimated itat types. Young pine stands with trees ,4 yr old had DECEMBER 2008 DIET OF THE NEW ZEALAND FALCON 259 open space between the trees and hence easy access Bird Abundance. We recorded 30 bird species in to the ground by a flying falcon. Intermediate stands Kaingaroa Forest from 2003 to 2005 (Appendix). were 10–14 yr old and canopy closure was almost Bird densities for the four pine-stand habitats are complete. Mature stands were .20 yr old and had presented in Table 2. Bird density increased signif- side branches pruned to approximately 7 m above icantly with pine-stand age (F2,90 5 19.06, P , 0.001, 2 the ground. The fourth habitat type was the bound- r 5 0.59), but was highest along stand edges (F3,120 ary between young and mature stands. These stand 5 25.92, P , 0.001, r 2 5 0.54). classes were chosen to represent the variety in stand Prey Abundance and Selection. Eighty percent structure present in New Zealand’s pine plantation (24 of 30) of bird species recorded in Kaingaroa forests (MacLaren 1996). Forest (Appendix) were recorded in the pellets Bird surveys were carried out during the breeding and prey remains of the falcons. Five species of season in 2004. Bird species abundance was assessed birds, European Starling (Sturnus vulgaris), Sacred using a belt transect census method and converted ( sanctus), Long-tailed Koel into density per ha by fitting a linear function (Bibby (Eudynamys taitensis), (Acridotheres et al. 1992). Biomass of bird species was estimated tristis), and (Passer domesticus), were using the same techniques used for prey items. recorded as prey but were not recorded in bird sur- Statistical Analyses. The differences in bird spe- veys. New Zealand Falcons were occasionally ob- cies abundance between different pine stand classes served hunting (Kikihia spp.), but these also were assessed using a general linear model. We used were not recorded in prey remains or pellets. stepwise multiple linear regressions to investigate Stepwise multiple linear regression analysis em- which habitat type contained bird species abun- ployed data from each of four classes of pine stand dances most similar to the proportions of bird spe- to predict the distribution of species abundance in cies recorded in the diet. Prey species that were falcon prey. The ‘‘young stands’’ habitat provided present in low numbers in the diet and the bird the best fit and the inclusion of the other three surveys were not included in the regression analyses. stand classes did not improve the fit. For the pro- portion of prey taken to prey present, young pine RESULTS stands show the best fit (r 2 5 0.52, P 5 0.02, N 5 Pellets and Prey Remains. We collected and ana- 20). The explanation of prey selection was not im- lyzed 442 pellets and 275 prey remains from 37 proved by adding prey abundance from any other nesting attempts. In these, we identified 999 indi- stand classes to the regression model. vidual prey items, comprising 24 species of bird, Chaffinches were taken in proportion to their four species of mammal and four species of insects. abundance, while Yellowhammers were taken in Birds composed the greatest proportion of the greater numbers than abundance would suggest diet, 83.6% by frequency and 74% by biomass (Ta- (Fig. 2). Conversely, (Zosterops lateralis), ble 1). Common Chaffinches (Fringilla coelebs) were ( macrocephala), Whiteheads (Mo- taken most frequently, but Eurasian Blackbirds houa albicilla), Common Redpolls (Carduelis flam- (Turdus merula) and European rabbits (Oryctolagus mea) and Grey Gerygones (Gerygone igata) were tak- cuniculus) contributed more by biomass. Mammals en less than expected. When accounting for made up 2.4% of the diet by frequency and 26% by biomass, some species were more important in the biomass. Insects made up 13.0% of the diet by fre- diet than frequency alone suggests (Fig. 3). Califor- quency but ,1% by biomass. Rabbits made up the nia Quail and Ring-necked Pheasant (Phasianus col- greatest proportion of mammal prey (52% by bio- chicus) were preyed upon relatively infrequently, but mass). Nearly all the insect biomass consisted of contributed significantly to the diet due to their huhu beetles (Prionoplus reticularis). Other species relatively large mass. Song Thrushes and blackbirds that made up relatively large proportions of the diet were also more important in the diet in terms of included European hare, California Quail (Callipe- biomass than frequency. pla californica), Ring-necked Pheasant, Song Thrush (Turdus philomelos), and Yellowhammers (Emberiza DISCUSSION citrinella). However, very large prey items such as Birds made up most of the diet of nesting New rabbit, European hare, and Ring-necked Pheasant Zealand Falcons, as in previous studies (Fitzgerald were not recorded at every nest site. Unidentified 1965, Fox 1977, Lawrence and Gay 1991, Barea et al. composed 18% of the diet by frequency. 1999, Stewart and Hyde 2004). Our data suggested 260 SEATON ET AL.VOL. 42, NO.4

Table 1. Prey species taken by New Zealand Falcon (Falco novaeseelandiae) during 2003 and 2004 breeding seasons in Kaingaroa Forest.

MASSa PERCENT BIOMASS PERCENT TOTAL PREY SPECIES (g) FREQUENCY CONSUMED (g) BIOMASS Birds Common Chaffinch (Fringilla coelebs) 22 20.3 4364 9.40 Yellowhammer (Emberiza citrinella) 27 11.3 3051 6.57 Greenfinch (Carduelis chloris) 28 7.2 2016 4.34 Eurasian Blackbird (Turdus merula) 90 6.9 6210 13.37 Song Thrush (Turdus philomelos) 70 4.6 3220 6.93 European Starling (Sturnus vulgaris) 85 2.0 1700 3.66 Skylark (Alauda arvensis) 38 1.9 722 1.55 Dunnock (Prunella modularis) 21 1.6 336 0.72 Californina Quail (Callipepla californica) 180 1.4 2520 5.42 House Sparrow (Passer domesticus) 30 1.4 420 0.90 (Zosterops lateralis) 13 1.1 143 0.31 Common Myna (Acridotheres tristis) 125 0.8 1000 2.15 (Petroica macrocephala) 11 0.5 55 0.12 ( albicilla) 17 0.4 66 0.14 New Zealand Pipit (Anthus novaeseelandiae) 40 0.4 160 0.34 Common Redpoll (Carduelis flammea) 12 0.4 48 0.10 Ring-necked Pheasant (Phasianus colchicus) 1300 0.3 3900 8.40 European Goldfinch (Carduelis carduelis) 16 0.3 46 0.10 Shining Cuckoo (Chrysococcyx lucidus) 25 0.3 75 0.16 (Prosthemadera novaeseelandiae) 105 0.2 210 0.45 Grey Gerygone (Gerygone igata) 7 0.1 7 0.01 (Petroica australis) 35 0.1 35 0.08 Bellbird ( melanura) 30 0.1 30 0.06 (Todiramphus sanctus) 65 0.1 65 0.14 Unidentified 20 18 3500 7.53 Unidentified bird 20 2 480 1.03 Total Bird 83.6 74 Mammals European hare (Lepus europaeus) 1781 0.2 3562 7.67 (Mustela erminea) 270 0.1 270 0.58 Rabbit (Oryctolagus cuniculus) 607 1.0 6070 13.07 House mouse (Mus musculus) 17 0.1 17 0.04 Unidentified lagomorph 607 0.1 607 1.31 Unidentified mammal 150 0.9 1350 2.91 Total Mammal 2.4 25 Insects Huhu beetle (Prionoplus reticularis) 2.0 8.6 172.00 0.37 Giant ( carovei) 2.0 0.1 2.00 0 Carabid beetle (Carabidae spp.) 0.5 0.2 1.00 0 Cockchafer beetle (Scarabeus spp.) 0.5 0.6 3.00 0.01 Unidentified beetle 0.5 4.1 20.50 0.04 Unidentified insect 0.5 0.3 1.50 0 Total Insect 13.9 0.43 a Mass estimates for birds from Heather and Robertson 1996, for mammals from Fox 1977. DECEMBER 2008 DIET OF THE NEW ZEALAND FALCON 261

Table 2. Bird abundance (density per ha) in each pine stand class, young (,4 yr old), intermediate (10–14 yr old), mature (.20 yr old), and stand edge (boundary between young and mature stands) during the 2004 breeding season in Kaingaroa Forest. Bird abundance was assessed using a belt transect census method and converted into density per ha by fitting a linear function (Bibby et al. 1992).

RELATIVE BIRD ABUNDANCE (% FREQUENCY) IN PINE STAND CLASSES

YOUNG INTERMEDIATE MATURE STAND EDGE (N 5 30) (N 5 30) (N 5 30) (N 5 30)

BIRD SPECIES MEAN 6 SD MEAN 6 SD MEAN 6 SD MEAN 6 SD Common Chaffinch (Fringilla coelebs) 11.5 6 19.8 17.9 6 12.6 22.5 6 11.8 35.9 6 27.8 Common Redpoll (Carduelis flammea) 7.6 6 7.4 7.4 6 7.5 1.0 6 2.0 2.0 6 2.7 Greenfinch (Carduelis chloris) 5.6 6 7.0 3.1 6 4.3 4.6 6 4.1 5.9 6 4.4 New Zealand Pipit (Anthus novaeseelandiae) 3.2 6 4.2 0.0 6 0.0 0.0 6 0.0 0.2 6 0.7 Skylark (Alauda arvensis) 1.9 6 2.9 0.0 6 0.0 0.0 6 0.0 0.4 6 0.9 Yellowhammer (Emberiza citrinella) 1.6 6 2.4 0.1 6 0.5 0.0 6 0.0 1.2 6 2.1 Tomtit (Petroica macrocephala) 1.5 6 2.7 6.4 6 3.7 6.0 6 3.6 6.7 6 3.7 Grey Gerygone (Gerygone igata) 1.0 6 2.1 6.1 6 5.2 3.1 6 3.5 5.8 6 5.7 European Goldfinch (Carduelis carduelis) 1.0 6 2.6 0.0 6 0.0 0.1 6 0.5 0.1 6 0.5 Silvereye (Zosterops lateralis) 0.6 6 1.9 6.1 6 5.0 4.9 6 5.9 27.5 6 39.6 (Gymnorhina tibicen) 0.5 6 1.7 0.3 6 1.2 0.0 6 0.0 1.7 6 2.4 Welcome Swallow (Hirundo neoxena) 0.2 6 1.0 0.0 6 0.0 0.0 6 0.0 0.4 6 1.4 Dunnock (Prunella modularis) 0.2 6 1.0 1.0 6 2.0 0.5 6 1.3 0.7 6 1.8 Eurasian Blackbird (Turdus merula) 0.1 6 0.6 3.9 6 3.3 3.4 6 2.7 3.5 6 3.5 Whitehead (Mohoua albicilla) 0.1 6 0.5 5.6 6 5.5 16.8 6 11.7 13.3 6 8.0 Song Thrush (Turdus philomelos) 0.1 6 0.5 0.6 6 1.4 0.5 6 1.1 0.4 6 1.0 Fantail (Rhipidura fuliginosa) 0.1 6 0.5 0.9 6 1.9 1.3 6 2.7 1.3 6 1.9 California Quail (Callipepla californica) 0.1 6 0.5 0.6 6 1.4 0.0 6 0.0 1.5 6 3.3 Tui (Prosthemadera novaeseelandiae) 0.0 6 0.0 0.0 6 0.0 0.0 6 0.0 0.1 6 0.5 Shining Cuckoo (Chrysococcyx lucidus) 0.0 6 0.0 0.0 6 0.0 0.3 6 0.9 0.1 6 0.5 (Acanthisitta chloris) 0.0 6 0.0 0.0 6 0.0 0.3 6 1.6 0.5 6 1.3 Ring-necked Pheasant (Phasianus colchicus) 0.0 6 0.0 0.1 6 0.5 0.1 6 0.3 0.4 6 1.0 North Island Robin (Petroica australis) 0.0 6 0.0 0.4 6 1.0 1.8 6 1.7 0.7 6 1.2 Kelp Gull (Larus dominicanus) 0.0 6 0.0 0.0 6 0.0 0.0 6 0.0 2.1 6 8.4 All Birds 30.7 6 25.2 49.5 6 22.7 57.4 6 20.4 95.1 6 54.3 that some bird species were preyed upon opportu- well represented in the diet. This may be explained nistically, and others were selected. Chaffinches by the low caloric gain relative to the energy ex- were the most abundant bird species present in all pended in hunting. stand classes and were taken in proportion to their Species that were taken more frequently than ex- abundance, suggesting that they were taken oppor- pected from their relative abundances included spe- tunistically. cies of open habitats (e.g., Yellowhammers), and Two factors likely explain why some species were those that offered an energetic benefit because of taken in relatively low proportions relative to their their larger mass (e.g., blackbirds), and we suggest abundance. The first was location. Species that favor these species are selected by falcons. The hunting forest habitats, e.g., Whitehead, New Zealand Robin techniques of New Zealand Falcons are similar to (Petroica australis), Tomtit, and Grey Gerygone, were those of Sparrowhawks ( nisus; Fox 1977), not well represented in the diet. This may suggest which prey on birds based on their vulnerability that it was more difficult for New Zealand Falcons to rather than abundance (Quinn and Cresswell catch prey in older stands than in younger, more 2004). Species of open habitats may be more vulner- open stands. Second, bird prey size was a contribut- able to predation from New Zealand Falcons be- ing factor. Species that were relatively small, such as cause young pine stands afford relatively little cover Redpolls, Silvereyes, and Grey Gerygones, were not (Suhonen et al. 1994). 262 SEATON ET AL.VOL. 42, NO.4

Figure 2. The distribution of prey species occurring in Figure 3. The relationship between the average body the diet of New Zealand Falcons as a function of prey mass of a prey species and the selection index for that species abundance in a pine plantation. Abundance is species in the diet of New Zealand Falcons. The selection the density of each bird species expressed as a percentage index is the ratio of the percentage prey occurrence in the of the density of all birds in the forest. Occurrence of prey diet to the percentage abundance in the forest. For exam- species is the percentage of each identified species in the ple, the selection index for Common Chaffinch was ca. 1.0 pellets and prey remains collected at falcon nests. Prey because it represented 32% of the identified prey individ- taken in equal proportion to their abundance in the forest uals and 32% of the birds estimated to be in the forest. would fall on the diagonal line. Species above the line The regression line is the second-order polynomial based occurred more frequently in the diet, and species below on the log-transformed data for both body mass (x-axis) the line less frequently, than would be expected based on and selection index (y-axis), Y 5 4.87 X 2 1.05 X2 2 4.75, their abundance in the forest. For all graphed percentages, r 2 5 0.53. Having accounted for the effect of mass and 0.1 percent was added to facilitate plotting on log scales. abundance, species above the regression line were taken Species for which either abundance or occurrence more frequently, and species below the line less frequently, equalled zero are: A, European Starling; B, House Spar- than expected. Most species above the line frequented row; C, Common Myna; D, Sacred Kingfisher; E, Welcome open, young forests. Most species below the line frequent- Swallow; F, Rifleman; G, Kelp Gull; H, Australasian Mag- ed older forests. pie; I, Fantail. norhina tibicen) and Kelp Gull (Larus dominicanus), Although large prey items contributed significant- are likely to be avoided, due to the additional threat ly to the diet of some pairs, there is a trade-off be- of injury posed by large, aggressive prey that congre- tween increased size of prey and the risks involved gate in large defensive groups (Heather and Robert- in capture (Fox 1977, Newton 1986, Barea 1995). son 1996). As a result, although they have been The smaller males (mean mass, 264 g) do most of recorded as items in the diet in other studies, most the hunting during the breeding season (Fox 1977), notably in the diet of the larger eastern form of the a characteristic common in the Falco (Cade New Zealand Falcon (mean mass of eastern form 1982). Medium-sized prey such as blackbirds and females, 531 g; Fox 1977), they were absent from Song Thrushes were important in the diet, and it our samples in Kaingaroa. is likely that falcons more easily take medium-sized Mammals made up 25% of the diet by biomass in prey than very large prey items such as Ring-necked Kaingaroa Forest, compared to 38% in the open hill Pheasant, rabbit, and European hare (Fox 1977). country of the (Fox 1977). This differ- Because female falcons (mean weight of 474 g) ence may be explained because the smaller bush are larger than males, females are more likely to form falcons we studied are not able to attack large hunt these larger prey (Fox 1977). However, some prey items as easily as the larger eastern form fal- large species, including the Australian Magpie (Gym- cons in the South Island. Additionally, this may re- DECEMBER 2008 DIET OF THE NEW ZEALAND FALCON 263 flect differences in mammal and bird prey abun- BIBBY, C.J., N.D. BURGESS, AND D.A. HILL. 1992. Bird census dance between the sites. Insects contributed very techniques. Academic Press, San Diego, CA U.S.A. little to the diet, with one species, the huhu beetle, BULLER, W.L. 1888. A history of the , constituting nearly all of the insects recorded. Second Ed. The Author, London, U.K. CADE, T.J. 1982. Falcons of the world. Cornell University Several bird species (European Starling, Com- Press, Ithaca, NY U.S.A. mon Myna, and House Sparrow) were recorded as FIGUEROA, R.A. AND E.S. CORALES. 2005. Seasonal diet of prey items but not in bird surveys. All of these spe- the (Falco femorales) in an agricultural cies are associated with human settlements (Heath- area of Araucania, southern Chile. J. Raptor Res. 39:55– er and Robertson 1996), and we suggest that these 59. were taken outside of Kaingaroa Forest in adjacent FITZGERALD, B.M. 1965. Prey of a family of New Zealand dairy farms. The fact that the average home-range Falcons. Notornis 12:181–184. radius for these falcons is ,2 km (Seaton 2007) FOX, N.C. 1977. The biology of the New Zealand Falcon likely explains the relatively low frequency of these (Falco novaeseelandiae). Ph.D. dissertation, University of species in the diet. Canterbury, Christchurch, New Zealand. Bird species density increased with pine-stand age HEATHER, B.D. AND H.A. ROBERTSON. 1996. The field guide to the birds of New Zealand. Penguin Books Ltd., Vi- and was highest along stand edges. Additionally, over- king, New Zealand. all bird diversity is promoted by a landscape contain- HITCHMOUGH, R., L. BULL, AND P. CROMARTY. 2007. New ing a variety of stand age classes (Seaton 2007). This Zealand threat classification system lists-2005. Science mosaic of pine-stand ages provides a variety of prey and Technical Publishing, Department of Conserva- and hunting conditions for New Zealand Falcons. tion, , New Zealand. Barea (1995) suggested that the forest-dwelling New HYDE,N.AND R. SEATON. In press. A new prey species record Zealand Falcons prefer hunting in open areas. We for the New Zealand Bush Falcon. Notornis. In Press. have illustrated that the prey found in falcons’ diet JAKSIC, F.M. 1989. Opportunism vs. selectivity among car- are most similar to prey abundances in young open nivorous predators that eat mammalian prey: a statisti- stands, which was unsurprising, as prey are generally cal test of hypotheses. Oikos 56:427–430. more vulnerable in open areas (Suhonen et al. 1994). JOY, S.M., R.T. REYNOLDS, R.L. KNIGHT, AND W.R. HOFFMAN. 1994. Feeding ecology of Sharp-shinned Hawks nesting In conclusion, our results suggest that New Zealand in deciduous coniferous forests in Colorado. Condor Falcons in pine plantations took the more abundant 96:455–467. species, those intermediate in size, and those fre- LAWRENCE, S.B. AND C.G. GAY. 1991. Behaviour of fledgling quenting the open habitat of young pine stands. New Zealand Falcons (Falco novaeseelandiae). Notornis 38:178–182. ACKNOWLEDGMENTS MACLAREN, J.P. 1996. Environmental effects of planted for- We are grateful to Kaingaroa Timberlands, Timberlands ests in New Zealand. New Zealand Forest Research In- Limited, Carter Holt Harvey, Hancock Forest Management stitute Limited, Rotorua, New Zealand. Ltd., New Zealand Forest Managers and the New Zealand MERSMANN, T.J., D.A. BUEHLER, J.D. FRASER, AND J.K.D. SEE- Tertiary Education Commission for jointly providing an GAR. 1992. Assessing bias in studies of Bald Eagle food- Enterprise Scholarship that funded this research. Our vol- habits. J. Wildl. Manage. 56:73–78. unteers Mathew Clement and Shane McPherson are ac- knowledged for their hard work in the field. We are also NEWTON, I. 1979. Population ecology of raptors. T. and grateful for the contributions of Massey University, the A.D. Poyser Ltd., Berkhamsted, U.K. New Zealand Department of Conservation, Wingspan ———. 1986. The Sparrowhawk. T. and A.D. Poyser Ltd., Birds of Prey Trust and the Raptor Association of New Staffordshire, U.K. Zealand. We gratefully acknowledge the very helpful com- QUINN,J.L.AND W. CRESSWELL. 2004. Predator hunting ments of an anonymous referee. behaviour and prey vulnerability. J. Anim. Ecol. 73:143– 154. LITERATURE CITED REAL, J. 1996. Biases in diet study methods in the Bonelli’s BAREA, L.P. 1995. Habitat use, diet, and nest site selection Eagle. J. Wildl. Manage. 60:632–638. of forest-dwelling New Zealand Falcons. M.S. thesis. REDPATH, S.M., R. CLARKE,M.MADDERS, AND S.J. THIRGOOD. University of Waikato, Hamilton, New Zealand. 2001. Assessing raptor diet: comparing pellets, prey re- ———, J.R. WAAS, AND K. THOMPSON. 1997. Nest site char- mains, and observational data at Hen Harrier nests. acteristics of New Zealand Falcons (Falco novaeseelan- Condor 103:184–188. diae) in a forested habitat. Notornis 44:213–218. SEATON, R. 2007. The ecological requirements of the New ———, ———, ———, AND N.H. HYDE. 1999. Diet provid- Zealand Falcon in plantation forestry. Ph.D. disserta- ed for chicks by New Zealand Falcons (Falco novaeseelan- tion. Massey University, Palmerston North, New Zea- diae) nesting in forested habitat. Notornis 46:257–267. land. 264 SEATON ET AL.VOL. 42, NO.4

SODHI, N.S. AND L.W. OLIPHANT. 1993. Prey selection by Appendix. Bird species recorded in surveys of Kaingaroa urban-breeding Merlins. Auk 110:727–735. Forest, 2003–2005. The asterisk denotes species recorded STEENHOF,K.AND M.N. KOCHERT. 1988. Dietary responses as prey of New Zealand Falcons. of three raptor species to changing prey densities in a natural environment. J. Anim. Ecol. 57:37–48. COMMON NAME SCIENTIFIC NAME STEWART,D.AND N. HYDE. 2004. New Zealand Falcons (Falco novaeseelandiae) nesting in exotic plantations. No- Australasian Magpie Gymnorhina tibicen tornis 51:119–121. Bellbird* Anthornis melanura SUHONEN, J., K. NORRDAHL, AND E. KORPIMA¨ KI. 1994. Avian Kelp Gull Larus dominicanus predation risk modifies breeding bird community on a Eurasian Blackbird* Turdus merula farmland area. Ecology 75:1626–1634. Californina Quail* Callipepla californica Common Chaffinch* Fringilla coelebs Received 27 August 2007; accepted 14 July 2008 Dunnock* Prunella modularis Associate Editor: Fabrizio Sergio Fantail Rhipidura fuliginosa European Goldfinch* Carduelis carduelis Greenfinch* Carduelis chloris Grey Gerygone* Gerygone igata House Sparrow* Passer domesticus Common Myna* Acridotheres tristis Long-tailed Koel Eudynamys taitensis Sacred Kingfisher* sancta New Zealand Pipit* Anthus novaeseelandiae North Island Robin* Petroica australis Common Redpoll* Carduelis flammea Rifleman Acanthisitta chloris Ring-necked Pheasant* Phasianus colchicus Shining Cuckoo* Chrysococcyx lucidus Silvereye* Zosterops lateralis Skylark* Alauda arvensis Song Thrush* Turdus philomelos European Starling* Sturnus vulgaris Tomtit* Petroica macrocephala Tui* Prosthemadera novaeseelandiae Welcome Swallow Hirundo neoxena Whitehead* Mohoua albicilla Yellowhammer* Emberiza citrinella