/ RaptorRes. 36(4):300-308 © 2002 The Raptor Research Foundation, Inc. NEST-SITE SELECTION OF THE CROWNED HAWK-EAGLE IN THE FORESTS OF KWAZULU-NATAL, SOUTH AFRICA, AND IVORY COAST TAI, Gerard Malan^ School ofLife and Environmental Sciences, University ofDurban-Westville, PB X5400f Durban 4000, South Africa SusANNE Shultz Population and Evolutionary Biology Research Group, School ofBiology, Nicholson Building, University ofLiverpool, Liverpool L69 3 GS, United Kingdom — Abstract. Structural characteristics of Crowned Hawk-Eagle {Stephanoaetus coronatus) nest sites were compared between forests in KwaZulu-Natal province, South Africa, and the Tai National Park, Ivory Coast, and key features of nesting trees and nest-placement sites were identified. Nest-tree heights and nest heights differed appreciably between three tree groups with the highest being indigenous Tai trees (x tree height = 52 m and x nest height = 36 m, N = 8 nests), followed by exotic eucalyptus (x = 44 and 22 m respectively, N = 10) and indigenous trees (x = 24 and 14 m respectively, N = 17) from KwaZulu-Natal. All the nest trees in Tai were eraergents, whereas 11 of 17 indigenous nest trees and only two of 10 eucalyptus were so in KwaZulu-Natal. Non-emergent eucalyptus nest trees were predom- inantly edge trees that may have provided easier access for flying eagles. Overall, nest forks were more accessible for flying eagles than random forks, although access did not differ between nests located in emergent and non-emergent trees. Crowned Hawk-Eagles transport long sticks and heavy prey items to their nests and access was probably the most critical feature of both the nest tree and placement ofthe nest. Wildlife managers must, therefore, ensure that lone-standing or emergent trees are cultivated and conserved, and flight paths to nests are kept open to allow Crowned Hawk-Eagles continued and easy access to their nests. Key Words: Crowned Hawk-Eagle, Stephanoaetus coronatus; nest access; emergent trees; nest-site selection; wildlife management. SELECCION DEL SITIO NIDO DEL AGUILA CORONADA EN LOS BOSQUES DE KWAZULU-NATAL, SUR AFRICA, YTAI, COSTA DE MARFIL — Resumen. Las caracteristicas estructurales de los sitios nido de las aguilas coronadas {Stephanoaetus coronatus) fueron comparadas entre los bosques de la provincia KwaZulu-Natal, Sur Africa, y el parque nacional Tai, Costa de Marfil, y se identilicaron los rasgos claves de los arboles nido y de los sitios de ubicacidn de los nidos. Las alturas de los arboles nido y las alturas de los nidos difirieron apreciable- mente entre arbol y grupo de arboles siendo los mas altos los nativos Tai (x altura del arbol = 52 m y X altura del nido = 36 m, N = 8 nidos), seguido por eucaliptos exoticos (x = 44 y 22 m respectivamente, N ~ 10) y arboles nativos (x = 24 y 14 m respectivamente, N = 17) de KwaZulu-Natal. Los arboles nido de eucaliptos no emergentes fueron predominantemente arbcdes de borde que podian proveer mas facil acceso a las aguilas en vuelo. En conjunto, las horquelas en nidos fueron mas accesibles para las aguilas que horquetas colocadas al azar, aunque el acceso no dilirio entre los nidos colocados en arboles emergentes y no emergentes. Las aguilas coronadas transportan grandes ramas y presas pesadas a sus nidos y probablementc el acceso fue el rasgo mas critico tanto para la seleccion del arbol nido como para la ubicacion del nido. Los manejadores de vida silvestre deben, por lo tanto, asegurar que arboles aislados o emergentes son cultivados y conservados, y que las vias de vuelo a esos nidos permaneceran abiertas para permitir a las aguilas coronadas continuo y facil acceso a sus nidos. [Traduccion de (iesar Marquez] Tree-nesting raptors select nesting trees and nest hide the nest from potential predators, insulate the sites on the basis of certain structural features that nest against adverse weather conditions, place the birds close to their hunting habitats and allow ^ Present address: Department of Nature Conservation, them easy access to the nest (Moore and Henny Pretoria Technikon, P.B. X680, Pretoria 0001, South Af- 1983, Speiser and Bosakowski 1987, Lilieholm et rica; e-mail address: [email protected] al. 1993, Burton et al. 1994, Selas 1996, Malan and 300 December 2002 Nest-seee Selection oe the Crowned Hawk-Eagle 301 Robinson 2001). Larger raptors often nest in an in addition to indigenous trees, consisting of most- exposed position that allows easy access to and ly White Stinkwoods Celtis africana) (Tarboton and ( from the nest to deliver long sticks and heavy prey Allan 1984, Boshoff 1988). (Speiser and Bosakowski 1987, Burton et al. 1994). The objective of this study was to compare To further facilitate access, large raptors nest in tall Crowned Hawk-Eagle nesting sites in three tree emergent trees or large trees with open branch groups and to use this information to provide re- structures that respectively allow them access to the source managers with silvicultural guidelines for nest both above and within the canopy (Moore and providing nest-placement sites and stands for Henny 1983, Burton et al. 1994, Malan and Rob- Crowned Hawk-Eagles. As the forests in the inson 2001). Unfortunately, these preferences KwaZulu-Natal province. South Africa, are relative- bring large eagles in direct conflict with man as ly small in size and patehy in distribution (Boshoff large trees often are selectively harvested for com- 1997, Midgley et al. 1997), nest site characteristics mercial and subsistence purposes (Bijleveld 1974, ofthese forests were compared with those from the Watson and Rabarisoa 2000). extensive and continuous, indigenous forest of the In the predominantly arid South Africa, the de- Tai National Park, Ivory Coast. These comparisons pletion of indigenous forest habitats and the arriv- clarify which structural features are most important al of commercial exotic Eucalyptus, Pinus, Acacia, when selecting a nest site, and how flexible and Populus trees have had a mixed impact on the Crowned Hawk-Eagles are with regard to these abundance and distribution of tree-nesting forest characteristics. Second, for KwaZulu-Natal, we ex- birds (Low and Rebelo 1996, Allan et al. 1997). amine stand size to determine the minimal habitat Although by 1997 the area under commercial pulp- requirements and compare topographical features wood and sawlog plantations (15 186 km^) was four with randomly-selected sites to determine the ea- times larger than the existing natural forests (Van gle’s selectivity for these features. der Zel 1996, Anon. 1998), the very short rotation StudyAreas intervals of plantations (8-16 yr) do not allow the In South Africa, Crowned Hawk-Eagle nest sites were trees to attain the size necessary to support large located for study during forest surveys in the KwaZulu- stick nests. However, isolated, non-commercial Natal (29°S, 31°E). Indigenous tree stands were surveyed m stands of large exotic trees are used for nesting by in forests characterized by a 10-25 high canopy, dis- tinct vegetation strata and numerous dominant tree spe- indigenous birds, including raptors (Steyn 1977, cies (Low and Rebelo 1996, Midgley et al. 1997). The Macdonald 1986, Malan and Robinson 2001). In mean annual rainfall in these forests range from 900- indigenous forests, the processes of deforestation, 1500 mm. Indigenous nest trees were sampled in the Or- forest fragmentation, and the selective removal of ibi Gorge, Vernon Crookes, Krantzkloof, Harold John- son, and Dlinza Eorest nature reserves, Ithala Game big trees from remnant patches alter the size, struc- Reserve, Hluhluwe-Umfolozi Park, all areas managed by ture, and availability of indigenous trees for nest- the KwaZulu-Natal Wildlife, and the Umgeni Valley Na- ing (Tarboton and Allan 1984, Allan and Tarboton ture Reserve and Tanglewood Natural Heritage Site. Ex- 1985, Seydack 1995, Vermeulen 1999). otic eucalyptus were surveyed in abandoned plantations, In South Africa, the Crowned Hawk-Eagle {Ste- self-sown stands, and planted trees in large domestic gar- dens, but none were known from commercial sawlog or phanoaetus coronatus) has recently become of for- pulpwood plantations. mal conservation concern and the status of the In the Ivory Coast, all nest sites were located within a species has changed to near threatened due to the 50 km^ area around the Station de la Recherche en Ecol- ogie Tropicale (SRET, 7°00'N, 5°50'W) near the western loss of its previously suitable, indigenous nesting edge of the park. The Tai National Park is the largest habitat to short rotation, exotic plantations continuous lowland forest in West Africa (454000 ha) (Barnes 2000) . Throughout much of its range, the and contains the last sizeable protected habitat for a Crowned Hawk-Eagle breeds in tall evergreen for- number ofUpper Guinea Forest endemics (Gartshore et ests but can also nest in deciduous forests and al. 1995). The mean annual rainfall at the research sta- woodland-forest mosaics (Tarboton and Allan tion is 1800 mm. The forest was selectively logged in the early 1970s, but the structure is essentially indistinguish- 1984). These birds prefer large forest trees for able from a primary forest. The main forest canopy is m nesting and the nest is usually situated in a major 30-40 in height, with emergent trees reaching to over fork, 8-30 m above ground but can be as high as 60 m (Guillaumet 1994). m 46 (Steyn 1982, Tarboton and Allan 1984, Brown Methods and Amadon 1989). In South Africa, Crowned The authors and conservation ofhcers located 27 Hawk-Eagles nest in exotic eucalyptus and pines, Growned Hawk-Eagle nests in KwaZulu-Natal and eight 302 Malan and Shultz VoL. 36, No. 4 m m Tai. Of the nests in KwaZulu-Natal, 19 were found by graph with 50 contour lines) to calculate stand size listening for the loud queee-queee soliciting calls of nest- and shape. From this photo, the maximum length (A) lings or by spotting large nests (Steyn 1982). Although and maximum width (B; perpendicular to the maximum this non-systematic search method may bias the sample length axis) of the nest stand was measured. All mea- toward accessible and conspicuous nests (Daw et al. surements from 1:10 000 orthophotos were rounded to m mm 1998), the nest-site data include nests from a wide selec- 10 to allow for a 1 measurement error. Stand tion offorest and nest-tree types. Sampled nest trees were shape (S) was defined as the maximum stand width di- located in indigenous forests, exotic monocultures, and vided by the maximum length, with values ranging from mixed forests, and nest tree species were grouped into one (square shape) to zero (elongated shape). Nest stand either indigenous or eucalyptus stands. shapes were grouped into square (Shape ^0.5) or elon- The following nest-tree characteristics were recorded gated (Shape <0.5). The surface area of planted forests from each nest site: the tree diameter at breast height was calculated from orthophotos by measuring the stand (14 m, DBH) of all stems >22 cm in diameter; tree lengths and widths. The surface area ofindigenous forest height (T), nest height (N), height of the first foliage, stands could not be calculated from orthophotos because and the height of the first side branch (R, irrespective if the edges of indigenous forests were not defined clearly Itwas dead or alive) All height measurements were taken and the surface area was, therefore, estimated as S = (A/ . with a clinometer. For trees with buttresses {N = 3), the 2)(B/2)(tt). From the orthophotos, the nest trees were circumference of the tree, including the buttresses, was also categorized as being located on the edge ofthe stand measured at breast height, a diameter calculated and di- (i.e., the first tree encountered on the edge of a forest vided by two as to provide a conservative estimate of stand). Lastly, distances to water, road, and nearest hu- DBH. The percent nest height was the proportional dis- man habitation were measured from the nest tree and tance the nest was placed from the top of the tree ((N/ one random tree selected from each nest stand. T)100) and the percent first branch height was the pro- All data were subjected to the Kolmogorov-Smirnov portional height the first branch was placed from the top one-sample test of normality. If the distribution of the of the tree ((R/T)100). data was found to be non-normal, the non-parametric Nests were classified as being placed within or below Kruskal-Wallis test or Mann-Whitney Latestwas employed the foliage. Each nest was scored as either being posi- The Tukey honest significant difference test for unequal tioned in a main fork, against the main branch (i.e., pri- sample sizes was employed to determine which groups mary axis, mainly vertical), or on a side branch (i.e., sec- are particularly different from each other after a signifi- ondary axes, mainly horizontal). The number of cant Kruskal-Wallis test was obtained from the Analysis of branches supporting the nest was also counted. Lastly, Variance. The Pearson’s Chi-square test was used to test the nest tree was classified as emergent ifthe branch and for patterns with categorical variables. All data were an- foliage structure protruded above the surrounding for- alyzed using the Statistica software package (StatSoft 1995) and probability levels were set at a = 0.05. est. For each nest tree, we identified large and open forks, excluding the nest fork, which could possibly support a Results m m Crowned Hawk-Eagle nest that was 2 wide and 2.5 Of the 35 Crowned Hawk-Eagle nests analyzed, deep (Steyn 1982). Each of these forks was categorized as being positioned in a central fork or crotch (i.e., be- 10 were located in eucalyptus and 17 in indigenous tween main branches), as against the main branch, or on trees in KwaZulu-Natal, and eight in indigenous a side branch, and numbered from tree bottom to top. trees in Tai. Indigenous nest trees identified in A random fork was selected from the category ofthe fork KwaZulu-Natal included Ficus spp. (7), Chrysophyl- that supported the nest (i.e., if the nest was against a main branch, the random fork was selected from similar lum viridifolium (3), Syzygium cordatum (2), Cussonia forks). If the random fork was not available from the spicala, Scholia brachypetala, and Celtis africana. The category that supported the nest, it was selected from a exotic nest trees were all eucalyptus. Nest trees combined sample of the remaining two positions. identified in Tai included Lofira alata, Klainodoxa For each cardinal direction (N, E, S, and W), accessi- gabonesis, Ceiba pentandra, and Alstonia boonei. bility of the nests and random forks were determined by whether the flying eagle would have a 30 m unobstructed All tree characteristics measured differed among approach on a horizontal plane. For a flying eagle, a the three tree groups (Table 1). Tai and eucalyptus flight path to the nest obstructed by foliage and/or nest trees were taller than KwaZulu-Natal’s indige- branches thus qualified inaccessibility. nous trees. Tai nest trees were larger in diameter, We sampled characteristics of the three trees closest to the nest tree. The distance from the nest tree to each and had higher first foliage, side branches and per- surrounding tree was measured. We calculated the mean cent first side branch heights than trees from area occupied by the trees by squaring the mean distance KwaZulu-Natal. Nest heights differed among all of the three trees from the nest tree. We then converted three tree groups, and the percent nest heights the result to the number of trees per hectare and cal- were lower in eucalyptus than Tai nests (Table 1). culated a tree density estimate at the nest tree (Phillips The number of branches that supported nests 1959). For KwaZulu-Natal nest trees, each nest was plotted on did not differ among tree groups (Kruskal-Wallis ^ a 1:10 000 orthophoto (black and white aerial photo- ~ 1.7, P = 0.41), and the eagles used on av- 2,35 . December 2002 Nest-site Sei.ection he Crowned Hawk-Eagee 303 c:>f i Table 1. Crowned Hawk-Eagle nest-tree characteristics of eucalyptus and indigenous tree groups in KwaZulu-Natal and Tai. Means ± one standard deviation and range in parenthesis. Values with the same superscripts indicate values that differed significantly from each other in the three-way comparison. Indigenous Eucai.yptus Indigenous Kruskal- N H Species Ciass KwaZui.u-Natal RWAZuriJ-NAIAL Tai Wallis DBH (cm) 93^' ± 29 126*> ± 32 234^'^ ± 66 35 21.6** (40-151) (83-206) (167-344) Tree height (m) 24ab + 5 44a + g 52'^ ± 14 35 25.7** (T5-34) (34-54) (33-67) Height of hrst 9“’ ± 6 12*’ ± 9 33^>'> ± 7 35 17.8** foliage (m) (1-19) (6-27) (26-42) Height of first side 9“ ± 6 15'’ ± 7 34’’ ± 9 35 17.8** branch (m) (1-20) (6-25) (25-47) Nest height (m) ]4ab + 3 22a<: + 7 ± 10 35 23.4** (7-21) (13-35) (2.5-49) Percent nest height 58 ± 14 52^' ± 13 71" ± 13 35 7.6* (43-93) (36-67) (44-90) Percent first side 36^' ± 21 32b 2: 12 66"’’ ± 13 35 branch height (4-62) (16-47) (44-78) ^ihc = p <; 0.05, I'ukey tests. * P < 0.05. P < 0.001. erage 3 ± 1 branches (A ± SD, N = 35 trees) to were from trees where this fork type was not the nest on. Twenty-seven of 32 nests (84%) were most abundant (x^ = 6.3; P < 0.001). Overall, 22 placed within the foliage (as opposed to under the (63%) of the 35 nests were not placed in the most foliage), and placement of nests in relation to the abundant fork category and nest placement could foliage was not associated with tree groups (x^ not be associated with the most abundant fork cat- 0.7, P = 0.70). In Tai, 63% of the nests {N = 8) egory of the different tree groups 1.0; P = (x'^ were placed on the lowest side branch, more fre- 0.59). quently than nests in indigenous (13%, N — \1) The number offorks per nest tree did not differ and eucalyptus trees in KwaZulu-Natal (10%, N = among the tree groups (1 1 ± 6 forks in indigenous 10, = 9.3, P< 0.01). KwaZulu-Natal trees, 14 ± 8 in eucalyptus, and 7 Of the 35 nests sampled, 20 (57%) were placed ± 3 in Tai nest trees; Kruskal-Wallis ~ ^-4? P m a central fork, nine (26%) on a side branch, and = 0.16). Whereas the number of central forks per six (17%) against the main branch; nest placement tree did not differ among tree groups (1 ± 1, Krus- was not associated with tree groups (x^ = 6.3; P — kal-Wallis 772,35 = 3.2, P = 0.21), the number of 0.17). Whereas seven (78%) of the nine side- side forks did (indigenous KwaZulu-Natal 5 ± 4 branch nests and four (67%) of the six main- forks, eucalyptus 2 ± 2, and indigenous Tai 3 ± 3; branch nests were from the most abundant fork Kruskal-Wallis 772 35 = 6.2, P< 0.05), although the category, 18 (90%) of the 20 central-crotch nests classes were not significantly different from each other (Tukey tests, all P > 0.05). Eucalyptus had more forks against the main branch (11 ± 8) than Table 2. The emergence of Crowned Hawk-Eagle nest indigenous trees in KwaZulu-Natal (4 ± 3) and Tai trees above the surrounding forest. = P< (3 ± 1; Kruskal-Wallis 9.6, 0.01; Tukey P < tests, all 0.05) Emergent Nest Trees Yes No Totai. All the nest trees in Tai and 11 of 17 indigenous — Indigenous KwaZulu-Natal 11 6 17 nest trees in KwaZulu-Natal were emergents, — Eucalyptus KwaZulu-Natal 2 8 10 whereas only two of 10 eucalyptus protruded above — Indigenous Tai 8 0 8 the forest canopy (x^ = 12.2, P < 0.05; Table 2). Total (Percent) 21 (60) 14 (40) 35 Overall, nests were more accessible to flying eagles 304 Malan and Shultz VoL. 36, No. 4 Table 3. The number of Crowned Hawk-Eagle nest Table 4. The number of flight path.s per Crowned trees, with flight paths sampled in four cardinal direc- Hawk-Eagle nest tree, sampled in four directions, which tions, which allowed access to nest and random forks for allowed access to nest forks in emergent and non-emer- 17 indigenous and 10 eucalyptus trees in KwaZulu-Natal, gent trees. and eight indigenous trees in the Tai Forest. Number of Number of Flight Paths None One Two Three Four Total Flight Paths None One Two Three Four x^ Emergent 0 0 5 7 9 21 Nest fork 0 1 12 12 10 Non-emergent 0 1 5 3 5 14 2.4 Random fork 4 12 8 4 7 18.6** p< ** 0.001. Nest and random tree distances to topographical features were not different for all variables when than were random forks (Table 3) Access to nests comparing means (Table and Crowned Hawk- . 6) could not be associated with their placement above Eagles were, therefore, non-selective regarding (as emergents) or within the forest canopy (Table these topographical features. One tree selected for m 4) In KwaZulu-Natal, seven of the eight non-emer- nesting was 20 from an inhabited brick house . gent eucalyptus were located on the edge of the and another 10 m from a used bitumen road. nest stand, whereas, all the non-emergent indige- nous trees were located inside the nest stands Discussion (x^ = P< 7.3, 0.01). Nest-site Selection. Tree-nesting raptors assess The mean distance from the nest tree to the variables such as vulnerability to predators, protec- nearest three trees did not differ among tree tion against adverse weather conditions, the cost of groups (indigenous KwaZulu-Natal 11 ± 6 m, eu- nest building, structural features of the nest tree, calyptus 12 ± 8 m, and indigenous Tai' 13 ± 5 m; and access to the nest when selecting a site to build Kruskal-Wallis 7^2,34 ~ 1-0, P = 0.62). The density their nest (Newton 1979, Moore and Henny 1983, of trees at nest sites also did not differ among tree Bosakowski and Speiser 1994, Burton et al. 1994). groups (all trees 156 ± 175 trees/ha, indigenous Whilst smaller raptors regularly conceal their nests KwaZulu-Natal 172 ± 183 trees/ha, eucalyptus 189 to avoid predation, larger raptors are less secretive ±219 trees/ha, and indigenous Tai 85 ± 62 trees/ and customarily put their nests in exposed posi- ha; Kruskal-Wallis 7^2,34 ^ 1-0, P = 0.62). tions (Speiser and Bosakowski 1987, Selas 1996). m m The areas of 13 Crowned Hawk-Eagle nest stands The large, 2-2.5 wide and 2.5-3 deep nests in KwaZulu-Natal were not normally distributed of the Crowned Hawk-Eagle (Steyn 1982) are very and were predominantly less than 50 ha in size (Ta- conspicuous. m ble 5). Nest stands were primarily small (20 in Although large raptors generally do not hide m width and 30-50 in length) and elongated in their nests as they can defend their nestling against shape (shape-index <0.5; Table 5). Sbape-index predators (Moore and Henny 1983), Crowned values could not be associated with eucalyptus and Hawk-Eagles do suffer some nest predation from indigenous tree stands (x^ = 0.12, P = 0.73). primates, especially if the nest tree can be accessed Table 5. Statistical distribution of KwaZulu-Natal Crowned Hawk-Eagle nest-stand variables and shape index with the Kolmogorov-Smirnov distribution test (K-S d) for normality. Dominant Cafegory (Percent) Mean ± 1 SD Range N K-S d Surface area (ha) 0-50 (77) 35.4 ± 73.7 0.05-250.15 13 0.42* Maximum width (m) 20 (69) 253 ± 363 20-1090 13 0.34 Maximum length (m) 30-50 (69) 759 ± 987 30-3520 13 0.32 Shape (0.0-1.0) 0.2-0.3 (23) 0.39 ± 0.22 0.04-0.80 13 0.16 * P < 0.0.5. December 2002 Nest-site Selection of the Crowned Hawk-Eagle 305 Table 6. Topographical characteristics measured from Crowned Hawk-Eagle nest and random trees in KwaZulu- Natal {N = 13 nests). Variables Nest Tree Random Tree Distance to water (m) 83 ± 147 (10-550)^^ 159 ± 199 (10-520) 0.86 Distance to house (m) 859 ± 1661 (20-6250) 906 ± 1738 (20-6550) 0.24 Distance to road (m) 282 ± 277 (10-810) 285 ± 341 (30-1010) 0.11 * Mann-Whitney fTtest. ^ Mean ± 1 SD (range). from nearby trees (Tuer and Tuer 1974, Kalina and 3-4 times their body mass, such as bushbuck Tra- ( Butynski 1994) This may be a reason why Crowned gelaphus scriptus; Daneel 1979), which they dismem- . Hawk-Eagles often select emergents for nest sites, ber and carry in parts to the nest. Brown (1966) especially in Tai where eight diurnal monkey spe- noted that, in the Karen Forest in Kenya, these ap- cies are found at very high densities (McGraw proach flights were always above the canopy, very m 1998). In Tai, the tall nest trees with their wide laborious and broken into short 91-137 stints so bases and high, first side branches (mean = 34 m as to rest between flights. Under these conditions, from the ground) may be extremely difficult, ifnot access to the nest would be critical in order to de- impossible, for monkeys to climb (T. Struhsaker liver nesting material and prey to the nest. Nesting pers. comm.). In KwaZulu-Natal, the presence of above the forest canopy in an emergent tree en- fewer primate species (three at the most; Smithers hances accessibility. 1983) may have resulted in reduced predation risk The large indigenous nest trees were simple in for nestlings and might have allowed for the use structure and provided, on average, one central of lower and non-emergent trees. fork, 3-4 forks against the main branch and 3-5 Sites may also be selected for nesting because forks on side branches for the eagles to place their the foliage protects the nest against adverse weath- nest. Notwithstanding, only 2-4 branches were er conditions (Moore and Henny 1983, Bosakowski used on which to build these large nests, indicating and Speiser 1994). Crowned Hawk-Eagle nests are that big, primary and secondary forks were select- usually situated within the leafy canopy, but the ed and not the smaller, multi-stemmed forks from birds also nest in exposed positions in partially col- within the canopy structure. Large raptors require lapsed or dead trees (Steyn 1982, Tarboton and a large tree-fork (crotch) to place the nest in and Allan 1984, Kalina and Butynski 1994). In this the more open branch structure may facilitate ac- study, 32 nests were located in or below the foliage cess (Newton 1979). The exotic eucalyptus differed and therefore sheltered, whereas the remaining from the indigenous nest trees in that they provid- three nests, two of which produced young during ed, on average, 1 1 more forks. This was largely due the study, were located in exposed positions in to the single main-stem growth form of these com- dead trees. Hence, although there was a trend for mercially-cultivated trees. Trees from these stands the birds to nest in a sheltered position, other fac- were also largely of similar height, probably be- tors, such as the availability of suitable nesting sites cause trees in these single species stands were and the cost of building a new nest, probably in- planted simultaneously. As seven of eight non- fluenced the continued occupation of a nest in a emergent, eucalyptus nest trees were located on dying or dead tree. the edge of the nest stand, the eagles may circum- Lastly, tree-nesting forest raptors may select trees vent the scarcity of emergent eucalyptus by select- for their size and structural features, such as a tall ing edge trees that have greater access to the nest. and open canopy, that allow unobstructed access In conclusion, because nests located within and to the nest (Speiser and Bosakowski 1987, Cerasoli above the canopy were equally accessible, access and Penteriani 1996). The Crowned Hawk-Eagle seemed to be the most critical feature identifying may require a nest that is easily accessible as it a Crowned Hawk-Eagle nesting tree and site. The m needs to fly to the nest carrying sticks up to 1.2 findings that indigenous nest trees in KwaZulu-Na- long and 8 cm thick (Steyn 1982). In addition. tal did not differ from eucalyptus or indigenous Crowned Hawk-Eagles are capable of killing prey trees from Tai Forest in terms of tree density and 306 MaiAN AND Shui.tz VoL. 36, No. 4 central and side fork availability, may indicate that able nest trees and nest-placement sites. Our rec- indigenous trees with their multiple main stems ommendations should therefore be treated with and open branch structure may be as accessible for some caution, as nests included in this study might flying eagles as emergent or edge trees. have been found unsuitable on the long term be- This study did not quantify the ‘openness’ and cause certain deficient nest features may have lim- accessibility of indigenous nest trees in KwaZulu- ited successful reproduction. Natal, particularly with regard to tree canopy di- Nonetheless, the nest trees must have open- ameter and volume, branch spacing and diameter, branch structures and large tree-forks. As nest trees and branch angle as nests were often placed on are typically emergents or edge trees, these trees near horizontal branches. Also, we did not exam- can be cultivated by felling surrounding trees or ine the inter-relationship between the largest-di- leaving the tall trees standing (Seydack 1995). In ameter side branches (required to support the this study more than half of the Crowned Hawk- large nests) and the position of the primary and Eagle nests were positioned in a central fork, there- secondary forks below or just inside the foliage, fore, the techniques of coppice-reduction or selec- related to openness and improved access. We also tive pruning could be employed to cultivate a tree did not take into account the slope at the nest site with the preferred 2-4 main branches. As Brown and aspect of the nest, as nests located on the (1966) demonstrated, suitable nest trees can be downhill side of the tree may have been more ac- identified a priori, and managers can therefore im- cessible to flying eagles. Given the floristic differ- plement these techniques to ensure a continued ences between forests in Tai and KwaZulu-Natal, a supply of suitable nest trees. comparison of nest sites Avith randomly selected To qualify as a nest tree, commercial eucalyptus sites, conducted at each nest stand, would have fur- should be managed to reach a minimum height of ther contributed toward the understanding ofwhat 34 m and DBH of 83 cm (i.e., minimum size se- constitutes a suitable nest tree. Lastly, data on how lected for nesting) Indigenous trees selected must . m easy arboreal primates can climb nest trees, partic- attain a minimum height of 15 and diameter of ularly from the base, would have added to our un- 35 cm. The mean stand density of 156 trees/ha can derstanding of how successful Crowned Hawk-Ea- be employed as a guideline for Crowned Hawk-Ea- gles are in eliminating the predation risk by gle nesting habitat. Although exotic stands must be nesting in tall, emergent trees. managed to a minimum size so as not to encroach Recommendations. Wildlife managers need to onto indigenous vegetation, nest-tree stand size it- manage forests by balancing timber harvesting self is nonessential. Furthermore, in plantations, with maintaining wildlife habitat and must employ nest stands cannot be placed at random as raptors multi-resource plans to do so (Lilieholm et al. often require nest trees to be located away from 1993, Vermeulen 1999, Malan and Robinson certain topographical features (Andrew and Mosh- 2001). These plans should incorporate both prac- er 1982, Malan and Robinson 1999). However, with tical and proactive management objectives to con- regard to the proximity of nests to human dwell- serve nesting habitat for large eagles in exotic and ings, water bodies, and public roads, the Crowned indigenous forests. Apart from silvicultural guide- Hawk-Eagles of KwaZulu-Natal were remarkably lines, other considerations must include the prox- non-selective and tolerant. In fact, the city of Dur- imity of nests to hunting habitat, their temporal ban, located in this province, harbors 12 active and spatial distribution, and tbe effects of human nests within its metropolitan boundaries. Inter- disturbance on nesting eagles (Lilieholm et al. stand distances were not recorded in this study, but 1993). Crowned Hawk-Eagles are known to nest 1.8—4.0 In this study, because we could not obtain reli- km apart and, thus, require only a relatively small able data on the age of the nests and how many patch of suitable hunting habitat (Tarboton and young were fledged from each nest over time, we Allan 1984, Allan et al. 1996, Mitani et al. 2001, did not compare the structural features of produc- Shultz 2002). Given the size of some of the prey tive between unproductive nests. Although other these eagles hunt, nest stands must preferentially factors also influence productivity, e.g., experience be located near the hunting habitat so as to sbort- of breeders, prey abundance, and persecution en flight distances to the nest. rates, the productivity analysis may have highlight- Because Crowned Hawk-Eagles use the same ed subtle differences between suitable and unsuit- nest for 10 years or longer, often until the tree col- December 2002 Nest-site Seitctton of the Crowned Hawk-Eagle 307 lapses (Brown 1966, Steyn 1982), suitable trees dation, Inc., Leslie Brown Memorial Award, the Pere- grine Foundation, a Wildlife Conservation Society Re- should not be felled. If the nest stand or tree must search Fellowship, and the Leakey Foundation. be harvested, the felling should be done outside the birds’ breeding season (August-March) and 6- Literature Cited 12 months after the nestlings have fledged to allow Atj an, D. and W.R. Tarboton. 1985. Sparrowhawks and sufficient time for the young bird to become in- plantations. Pages 167-177 mL.J. Bunning [Ed.], Pro- dependent (Steyn 1982, Tarboton and Allan 1984). ceedings of the symposium on birds and man. Wits Given that a nest takes 4-5 mo to build (Brown Bird Club, Johannesburg, South Africa. 1966), replacement nest trees, located in the vicin- D. Johnson, and T. Snyman. 1996. The crowned , ity of the nest tree in use, should be cultivated long eagles ofDurban and Pietermaritzburg. Afr. BirdsBird- in advance to provide a suitable alternative nest. ing 1:2-13. The Crowned Hawk-Eagle in South Africa has J.A. Harrison, R.A. Navarro, B.W. Van Wilgen, , been classified as near threatened because of past AND M.W. Thompson. 1997. The impact of commer- exploitation of nest trees and the likely destruction cial afforestation on bi—rd populations in Mpumalanga Province, South Africa insights from bird atlas data. of nesting habitat in the near future (Boshoff et al. Biol. Conserv. 79:173-185. 1983, Barnes 2000). Occupied nests should be Andrew,J.M. andJ.A. Mosher. 1982. Bald Eagle nest-site closely monitored to assess the status ofthis species selection and nesting habitat in Maryland. Wildl J. and to collect data on what constitutes productive Manage. 46:383-390. nests. Large tree-nesting forest raptors will always Anonymous. 1998. Commercial timber resources and have few suitable trees to nest in as large trees and roundwood processing in South Africa 1996/1997. forks are less abundant than smaller ones (Newton Dept, of Water Affairs and Forestry, Pretoria, South 1979). When nesting in large trees, eagles also Africa. compete directly with humans for this scarce re- Barnes, K.N. 2000. The eskom red data book ofbirds of source (Boshoff et al. 1983, Watson and Rabarisoa South Africa, Lesotho, and Swaziland. BirdLife South Africa, Johannesburg, South Africa. 2000). It is, therefore, no longer adequate simply Bijleveld, M. 1974. Birds of prey of Europe. Macmillan to protect forests for birds of conservation con- Press, London, UK. cern, but specific efforts must be made to satisfy Bosakowski, T. and R. Speiser. 1994. Macrohabitat selec- the nesting requirements of the Crowned Hawk- tion by nesting Northern Goshawks: implications for Eagle and other tree-nesting forest raptors; e.g., in managing eastern forests. Pages 46—49 inW.M. Block, South Africa the Bat Hawk {Macheiramphus alci- M.L. Morrison, and M.H. Reiser [Eds.], The North- nus), Ayres’s Hawk-Eagle (Hieraaetus ayresii), and ern Goshawk: ecology and management. Studies in Fasciated Snake-Eagle {Circaetus fasciolatus) avian biology No. 16. Cooper Ornithological Society, (Barnes 2000, Malan and Marais in press). Ulti- Sacramento, CA U.S.A. mately, a species-specific management plan should Boshoff, A.F. 1988. The spacing and breeding periodic- be developed for these and other tree-nesting for- ity of Crowned Eagles in the southern Cape Province. Bontebok 6:34—36. est birds and the maintenance of nest-tree struc- 1997. Crowned Eagle Stephanoaetus coronatus. Pag- . tural and topographical features incorporated into m es 194—195 J.A. Harrison, D.G. Allan, L.G. Under- management decisions. hill, M. Herremanns, A.J. Tree, V. Parker, and C.J. Brown [Eds.], The atlas of southern African birds Acknowledgments We want to thank Natal Portland Cement and the Vol. 1. BirdLife,Johannesburg, South Africa. KwaZulu-Natal Ornithological Trust for sponsoring this , C.J. Vernon, and R.K. Brooke. 1983. Historical project. We also thank KwaZulu-Natal Wildlife for allow- atlas of the diurnal raptors of the Cape Province ing us to work in their reserves and park. Bill Howells (aves: falconiformes). Ann. Cape Prov. Mus. Nat. Hist and DavidJohnson were particularly helpful in locating 14:173-297. nest sites. Guy Tedder, Denise James, Martin Buchler, Brown, L.H. 1966. Observations on some Kenya eagles. Gavin Lorry, and Bill Walker also informed us ofnesting Ibis 108:531-572. localities. In Tai, we thank Professor Ronald Noe for host- and D. Amadon. 1989. Eagles, hawks, and falcons ing the Crowned Hawk-Eagle project, the Centre Suisse of the world. Wellfleet Press, New York, NY U.S.A. des Recherches Scientifiques, Centre de Recherche en Burton, A.M., R.A. t\lford, and Young. 1994. Repro- Ecologie, the Project Autonome pour la Conservation du J. ductive parameters of the Grey Goshawk {Accipiterno- Parc National de Tai for logistical support, the Minstere de la Recherche and the Direction de la Protection de la vaehollandiae) and Brown Goshawk {Accipiterfasciatus) Nature for permission to conduct the study. Funding (for at Abergowrie, northern Queensland, Australia J S. Shultz) was provided by the Raptor Research Foun- Zool. Land. 232:347—363. 308 Malan and Shuitz VoL. 36, No. 4 Cerasoli, M. and V. Penteriani, 1996. 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