Prácticas tema 4

3.4.1 Range size and overlap

The home range sizes of brown kiwi in Paerata were remarkably similar to those in Hawkes Bay (McLennan et al. 1987). Paerata home range sizes did not differ significantly from those in Hawkes Bay when determined by either the field worker method (F[ 1 ,24] = 0.87; P > 0.05), or the convex polygon method based on

the first 80 radio fixes for each bird (F[1 ,22] = 0.07; P > 0.05). The Paerata kiwi

grid cell estimate for 80 fixes per bird was, however, significantly less than the same estimate for Hawkes Bay kiwi (F[ 1 ,22] = 4.78; P

<

50% 40% 30% 20% 1 0% 0% S P RING (n = 373) _ THICK BUSH PASTURE SUMMER (n = 3 1 6)

IIIIIIIIIIII OPEN BUSH

o BUSH EDGE

AUTUMN WINTER

(n = 1 30) (n = 203)

_ LONG GRASS/SWAMP

FIGURE 3 .6: Seasonal use of different habitat types by kiwi at Paerata.

35 reflect the different patterns of roost use between these populations. Paerata kiwi reuse their roosts far more intensively than kiwi in Hawkes Bay. This would result in a less rapid increase in the number of grid cells recorded for Paerata kiwi than Hawkes Bay kiwi, producing a corresponding difference in their estimated grid cell range for a set number of radio fixes.

The field worker estimates of about 30 ha per bird in both P aerata and Hawkes B ay contrast with home range estimates of about 5 ha per adult p air reported for brown kiwi in Waitangi S tate Forest (Colbourne & Kleinpaste 1983). That study relied on a very different method of data collection. Kiwi were caught, banded, and individually colour coded with reflective markers. On subsequent nights they were searched for by torch light. The 84 kiwi caught and banded in Waitangi were resighted on average less t han 4 times each. The home range estimate of 5 ha per p air was based on kiwi " recaptured 1 5 times or more" (Colbourne & Kleinpaste 1983). This was extremely few observations compared with the numbers obtained by radio telemetric means in Paerata and Hawkes Bay. All range estimate methods are sensitive to the number of fixes obtained (Figure 3. 1). Therefore, Colbourne & Kleinpaste (1983) may have underestimated the home range size of kiwi in Waitangi State Forest. This possibility is supported by the findings of a recent radio telemetric study in this same forest (M. Taborsky pel's. comm.).

The extent of kiwi home range overlap observed in P aerata exceeds any overlap previously documented, and is discussed further in the section on spacing behaviour (Section 3.4.4).

3.4.2 Daytime roost selection

P aerata kiwi reused roost sites far more often than Hawkes B ay kiwi (McLennan et al. 1 9 87). They also showed a marked dichotomy in the types of roosts used when alone or with their mate. When roosting w ith their mate they preferred those sites offering the greatest shelter and security. These were also the roosts for which there was greatest competition, as indicated by the numbers of different kiwi that roosted in them. The extent of compe tition for some roosts suggests that quality roosts may have been at a premium in Paerata. If so, the defence of prime sites may explain why some kiwi intensively used some of their roosts. The different patterns of roost use for solitary birds and those with a mate suggests that quality roosts may be important to pair bonding (Section 5.4.5).

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3.4.3 Night-time habitat use

Paerata kiwi were selective in their use of habitat at night. Kiwi have

previously been recorded feeding on pasture i nvertebrates (Watt 197 1 ) and on

numerous occasions were observed feeding in pasture around Paerata. However, they spent much less time in this open environment than expected from the amount

of pasture included in many of their home ranges. In contrast, open bush and bush

edges were used significantly more than expected from the relative abundance of these habitats.

Kiwi are extremely difficult to observe for extended periods and so it was not possible to determine absolutely in which of these habitat types kiwi most often fed. How ever, when kiwi were observed in open bush or at bush edges they were freq u e n tl y seen feeding. Paerata h a s a h i s tory of b e i n g grazed by c attle. Comparative invertebrate counts in the different habitat types were not made, but if the preference kiwi showed for open bush and bush edges was food-related the cattle indirectly may have been beneficial to the kiwi through maintaining these habitats. The advantages and disadvantages of having cattle in kiwi reserves deserves further investigation.

The tendency for Paerata kiwi to use open bush slightly less and long grass and swamp slightly more in summer than winter supports Colbourne & Kleinpaste' s

( 1983) assertion that during dry periods kiwi tend to feed in damp areas where the ground is more penetrable and soil inveltebrates more available.

3.4.4 S pacing behaviou r

Previous studies on brown kiwi i n Waitangi S tate Fores t (Colbourne &

Kleinpaste 1 9 83) and Hawkes Bay (McLennan et al. 1 9 87), as well as on little spotted kiwi on Kapiti Island (J. Jolly pers. comm.) have indicated that kiwi are territorial (sensu Mace et al. 1983, i.e. they maintain non-overlapping areas from which other individuals are ac tively excluded). Colbourne & Kleinpaste ( 1983)

observed fighting and birds calling repeatedly at each other in Waitangi State Forest. This type of behaviour was not obvious in either Paerata or Hawkes B ay (McLennan

et al. 1 9 87). Bouts of calling were frequently heard in Paerata but it was not clear to whom the calls were directed. Breitwisch & Whiteside (1987) h ave recently shown that mockingbird song, traditionally interpreted as a ten'itorial warning from one

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male to another, is predominantl y directed at actual or potential mates (also see Lewin 1987). Eriksson & Wallin ( 1986) have similarly demonstrated that in some flycatchers male song is largely a mate attractant. Colbourne & Kleinpaste (1984) reported that female kiwi frequently called in response to their mate ' s call. In Hawkes Bay an aggressive response could be readily induced in kiwi by simulating kiwi c alls on a whistle, or by p laying tape recorded calls. Resident kiwi would frequently respond to these calls by calling themselves and then running, often noisily, towards the source of the call (pers. obs.). This response was extremely useful in catching kiwi in Hawkes Bay, but failed almost completely in Paerata. When simulated or recorded calls were played near radio-tagged kiwi in Paerata the resident kiwi either remained motionless or fled, but (with one exception) never approached. This hide or flee response implies an aggressive component to the call, but without further s tudy it is not possible to quantify how calls contribute to territory defence and pair bonding.

The relationship between optimal territory size, food density and intruder pressure is complex (Schoener 1 98 3 ) . Colbourne & Kleinp aste ( 1 9 83) and McLennan et al. ( 1 9 87) equated home range w i th territory , but many other possibilities exist (Mace et al. 1 983; Kaufmann 1 983). Although the home range sizes of Paerata kiwi were comparable with those in Hawkes B ay, the population density was nearly 10 times as great. The resulting overlap in ranges prohibits the equating of home range and territory for the Pae rata kiwi. Intruder pressure in Paerata may have been so great as to render uneconomic the defence of a complete home range. If Paerata kiwi were actively defending areas, these 'territories' must have been far more restricted in time and space than was apparent in Hawkes Bay.

The density and distribution of kiwi in the Paerata area must have been affected by the local history of land clearance and habitat modification. Land clearance can lead to species crowding into remaining patches of bush (Lovejoy et al. 1986), but whether this accounts for the observed density of kiwi in Paerata is uncertain. Whatever the proximate cause of Paerata's high density of kiwi, similarly high densi ties may once have been widespre ad. C. O 'D onnell (reported in McLennan et al. 1 9 87) recently found that brown kiwi on S tewart Island also occupy overlapping ranges, with one lO-ha patch of kanuka being used by at least 23 different kiwi. And Buller (1888) describes kiwi hunts last century in which "a hundred or more" were caught with the aid of a dog in a single night. Buller ( 1 888) believed kiwi to be gregarious, going together "in companies of six to twelve". There is no evidence now of such groups, but even allowing for exaggeration and

3 8 misinterpretation, kiwi were formerly present i n very high densities compared with those observed now.

There is growing evidence that the North Island brown kiwi population is in

I

decline (McLennan 1988). To reverse the trend we need to stop further destruction of kiwi habitat and to identify the other factors causing this population decline. We also need to understand why the density of kiwi in Northland forests is so much greater than that in other parts of the North Island.

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