Bellbird breeding habitat in Port Hills/Christchurch area – research project
At Landcare Research, Lincoln, we are studying what types of habitat bellbirds are using during the breeding season. Breeding habitat is critical for sustaining bellbird populations in the long term.
INTRODUCTION & AIMS
During the winter months, many bellbirds are nomadic, moving around food sources on the Canterbury Plains and Christchurch City. However, during the breeding season (approximately September to February), bellbirds are found mainly in the Port Hills. Bellbirds are known to mate with the same partner year after year, and the pair maintains the same breeding territory each year. During the breeding season they do not move far from their territory, apart from brief forays to feed on local food sources.
We know that large areas of mature native bush provide suitable breeding habitat. But the suitability of small bush fragments, exotic plantations, urban vegetation and wooded areas on farms is much more complicated to assess. So we aim to characterise suitable breeding habitat in terms of:
- Trees of suitable height and structure for nesting
- Types, variety and amount of food sources in the breeding territory
- In cases where food sources are limited within breeding territory, the distance that male and female bellbirds will travel to forage
- Any preference for young birds to select a breeding territory near their parents or within existing groups.
DATA COLLECTION
To understand bellbird distribution and habitat requirements on the Port Hills during the breeding season, Landcare Research undertook intensive fieldwork during the summers of 2001/02 and 2002/03 in four study areas.
Each study area included a valley and ran from the top to the base of the Port Hills. The Ahuriri area ran from Coopers Knob down through Ahuriri Scenic Reserve to Otahuna Road, and contained relatively large and connected patches of native bush and native shrubs. The Halswell area ran from Kennedy's Bush Scenic Reserve, near the top of the Port Hills, down-slope through introduced gorse and broom to the base of the Port Hills on Early Valley Road. The Victoria Park area covered both sides of Dyers Pass Road and ended in the urban environment of Cashmere. One side of the valley is pine forest while the other has mixed native and introduced vegetation (Victoria Park). The fourth area is smaller, and runs down a valley between Ahuriri Scenic Reserve and Cass Reserve.
Study areas, colour-coded by vegetation type
Three hundred points were visited in the first three transects, and then another hundred in the fourth transect and other outlying patches (collected and analysed separately for checking purposes). Bellbird presence and the vegetation were recorded for each point.
Dots showing locations visited during breeding season fieldwork. Bellbird presence is shown as a red dot, and absence as a black dot.
RESULTS
The results confirmed our expectations that bellbirds prefer to nest in areas where there is relatively tall, structured vegetation, and an abundance of plant food species nearby. Our results also provide valuable detail of exactly what types of vegetation bellbirds prefer during the nesting season. Bellbirds were found in native forest, kanuka-manuka shrubland, mixed introduced-native forest, and Douglas fir plantations. These vegetation types mostly contained a higher number of plant food species than those where bellbirds were not found. Common plant food species in vegetation where bellbirds were found include native small-leaved Coprosma species, mahoe, lemonwood, five-finger, horopito (pepper tree), and introduced Eucalyptus.
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Our study has also uncovered some surprises. We repeatedly found that bellbirds used mature homestead gardens in the Port Hills valleys during the breeding season. The gum trees and other plantings in these gardens appear to draw bellbirds from surrounding nesting territories. Interestingly, we also found that bellbirds were present in Douglas fir forests, but not in pine forests. Douglas fir forests may have a more diverse range of insects, which are an important food source for bellbirds. The Douglas fir plantations may also have a denser branch structure and foliage (for safe nesting) than the high-pruned pine trees.
CONCLUSIONS SO FAR
In the Port Hills we have found that breeding bellbirds use areas that have relatively tall (greater than 8 metres) vegetation, and a variety of food plants (generally more than five different species). Bellbirds were observed in all the patches of native bush that were visited in the Port Hills, even several small ones (0.5 hectare). They were also found in mature Douglas fir forest. Important food species include mahoe, small-leaved coprosma, five-finger, broadleaf, lemonwood, lacebark, fuchsia, horopito (pepper tree), and marbleleaf.
We have formed a set of criteria for preferred bellbird habitat by drawing together our observations of vegetation composition and structure, patch size, and proximity to other food resources and bellbird breeding locations. We have applied these criteria to our fourth study area (shown in map above) and other outlying patches of vegetation to predict where we expected bellbirds to be nesting. We then compared our predictions with independently collected fieldwork.
We found that our simple model does predict bellbird breeding habitat suitability in many cases. The process of constructing and testing the model had also highlighted gaps in our knowledge about bellbird breeding ecology, which we will seek to fill over the next few years.
Documents available for download on this modelling work:
- Conference abstract: Habitat and Distribution of Korimako/Bellbird
in and around Christchurch
- Conference poster: Habitat and Distribution of Korimako/Bellbird
in and around Christchurch
NEXT STEPS
Our plans after this are to use radio-tracking and resighting of colour-banded bellbirds (Colour-banding Bellbirds in Port Hills) to determine:
- How far male and female bellbirds travel to forage while nesting
- Breeding territory sizes in different vegetation types
- The movements of juveniles in their first winter, and whether they return to the natal territory to breed nearby.
These are important parts of the puzzle as we seek to understand habitat suitability for bellbird breeding in fragmented and heterogeneous landscapes.