3.1. Sap Feeding Observations
Forty-one observations of sap feeding were made, totaling 555 minutes of sap feeding observation. Twenty-one individual kākā were identified foraging for sap, the majority of which were observed once (
Table 1). Sap feeding was observed on 28 occasions at the Wellington Botanic Garden during systematic behavioral sampling. Remaining observations of sap feeding were made at Karori Cemetery (
Figure 1, 1 observation), Karori Park (1), KWS (5) and in the suburbs of Highbury (1) and Northland (5).
All observations of sap feeding at Wellington Botanic Garden were on Eucalyptus leucoxylon. Elsewhere in Wellington, sap feeding was observed on macrocarpa (Cupressus macrocarpa), Lawson cypress (Chamaecyparis lawsoniana), Himalayan cedar (Cedrus deodara) and mahoe (Melicytus ramiflorus).
Table 1.
Number and total duration of behavioral observations of kākā observed foraging for sap in Wellington between November 2011 and May 2013.
Table 1.
Number and total duration of behavioral observations of kākā observed foraging for sap in Wellington between November 2011 and May 2013.
Leg band code 1 | Sap feeding observations | Season fledged | Sex | Method of sex determination 3 |
---|
No | Duration (mins) | Location 2 |
---|
BG-V | 1 | 11 | WBG | 11/12 | M | Estimate from DFA |
B-KB | 1 | 16 | BG, KWS | 08/09 | F | Breeding |
BP-P | 1 | 8 | KWS | 02/03 | M | Breeding |
GG-V | 6 | 122 | Northland, BG | 11/12 | F | Estimate from DFA |
GW-V | 2 | 4 | WBG | 11/12 | M | Estimate from DFA |
KO-G | 1 | 30 | KWS | 04/05 | F | Breeding |
LW-O | 2 | 36 | WBG | 10/11 | M | Estimate from DFA |
MG-V | 1 | 11 | WBG | 11/12 | F | Estimate from DFA |
MP-V | 1 | 2 | WBG | 11/12 | F | Estimate from DFA |
MR-O | 1 | 15 | WBG | 10/11 | F | Breeding |
MW-O | 1 | 2 | WBG | 10/11 | F | Estimate from DFA |
O-MY | 1 | 19 | WBG | 10/11 | M | Estimate from behavior |
PB-V | 1 | 2 | WBG | 11/12 | M | Estimate from DFA |
PL-O | 1 | 28 | KWS | 10/11 | F | Estimate from DFA |
RP-V | 1 | 1 | WBG | 11/12 | M | Estimate from DFA |
V-YW | 1 | 14 | WBG | 11/12 | F | Breeding |
WB-W | 1 | 13 | KWS | 07/08 | F | Estimate from DFA |
WK-O | 1 | 15 | Highbury | 10/11 | F | Breeding |
W-OO | 1 | 52 | Karori Park | 08/09 | F? | Unknown |
YK-O | 1 | 5 | WBG | 10/11 | M | Estimate from DFA |
Y-RO | 2 | 53 | Northland | 08/09 | F | Breeding |
Unbanded | 8 | 62 | WBG, Karori Cemetery | | | |
Unidentified | 4 | 34 | WBG | | | |
Two types of tree damage have been observed in Wellington; transverse gouges and removed patches of bark (
Figure 2). Both adult and juvenile kākā were observed engaging in both types of bark damage and bark removal behavior differed between the two types of damage. Transverse gouges were made by using the beak to prise a deep gouge through the bark layer (
Figure 3). The lower mandible was hooked under the bark and prised away from the bird, with the upper mandible held against the outer side of the bark to assist with leverage. This resulted in the bark gouge being extended away from the bird. Lapping sap and deepening or lengthening the gouge could not be distinguished as they occurred simultaneously. A sap foraging kākā would move between multiple gouges regularly during a sap feeding bout, spending between 1 second and 2.5 minutes at a single gouge (
x ± SD, 45 ± 43 seconds, n = 21) before moving to another one nearby. Up to six bark gouges were utilized during a single sap feeding bout.
Figure 2.
The two types of bark damage resulting from kākā sap feeding in Wellington, (a) transverse gouges and (b) removed patches of bark.
Figure 2.
The two types of bark damage resulting from kākā sap feeding in Wellington, (a) transverse gouges and (b) removed patches of bark.
Figure 3.
A juvenile kākā sap feeding by forming transverse gouges through the bark of Eucalyptus leucoxylon. Anderson Park, Wellington Botanic Garden, September 2012.
Figure 3.
A juvenile kākā sap feeding by forming transverse gouges through the bark of Eucalyptus leucoxylon. Anderson Park, Wellington Botanic Garden, September 2012.
The other type of tree damage was characterized by the removal of patches of bark from a trunk or branch. The sap feeding bird would begin by prising off small pieces of bark until the cambial layer was reached. The mandible was then used to lever off small pieces of bark from around the edge of the bark wound, gradually enlarging its size. Bark was removed using the same technique as for horizontal gouges, with the upper mandible providing leverage and the lower mandible hooking under the bark and levering away from the bird. Removed pieces of bark were dropped to the ground often with a flicking motion of the head and the ground beneath recently damaged trees was often littered with bark pieces. At these types of bark wounds, a kākā would usually forage from only one or a few patches, alternating between enlarging the patch and lapping sap from edges that had previously been exposed. During this type of bark removal, lapping of sap could often be observed directly, particularly when large areas of cambium had been exposed. This occurred by the kākā holding its bill open and using the tongue to lick the exposed cambial surface, predominantly at the edges of the removed bark. The bird would also sometimes tilt its head and run the side of its bill over the exposed cambial surface lapping sap that had exuded. Sap was also often licked from the underside of a piece of bark immediately after it was removed from the tree.
Despite their strong beak, removing bark took considerable time and effort. When initiating a bark wound a kākā may test various points on the bark, presumably to find a weak spot such as a knot or ridge in the bark. Once the kākā had a firm grasp under the bark, it would lever the bark off. The head and neck would be used to lever off thinner bark but for thicker barked trees, a kākā would use its entire body as leverage. Sometimes a kākā would move around to find an improved foothold to increase leverage. The sap feeding bird may stand on a lateral branch but often clung to the trunk in any orientation.
The number of minutes spent sap feeding in a single bout ranged from less than 1 minute to 52 minutes, with a mean of 13.5 ± 12.5 minutes. Kākā were already engaged in sap foraging when sampling began in 34% (n = 14) of observations so bout length is likely to be underestimated.
Sap feeding was observed on trees with many hundreds of scars and also on trees with no previous damage. Kākā returned to individual sap feeding trees repeatedly on multiple days for at least three weeks. Multiple observations of the removal of bark patches on three trees at two sites suggest that kākā may remove bark patches vertically down a tree trunk. Over the course of two to three weeks, new patches were observed to be removed beneath those already present or current patches were extended downward. No patterns were observed in the placement of transverse gouges on a tree.
All bark removal observed during this study was assessed to be for the purpose of sap foraging. Invertebrate feeding was not observed during the study, however invertebrates may have been gleaned while removing bark to access sap.
3.2. Characteristics of Sap Feeding Individuals
Eight kākā observed sap feeding were identified as juveniles (38% of identified sap feeding kākā), having fledged in the 2011/2012 breeding season. Seven kākā fledged in 2010/2011, three in 2008/2009, and one each in 2007/2008, 2004/2005 and 2002/2003 (
Table 1).
Six individuals observed sap feeding were known from previous breeding history to be females and one was known to be male (
Table 1). Behavioral observation of attempted mating during the course of this study suggested that one other bird observed sap feeding was male. The sex of one sap feeder was unknown as it was found as a juvenile, so nestling measurements were not obtained. The sex of 12 of the remaining 13 identified birds was estimated from nestling measurements. Six were estimated to be male and six female. Based on individuals whose sex was known or able to be estimated (n = 20,
i.e., excluding one banded bird), 60% of sap feeding birds were female (n = 12). This is not significantly more than expected by chance (exact binomial test,
p = 0.868).
Sap feeding appears to be a predominantly solitary activity. Of the 41 observations of sap feeding, only four occurred when a conspecific was in the same tree and two with a conspecific within 1 meter of the sap feeder. Vocalization was rare during sap feeding, compared to frequent calling during other foraging behaviors. Sap feeding bouts were significantly longer when there were no conspecifics present in the area (no conspecifics observed or heard from the observation point, unequal variances t-test, t15 = 4.96, p < 0.001). The mean length of a sap foraging bout was 26.3 ± 12.8 minutes (n = 13) when the feeder was alone and 7.6 ± 6.6 minutes (n = 28) when conspecifics were present in the area.
We recorded eight instances of a kākā displacing a conspecific from a bark wound. This usually occurred simply by the bird approaching the sap feeding kākā who then flew off or moved away. The displaced kākā usually resumed sap feeding at a nearby wound within one minute. We observed one instance of a sap-feeding kākā chasing away a conspecific that landed nearby and two instances where a newly arrived bird unsuccessfully attempted to displace a sap feeding bird from a bark wound. On one occasion a tui (endemic honeyeater, Prosthemadera novaeseelandiae) was observed attempting to access sap while a kākā was foraging at bark wounds on Lawson cypress. The tui approached a recently made bark wound and was chased away by the kākā. After three similar attempts, the tui was able to access a bark wound and fed on sap from the edges of the removed bark for four minutes before being chased away again by the kākā.
Twenty of the twenty-one individuals observed sap feeding during this study have been recorded during monthly surveys or by a microchip reader as visiting supplementary feeding stations within KWS in 2012. These birds were recorded feeding from stations between 1 and 1,696 times over the course of the year. Two of the females observed feeding on sap bred at monitored nests within Karori Wildlife Sanctuary in the 2012/13 season and an additional two birds bred in both the 2011/12 and 2012/13 seasons. The known male bred in the season preceding his observation.