Listeners in the Night

Listeners in the night

Counting kiwi calls in the Orokonui Ecosanctuary An exploratory study

Valerie Fay, Michael Fay and the listening team of Francie Beggs, Patricia Dean, Debra Fairley-Aldridge, Leslie Gowans, Leonard Guy, Claire Haggland, Sue Hensley, Pam Hill, Maree Johnstone, Jan Littleton, Fiona Nyhoff, Robin Nyhoff, Derek Onley, Rosemary Penwarden, Hillary Phillips, Mary Thompson and Sophie Welvaert A Statistician on Method We must use all available weapons to attack, face our problems realistically and not retreat into a land of fashionable sterility, learn to sweat over our data with an admixture of judgement and intuitive rumination, and accept the usefulness of particular data, even when the level of analysis available for them is markedly below that available for other data in the empirical area. (Binder, 1964)

Acknowledgements Kelvin Lloyd and Derek Onley for proof reading and editing, Sue and Grant Riesman for allowing use of their property, and Murray Efford for guidance on automated call capture techniques.

Abstract

The objective of the project was to evaluate how well the technique of ‘call counting’ would work in the Orokonui Ecosanctuary, to identify the peak calling time (month) and to lead to a decision as to whether a repeat call count survey could produce enough useful information to justify the considerable effort involved. A team of volunteer listeners were positioned at ten locations in and around the perimeter of the Orokonui Ecosanctuary, recording all kiwi calls heard in two hour periods commencing 45 minutes after sunset on sixteen nights. Listening took place on four nights per month for four months from February through May 2013, and following standard procedures, nights of bright moonlight were avoided.

The following information was noted for each call: time, number of notes, sex of bird, compass bearing and approximate distance from listening site. Additionally, for each hour the weather conditions at each site were noted. These data were analysed using Microsoft Excel (statistical analysis) and Microsoft Word (mapping), and in conjunction with the detailed field experience of the first author. In both its execution and analysis, this study leant heavily on the experience and findings of earlier work on kiwi in the Ecosanctuary.

Study findings a) Confirmation that kiwi continue to be concentrated in the southern half of the Ecosanctuary. b) The mean number per night of male calls reported (16.0) was almost twice as many as that for female calls (8.9). c) The number of calls increased from February to April (for males) and into May (for females). d) Although problems with reliably calculating bird numbers from call counts have been noted, a reliable* (but not necessarily accurate) model for estimating bird numbers was developed for this data set. e) The lowest number of calls heard was nine on 7th February from an estimated six birds, and the greatest number of calls was forty on 9th April from an estimated thirteen birds. f) Using time, bearing and distance of calls, the formation of five male/female pairings of kiwi is tentatively proposed. *Used in a statistical sense, ‘reliable’ is akin to ‘consistent’. A clock that is consistently five minutes fast or slow would be described as ‘reliable’ (and still be very useful).

The value of undertaking further call count surveys should be critically assessed. We have been impressed by the usefulness of field knowledge in interpreting call data, and suggest that a grid or track-section based systematic count of field signs (scat, feathers, probe holes, footprints, burrows, sightings) supported by the present generation of listening devices might be the more cost effective means of providing the same type of decision assisting information as has been presented in this report. New monitoring techniques could also result in automated capture of data, thus reducing the amount of volunteer time required.

Background The Orokonui Ecosanctuary, which began operation in 2007, is located north of Dunedin in the South Island of New Zealand at latitude 45 degrees south. The Ecosanctuary surrounds the valley of the Orokonui Stream and comprises a 307 hectare area bounded by 8.7 km of predator resistant fence. Elevation above

2 sea level falls from 340 m in the south-east to 15 m in the north. The Ecosanctuary’s objective is to provide a safe haven for New Zealand’s endangered flora and fauna, encapsulated by the phrase “A future for our past”.

Over the last five years several endangered species, including kiwi, have been introduced to the Ecosanctuary. The sub-species of kiwi introduced to the Ecosanctuary is the Haast tokoeka (Apteryx australis australis) from the mountains of South Westland, and are among the most endangered kiwi taxa, with an estimated 350 birds surviving in the wild. Three groups of birds have been introduced to the Ecosanctuary: Eight in October 2010, a further ten in October 2011, and three more in November 2012. The 2010 and 2011 birds were telemetrically monitored each month from release until May 2012. Two of the 2010 release died soon after release from accidental causes, but the remaining 16 birds were captured alive in July 2012. Their transmitters were removed at this time, birds weighed and their condition rated. Fifteen of these 16 birds were assessed as being in excellent condition, with the sixteenth being lighter than others. At the time of writing the Ecosanctuary population of kiwi was estimated to be 19, assuming no births and deaths since July 2012 with ages ranging from 13 months to over four years. However, suggestion of pair formations from the telemetric surveys in 2012, current field signs (small scat and probe marks), and that a ranger “actually observed what was, in all likelihood, a kiwi chick “(personal communication from E.Smith), strongly suggest that breeding has occurred.

Figure 1 Roosting sites May 2012 Each monthly telemetry survey, which was done in daylight when the birds were roosting, yielded a map of the location of all birds at that time (see Figure 1 below), a tracking map for each bird, and finally a map indicating the roosting range of each bird (Figure 2).

A location map (left) was constructed from data gathered in May 2012. It indicates, with different coloured and shaped symbols, the positions of the sixteen individual birds extant at that time. Although this pattern, with all birds clustered in the south of the Ecosanctuary, was typical, there were months when telemetry indicated that one or two birds had taken up temporary residence in the northern part of the Ecosanctuary.

Roosting areas, based on an amalgam of data collected for all birds each month during the last six months of monitoring (December 2011-May 2012), are shown in Figure 2...

Figure 2 Roosting ranges

Dec ’11- May ‘12

Each ellipse in Figure 2 covers the roosting sites of each bird as determined by the monthly telemetric surveys from December 2011 to May 2012. Yellow boxes indicate the six surviving birds of the 2010 release, and the white boxes the ten birds from the 2011 release. The letters are the identification number of the bird and the number beside each identification code is the area (ha) of the roosting range (note that BR and MG had completely overlapping ranges on the western boundary of the Ecosanctuary).

Our conclusions from all the data gathered and analysed were that; a) All birds were normally resident in the southern half of the Ecosanctuary. b) The size of roosting ranges varied enormously (0.6 ha to 21 ha.). c) At least three, but possibly more, pairs of kiwi appear to have formed.

Note: Detailed information covering the first eighteen months of Kiwi in the Orokonui Ecosanctuary are contained in the report, “Haast tokoeka at Orokonui Ecosanctuary”, August 2012, Valerie Fay and Michael Fay.

Call listening 2013 Following their successful introduction and concern that regular disturbance could be detrimental to the birds settling into territories, it was decided In July 2012 that no further telemetric monitoring and capture of the kiwi would take place for five years. In the spring of 2012 the first author was asked to implement a call monitoring project to see if it could be practically undertaken at the Ecosanctuary, and if so, whether it would yield information that would benefit management decision making. Ten listening posts were Stile established in and around the perimeter of the Figure 3 Listening post Ecosanctuary (Figure 3). The Listening Posts were locations Valley post 1300 located on ridges and at the top and bottom of the valley so that kiwi calling in any area of the Ecosanctuary could be potentially heard at one or Stile more Listening Post. This would offer the possibility of fixing a call’s location by Valley post 1300 triangulation if a call was heard simultaneously at

Mopanui Rd two or more listening posts.

Figure 3 W M Following established protocols, field data forms Listening post locations Fence post 114 Cabbage tree were designed on which the following

information was recorded: Fence post 122 Location and date Listener(s) and listening times Stile S.W. corner Weather and noise conditions Grassland Time of each kiwi call Kanuka downs Sex of calling bird Compass bearing of each call Mopanui Rd Estimated distance of call from the listening post in three categories (-100m, 100-500m, + 500m). Cabbage tree During the project the number of separate notes in each call was added as information to be recorded as it became clear that this was useful information for attributing calls reported from different listening posts to the same or different birds.

Grassland Call data were also gathered for morepork (Ninox novaeseelandiae) (which will be reported separately), and for other noises (other birds such as South Island kaka (Nestor meridionalis meridionalis) and paradise duck (Tadorna variegata), and other noises such as possum, pig, tuatara, cattle, trains and a donkey) were Kanuka Downs also gathered to allow confusing noises to be understood and eliminated during analysis.

The plan was to have a team of listeners working on the first two suitable nights of each month, beginning in February 2013. To be deemed “suitable” the night had to have little or no wind (calls can not be heard when it is windy), to have little or no precipitation (it is unpleasant to sit in the rain for two hours and to keep equipment dry), and not to have the probability of bright moonlight (kiwi are reported to call less frequently on nights with bright moonlight). Trained volunteer listeners would meet at the Ecosanctuary visitor centre to be briefed, receive equipment, and to synchronise time machines. One or two listeners 5 would be directed to each listening post and would begin recording 45 minutes after sunset for the subsequent two hours. Listening was subsequently carried out in the months February, March, April, and May with listening beginning at 9.50 pm in February and slowly coming forward to 6.05 pm in May as day length shortened. By this time it was judged that sufficient information to evaluate the value of the project had been gathered, and it was also becoming difficult for listeners who worked during the day to get to the Ecosanctuary at the earlier start times.

What is heard and reported when listening for bird calls Interpretation of bird call data would be very easy if all bird calls within a prescribed distance were heard, and their direction could be accurately determined. Unfortunately there are several factors operating against this ideal state.

Figure 4 A theoretical distribution of kiwi Figure 4 is an example of the perfectly regular world inhabited by statisticians to show that the world is often not so conveniently arranged. It demonstrates the distribution of kiwi, and consequently of calls, that would exist in this statistical world where kiwi are distributed evenly within the Ecosanctuary. The blue semi-circle (100 m radius) contains only 1% of the total area and in this statistical world would contain only 1% of the kiwi; similarly the red and green areas would theoretically contain 24% and 75 % respectively of kiwi. In practice, as a consequence of the two factors discussed below and of possible measurement errors, it is most unlikely for this pattern to emerge from fieldwork. Indeed, if it were to do so there would be grounds for serious questioning of field work quality.

Firstly is the nature of the terrain, which can hopefully be demonstrated by a stylised representation of a west-east cross section through the Orokonui valley (Figure 5). A listener at point “L” on the western boundary might not hear a kiwi call from point “K1” due to the kiwi being down by the Orokonui stream, with ground contours and vegetation interrupting the sound waves on their journey between the two points. Conversely, although position “K2” is nearly twice as far away from the listener, a call from this point might be heard at “L” because there is nothing to inhibit the passage of sound waves between these points. A graphic illustration of Figure 5: Contour effects contour effects was provided h 220 e 210 when gunshots coming from m L i 200 K2 L e beyond the south-east corner of g 190 a t180 the Ecosanctuary were heard h n r170 clearly on the sanctuary’s t d e160 150 western boundary but not heard s i 140 K1 by listeners at a south-eastern

n 130 listening post (Cabbage Tree, 120 Distance from listening point in 50 metre increments Figure 3) on Mopanui Road. 6

Secondly, under good conditions the human ear can pick up sounds as quiet as 4 decibels and the human voice talking at a normal conversational level is about 62 decibels. The apparent loudness of a sound diminishes with the square of the distance of the listener from the call, and consequently a sound that would be easily audible when the listener is close to it has to be much louder as distance increases. Figure 6 (below) illustrates that a 38 decibel sound is audible at 65 metres, but would need to increase to 58 decibels to be heard by a listener 130 metres away, to 62 decibels to be heard 250m away.*

Figure 6 Aproximate decibel level required at source for a sound to be audible at different distances D e 80 c 60 i 40 b e 20 l 0 s 0 100 200 300 400 500 600 700 800 900 1000 1100 Distance from source in metres * The Decibel Scale, like the Ricter Scale, is a log scale to accommodate the great differences in magnitude (energy) of the phenomena being measured. A kiwi call is usually between 70-80 Db.

Procedure A team of 19 volunteer listeners were recruited and trained in compass use, and with the aid of a CD, in the recognition of male and female kiwi calls and of other bird and animals calls. In practice this number of listeners proved insufficient to provide the planned level of coverage from all listening posts for three reasons: a) The necessity to reschedule listening nights at short notice leading to listener unavailability. b) The varying acuteness of hearing among the volunteer team. c) The need for listeners to operate in pairs because of health and safety concerns. It quickly became apparent that kiwi calls were concentrated in the southern part of the Ecosanctuary, leading to the limited resources being concentrated on the five southern and south-western listening posts with only minimal coverage of the five northern and north-eastern posts. Results a) Number of calls noted Although the number of calls heard on each night showed considerable variation (Figure 7), it is clear that they increased from February (57) to April (125), and then maintained a high level in May (108).

Figure 7 - Calls per night - all kiwi 50 C 40 a l 30

l 20

s 10

Month

b) Calling variation by month and sex of bird The monthly data indicated a differing pattern between the number of male calls and female calls heard. For the first three months there were approximately twice as many male calls as female calls (Figures 8 and 9). The levelling off of kiwi calls in May was a consequence of the number of male calls reducing whilst the number of female calls continued to increase.

Figure 8 - male kiwi calls Figure 9 - female kiwi calls 100 100 90 80 80 70 60 60 50 40 40 30 20 20 10 0 0 Feb March April May Feb March April May

c) Clustering of calls The distribution of calls over the two hour listening periods was characterised by periods of frequent calling followed by longer periods when few or no calls were made. Figure 10 below (from 13th May) is an illustrative example.

Figure 10 - Distribution of kiwi calls - May13th 2013 4

3 C a 2 l l 1 s 0 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96 101 106 111 116 Minutes intervals begining 45 minutes after sunset

d) The number of calls reported at each listening post As mentioned earlier in this report the number of calls heard at the listening posts varied widely. Because varying amounts of time were spent at different listening posts the data has been presented as number of calls per listening hour (Table 1).

Table 1. Kiwi call rates at the different listening posts. Times post used Hours Male calls per hour Female calls per hour Total calls per hour All listening posts 81 162 1.64 0.92 2.4 Grasslands 16 32 1.69 1.38 3.1 Kanuka Downs 16 32 1.91 1.19 3.1 S-W corner 16 32 1.89 0.92 2.8 Fence Post 122 16 32 1.63 0.81 2.4 Fence post 114 11 22 0.86 0.09 1.0 Fence post 1760 2 4 0 0 0 WM 1 2 0 0 0 Mopanui Road stile 1 2 1 0 1.0 Mopanui Road 2 1 2 0 0 0 Cabbage tree 1 2 1 0.50 1.5

The minor but satisfying point to emerge from this data is that all listening posts (with any calls at all) reported more male calls than female calls. The major point was that it quickly became apparent that the origins of calls were heavily biased towards the southern half of the Ecosanctuary. Taken in conjunction with the work in 2011/12 (referred to in the ‘Background’) that had indicated that birds were concentrated in the same southern area, it was considered that the optimum use of scarce volunteer resources was to concentrate them at the listening posts covering the southern sector. Nonetheless, we were able to cover at least one northern Listening post on 12 of the 16 nights, and on some nights more that one of these northern posts was covered giving 17 listening occasions in all. The mean call counts per hour were 0.53 for the northern posts and 2.81 for the southern posts.* *After the conclusion of the formal part of this study a further check of the six northern Listening Posts was carried out at the beginning of June. The mean call count per hour was 0.66 compared with 0.53 in the formal study.

How many birds As a consequence of the factors discussed earlier in this report, and due to possible measurement errors in estimating the distance, direction, sex and even time of calls, the process of estimating bird numbers S.W corner from call counts is fraught with difficulties and generally considered to be unreliable. However, it was decided to attempt the task by working with each night’s data as it became available and to repeat the exercise Figure 11 when all data had been collected to check that there had been no changes to the criteria during the four months of the study. The maps (right) were constructed from records of calls made in the evening of 7thFebruary 2013 (Fig.11) and 9th April 2013 (Fig. 12) when nine and 40 calls respectively were noted (each arrowhead represents a call). Counter intuitively, the greater the number of calls the more difficult it becomes S.W. corner to allocate calls to a constructed kiwi* because of the plethora of alternatives. The analyst has to carry out a process often described as “fuzzy logic”, where all the data Figure 12 is subject to error and the importance of any 9

one piece of information can vary from ‘crucial’ to ‘doubtful’. In our case there were seven strands of evidence: time of call, sex, bearings and cross-bearings, distance from listening post, terrain, and kiwi behaviour including mobility (could a kiwi have walked that distance in that direction in that time?). Untangling and weaving together this information was a task of many hours.

Figure 13 - Regression - nightly data - all calls and birds Notwithstanding the concern 16 over the reliability of estimating 12 bird numbers from calls, the b relationship appeared to be E i 8 s r strong in this study (Figure 13). This was particularly so when t d 4 s the data for the four nights in 0 each month was averaged, 0 10 20 Calls 30 40 50 eliminating the effect of night to night variation (Fig. 14).

Figure 14 - Regression - monthly data - all birds and calls Using this monthly data we can say 16 that within statistical error the b 12 y = 0.2761x + 3.005 R² = 0.99 number of birds calling (y) equals E i the number of calls (x) times 0.276 s r 8 plus 3. For example, if there had t d 4 been 18 calls, the number of birds s

responsible would be estimated to 0 be: 10 15 20 25 30 (18 x 0.276) + 3 = 8 s.e. = 0.7 Calls

*We could not find a satisfactory word to describe an object that has no corporeal existence but is constructed from pieces of evidence that point to its existence. Medicine, when dealing with circumstantial evidence of this kind, uses “syndrome” which is clumsy but does fit the problem they are faced with.

Pair formation

A necessary prelude to mating and reproduction is male/female pair formation, and data from the 2011/12 study had suggested that it could be occurring. Possible pairing was investigated in the present study by searching for linkages in time and space of male and female calls, i.e. a male call closely followed by a female call from the same or very close position. Of the 390 calls recorded, thirty-three pairs of

Figure 15 male/female calls (18% of all calls) were identified with each pair indicated on the map by a green dot. On the basis of the clustering of these paired calls, and of data from the 2010/2012 telemetry study, ellipses (yellow) were used to suggest groupings of paired calls that might have been made by the same two birds.

Discussion As an exploratory study the questions requiring answers were: Could we run a Call Count study successfully? Is the technique sensitive enough to make it applicable to the particular information needs of the Orokonui Ecosanctuary?

The answer to the first question is “yes but”, an answer that is not unrelated to learning that sitting out in the dark for two hours with only the stars, animal noises and a quiet companion for company is quite a pleasant experience. However, there are important corollaries in terms of value of the information and cost. The answer to the second question, which we will address first, has to be more equivocal in that applicability is related to the usefulness of the information that is gained. Plainly some interesting information has been gained that has allowed formal and informal predictive models to be constructed, but unless the information from this study and follow-up studies could be used to improve the performance of the Ecosanctuary, either inside or outside of the fence, its cost-effectiveness must remain an open question. Whilst we cannot answer this we can summarise the knowledge gained, which may help a decision on applicability and value.

a) Call rates were low in February, rising through March to an apparent peak for males in April. Female calls continued to increase into May and because of this difference we cannot be confident that the peak calling time has been located. However, we feel confident in suggesting that call counting need not begin until mid March, and that it would seem sensible that it should continue into May. However, the early start time required to proceed beyond May (6.05 pm) could make it very difficult for volunteers who work during the day to attend. b) Over the whole period of the study the equal number of calls in the first and second hours (commencing 45 minutes after sunset), raises a question of whether the two hour time period could be shortened. Unfortunately, the average disguises irregular differences in the call rates between first and second hour; irregularities that are abetted by the distinct patterns of peaks and troughs in the numbers of calls heard. These factors strongly argue against any move to shorten listening time. c) The differing call rates noted at the ten listening posts concur with the evidence for the uneven distribution of birds in the Ecosanctuary in the 2011/12 telemetry survey. There is no incontrovertible evidence of why this favouring of the southern part of the Ecosanctuary by kiwi occurs, although it has been suggested that the greater amount of food-rich grassland may have an influence. d) Although the proportion of calls from the northern half of the Ecosanctuary was very low a significant number of field signs (scat, probe holes) had been noted. This may be an indication that some of the birds in the northern area are immature and thus not vocalising to any great extent. e) The reliability of the translation of call numbers into bird numbers (Figure 14) is possibly a product of the large number of call counts (81), knowledge of the terrain and kiwi behaviour by the analyst, and careful interpretation of the data. The data on ‘pairings’, which is possibly the most significant 11

of the findings (Figure 15) is supported by earlier work, and consequently whilst not unexpected, is encouraging for the future of Orokonui‘s kiwi population. g) Although the information that has been gained is interesting and even helpful, any repeat survey must be judged against a different set of criteria in that it is highly unlikely that any changes could be interpreted with any degree of confidence. This is a consequence of the following factors:

i) Natural or random year to year variation in call levels, a phenomena that would seem likely and about which we know nothing. ii) Possible increases in calling as a consequence of a more mature population. iii) Possible decrease in calling due to a number of pairs and territories having been established in 2013. iv) If calling increased by very much, the density of information might make the already difficult task of interpreting the data overwhelming. It could reach the “point of confusion”.

There would seem to be only two situations in which the findings of a repeated study could be reliably interpreted. Firstly, a move by maybe four or more birds northwards, particularly if pairings could be identified, would be readily apparent. Secondly, no calling at all, or a large fall in the amount of calling, might signal a major decline in the kiwi population. We trust that the second of these scenarios is unlikely and suggest that should it be judged that ongoing information is necessary a more targeted survey technique would best be employed.

Methodological improvements Should the study be repeated we would recommend the following methodological changes. a) Every effort should be made to ensure that there are always enough volunteer listeners to cover all listening posts on most nights. A team of thirty listeners would not be too many b) When a bird call is heard there are several variables to be noted: species (the survey is run in conjunction with a morepork study), sex, time, compass bearing, distance from call and number of individual notes. All these are aids to bird identification and the accuracy of all of them can be improved, either directly, or indirectly through making other tasks easier. i) Identification of species and sex of kiwi would be helped by refresher sessions at frequent intervals. ii) Noting of the correct time of a call would seem easy, but there is evidence to suggest that this is not always the case despite synchronisation of time machines (watches/cell phones) before departure to Listening Posts. This is probably due to forgetting, in the pressure of the moment, to adjust for the two minute error of their machine. Moving the time when calls are recorded from the start to the end of chirrups would reduce this pressure and might lead to greater accuracy. iii) Compass bearing is a particular problem as the small, hand-held compasses we have tend to be a bit erratic when used hurriedly in the dark at the same time as other activity. The accuracy of bearings, and all of the other operations too, would be improved by having a ‘compass table’ with a big ‘needle’. The compass table would be oriented to magnetic north (to avoid confusion, adjustment for magnetic deviation is carried out during data processing) and the needle pointed at the call as it occurs and noted later. Counting of the

number of notes (another very useful aid to call/bird identification) should also benefit from lack of distraction. iv) The record sheet has columns for ‘under100metres – ‘100 to 500 metres’ – ‘over 500 metres’, which probably best translates as loud,intermediate and faint. The estimation of the distance of the call is a difficult task for listener. There is little we can do to directly improve this (see v) below). v) Like most volunteer groups, the bulk of the listeners are of mature years, and one consequence of this is that hearing has begun to deteriorate for some of them. The possible extent of this problem first came to notice during the set-up phase when one of the listeners (the second author) heard far fewer calls than his partner. Unfortunately it became apparent during the course of the project that there were other members of the team whose hearing was not as acute as others, which does not mean that they were of no use to the project but rather that they should be paired with a listener whose hearing is better. Team members should be encouraged to alert the team leader of any problems so that optimum pairings of listeners could be arranged.

Cost and value Apart from minor expenditure for equipment such as compasses and clip-boards, the bulk of the cost is volunteer time. With briefing and travelling time included, each listener gives about three hours every listening night, which over the February – May period of the study amounted to approximately 580 hours for all listeners. Additionally there is time involved in planning, data processing and report writing, which together will have totalled not less than 150 hours; a grand total of 730 hours. If volunteers are costed at a modest $20 per hour the equivalent of $14,600 of volunteer labour has been used up. It might be that a future study would need to be run for only three months, but a larger team of listeners would be required to ensure coverage of the northern listening posts, which is essential if we want to measure any spread of kiwi from their southern redoubt. Whether a large team could be recruited is open to serious question.

In view of the value of the information that has been gathered, and the difficulties and cost encountered in doing so, the Orokonui Ecosanctuary management and committees might like to carefully consider what its kiwi related information needs are for efficient management within the fence and for the wider role it has in the Otago community. If this process leads to a conclusion that the type of information presented in this report is of value in meeting either or both of these requirements, some alternative approaches might be worthy of consideration. a) An annual repeat, in modified form, of the project detailed in this report. b) As above, but supported by electronic listening/recording devices. A trial of these devices by the Ornithological Society has been carried out in conjunction with the human listener project and its results will be available in due course. At present the data provided by these devices is limited to identifying that a call (kiwi/male or female/number of notes/time) has been made, with loudness as a surrogate measure of distance. c) To wait until affordable devices are developed that can indentify individual birds from the acoustic pattern of their calls (which is under investigation), and/or have sufficiently accurate clocks (accurate to a 10th or even 100th of a second) to allow the pin-point positioning of a bird by the time difference in reception of the call by two or more devices. An array of these devices (which 13

must already exist for locating nuclear submarines) could be linked to a central computer which would be able to provide real-time information on location and behaviour of all kiwi that deigned to call. We presume such devices would still have problems with terrain features. d) As was stated in the abstract, we have been impressed by the usefulness of field knowledge in interpreting call data, and suggest that a track-section based systematic count of field signs (scat, feathers, probe holes, footprints, burrows, sightings) supported by the present generation of listening devices might be the more cost effective means of providing the same type of decision assisting information as has been presented in this report. e) If it was thought that knowledge of the position of nest sites would be useful, it might be possible to adapt the procedure of this study by having listeners or listening devices set up around the areas where pairs of birds were calling in this study. However, it should be noted that many hours of volunteer time could be required to do this. f) And finally, this report may require new recommendations when the recorded acoustic data is analysed as it will allow comparisons that may highlight the benefits and shortcomings of each methodology.

Valerie Fay and Michael Fay July 16th 2013