Bernhard Wessling (email: [email protected]) Individual recognition of cranes, monitoring and vocal communication analysis by sonagraphy Development and broad application of a powerful bioacoustic technique

Abstract A sonagraphical method for individual recognition of crane pairs and crane individuals for long-term monitoring and gathering of individual life history facts without the need to capture and band them will be described. Results in various regions (for grus grus over a period of 10 years) and with other crane (in Asia and North America) species will be shown. In addition to the monitoring capability, the method opens the possibility of analysis cranes' vocal communication and regionally specific "language" structures. The method was practically applied also in projects for the protection of endangered crane species, predominantly the Whooping crane, and here in the raising and training of captive reared cranes for release into the wild and ultralight airplane-led migration.

Introduction Before I started developing this new method, there was no method available for individually recognizing any bird species, hence also not cranes, and no indication whether that could be possible at all. The long version of this paper, published online here1 describes the status in detail and also that still until now, no broad monitoring of any bird species has been performed except the ones reported about below.

The method I developed a lightweight system consisting of a transportable minidisk recorder, fed by a long range microphone (Sennheiser 486) with highest sensitivity and resolution plus an intermediate amplifier ("booster"), resulting in digital files on minidisk and followed by analysis using two different computer based Fast Fourier Transformation analyses.

The most productive procedure is to be present near the breeding territories about 1 hour before dawn, well before sunrise, and to either wait for the morning unison call or provoque such call by displaying a suitable unison call file via a megaphone2. The method allows to record many calls at various places, from distance, without the need of penetrating the territory or to come even close to the nesting area.

Usual and practical distances are between 250 and 500 m, but recordings from a distance of 1 km or more have also been successfully made and analysed. The recorded files are transferred into a PC after the field work. The files are recorded in Mono, and transferred into the computer with 20 kHz sample rate.

The analysis is performed in two steps: 1. using the program "SoundForge 4.0", which generates a qualitative sonagram (Figure 1) between 0 and 2000 Hz – in contrast to earlier sonagram practice which show the full bands of overtones up to 3 or 6 kHz which is not practical and not necessary; the program is not made for voice or speech analysis; therefore, the resulting sonagram is not a data file, but only a screen picture which can be printed, but not be used for pattern analysis. It shows a qualitative picture of the call, it helps to identify noise like potential human voice,

1 Extended and more detailed version of this short proceeding contribution to be found here; a pdf can be sent by the author to interested people https://www.researchgate.net/publication/328676275_Individual_recognition_of_cranes_monitoring_and_vocal_communication_ana lysis_by_sonagraphy_Development_and_broad_application_of_a_powerful_bioacoustic_technique 2 Suitable files can be provided by the author to interested people disturbing bird calls (like geese, ducks, cuckoo) and to direct where to cut the files into useful pieces free from such disturbances.

2. based on "mathematica 4.0" (Wolfram Research), with a specially developed script [10] (protocol), a so-called "power spectrum" (Figure 2.2) is calculated (which is the plot of the intensities at certain frequencies, derived from the addition of all intensities at these frequencies over the time of the recorded call, a 3D spectrum, Figure 2.1); these results are data, or better: lists of data, which can be analyzed and compared. This analysis is preferably made between 600 and 1200 Hz at a very high resolution, and can be changed according to needs (e.g., there are cranes which call below 600 or above 1200 Hz). (With this program also sonagrams are created which are then available as 3-dimensional lists of data - frequency, time, intensity - for further analysis in the power spectrum, but not yet in the sense of a pattern or image analysis.)

The "power spectrum" was considered by me to be a "vocal fingerprint", „acoustic fingerprint“ or „voiceprint“ based on the fact, that the properties of the sound generating organ (the trachea) will determine the frequency spectrum of the generated sounds of an adult crane (after complete development of the voice).

Results (1): identification of crane individuals / pairs

In 1998, about 200 files from 7 pairs in their territories and outside of it, one adult unpaired male, and a few calls of unpaired youngsters had been recorded from late March to May. The main result was that the sonagram and the "vocal fingerprint" for a given pair are very stable and can be safely recognised (Figure 3). Calls from the same pair only differ by less than 5% (as calculated by frequency comparison) during a season or from year to year.

All calls, all the voiceprint spectra show enough different features from pair to pair so that they can be differentiated, cf. Figure 4. These differences are much larger than 5%. Also remating can nicely be identified (Figure 5).

So far unison calls and other calls have been recorded and analysed from 7 crane species:

- Common Crane (CC) in Hamburg (and neighbouring areas) during continuous 10 years, in total 25 different pairs 112 crane pair years, 61 different individuals had been identified; here, in addition, also some older video recordings given to me by different people were digitalized and analyzed as well, and broadened the knowledge; in Brandenburg during 4 years; and in a bigger study area in Mecklenburg (comprising around 120 breeding sites in 635 km² with 85 nesting pairs (in 2000), of which 57 territories had been visited and 52 pairs identified during 3 years with only 2.5 days recording per year;

- Red crowned Cranes (in captivity: Baraboo, ICF; Vogelpark Walsrode, Germany; wild on Hokkaido, Japan, and in the Demilitarised Zone in Korea), in total over 60 different wild pairs, 5 of which were banded (recordings from banded cranes in winter 99/00)

- Whooping cranes (WC) in captivity (Baraboo, ICF, and Patuxent, Washington - almost 20 pairs), in the wild in Aransas National Wildlife Refuge (USA), and in the breeding area in Wood Buffalo National Park (Canada), in total 80 different pairs;

- 10 pairs of sandhill cranes (captive ones in Baraboo, ICF, and some wild ones in ANWR) - White-naped Cranes (wild, DMZ in Korea), more than 30 pairs - Siberian Crane (in captivity: ICF, Baraboo, and Vogelpark Walsrode, 8 pairs) - Black-necked Cranes (captive in Hokkaido and Vogelpark Walsrode, 2 pairs).

Results (2) Banded wild birds

Before reporting on such experiments performed several years ago, it should be noted that it was also possible to record, analyse and assign captive crane pairs (especially Whooping Cranes, but several other species as well) with this technique, and that spectra of different calls of the same pairs recorded at different days show a comparable degree of similarity as do calls expressed by pairs in the wild which can be assumed to be the same as they live and call in the same territory.

Anyway, various calls from banded cranes whereby the birds were visually observed during the calling and recordingin order to eliminate potential remaining doubts. The following banded cranes have been recorded: grus grus: "Rosa" (banded) in 2001, 2003 and 2004 (Fig 6); "90-Morgenschlag" in 2001, 2003 and 2004 (Fig 3.2) "Zabelsee" (Zs) in 2001 and 2003 grus americana: pair # 1 "Herons Flats" (1999) (Figure 7) pair # 17 "Pipeline North" (the banded male was the oldest banded crane, at that time he was 23 years old; he lost its ring in 2001 but could be found again later.

Results (3): life history facts overview, (a) Hamburg / Klein Hansdorf 1998 - 2007 (see table 1)

- During 10 years of continuous monitoring, almost 2000 calls have been recorded and analyzed: 25 different crane pairs had been identified (112 crane pair years), 61 different individuals, 18 pairs spent more than 1 year in the area, 14 pairs at least 3 years represen- ting 80 crane pair years;

- out of 3 pairs, one individual was present during all 10 years (however, with different part- ners); pair M5F5 spent 9 out of 10 years, always with the same partners; pair M4F4 in 9 of 10 years, M4 in one year with a different partner, however partnered with F4 again in the following year;

- 6 pairs which spent at least 3 years (= 42.1% of those pairs) in the Hamburg area consis- ted all the years of the same individuals, 8 other pairs being here at least 3 years (57,1% of those pairs) had 10 new partners, M6 (also present in 9 out of 10 years) had 4 different female partners and 8 offspring (most successful male crane);

- only 2 pairs had spent all the breeding seasons during the monitoring period in the same territory; many territory changes have taken place.

Results (4): Life history facts – some details

Such very interesting and surprising detailed life history can be found in the extended version (footnote 1, page 1), most from 10 years Hamburg area, but also others. International projects Japan (Hokkaido): On this island, recordings have been made once in winter and once in spring, showing that also red-crowned cranes can successfully be „voiceprinted“ (individually recognized). Although everything was well prepared including hardware, which I had supplied, the monitoring was not continued even though I had offered to analyze recorded calls. More details – including about some specific vocal codes – can be found in the extended version (footnote 1, page 1).

Korea (demilitarized zone): Starting with the many recording gathered in Japan, calls of wintering red-crowned cranes have been collected in the DMZ between North and South Korea, the call pattern (= „language“) of Japanese (Hokkaido) and Asia mainland (China, Russia) RC has been compared. It was found that cranes from these different populations, separated since about 200 years or more, have developed a different language and would not understand each other (see also footnote 1, page 1).

USA / Canada: The certainly most important study was connected with the North- American Whooping Crane (WC), the most endangered crane species with (at that time, around year 2000) only 188 living individuals in the last surviving wild and self-reproducing population. Banding of young whooping cranes has been stopped about 12 years before. On behalf of the Whooping Crane Recovery Team (WCRT, USA / Canada), I have taken recordings of calls of wild grus americana pairs in 2 winters in the wintering area; later, with the help of recordings made by 3 WCRT members in the breeding and in the wintering area of the last wild and self reproducing population of the very endangered Whooping Crane (grus americana), in total 9 seasons (5 spring/summer and 4 winter seasons) had been analyzed. Both areas are vast and hard to access, especially the breeding grounds in WBNP, where each crane territory has to be accessed by helicopter. The Whooping Crane territories are about 4 times larger than a common crane‘s territory, and WC defend territories also while hibernating.

In my first expedition to the wintering grounds in the Aransas National Wildlife refuge in Texas in 1999, 27 pairs have been characterised with the "vocal fingerprint" (voiceprint). During the 2nd expedition to Aransas, I recorded 250 calls, identified 32 pairs, 21 of which I had known from the previous winter. (Figure 8 shows an example of the territorial dynamics.)

During in total 9 seasons, partially with the help of other people, 918 calls had been recorded and analyzed, belonging to 80 different pairs. These were 85% of all breeding pairs which had been identified. 11 of the pairs found in WBNP have been identified in ANWR as well (Figure 9). I was able to draw number of interesting conclusions:

- the mortality is higher than in other crane species (probably due to high degree of in- breeding);

- at least 14% of the pairs have a different partner in the following season which is less than in CC in my Hamburg / Klein Hansdorf study area; this could be due to 3 reasons: a) WC do not change partners as easily as Common Cranes do, they are not as social as CC (WC do not migrate in flocks but as a pair or family and keep territories also in the wintering area, by the way much bigger than CC territories in spring / summer: ~2 km²) b) WC simply can not find another available „single“ even if they wanted as there were only little more than 180 individuals at that time c) I may have overlooked remating events as male and female call frequencies are overlapping (see Figure 7) which is not the case in CC, so it is more complicated to differentiate between male and female frequencies; - 20% of the pairs can be found in a new territory, much less than I found in CC, but much more than was guessed by WC experts; the maps with the territories are showing remarkable dynamics;

- on Matagorda Island (part of the ANWR), territory changes are significantly more common than on the mainland;

- using my voiceprint technique, I had identified 11 more pairs on ANWR mainland than had been detected by aerial survey, on Matagorda 3 more pairs;

- it was especially interesting to see that on Matagorda Island more than 50% of the pairs are neighbours which are also neighbours in the WBNP breeding grounds!

Whooping crane reintroduction project The growing knowledge about the importance of vocal communication for cranes was also an important part of the project (carried out by the "Whooper Crane Recovery Team") to establish a second migrating population by release of captive reared cranes into the wild. (A non-migrating population is in the process of being established in Louisiana, after a comparable project for Florida was stopped.)

As a last test run before doing so with captive reared Whooper cranes, the team was flying the same way with captive reared sandhill cranes. For the first time in such raising and training for UL-led flights, calls recorded by me from wild sandhill cranes were used to communicate with the young cranes. I provided 6 different calls which were played using wrist-held small loudspeakers and powerful megaphones attached to the airplanes. The calls are interpreted to be used by the sandhills with the understanding of "attention", "danger", "continue flight", "come here / contact", and the guard and the unison calls.

The first experiences had been outstanding: the vocal imprinting seems to be much more powerful than pure visual imprinting (after hatching): whereby it was very complicate in earlier trial projects to bring the young cranes to follow the airplane in the first weeks (because they preferred to stay the ground together with the - costumed - caretaker), they now followed the subject or object making the "contact" call. It is easy to tell the cranes to follow the airplane or the caretaker, to go in or out of the fenced area. It was even possible to call a group of young cranes back to the training centre when they had been "kidnapped" by a wild crane pair.

In 2001, the first class of young captive-reared whooping cranes was reared and trained using my calls; I provided the same set of vocal codes, only those recorded from wild Whooping Cranes. The young cranes followed the UL airplanes from Wisconsin to Florida and returned to Wisconsin in the following spring on their own. In total, including up to 2015, 15 classes of cranes have been guided to Florida. The Wisconsin population is growing, re-introduced birds are mating and breeding, however due to several drwawbacks (mainly: black flies) not yet self-sustaining.

Conclusions

This sonagraphical method for identifying crane individuals provides a relatively simple and easy to handle tool for identifying and monitoring cranes and their life (partner and territory fidelity). It also allows to count how many different territorial crane pairs are present in a certain area, much easier, more productive and more reliable than by just visual observations.

The collection of recordings made by systematic visits to the areas of interest especially early in the morning, but also statistically distributed over the days gives a picture of the minimum number of pairs (and individuals) present in the area under supervision.

Wherever it is not possible or not advisable to band (which is the majority of areas), this method is the only method which can practically be applied by almost every ornithologist or observer. A long term monitoring of cranes leading to individual life history facts is possible. All these advantages without even once touching the cranes, from distances between their flight distance up to 1 or 2 kilometres.

This method is even superior to banding as one would usually band young unfledged cranes, however, they will later mate with unbanded cranes, males usually in the breeding grounds, females usually (far) away. Sonagraphy can identify pairs from the time when they begin to unison call, even before they start nesting.

In research projects where a continuous and dense banding is in place, acoustic monitoring is an excellent additional tool and provides information not accessible by visual observation of the banded birds. It has the advantage that the cranes do not need to be disturbed at all, it is even not necessary to see them (and it is preferred not to be seen by them).

Cranes are much more flexible as one would conclude from just visual observations. They change their territories (in CC: around 40% of the territories in a given area are occupied by a different pair than in the previous year) and partners to a surprisingly high degree (CC: around 50% of the crane pairs divorce or get a new partner during their life).

It is therefore not any more unlikely that partner loyalty may be a matter of the degree of the partners "fitting together" and a change of the mate a matter of choice by both sexes. This is supported by our observations in Hamburg, where a single adult crane tried for a whole spring season to win a mate bound with another male, however without success. Together with behaviour observations made by me over years in Hamburg, indicating a higher degree of cognitive abilities and even some degree of awareness, these results may motivate further deeper research both in the field as with captive cranes. They do at least demand more respect for them as subjects (individuals) rather than objects.

Regarding my sonagraphical individual recognition method, it is a pity to see that it was not used at all for acoustic monitoring of cranes (neither of other birds). Except for one very small study involving a handful of crane pairs over 3 years in Czech Republic [17] which was based on my method, no other paper was found in the literature nor had anybody told me that acoustic monitoring was performed over years with many birds anywhere else, regardless what method was used.

References

(cf extended paper: footnote 1, page 1) Table 1: Pair recognition in Hamburg Duvenstedt / Klein Hansdorf Book 1998 – 2007 detailed table to be found in footnote 1, page 1

Summary:

- 25 different crane pairs (including remated pairs with 1 individual from starting pair) - 112 crane pair years - 61 different individuals - 18 pairs at least 2 years in the area - 14 pairs at least 3 years representing 80 crane pair years - out of 3 pairs, 1 individual present during all 10 years (however with different partners); pair M5F5 spent 9 out of 10 years, always with the same partners; pair M4F4 also in 9 of 10 years, M4 in one year with a different partner, however partnered with F4 again in the following year - 6 pairs which spent at least 3 years in the area (= 42.9% of 14 pairs) consisted all the years of the same individuals, 8 other pairs being here more than 2 years (57,1% of those pairs) had 10 new partners, M6 (also present in 9 out of 10 years) had 4 different female partners and 8 offspring (most successful male crane); - only 2 pairs had spent all the breeding seasons during the monitoring period in the same territory; many territory changes have taken place.

Next pages: attachments (for complete attachment, use the link in footnote 1 on page 1) Fig 1 Sonagram

Fig 2.1 3D power spectrum from „mathematica“

Fig. 2.2 power spectrum generated from the data in Fig 2.1 1

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675. 750. 825. 900. 975.1050.1125.1200. Fig 3.1 M1F1 in 1998 (top) and 1999 (bottom)

Fig 3.2 Brandenburg territory „90-Morgen-Schlag“: in 2001 and 2003 same pair, 2004 male remated with different female Fig 4 Two different pairs, M5F5 (top) and M2F2 (bottom)

Fig 5 Remating: M6F6 (1999, top), M6F11 (2000, bottom)