Open access peer-reviewed chapter - ONLINE FIRST

The Vocal Activity of Twelve African Owl Species

Written By

Heimo Mikkola and Anita Mikkola

Submitted: November 9th, 2021 Reviewed: February 22nd, 2022 Published: April 25th, 2022

DOI: 10.5772/intechopen.103887

IntechOpen
Owls - Clever Survivors Edited by Heimo Mikkola

From the Edited Volume

Owls - Clever Survivors [Working Title]

Dr. Heimo Juhani Mikkola

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Abstract

Vocalization of different species of owls carries a lot of scientific information on their distribution and diversity. There is little information on the owl vocalizations in the tropical environments. The calling of 12 African owl species was studied in Malawi 1993–1998, and in The Gambia 1998–2004. The direct listening method was used to collect some 2062+ vocal records mostly at the house gardens or sometimes on the balcony at wildlife lodges and rural hotels. Owls are normally vocal most actively especially just before breeding, but in this material, the peak months coincided very little with the given breeding times in Malawi and The Gambia. It is possible that the validity of the breeding times is not enough, but other reasons are not clear because the sampling was opportunistic rather than systematic. If vocalizations are used to estimate owl populations, it is important to identify the environmental factors affecting owl calling. Heavy rain and wind were silencing the owls or at least made it impossible to hear their voices due to the background noise. Barn Owls Tyto alba were often calling immediately after the heavy wind calmed and no precipitation was falling. The temperature is not so important if the other conditions are suitable for calling, Barn Owl and Pearl-spotted Owl Glaucidium perlatum were vocal as well in +37°C as in +15°C. Some owl species may increase vocal displays during full moonlight (like the African Barred Owlet Taenioglaux capense, Pearl-spotted Owl, and Southern White-faced Owl Ptilopsis granti) but others call less or not at all during the full moon (Barn Owl). The impact of the full moon was not that obvious as the bright sky can also activate the Pearl-spotted Owl. Barn Owl started to call actively again when the moon was diminishing to 60% of its full size and its luminosity. It was noted in The Gambia that the obvious predation risk and interference competition was altering the vocal activity of the African Scops Owl Otus senegalensis, which stopped calling when the Barn Owl was active. Barn Owl is a predator that can attack the smaller African Scops Owl. In Malawi Spotted Eagle Owl, Bubo africanus calling bouts were suspected to silence the Pearl-spotted and Southern White-faced Owls as the larger owl could prey on these smaller owls if hearing their calls.

Keywords

  • owl vocalization
  • daily activity
  • seasonality
  • Strigiformes
  • Malawi
  • The Gambia

1. Introduction

Most owl species have nocturnal or crepuscular habits, and due to darkness, owl communication relies greatly on vocal activity. In temperate regions, it is the owls which in late winter or early spring fill the night with music, and in the tropics, owls are just part of a formidable chorus of animal songs and calls. Calls are completely diagnostic of species, and owls are likely to recognize other individuals by voice as by sight during their travels in the dark [1, 2]. Every vocalization in an owl’s vocabulary has a precise meaning in the communication with conspecifics. Calling is advertising their presence, to locate and attract potential mates, and to establish or to reaffirm breeding territories [3].

In Africa, some owls call almost daily at sunset or soon thereafter, and others are vocal in the still hours before dawn. Often their calling bouts are only momentary and fragmentary, but sometimes, especially just before breeding, they are loud, complex, and prolonged, extending almost throughout the night [4]. Calling at dusk may be mandatory—at least in species that reside in their territories throughout the year—as a notification to neighbors that the owners are still in residence. Later calling may be timed to take advantage of good conditions for sound transmission, or it is a response to social pressure such as neighbors calling, intruders present in the territory, or prospective mates being noticed [4].

The chapter tries to tackle the following questions: (a) What are the main factors influencing the temporal patterns (daily and seasonal) of vocal behavior of African owls; (b) how some environmental variables, like moon, wind, and rain, will influence the calls for some species, and (c) if and how useful vocal records are in surveying the distribution and population size of the different owls. At the same time, this chapter will also give some anecdotes collected on the human nightlife and the nocturnal behavior of some domestic animals and wildlife near the house.

Nowadays, it starts to be outdated and old fashion to collect vocal activities of any owls just by listening and writing down the results as the use of automated bird presence recognition is becoming the modern method for wildlife monitoring. It is felt to be more beneficial for avian biodiversity conservation [5].

This could be the last opportunity to put on record these old African owl call studies from Malawi and The Gambia between 1993 and 2004.

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2. Material and methods

The vocal activity of 12 African owl species was recorded in Malawi 1993–1998, and in The Gambia 1998–2004. The main species studied were as follows:

Barn Owl Tyto alba (Malawi and The Gambia).

Pearl-Spotted Owl Glaucidium perlatum (Malawi and The Gambia).

Southern White-faced Owl Ptilopsis granti (Malawi).

Northern White-faced Owl Ptilopsis leucotis (The Gambia).

Spotted Eagle Owl Bubo africanus (Malawi).

To a lesser extent also African Barred Owlet Taenioglaux capense, African Scops Owl Otus senegalensis, Eurasian Scop Owl Otus scops, Greyish Eagle Owl Bubo cinerascens, Milky Eagle Owl Bubo lacteusand Pel’s Fishing Owl Bubo pelihave been studied. And a few literature references are given on African Wood Owls Strix woodfordiithat was rarely heard only in Malawi. Summary of the species studied and the number of observations are listed in Table 1.

Countries/SpeciesMalawi(M)
Number of calls
The Gambia(G)
Number of calls
Total calls recordedRemarks
African Barred Owl(ABO)20020Occurs only in The Gambia
African Scops Owl (ASO)102030
African Wood Owl (AWO)505Rare in The Gambia
Barn Owl (BO)222504726
Eurasian Scops Owl (ESO)03030Rare in Malawi
Giant or Milky Eagle Owl (MEO)10212
Greyish Eagle Owl (GEO)0++Gambia Sound recordings exist
Northern White-faced Owl (NwfO)06262Occurs only in The Gambia
Pel’s Fishing Owl (PFO)+1010Occurs but not heard in Malawi
Pearl-spotted Owl (PSO)74358801
Spotted Eagle Owl (SEO)54054Occurs only in Malawi
Southern White-faced Owl (SwfO)3120312Occurs only in Malawi
Other animals:
MosquitoregularregularnrCft!
TermitesseasonalrarenrCft!
Hyenaregular0naNot heard in The Gambia
DogsregularregularnaCft!
RoosterregularregularnaCft!
Spitting Cobrarare0NrNot seen in The Gambia
Human activities:
African drumsregularregularnaCft!
Muslim prayers0regularnaHeard only in The Gambia
Heavy shootingregular0naHeard only in Malawi
Total of calls1376+686+2062+

Table 1.

Summary of studied 12 owl and number of calls recorded in Malawi 1993–1998 and the Gambia 1998–2004.

Other animal species and some disturbing human activities are also recorded. In the brackets, all abbreviations are used in the text when presenting the results. In this table: No = Number; na = not available; nr = not relevant; and Cft = Cf the text!

Direct listening was the method used and mostly at the house gardens or sometimes at lodges and hotels on the balcony. Like most Africans, many evenings and even night hours were spent outside the house but sometimes a good TV program was disturbing the study as was heavy rain and strong wind. Similarly, the annual leave spent in May–June in Finland explains a low number of observations in those months. Field notes included time, weather especially if something unusual in wind, rain and temperature, and the visibility and phase of the moon.

Similarity index

In Tables 2 and 3, the similarity index has been calculated to show if there are noticeable time and seasonal differences in the calling activities between Malawi and The Gambia. The index used is modified from MacNaughton & Wolf’s [6] “Index on Community Similarity”:

OwlBOBOPSOPSOSwfONwfOSEO
Country/HoursMalawiGambiaMalawiGambiaMalawiGambiaMalawi
00:00–01:0010.411.53.53.44.2
01:00–02:005.95.21.70.63.213.0
02:00–03:009.93.01.56.91.911.3
03:00–04:005.42.20.66.93.512.95.6
04:00–05:004.94.41.56.95.814.53.7
05:00–06:000.93.813.814.53.7
06:00–07:001.01.110.36.5
07:00–08:000.93.4
08:00–09:000.3
09:00–10:000.4
10:00–11:000.4
11:00–12:001.3
12:00–13:000.5
13:00–14:000.9
14:00–15:000.1
15:00–16:000.6
16:00–17:001.16.9
17:00–18:005.1
18:00–19:0018.05.512.18.433.3
19:00–20:009.011.37.45.320.64.813.0
20:00–21:005.018.613.51.711.614.511.1
21:00–22:009.915.521.010.319.69.77.4
22:00–23:0012.213.120.53.519.35.6
23:00–24:008.610.111.08.64.58.13.7
Total100.1100.1100.0100.0100.0100.0100.1
No of calls222504743583126254
Similarity Index0.340.260.18

Table 2.

Timing of the African owl calls as hourly percentage from the total calls.

BO = Barn Owl; PSO = Pearl-spotted Owl; SwfO = Southern White-faced.

Owl; NwfO = Northern White-faced Owl, and SEO = Spotted Eagle Owl.

OwlBOBOPSOPSOSwfONwfOSEO
Country/MonthMalawiGambiaMalawiGambiaMalawiGambiaMalawi
January1.47.510.313.1
February3.61.78.2
March2.20.81.79.858.8
April25.212.11.0
May19.83.0
June0.40.6
July9.029.90.60.6
August6.818.20.93.42.62.9
September4.98.75.63.513.1
October9.05.929.920.78.2
November18.514.162.943.195.245.932.4
December3.27.90.13.51.75.9
Total100.0100.0100.0100.0100.0100.0100.0
No of calls222504743583126254
Similarity Index0.420.210.05

Table 3.

Timing of the African owl calls as monthly percentages from total calls.

BO = Barn Owl; PSO = Pearl-spotted Owl; SwfO = Southern White-faced.

Owl; NwfO = Northern White-faced Owl, and SEO = Spotted Eagle Owl.

SimilarityIndex=2m/a+b

in which: a = percentage in Malawi, b = percentage in The Gambia, m = minimum percentage in either country. The nearer 1.0 the index is, the higher is the similarity between the countries and less important are the noted differences. Due to the non-systematic nature of material collection, no further statistical tests were undertaken.

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3. Results

3.1 Timing and seasonality of the calls

Table 2 shows the hourly timing of 1955 calls listed for Barn Owls; Pearl-spotted Owls; Southern White-faced Owls; Northern White-faced Owls; and Spotted-Eagle Owls. Most of the Barn Owl calls (18% of all calls) in Malawi were heard between 18:00–19:00 h. and in The Gambia between 20:00–21:00 h. (18.6%). Daytime calling was recorded only in The Gambia. The similarity index between the timing of the Gambian and Malawian Barn Owls was low 0.34 (Table 2).

Pearl-spotted Owl’s most active calling took place between 21.00 and 22:00 h. in Malawi (21%) and 18:00–19:00 in the Gambia (12%). In the much larger material from Malawi, also the daytime calls were recorded almost every hour of the day, while in The Gambia, there was a real break in the vocal activity between 08:00–16:00 (Table 2). Lack of daytime calls in The Gambia may explain the low similarity index between the two countries, 0.26.

In Malawi, the Southern White-faced Owl had the most active calling time 19:00–20:00 h. (20.6% of all calls), and no call was recorded between 05:00–18:00. In The Gambia, Northern White-faced Owl was most active in the small material between 03:00–06:00 with 42% of all calls. The similarity index between The Gambian and Malawian White-faced Owls is very low (0.18) (Table 2). This could be partly due to the generous size difference in the materials but could also support the species separation.

Spotted Eagle Owl material from Malawi was much larger but every night callings AM was hearing when preparing the dinner in the kitchen were not written down daily. However, even all noted calls show that Spotted Eagle Owl is the most active vocally between 18:00–19:00 h. (33% of all calls). No daytime calls were recorded between 05:00 and 18:00 h. (Table 2).

The seasonality of the vocal activity on the same owl species is presented in Table 3. Barn Owl was most vocal in April and November in Malawi and in July, August, and November in The Gambia but calls were heard all year round in both countries, especially when noting that June was not sampled due to the absence in the country. The breeding season of the Barn Owl in Malawi is May–November and September–April in The Gambia [7]. The similarity index between The Gambian and Malawian Barn Owls was a little higher in the months (0.42) than it was in the hours (0.34).

In Malawi and The Gambia, Pearl-spotted Owl was vocally active mainly in October and November, in Malawi (93% of all calls) and in The Gambia (64% of all calls). Interestingly, these months are not coinciding at all with the later presented breeding seasons for this owl neither in Malawi (August–September) nor in The Gambia (February–April) [7]. The similarity index was almost the same in the months as it was in the hours (0.21 vs. 0.26) (Tables 2 and 3).

In Malawi, the Southern White-faced Owl was heard almost entirely in November (95%), again not coinciding with the peak breeding season stated to be August [7]. In The Gambia, the Northern White-faced Owl had in this small material two clear peaks, one in January and the other in September and November (Table 3)—once more these months are not well in line with the listed breeding seasons [7]. The similarity index was almost nil (0.05) between these closely related species (Table 3).

In Malawi, Spotted Eagle Owl had two peak months, March (nearly 60% of all calls) and November (32%). These months are also outside the given breeding season limits, August–October, in Malawi [7].

3.2 Some interesting owl calling observations

3.2.1 Barn Owl T. alba

M: 03/11/96 own Rooster started to call 03:55 and BO vocal immediately after the Rooster stopped 04:05.

M: 12/10/97 BO very vocal 02:00–02:05 when the Rooster started to call as well.

G: 04/08/99 BO calling 05:34—still dark and the Rooster started at the same time.

G: 06/08/99 BO calling once 06:06 and again 06:07—thrushes singing already and Rooster calling, even it was still dark, but daylight was coming soon after.

3.2.2 Southern White-faced Owl P. granti

M: 12/11/96 SwfO calling continuously 8–10 s intervals 04:20–04:30 when two Pearl-spotted Owl also calling, but one nearest the SwfO started to warn whistle “kii-kii-kii.” Last call of PSO 04:45 when started to be light and other birds singing so loudly that it was difficult to hear the owls any longer.

M: Rooster calling 14/11/96 with the SwfO one after the other 03:00–03:30 h.

M: 20/11/96 SwfO calling 00:50 onward until 01:00 with two PSOs every minute together and unnoticed from each other.

3.2.3 Pearl-spotted Owl G. perlatum

M: 01/11/96 continuous calling of at least 6 owls: 3 PSO and 3 SwfO together and on top of each other 21:15–21:22 Hyena yelling, and dog barking silenced the PSO’s and SwfO’s, but SEO calling over the dogs and hyena 21:40–21:45—maybe that large owl silenced the smaller owls (See Discussion).

M: First gun shooting from distance 22:19 and endless drumming from 2 to 3 location. Sudden silence with dogs and owls—only Mosquitos made noise!! Dogs getting mad again 22:59 as well as the African drums. First BO called 23:00 and two PSO’s continued calling 23:20–23:34.

3.2.4 Weather impact

M: 02/11/96 no owls 19:18–20:30 because of a heavy wind rising and a new rainstorm building up.

M: 04/08/98 BO calling next to the FAO office 18:00 despite very cold (+15C).

weather.

G: 14/09/98 massive storm during the night and BO calling immediately after rain stopped at 03:30 h.

G: 30/06/99 BO calling behind the house 23:50—rainy day, but in the evening the rain stopped, bats also very active-eating mangoes!

G: 11/07/99 BO calling at 22:28—rainy day, but the rain had stopped before the owl was calling.

G: 11/08/99 BO calling 22:00 behind the house after three days of heavy rains explaining why not heard in last few days.

G: 22/08/99 BO calling 22:05 after a heavy storm, although still raining slowly.

G: 07/09/99 BO calling 19:40 after heavy rain.

G: 27/12/99–02/01/2000 very few BO calls—if any—weather relatively cool ca. +20C at lowest and often heavy winds!

G: 01/11/2001 PSO calling in daylight (07:00) in Pakalinding after heavy rain.

3.2.5 Full Moon impact

M: BO calling 23/04/97 00:20 but total silence during the full moon 24–26/04/97.

Vocal again on 27/04/97 22:15 onward when the moon was some 60%.

M: 10/11/97 Club Makokola PSO calling in moonlight 20:00–20:10—very hot +37–38°C, humid and no wind.

G: 23/01/98 PSO calling in flight at 06:00 and again 07:00 when still very dark this time of year and relatively cold (+16°C) but cloudless sky and no wind.

3.2.6 Some remarkable sites

We don’t knows very many sites in the world where one could hear more than one owl or a maximum of two species by sitting comfortably in a balcony chair with a glass of wine. However, in Africa, we were lucky enough to have all the rented houses in such places, especially in Malawi (five different houses in Lilongwe and two in Cape Point in The Gambia). Some wildlife lodges were such wonders both in Malawi and in The Gambia. We want to mention especially Njobvu Safari Camp in Malawi where at least ASO, PSO, PFO, and SEO should be possible although 05/08/95 only PSO was calling several times after 23:00 h; the Dream Bird Hotel in Georgetown, The Gambia, where one can hear, for instance, on 22–23/04/2003 ASO and several PSOs; Fullady Camp where one can listen to ASO, NwfO, and PFO during the same night; Janjanbureh Bird Safari Camp wherein one night 12–13/11/2000 several voices of ASO, ESO, and PSO were recorded, and another night10–11/01/2001 a record number (6) of owl species were heard as follows: ASO, BO, MEO, NwfO, PFO, and PSO. To add a few favorite sites: Sindola Camp particularly good to hear PSOs; Tendaba Camp where ASO, BO, NwfO, PFO, and PSO are regular daily and nighttime guests, and the last but not the least Kiang West National Park that can offer ASO, GEO, MEO, and NwfO (John Clayton, in litt.).

3.3 Additional remarks on less-studied species

3.3.1 African Barred Owlet Taenioglaux capense

One house in Lilongwe, Malawi, had at least five owl species calling often in the evenings. For instance, on 05/11/95 ABO calling together with the SwfO between 19.00 and 19:20 h in the full moon. The same species heard following nights but not so actively as during the full moon.

3.3.2 African Scops Owl O. senegalensis

In Namibia near Windhoek, ASO calling activity was studied near the nest and no calling took place before the last light about 25 min after sunset. The male called most actively during the first hour of darkness (19:00–20:00) but some calls were heard throughout the night until 06:00 [8]. This coincides well with a Malawi record when the ASO was vocal 05/11/95 between 19:00 and 19:20 h. In The Gambia, ASO calling 19:30–20:30 near Kanifing on 15/11/2000 together with more than two NwfO’s; in the Kiang West National Park ASO frequents near the camp (John Clayton, in litt.); near the Fullady Camp, 15/02/99 ASO calling in the evening. Same in the Tunku Creek, near Tendaba Camp, after 17:30 on 11/03/99 (Wandi Touray, in litt.). Janjanbureh Safari Camp 11/01/2001 AOS vocal between 03:20–04:00 but only when BO was not calling. BO vocal at 21:13; 03:20, regular 04:30–05:05 and last morning call 05:45; See Discussion); Eddy’s Hotel in Farafenni 30/10/2002 ASO calling around 05:00 in the morning regularly but not so actively as nearby PSO and NwfOs; Georgetown Dream Bird Hotel 23/04/2003 AOS calling from distance between 02:00 and 03:00 h.

3.3.3 African Wood Owl S. woodfordii

In a study in Kibale National Park, Uganda, it was noted that the vocalizations of AWO were more numerous during the full moon and on clear nights [9]. Very few call records were made in this study, although one AWO was recuperated at home in 1982 in Ivory Coast. In Malawi, in the hill forest of Zomba AWO was said to be very common (John Wilson, in litt.). In Lilongwe one AWO was calling in the dawn at 18:30 on 14/11/93. In the Kamuzu One, dam AWO was seen just before lunchtime on 26/06/95. One pellet was found under the roosting place, and it contained one house mouse Mus musculus. In The Gambia, AWO was never hear but one was seen near the Abuko Education Centre 15/11/2000 (Solomon Jallow, in litt.).

3.3.4 Eurasian Scops Owl O. scops

On MacCarthy Island in The Gambia “frog-like” calling of ESO was heard 12/11/2000. That owl calling 8 to 9 s intervals almost all night. As the owl was turning its head and changing the site, one felt there being several of them calling. Next night in the Bird Safari camp ESO was vocal 01:00–01.30 h with a very short “grrr” notes and another owl was answering always with whistling type of voice. Then, 02.40 ESO gave a Little Owl like “kuiv-kuiv-kuiv-kuiv” call and another owl responded with a similar call.

3.3.5 Giant or Milky Eagle Owl B. lacteus

In Malawi, we got a young MEO what Dr. Lawrence had confiscated from beachboys in Senga Bay on 11/09/1994 (Figure 1). It was estimated that the owl was born ca. 22 August. A month later the weight was already about 500 g and wing feathers showing already. Two-month old was flying fluently. This owl was in the house until 14/04/95 but stayed in the garden even after that. As a farewell show, it started calling in a tree where we had a nest box. Between 22:00 and 23:30, it was calling loudly without any breaks. That made the dogs crazy, but they calmed down when told that it is our owl. MEO kept calling even if we walked with the dogs in the garden. In July 1995, John Alder found an MEO nest in Lilongwe Nature Sanctuary, not far from the house. It was tempting to think it was our owl. It was possible only to post confirm the breeding by finding below the nest a fresh MEO wing feather on 15/11/96.

Figure 1.

Young Milky Eagle Owl Bubo lacteus (left) and Spotted Eagle OwlBubo africanusin their large open-air closure in our house in Malawi. Photo: Heimo Mikkola.

In the Gambia, MEO was seen in both Abuko and Tendaba in December 2003, but no calls were recorded; in Kiang West National Park MEO pair duetting near the camp in 1998 but timing was not taken down (John Clayton, in litt.); Janjanpureh Safari Camp MEO calling bouts heard two times during the night on 11/01/2002.

3.3.6 Greyish Eagle Owl B. cinerascens

After having kept three GEOs at home both in Ivory Coast (1983–1984) and one in The Gambia (2001–2002) to recover from serious mal-handling of humans, we never heard them calling. Based on that, it was concluded that GEO is a much more silent species than the closely related Spotted-Eagle Owl many of which had also been recuperated at our home in Malawi [10]. Luckily the modern sound recordings from The Gambia of breeding and non-breeding GEOs have proven that this owl is not mute. Clive Barlow’s recordings will be part of an extensive study to be undertaken by Magnus Robb of the Sound recordings [11].

3.3.7 Pel’s Fishing Owl Bubo peli

M: One was supposed to hear PFO in Njobvu Safari Camp but on 05/08/95 this failed as it did also later in Malawi. In the Liwonde National Park, the African Cuckoo Hawk Aviceda cuculoideswas seen to attack the PFO in September 1996 (von Bechtolsheim, in litt.).

G: Bao Bolon swamp 05/02/98 PFO calling at 08:00 until 09:10 h; faint but a record shot of moans (Clive R. Barlow in litt.).

G: Fullady Camp 15/02/99 PFO calling between 02:00–03:00 during the night.

G: Bao Bolon 11/03/99 PFO seen at 17:30 h. (Wandi Touray, in litt.)

G: Bao Bolon swamp 28/08/99 PFO near the broad river 10:30 h sitting in a large tree but escaping after an intensive binocular session.

G: Bao Bolon 31/10/2000 two PFOs (a pair) sitting in a tree at 09:00 drying themselves in the morning sun.

G: Kissi end of Bolon 30/09/2001 a new site for the PFO (Wandi Touray, in litt.)

G: Janjanpureh Safari Cam 11/01/2002 PFO calling three times during the night.

3.3.8 Nightlife remarks

3.3.8.1 Human activities

M: Heavy shooting normally with AK47Kalasnikov’s automatic rifle: 01/11/96 first rifle shooting from distance at 22:19 and endless drumming from 2 to 3 location; 02/11/96 shooting at 18:48; 08/11/1996 rifle shooting 22:59; 09/11/96 00:05 and 23:01; 13/11/96 at 22:08. Malawi had serious security problems due to political turmoil before the death of the old President.

M: African drumming took place often: 01/11/96 drumming started 22:03 and Spotted Eagle Owl vocal again 22:05.

In G, there was not much shooting, but Muslim prayers sometimes stopped owls calling: Two Pearl-spotted Owls calling at 02:00 at regular intervals until the Muslim Praying started in the Mosque at 05:00 when it was still dark but hot and calm on 23/04/2003.

3.3.8.2 Mosquito

Mosquitoes are scaring people in Africa as they carry malaria which has killed more people than any other disease this far. Mosquitoes make a whining sound instead of a buzz. They are most active from dusk to dawn.

M: 02/11/96 Mosquitos started whining at 21:34 when the wind was over and no rain—before that a heavy wind and a rainstorm, temperature + 22C.

M: 09/11/96 mosquito whining started already at18:46 h.

3.3.8.3 Termites

M: Incredible termite attack stopped all hearings—hundreds of female termites decided to enter our house from 23:40 onward on 01/11/96 when the temperature was +22 C.

3.3.8.4 Hyena

M: One of the most disturbing animals in owl hearing was nearby moving Spotted Hyena Crocuta crocutaalso known as “Laughing hyena” or “Tigerwolf.” Its loud “who-oop” call, along with maniacal laughter is among the most recognizable sounds in Africa. Whoop sound can be heard more than 5 km away. Our dogs (Figures 2 and 3) heard it always well before us and their crazy barking was stopping us the hearing neither the hyena nor the owls. In Malawi, hyena populations occurred in those times at reasonable densities but have since gone down due to growth in human population, habitat destruction, and reduction in prey [12].

Figure 2.

Turo would like to taste the day-old chicken menu of the Spotted Eagle Owl. Photo: Anita Mikkola.

Figure 3.

Pepe testing the friendliness of the young Spotted Eagle OwlBubo africanusin Malawi. Photo: Anita Mikkola.

M: Hyena calling 01/11/1996 and heavy dog barking spoiled owl listening at 20:30–20:40, “Turo” very excited and ready to go for the hyena 21:30; our dog’s hyena barking started 19: 32 on 09/11/96—hyena continued at 23:10 but the dogs were too tired to bark.

M: Hyena howling agitated the dogs: 14/11/96 at 20:17 h.

M: Hyena hysteria again: 16/11/96 at 23:33 h.

3.3.8.5 Spitting Cobra

M: Somewhat disturbing was when a large snake, most likely spitting cobra Najaspp. took all attention for 20 min followed by the African drums at 19:29 on 13/11/1996.

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4. Discussion

Before commenting 2062+ owl calls recorded in Malawi and The Gambia below is short summary for each species on what the handbooks [7, 13, 14, 15, 16, 17] and papers [18, 19, 20, 21, 22, 23] say about the calling and main breeding times of these species:

African Barred Owlet: Late afternoon one can hear a repetitive, mournful “krroo, krrooo, krrooo” call rather like that of a Ring-necked Turtle Dove Streptopelia capicola(Previous Cape Turtle Dove). It lacks the vivacity of the Pearl-spotted Owl’s crescendo whistle [13]. Another book says: “Its call is a series of 6–10 low, whistled notes with a half-second interval between notes: ‘hue-hue-hue’; usually 2–6 second pauses between series. Series may rise and fall in volume and sometimes one series follows immediately by another. Calls mainly at night but sometimes in daylight” [7]. A third book describes the voice: “Repeated fairly high-pitched series of notes ‘purr purr piu piu piu piu’, rising slightly in volume; also 2-syllabled slightly trilled ‘prr-purr, prr-purr’, second note slightly higher than first.” [14]. In Malawi, the breeding season is October [7] and Southern Africa from September to October [14].

African Scops Owl: This owl calls regularly in the evening at dusk, the female and male answering each other with an insect-like ventriloquial “prrrup” at approximately five-second intervals. It is a call that carries over a considerable distance and, if one is sitting by a campfire, it immediately enhances the whole bushveld atmosphere. Often, however, one may not recognize it as an owl at all [13]. The call resembles insect voices so much that most likely it was missed often on noisy African nights, especially in Malawi. In The Gambia, breeding in September [7] and Southern Africa from September to November, but also in June in Zimbabwe [14].

African Wood Owl: Songs almost every night and loud calls are audible over at least 500 m and show sufficient individual variation for an observer to discriminate between some individuals [19]. The male song is typically described as a rhythmic “chuckle” sequence of clear hoots, “hoo-hoo,hu,hu, hu,hu -hu,”the last five syllables delivered unevenly with a syncopated rhythm. Female has a higher-pitched “eeyow”to which the male answers by a low gruff “hooor woo”depending on the listener’s interpretation [20]. The breeding season in Sierra Leone is February [7] and in Southern Africa August to November but in Zimbabwe also one April record [14].

Barn Owl: In South Africa, the calling in the garden intensified during February and the beginning of March. The call most often heard is a drawn-out tremulous screech—schrreeee—an eerie sound which serves a variety of functions: for territorial advertisement, courtship, and a contact call [13]. The male is said to screech more often at beginning of the breeding season when courtship chases are common [7]. In The Gambia breeding September–April [7] and Southern Africa from February to May, but breeding is possible in all months [14].

Eurasian Scops Owl: Palearctic migrants wintering in Africa call very little during their stay making them difficult to study [15]. However, a soft frog-like croaking “drrrr…drr..” was heard in The Gambia and first labeled as owl x. Other owl x voice was a Little Owl Athene noctualike “kiev, kiev, kiev” notes. Only in Hungary we realized that the Gambian owl x was O. scops[21]. During the winter survey in Italy, it was found that the few Eurasian Scops Owls wintering there responded more strongly to playback of the Little Owl than they did to Eurasian Scops [22].

Giant or Milky Eagle Owl: The normal call is a very deep double hoot “oop-poop,” almost as deep as the call of the Ground Hornbill Bucorvus leadbeateri. These two species could be confused, as both may roost and call from the riverine Acacia Forest at dawn and dusk. Luckily, the owl has a variety of other calls. The presumed male emits a series of short, grunting hoots “uh.uhu-uh-uh”and is answered by a deeper “uh-uh”from his mate. This duet once continued for 15 minutes [23]. Distinctive gruff hooting call is described also as “hook-hook”; uttered with inflated throat at variable rate and volume but in series of 1–5 hoots with an interval between series [7]. The call is said to carry for up to far as 5 km, but this is hard to believe [16]. In The Gambia breeding November–February [7] and Southern Africa from March to September, mainly June–August [14].

Greyish Eagle Owl: The song of male Greyish Eagle Owl recorded in Mali and Ivory Coast consists of two clear syllables and has been rendered as “kuo-wooh”[16] or “koo-whoo”[17]. The first syllable is rather explosive, and the second syllable is somewhat downward inflected, lower-pitched, and extended. This call is uttered in intervals of several seconds [13], and it is not like that of the Spotted Eagle Owl [17]. Breeding mostly from November to April almost throughout the species range [17], but in The Gambia, two well-studied nests had eggs in March [11].

Northern White-faced Owl: A disyllabic call is mellow fluting “po-proo”at 4–8 s intervals [7]. The first note is a very short, longer second note following 0.6 s [16]. In other words that voice has been described livelier as “cuk-coooo”: a brief note, followed less than a second by another note, somewhat louder, elongated and descending. This motif sounds rather pigeon-like and is repeated at intervals of 5–12 (average 6.49) s [17]. The main call is quite different from the Southern White-faced Owl. In The Gambia, breeding takes place in February–April, but there are records also from the October–December period [7].

Pearl-spotted Owl: The sheer volume of its whistling call “tiu, tiu, tiu, tiu”is amazing for such a small bird. Notes began softly but increased gradually in intensity before achieving a penetrating crescendo. Sometimes a second owl would join in antiphonally. In addition, “too-woopand tee-weep”calls, the latter higher-pitched call that of the female; these soft calls are used by the pair to maintain contact [13]. In The Gambia breeding February–April and Malawi August–September [7].

Pel’s Fishing Owl: Its main call is a deep sonorous hooting preceded or followed by low grunt “hooommmmm-hut”; repeated horn-like “hoom-hoom”; resonance from inflated air sacks. Sometimes male and female call in duet, male starting with grunting “uh-uh-uhu” building up to high “hoommm”; female answering by deeper hoot [17]. The hoot carries over a great distance, up to three kilometers on a calm night. Unlike many other owls, they do not become vocal at dusk and call mainly from midnight to dawn and the hoot is used throughout the year as a contact call [24]. In Nigeria, a young in a nest in February [7], in Zimbabwe breeding April, May, and October and in Botswana mainly February–April [14].

Southern White-faced Owl: A nuptial display consists of the bubbling hoot, and the male may approach the female along a branch while bobbing his head up and down and hooting [13]. A pair defends territory by calling; male calls regularly at dusk and dawn but also the night; female may join in. The bubbling polysyllabic “popopopo-popeeu”has a very fast stutter at first and the second part is more mellow, fluting, and rising in pitch. In other words, the same voice has been described as a rapid series of 5–11 (average 9) hoots, the last one being somewhat higher and accented, repeated at intervals of 7–15 (average 9) s. This song may be written “w-h-h-h-h-h-h-h-oo,” pronounced as rapidly as a man may do [18]. It is quite different from the Northern White-faced Owl [7]. In Southern Africa breeding May to November, in Malawi peak is in August [14].

Spotted Eagle Owl: Increased hooting during the courtship period, the male’s “hoo-hoo”being answered by the female’s triple hoot “hoo-hoohoo,” the middle “hoo”higher, so that the call has a pleasing cadence. Usually, the pair would duet, the female answering her mate immediately so that it sounds like a single owl hooting [13]. Both sexes may call at any time, the male usually around dusk and dawn and female in the early hours of the night [7]. In Malawi breeding season August–October [7].

From the studied 12 species, the far most vocal were Barn Owl and the Pearl-spotted Owl. The Southern White-faced Owl can also be audible most of the year, and in the captivity in Mozambique 1992, it was the most vocal of any of those owl species we have recuperated at home. Also, the less studied owl species can be more vocal than anticipated but this material is not enough to prove that.

The similarity index was low when comparing the calling hours and calling months between The Gambia and Malavi, and there was no similarity at all between two closely related White-faced Owls in The Gambia and Malawi. This may support further the separation of these owls.

Several factors are known to influence the patterns of vocal activity of nocturnal birds. One of the most obvious is the time of year, with the calling rate varying within the breeding cycle [25]. Owls are normally calling most actively especially just before breeding [4], but in this material, the peak months coincided very little with the given breeding times in Malawi and The Gambia. It is possible that the validity of the breeding times is not enough, but it is also clear that little seasonality was noted in the calling activity of the most owls studied throughout the year. This is something particular to the tropical weather conditions. The territorial calling of the Northern owls is more limited to the breeding cycle, like that of the Eurasian Pygmy Owl Glaucidium passerinumfrom March to May [1].

The overall activity pattern governs the calling as well, that is, strictly night-active species are mainly vocal in the dark while at least partly day-active species can call all around the clock. Well studied Malawi Pearl-spotted Owl is a good example of that as there are only two hours in 24 h, without any recorded calls. Month-wise the Barn Owl call all year round but has a clear break in the calling during the daytime. Similarly, White-faced Owls and Spotted Eagle Owls were not heard during the daytime.

This chapter wanted to give particulars species by species also commenting how well limited calling activity surveys are likely to reveal the actual number of existing owls.

Differences in calling rates among owls suggest that not all owls will be equally detectable using calling surveys [cf. 26]. It seems that in Africa, the Pearl-spotted Owl and Southern White-faced Owl populations and distribution should be possible to study by using the vocal surveys. They both are laud and calling actively in the evening hours. The nocturnal calling survey is not as good to map the distribution of the Barn Owls in the area as they seem to call erratically and between long intervals. Malawian data for Spotted Eagle Owl are limited but give the impression that vocal studies can serve to map the population size and distribution as the call takes place at least during the breeding times. In Kruger National Park, South Africa, it has been determined that individual African Wood Owls can be identified reliably by their vocalizations [27]. Identification of individuals by their calls has the potential for censusing, long-term population monitoring and is a valuable aid for planning the conservation of this species in Africa [27].

The influence of the weather was also studied. Heavy rain and wind are silencing the owls or at least make it impossible to hear their voices due to the background noise. Barn Owl was often calling immediately when the heavy rain and windy storm stopped. There are some examples that the temperature is not so important if the other conditions are suitable for calling, Barn Owl has been heard in +36°C as well as in +15°C; similarly, Pearl-spotted Owl records cover a similar temperature range from +37°C to +16°C.

The effect of moon luminosity on owls was also studied but with somewhat contradictory results. It seems that some owl species may increase vocal displays during full moonlight (such as the African Barred Owlet, Pearl-spotted Owl, and Southern White-faced Owl in this material) but others call less or not at all during the full moon (Barn Owl in this material). The impact of the full moon was not that obvious as the bright sky can also activate the Pearl-spotted Owl. Barn Owl started to call actively again when the moon was diminishing to 60% of its full size and its luminosity. It has been noted with other owls that they call more in the last quarter and the new moon phase of the lunar cycle [26]. In the classic Tawny Owl Strix alucostudy in Denmark the owl called less when the moon was up than when the night was cloudy and overcast [28]. And recently studied Long-eared Owl Asio otusin Russia was calling both during the rising and waning phases of the moon but again no calls were recorded during the full moon [29]. It has been suggested that small mammals and even some small birds are more active on moonlight nights, with the result that owls then hunt more and call less [16].

The pitch at which an owl calls is related roughly to its body size. Small owls usually utter higher calls than their larger relatives, but sufficient for the smaller area of the territory they defend and the shorter distances over which they must communicate. Furthermore, in owls, as in other predatory birds, females are larger than males and so their calls are usually, but not always, pitched slightly lower than those of their mates (e.g., Milky Eagle Owl in this material).

Owls seem to call more frequently on still nights when there is little interference with sound transmission. The larger owls with deep voices are especially wont to call in the still hours before dawn. They may be taking advantage of layers of air of different densities—the cool dense air of the pre-dawn chill has warmer air above—that bounce back some sound from their interface and enable calls to carry over greater distances. This also ensures that they have their say before being drowned out by the dawn chorus of diurnal birds [4].

Notably, owls usually fly to prominent perches (like our garden Spotted Eagle Owl in Malawi came often on the rooftop) before they call, in this way avoiding the absorption of sound by the ground. This could entail a risk for smaller owls, whose calls might attract larger species to prey on them, but the advantage of successful communication would have to be weighed against this threat. Such interactions may explain the choice of some of the sites from which owls call, as well as the ventriloqual nature of some of their calls [4].

The predation risk, indeed, is among the most principal factors that will influence the patterns of vocal activity in owls [30, 31]. In this study, it was noted that the obvious predation risk and interference competition was altering the vocal activity of the African Scops Owl which stopped calling when the Barn Owl was active. A larger Barn Owl can be a predator that eats the smaller African Scops Owl [31]. In Malawi, it was also suspected that Spotted Eagle Owl calling silenced the Pearl-spotted and Southern White-faced Owls. And there are clear indications that Spotted Eagle Owl could prey on these smaller owls [13].

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Acknowledgments

In Malawi John Alder, Matthias Frhr. Von Bechtolsheim, and John Wilson kindly gave us some owl observations, and Clive Richard Barlow, John Clayton, and Solomon Jallow did the same in The Gambia. Wandi Touray was showing us several times Bao Bolon Pel’s Fishing Owls in The Gambia and as always Alan Sieradzki sent us some old papers, we could not find in our forest library. An anonymous referee made constructive comments at the review stage which helped to improve the manuscript. We thank them all very warmly.

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Written By

Heimo Mikkola and Anita Mikkola

Submitted: November 9th, 2021 Reviewed: February 22nd, 2022 Published: April 25th, 2022