Nesting martial (Polemaetus bellicocus) diet: Influence of prey delivery and diversity in two Kenyan ecosystems.

Biological baseline study

Häckande stridsörns (Polemaetus bellicocus) diet: påverkan av bytesleverans och variation i två kenyanska ekosystem Biologisk baslinjestudie

Hollie Manuel (M’gog)

Faculty of Health, Science and Technology Biology: Ecology and Conservation Biology Master’s thesis, 30hp Supervisor: Larry Greenberg Examiner: Eva Bergman 2020-06-05 Series Number: 20:14

Abstract

Populations of of prey, henceforth raptors, have declined worldwide, mostly from anthropogenic causes. Because their role as apex predators in ecosystems is considered vital for ecosystem health, conservation efforts have been implemented throughout their distribution. In many cases, we do not know enough about their basic food and requirements, which is requisite if we are going to be able to protect them. The purpose of this study was to describe the habits and biology of nesting martial by looking at the chick’s diets and the roles of male and female eagles in provision and presentation (dismemberment) of prey to the chicks. Data were collected non-obtrusively by fitting five nests in the and one in the Rift Valley region of with cameras that were both motion-triggered and programmed to take images every five minutes. Based on analysis of 214,000 image frames, the diet of nesting martial eagles and their chicks was found to be comprised of 23 different species within four broad prey categories (gamebirds, domestic poultry, large and small ungulates), of which gamebirds were the most important. There were sex-based differences in parental feeding, with females selecting for larger and heavier prey items than males. Males were the primary foragers for the chicks up until the eighth to eleventh week of chick development, after which the females became more involved. In addition, before delivery to the nest, large prey were more often dismembered than small and medium-sized prey. This study is the first in to use nest-cams to study martial eagles over the breeding season, corroborating previous studies that have shown sex- dependent differences in chick nurturing. My results contribute to establishing a fuller picture that can be used in future conservation actions and management decisions that can be used to protect this species and their prey base.

Sammanfattning

Beståndet på rovfåglar (hädanefter raptor) har minskat över hela världen, mestadels på grund av all antropomorfisk verksamhet. Eftersom deras roll som topprovdjur i ekosystem anses vara oerhört viktig för ekosystemens hälsa har bevarandeinsatser genomförts i alla deras habitat. I många fall vet vi inte tillräckligt om deras grundläggande mat- och livsmiljökrav, vilket är nödvändigt om vi skall kunna skydda dem. Syftet med denna studie var att beskriva habitat och biologi hos häckande stridsörnar genom att titta på ungarnas dieter och rollen som hanor och honor i tillhandahållande och presentation (rivning) av byte till ungarna. Data samlades in genom att använda en icke-störande teknik. Kameror som var både rörelsestyrda och programmerade att ta bilder var femte minut monterades vid fem bon i Maasai Mara och en i Rift Valley-regionen i Kenya. Baserat på analys av 214 000 bildramar konstaterades att dieten för häckande stridsörnar och deras ungar bestod av 23 olika arter inom fyra breda byteskategorier (viltfåglar, tamfåglar, stora hovdjur och små hovdjur), varav viltfåglar var de viktigaste. Det fanns könsbaserade skillnader i kost som ungarna fick, med honor som valde större och tyngre byte än hanar valde. Hanar var de främsta furagerare fram till den åttonde veckan av ungarnas utveckling, då blir honor mer involverade. Dessutom blev stort byte ofta delade ned innan leverans till boet än små och medelstora byten. Denna studie är den första i Afrika som använde kamror för stridsörnar under Häckningssäsong och den bekräftar tidigare studier som har visat könsberoende skillnader i skötsel av ungar. Mina resultat bidrar till att skapa en mer fullständig bild som kan användas i framtida bevarandeåtgärder och förvaltningsbeslut som kan användas för att skydda denna art.

Introduction

It is widely believed that we are currently in an extinction crisis, the seventh mass extinction of its kind (Carpenter & Bishop, 2009). If a species is not at risk of extinction, it is most certainly in decline as a direct result of anthropogenic disturbance and/or activities (Lande, 1998; Hunt, et al., 2017). This huge loss of biodiversity will serve to disrupt ecosystem services, which in turn will affect human well-being (Ceballos et al., 2015).

Raptors are considered indicators of ecosystem health and are well documented to provide ecosystem services such as the elimination of disease through carcass removal and the reduction of fly populations as a result (O’Bryan et al., 2018). Apex avian predators are both threatened and understudied, and their seemingly important roles in food webs are not well understood (Amar et al., 2018; Runge et al., 2014). On a positive side, in many cases, the causes of raptor declines have been identified and actions have been taken to stabilise the populations, some of which have resulted in dramatic recoveries such as seen for peregrine (Mizera & Sielicki, 2009) and bald eagles (Grier, 1982),whose numbers rebounded after DDT was banned. Another raptor, the vulture is beginning to slowly recover on the Indian sub- continent, after it was identified that the drug, diclofenac, was the cause of their crash in numbers (Green et al., 2004).

Factors believed to contribute to the decline of raptors - electrocution, drowning, poisoning, availability of prey and nesting trees, habitat loss and chick survival rates, direct and indirect anthropogenic impacts - mean that many species may not be able to breed fast enough to counter their losses (Brandl et al., 1985; Boshoff & Palmer1980; Sorley &Anderson 1994 & BirdLife International 2012 & 2017). This exposes entire species to the threat of extinction (Ferguson-lees & Christie, 2001; Sorley & Anderson, 1994; Lande, 1998; Hunt, et al., 2017)and makes it all the more important for protection of avian apex predators to be included within conservation management plans (Machange et al., 2005). Conservation of these apex avian predators poses a unique challenge. They rely upon many habitat types for survival while the males and females utilise space differently, especially during breeding season (Sonerud et al., 2014; Hatfield, 2018). Diet (prey base), home ranges and territories, feeding behaviour and nesting, need all to be considered (Amar & Cloete, 2017) as well as their conservation in relation to people (Brown, 1991; Lande, 1998).Because raptors are of primary importance to ecosystem health, more detailed scientific knowledge about them can bring them to the fore in conservation planning (Machange et al., 2005). Martial eagles are, as with all raptors, slow breeding (Cloete, 2013; Newton, 1979) apex predators that are low in density (Amar et al., 2018). They have reclusive habits and as a result are very difficult to monitor and gather qualitative and/or quantitative data (Ripple et al., 2014; Amar et al., 2018). The is listed as vulnerable, in fast decline throughout large portions of its range (Brown, 1991; Simmons & Jenkins, 2014; Hatfield, 2018) and uncommon by the International Union for Conservation of Nature (Birdlife International, 2017; Nature Kenya, 2018; Simmons & Brown, 2004). Nevertheless, this eagle is still widespread and occurs throughout sub-Saharan Africa in a wide range of (not dense forest), up to 3,000m asl (Ferguson-lees & Christie, 2001; Simmons & Jenkins, 2014; Hatfield, 2018), from semi- to savannah grassland to thorn scrub (Cloete, 2013; Amar et al., 2016). Breeding of the eagle is known to be erratic and is very much dependent on prey availability and the length of the post-nest dependence period (Ferguson-lees &Christie, 2001; Hatfield, 2018; Brown, 1963). When they do breed though, it is either annually or biennially (Boshoff, 1993; Brown, 1963) with a single laid (Boshoff, 1993; Ferguson-lees & Christie, 2001). More often than not it is the martial female that incubates the egg (custodian adult) and stays at the nest with the chick for the majority of the time so as to deter predators, provide shade and rip prey into smaller pieces for the chick (Hustler & Howells, 1987). As the chick grows and can be safely left alone at the nest, both male and female eagles forage and deliver prey (Boshoff, 1990; Brown, 1991).

To date, in-depth dietary studies of martial eagles have been conducted in the Cape provinces of (Boshoff & Palmer, 1980; Steyn, 1980; Boshoff et al., 1990) and in , Kenya (Smeenk, 1974) and one other study that used web-sourced photography of martial eagles with prey species (Naude et al., 2019) .These studies, based on identification of prey remains and castings found at nest sites, provide a basic understanding of martial eagle diet. The results did not reflect prey diversity or numbers of individuals preyed upon, and were not able to attribute kills to either male or female eagles (Bakaloudiset al., 2012; Boshoff& Palmer, 1980; Redpathet al., 2001; Marti, 1987). In general though,martial eagle diet is thought to be composed in large part, of small , but also birds and (Ferguson-lees & Christie, 2001; Boshoff& Palmer, 1980; Boshoffet al., 1990). Dietary differences among populations arise from the availability of prey in different habitats (Boshoffet al., 1990; Boshoff, 1993) and proximity to anthropogenic activity (Ferguson-lees & Christie 2001). The eagles exhibit reverse sexual dimorphism, with the female having a greater body mass and hence the ability to select for larger prey items (Boshoffet al., 1990; Brown, 1991; Hatfield, 2018).

It is known that there are around 25 breeding pairs of martial eagles in the greater Mara ecosystem (3- 3,500 km2) (Hatfield, 2018; Mara Raptor Project, annual report 2018) and an older study showed that in Kenya, 55% of immature martial eagles do not survive to adulthood (Brown, 1952; Brown, 1966).The aim of this study was to collect baseline data on the diet of the nesting martial eagle. I looked at the types of prey (diversity and number) with the expectation that gamebirds would be the most important prey species. I looked at the roles of the male and female in capturing and delivering prey. Here I predicted that males would be the key prey provider early on in the nesting period, hunting smaller and lighter prey species, with females coming in to help hunt and deliver larger and heavier prey at around the 9th week. I analysed at the presentation of this prey at the nest and predicted that there would be a significant difference in dismemberment of very large and large prey species compared to medium and small. All of these predictions come from looking at the behaviour already partially described for non- nesting martial eagles (Boshoff & Palmer, 1980; Steyn, 1980; Boshoff et al., 1990; Smeenk, 1974; Naude et al., 2019) and in studies of other raptors found within Africa (Amadon, 1975; Hustler & Howells, 1987; Krüger, 2005).

Data collected in this study are expected to give key insights into the importance of habitats, prey species and food webs. It is generally recognised that links between these are key elements for conservation of this species.

Material and Methods

Study Area

The Maasai Mara (henceforth referred to as the Mara or greater Mara) is part of the Mara-Serengeti savannah ecosystem in southwest Kenya (1° S, 34-35°E) and is comprised of government, community and privately protected spaces that lie at an altitude of 1400 to 1900 m (Figure1).

Figure 1: Rangeland vegetation map of the central conservation area of the Maasai Mara, overlaid with the nest locations of seven of the eight pairs of martial eagles studied. Inset shows the country of Kenya with the red shading depicting the location of the greater Mara ecosystem. PR7 nested on Soysambu Conservancy in the Rift Valley (not shown on map) Map Source: MauMaraSerengeti (MaMaSe) Sustainable Water Initiative, 2018.

The greater Mara ecosystem consists of a variety of habitats, including rocky hillsides and outcrops (called kopjes), (usually ), forest, grasslands (both tall and short) and scrublands (Oindo et al., 2003; Bhola et al., 2012). The Mara experiences a mild tropical climate that usually brings two rainy seasons, the short rains (November to June) and the long rains (March to May) (Hatfield 2018; Bhola et al., 2012). Typically the annual rainfall is between 700-900mm on deep nutrient-rich soils (Løvschal et al., 2017; MauMaraSerengeti Sustainable Water Initiative, 2018), which result in this highly productive and bio-diverse ecosystem (Figure1). These conditions, as well as the protection afforded to the land, mean that many avian predators are able to exist on a solid prey base. Seventy species of raptors have been recorded as living or surviving within the Mara-Serengeti ecosystem (Nature Kenya, 2018). The ecosystem is also inhabited by the Maasai people, who traditionally are involved in pastoralism/ husbandry and, more recently, in and wildlife centred ecotourism (Waithaka, 2009). Human populations within and around this important ecosystem are expanding and, along with changing rainfall, increased incidences of drought and high numbers of tourists, the natural habitats are being altered and biodiversity is being considerably affected (Waithaka, 2009; Oindo et al., 2003). Approximately 3,200km2 of the Mara is under some sort of protection, but the methods of protection and their success are widely different (Waithaka, 2009).

Methods

An initial survey was conducted using past data and sightings to identify known martial eagle nest sites within the greater Mara ecosystem of which there are fewer than 25known ones (Hatfield, 2018). Using guides’ knowledge, the nests most likely to be active in the next breeding season were identified, adults were observed for signs of courting or copulating behaviours and, when the females were some time into incubation, eight nests were fitted with nest-cams (Bushnell Trophy Trail Camera, model number 119977C). The initial eight nests represented eight pairs, sixteen individual martial eagles. The aim was to have mounted the nest-cam after the were laid but before the chicks hatched, but some nest-cams were mounted after hatching. The camera batteries were changed on average once at each nest for each breeding season. The nest-cams were programmed to take one image every five minutes. They were also triggered by movement and then programmed to wait a further ten minutes before resuming the five minute interval image taking again.Every3 weeks, a field technician drove to each nest site and, using binoculars, identified that a) the nest was still active b) the breeding attempt was still considered successful c) presence/absence and approximate age of the chick. Each observer had dealt with raptors before and was trained in nest observation protocol. The following data were collected from the recordings: date, camera ID, prey item, % of prey item upon delivery to nest, sex & age of prey item, delivered by male or female martial eagle, time prey item remains in nest (uneaten to eaten). Two hundred and fourteen thousand image frames were cached with 22,625 frames as the lowest number of frames for one nesting pair and 54,381as the most. Twenty-four of 502prey items observed in the frames were discounted in the prey species analyses as they were unidentifiable. Cross-tabulations and a chi-squared test at a 95% (p <.05) confidence level were run, and I used rarefaction curves to assess prey species richness. These curves, as they plateau, signal a sampling confidence that all prey species within the community have been accounted for. They are based on plots of species accumulation against number of kills.

I estimated the percentage of full body size of different prey species delivered to the nest and the time the prey remained in the nest from the recordings. The age of the prey species was placed in one of three categories: juvenile, sub-adult, adult and into one of four weight classes: very large, large, medium, small. Diet species compositions were calculated using information on the proportion of each prey species and category in relation to total sample size (Figueiredo, et al., 2020).Shannon’s Diversity Index 1 (H ) was calculated to measure diet evenness where pi = proportion of prey species i in the diet.

Diet evenness had to be standardised on a scale of 0 (uneven diet) to 1 (even diet). This was done using the Shannon equitability diversity (Eh) formula where H’ = Shannon’s Diversity Index, H’max = In(S) where S represents the total number of prey items:

I determined diet diversity (raw richness, Shannon diversity), equitability (breadth, evenness), and niche overlap (Pianka niche overlap) and compared consumed prey species diversity (at operational taxonomic unit level following Razgour et al., (2011)). Here the Shannon’s diversity index (H) was calculated for each species diet using the vegan package (Oksanen et al., 2017) in R version 3.6.2 (R Core Team 2019). I determined how uniformly prey resources were being utilized by each pair using the standardized Levins’ measure of niche breadth index (BA) (Razgour et al., 2011;Lanszkiet al., 2019), where pi is the proportion of samples in which species i was found and n is the number of possible species in the diet.

Pianka’s adaptation of the niche overlap (Ojk) metric was used to determine diet overlap among all pairs of eagles (Pianka, 1973; Hurlbert, 1978),where pijis the proportion of prey species iin eagle species j diet, pikis the proportion prey species iin eagle species k diet, n = total number of available prey species. Ojk=

0 represents no overlap, whereas a value of Ojk= 1 represents complete overlap:

Sexual differences in prey delivery were compared using t tests. In the comparisons, I took into account the age of the chicks in weeks and the weight (g) of the adults when known. Despite the assumption of equal variances not being met in Levene’s test (p <0.05), the t-test is robust against moderate violations, and hence I used the t-test to compare sexual differences in prey delivery (Moreno-Opo et al., 2016).

Some prey items were delivered to the nest without visuals identifying whether it was a male or female delivery. Of the 502 prey deliveries made, only 421 of these were used in assessing prey size and predatory dimorphism. A one- and a two-way ANOVA (p < .05) tested for significance between prey size delivered by male and female eagles separately. In sampling prey dismemberment before delivery to the nest, I used body classes pre-assigned to identified prey by a previous study (Hatfield, 2018). A total of 468 prey deliveries were assessed for significance between and among the pairs, using ANOVA and the Bonferroni post-hoc test. To determine if frequency of kill was related to prey mass delivered to the nest (g) and if there was a significant trend, the number of kills and total prey weight delivered for each week of the chick’s development across all six nests was averaged and then an independent samples t-test was used. A Pearson’s coefficient value was calculated to test for correlation between the amount of prey delivered to the nest (g) and the frequency of delivery (male and female birds).

Most statistical analyses were performed using the SPSS statistics 26 package under Karlstad’s University licensing agreement. A select few tests were conducted using R statistical package (version 3.6.3). Results were considered significant if p-values were ≤0.05.

Results

Between 13 July 2016 and 13 April 2020, eight nesting pairs of eagles were identified (Table 1), seven in the Greater Mara ecosystem (Mara pairs) and one pair at the Soysambu Conservancy in the Rift Valley near Lake Elmentaita (outlying pair). Nest-cams captured portions of these eight breeding seasons (Table 2). Of the eight nests in which nest-cams were set up, eight adults wore transmitters and had been weighed for a previous study. Only the images from six cameras were usable.

Table 1: Information regarding breeding attempts and nest locations as well as weights of tagged adult martial eagle pairs; the G codes refer to the rangeland vegetation map codes in Figure 1.

Breeding Vegetation Habitat & Tree Pair Protected Male Female Attempts & Type Species ID Area weight (g) weight (g) Success Nest Riverine Maasai One attempt directly in PR1 3370 4840 Mara Successful G6 Podocarpus rangeland falcatus Surrounded Riverine Maasai Not One attempt by G6 and Woodland PR2 3680 Mara weighed Successful G7 Ficus sp. rangeland Two attempts Nest Riverine 2017 – directly in Woodland Maasai PR3 3210 4770 ate chick G6 Acacia gerardii Mara 2019 – Egg did rangeland not hatch Surrounded Riverine Maasai One attempt PR4 3290 4560 by G6 Woodland Mara Unsure rangeland Euclea sp. Two attempts Surrounded Riverine 2016 – by G6 and Woodland Maasai Not PR5 3390 Successful G5 Olea africana then Mara weighed 2018 – Egg did rangeland Ficus sp. not hatch Two attempts Rift Valley Caldera 2016 – Conservanc Cussonia sp.and Elmentaita, Not Not Successful y (not on Acacia sp. PR6 Rift Valley weighed weighed 2018 – Camera fig 1) battery life ended

Table 2: Observation periods, based on when the nest-cams were operational, during chick development for the six pairs of martial eagles. The grey shaded rows show the weeks of the chick’s development that were captured on film, and the number in these areas indicate the number of image frames taken.

Chick Age in Weeks 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 15 17 18 19 20 PR1 20,620 PR2 37,697 PR3 34,804 PR4 22,625 PR5 54,381 PR6 44,364

A total of 526 prey items of 23 different species were delivered to the nests of these six nesting pairs of martial eagles (Figure 2). This prey species count will be approximately 4 species less than in actuality due to the combining of cape and scrub hare as ‘hare’ and the rock and tree as ‘hyrax.’ There was also one unknown sp., 25 small unidentified spp. and one unknown species, each of which could have been a non-documented prey species. Most prey species fell into four broad prey categories (reptiles, primates and large ungulates were represented only once, twice and three times respectively, each kill made by the PR1 pair).The ratio of number of kills to number of species preyed upon by males and females was dependent on eagle pair (χ2= 459.7, df = 15; P<0.001; Figure 2).

Male Kills Female Kills Number of Species

140

120

100

80

60

40 Number Kills/species Number 20

0 PR2 PR5 PR6 PR1 PR4 PR3 20 1 19 9 9 7 1 Eagle Pair Number

Figure 2: The total number of kills made by males (blue) and females (pink) and the total number of species killed by each pair (green). The numbers beneath each eagle pair number show the total number of weeks during which each eagle was monitored.

Within these four broad prey categories (gamebirds, domestic poultry, non-ungulates and small ungulates), gamebirds were significantly the most important, this calculated using a sample of 503 of 523 prey species delivered to the nest (χ2= 503.7, df = 35; P<0.001). A cross-tabulation showed that that gamebirds make up the highest percentage of diet of all the eagle pairs excepting PR6 and PR3 (Figure 3). Within the category of non-ungulates, , hares and were commonly preyed upon as well as a select few bat-eared foxes. piglets formed the main prey species within the small prey category. 100% 2 2 4 90% 10 24 26 80% 17 12 13 70%

60% 18 23 82 Small Ungulates 50% 12 Non-ungulates 40% Domestic Poultry 103 95 30% Gamebird % of total number kills of number total of %

20% 16 17 10% 6 16 0% PR1 PR2 PR3 PR4 PR5 PR6 Eagle Pair Number

Figure 3:The number of kills as a percentage of the total number of kills (number annotated on bar) within the most common broad prey categories for each nesting martial eagle pair.

The mean mass of prey delivered by male eagles was 744g (N= 322). All these were deliveries of prey that were categorised as small or medium. The mean mass of prey delivered by female eagles was 1374g (N = 99). These were deliveries of prey that were categorised as very large, large, medium and small. This difference in mean prey masses delivered was significant (t419 = 10.23, p <.001). The mean mass was skewed as a result of the male and female of PR6 preying primarily on domestic poultry(Figure 4 and 5), the average prey masses delivered between sexes differed by only 108g while the average prey masses delivered between sexes amongst the Mara eagle pairs was > 1,200g.

Figure 4: Prey network web of all 526 kills recorded for each of the eagle pairs (grey circles). The labelled green circles differ in size, denoting the importance of that prey species overall. The importance to each eagle pair can be seen in the strength and colour of the connecting lines.

Figure 5: Prey network web contrasting prey preference between male and female eagles for all 526 kills recorded. Males of each pair are in purple while females are in green. The labelled blue circles differ in size, denoting the importance of that prey species overall. The importance to the male and female of each eagle pair can be seen in the strength and colour of the connecting lines.

Species accumulation curves were assembled by assessing how prey diversity increased against number of kills; this allowed me to build rarefaction curves to identify the asymptote, which indicates that all the prey species in the community had been sampled (figure 6). The upwards trajectory on the curves show that, for each eagle pair, I cannot be confident that I have sampled all possible prey species.

Figure 6: Linear species accumulation (rarefaction) curves for PR1-5 and a polynomial (order 2) trend line for PR6, each curve extended by 20 kills. The approach of an asymptote indicates that all the prey species in the community had been sampled.

Overall there was little niche (Pianka) overlap between the eagle pairs. However, a 70% niche overlap was seen between PR1 and PR2. There was a higher niche overlap between the males of these pairs than the females (67% to 58%). The highest overlap was between the male and female of PR6 (99%) and the females of PR4 and PR5 (95%). The males of PR2 and PR4 overlapped by 74% while PR4 and PR5 males overlapped by 71% (Table 3).

Table 3: Tabulating percentage niche overlap between and among the nesting eagle pairs using Pianka niche overlap. Habitats that overlap noticeably are highlighted in blue.

PR1-M PR2 PR3 PR4 PR5 PR6 PR1-F 26% PR1-F PR1 70% 53% 58% 20% 8% PR2-M 67% 24% PR2-M PR2 44% 46% 27% 31% PR2-F 38% 58% 26% PR2-F PR3 45% 21% 5% PR5-M 13% 9% 27% 12% PR5-M PR4 58% 6% PR5-F 32% 33% 6% 29% 15% PR5-F PR5 8% PR3-M 42% 37% 38% 57% 19% 2% PR3-M PR6 PR3-F 19% 64% 10% 65% 14% 28% 29% PR3-F PR4-M 55% 32% 74% 42% 71% 16% 57% 24% PR4-M PR4-F 32% 26% 3% 43% 10% 95% 11% 37% 16% PR4-F PR6-M 9% 3% 34% 3% 8% 1% 6% 0% 12% 1% PR6-M PR6-F 7% 1% 28% 4% 9% 1% 4% 0% 9% 1% 99%

Niche breadth and diet evenness between males and female and among eagle pairs (table 4) showed the eagle to be mostly generalist predators with almost even diets.

Table 4: Tabulating niche breadth and diet evenness of each of the six pairs of eagles’ prey preferences alongside the recorded species richness

Species Shannon’s Diversity Index Pielou’s Standardised Niche Richness on a scale of 1.5 to 3.5 Eveness Breadth (by pair)

Value increases as both the 0 (uneven 0 (specialist predator) Description Number of richness and the evenness of diet) of possible species killed by the community preyed upon 1 (generalist predator) outcomes each individual increases 1 (even diet) PR1-M 13 2.24 0.87 0.54 PR1-F 7 1.84 0.95 PR2-M 11 2.02 0.84 0.45 PR2-F 8 1.96 0.94 PR3-M 8 1.71 0.82 0.47 PR3-F 4 1.24 0.90 PR4-M 10 1.99 0.86 0.47 PR4-F 5 0.87 0.54 PR5-M 10 1.24 0.54 0.15 PR5-5 5 0.99 0.62 PR6-M 6 0.84 0.47 0.08 PR6-F 7 1.02 0.52

In looking at all eagle pairs together, the male delivered the most prey (349 deliveries) up until the chick was 51 days (8 weeks), the female then delivered more prey (109 deliveries) from when the chick was

70 days (t456 = 6.03, p <.001, Figure 7).Two pairs were then further compared against one another as they had nest-cams running for similar week numbers, this was done to confirm the significance found when comparing all eagle pairs. Nest-cams in PR6 and PR2 recorded from the 1stweek of the chick’s development right through to the 19th and 20th respectively. An independent samples t-test looking for significance between just the PR6 and PR2 pair also recorded significance (t211 = 5.47, p <0.001). This showed that female deliveries increased in frequency at the 12th week of the chick’s development. Nest- cams in PR4 and PR5 recorded from 3rdweek of the chick’s development right through to the 11th and 13th respectively. An independent samples t-test looking for significance between just the PR4 and PR5 pair also recorded significance (t162 = 4.27, p <0.001). This showed that female deliveries increased in frequency at the 9th week of development.

Figure 7: The percentage of prey deliveries to the nest for each week of the chick’s development by both males and females. The lower row indicates how many nest-cams were active in each week of chick development.

Up until week eleven of the chick’s development, the frequency of prey delivery and the total prey weight delivered were positively correlated (Pearson’s correlation: r= 0.65, P<0.001, df=77, R2=0.42). From week eleven onwards, when the female took a larger role in hunting and delivering prey, the frequency of kills dropped and then levelled off while the total prey weight delivered increased until the th chick flew the nest in the 20 week (paired t test: t297=19.67, df=75, (p < 0.001)).

Mean mass of prey delivered (by both sexes in the pair) in the first 20 days of chick development was 862g, then dropped to 709 between day 21 and 40. Between day 41 and 125, it increased to 949g where it plateaued briefly, rose again in the final 10 days the chick was in the nest to 1042g, then fell sharply as the chick flew the nest and either began to hunt on its own or was fed outside the range of the camera. There is a significant difference between the prey mass delivered between prey weight classification groups; small, medium, large and very large (F3,96= 4.74, p = 0.004). A Bonferroni posthoc test showed the percentage of prey mass of medium, large and very large species (dismemberment) delivered by males was significantly (p <0.001) less than females. Discussion

This study set out, with certain expectations and predictions, to investigate chick feeding of martial eagles using nest-cams as my study tool. It looked to determine what diversity and category of species constituted the major parts of the diet and, to what extent predatory sexual dimorphism could be seen in terms of size of prey captured and presentation of the prey at the nest. I was interested in the pattern of chick rearing – if the role of the sexes changed as the chick developed and if I would be able to determine reasons for the female leaving the nest in the first semester of chick growth.

I found that 23 different prey species formed the prey base for the eagles, although based on the rarefaction curves, all eagle pairs excluding PR4, did not reach a species accumulation asymptote. This indicated that not all the prey species in the community had been sampled and that species richness is likely to be larger than 23. Boshoff et al., (1990) recorded martial eagles in grassland areas preying on 27 different species (birds (11), mammals (15) and reptiles (1)) when collecting prey remains beneath nests. Naude et al., (2019), using web-source photography, recorded 15 species, 23 species and 3 species, giving a total of 42 species preyed upon by martial eagles, and Hatfield (2018), recorded 26 different prey species preyed upon by martial eagles in this Maasai Mara region. While I recorded a diverse prey base, it is difficult to directly compare to these other studies due to habitat and methodological differences between studies. Nevertheless, the studies together corroborate each other, highlighting the importance of hyrax, mongooses and hares as well as , , francolin and spurfowl to the diet of martial eagles across southern and eastern Africa (Boshoff & Palmer, 1980; Steyn, 1980; Hatfield, 2018; Naude, 2019).

My prediction that there would be sex-based dietary differences and that the larger female eagles would prey on larger prey species was confirmed. Previous studies have also recorded similar sexual-based differences for martial eagles (Kokko, 2008; Sonnerud et al., 2014), and a large number of studies have also reported food niche partitioning between the sexes (Sonnerud et al., 2014; Amadon, 1975; Reynolds & Meslow, 1984; Garcia & Arroyo, 2004), especially in breeding season (Miranda, et al., 2018).These differences in prey size selection have been well documented amongst and within other numerous raptor species, in the breeding and non-breeding season too (Garcia & Arroyo, 2004; Slagsvold & Sonerud 2007; Hatfield, 2018). It has been argued that this division of food resources means that there is less direct competition between pair mates and age classes of the same eagles that prey on species within the same area/territory (Amadon 1975; Kokko, 2008;Moreno-Opo et al., 2016), at least during the breeding season.

It is known that males and female play different roles from when chicks hatch to when they fly the nest, this is characteristic of many large raptor species (Brown & Amadon, 1968; Newton, 1979). Males tend to play a critical role in breeding success by being the initial prey provider while the female stays with the chick (Fairbairn et al., 2007). As the chick grows and improves its thermo-regulatory capabilities, females are able to spend less time brooding and shading the chicks and as a result hunt more. Thus, it is often by week 5 to 7 that the female begins to deliver prey to the nest (Collopy, 1984; Fairbairn et al., 2007). In my study I found that the male was the primary custodian adult up until the chick was around 8 weeks old, hunting to feed both chick and female. These were frequent deliveries of small prey species, which meant less dismemberment. I found that between the 8th and 11th week the female began to hunt for prey; these were less frequent deliveries of larger prey, and it is likely that she was feeding herself away from the nest, which meant that less prey mass was required at the nest than in the early weeks (Newton, 1979; Collopy, 1984). In many raptor species, it is in the last phase of chick development that the female delivers greater masses of prey, which reduces the relative contribution of the male (Collopy, 1984). For my study I found that in the final weeks of development, with the chick now large and hungry, the required prey mass increased before finally dropping as the chicks prepared to fly the nest. These findings corroborate those of Amadon (1975), who observed changing roles for males and females over time, keeping the chick fed at the nest. Parental care facilitates offspring performance and fitness; indeed, survival and development are inextricably linked to it, therefore knowledge of this and feeding ecology are important if conservation management policies are to be implemented in managing this declining species.

I expected martial eagle pairs to be more generalised feeders, selecting similar numbers of prey from all the species preyed upon. Niche breadth and diet evenness calculations confirmed this prediction for pairs 1 to 5. Pair 6 (and to some extent, PR2) was more of a specialist predator, feeding disproportionately on domestic poultry. This disproportionate reliance on domestic poultry, as indicated by an uneven diet score (Pielou’s evenness) and a 95% niche overlap between male and female of PR6, may be related to the fact that the nests of PR6 and PR2 were close to human habitation. The linkage between prey preferences and proximity to human habitation was described by Woodroffe & Ginsberg (1998), and termed ‘edge effects’. On a broader level, I was limited in my ability to relate prey selection to availability, as I was unable to collect or find any data on prey abundance in the Greater Mara ecosystem. This could be improved upon in future studies, if effort is made to estimate prey abundances, allowing the calculation of electivity indices, which tests for prey selection and avoidance.

The prey species that I sampled fell into seven broad categories, of which four were the most common – gamebirds, small ungulates, non-ungulates and domestic poultry. My expectation that gamebirds would constitute a major part of the diet of the nesting eagles was confirmed for all eagle pairs, except for PR6, which focused on domestic poultry. In a study in South Africa, Boshoff et al.,(1990) also looked at the importance of gamebirds in the diets of nesting martial eagles from two regions, the Nama- region (a vast open and arid with a volatile and harsh climate)and a protected grassland. They found adifference in importance of gamebirds in the diet, with 7% in the Nama-karoo, and 32% in the grasslands, which probably reflects the higher species richness in the grassland. The greater Mara is comparable to these grasslands, and my findings reflect this diversity and high reliance on gamebirds by martial eagles in this region. Adult martial eagle are far more practiced and adept at hunting and, as gamebirds are generally a very tricky prey to hunt due to their speed and mid-air manoeuvrability, younger martial eagles prey less on them while adults can, and in some locations, primarily hunt gamebirds (Slagsvold & Sonerud, 2007).

Naude et al., (2019) found that mammals made up almost half of the diet of martial eagles in Kenya, gamebirds made up just over a quarter and reptiles made up just less than 20%. They observed that in eastern Africa (Kenya and combined) the diet of the martial eagles is predominately mammalian. I found that the diet in the Mara ecosystem consisted predominately of gamebirds. I would argue that this shows the biases in using web-sourced photography to explore diet where the images taken and loaded onto the web (and ultimately used for the study) select for larger, photographically aesthetic prey species (mammals), thus not accounting for the numbers of gamebirds preyed upon. A photographer is less likely to photograph a martial eagle carrying a small, easily portable, less eye- catching prey than he/she would if the prey is noticeable and large. This study, the only other formal comparison for diet in Kenya for this species, found the four most important mammalian prey species to be Thomspson’s , , common and while I recorded only seven Thomspson’s , three impala, three dikdik (comparable to common duiker) and twenty-three banded mongoose. In contrast, the four most important mammalian species in my study were warthog piglets (47), hares (43), banded mongoose (23) and hyrax (12). Where monitor lizards dominated the reptile category by 21% in non-nesting pairs in the Naude et al., (2019) study, I recorded only two kills of monitor lizards by only one pair. Finally Naude et al., (2019) identified as the most important bird prey in eastern Africa while my study identified as the most important bird prey species; this difference may result from breeding seasons of eagles and either guineafowl and/or coqui overlapping.

Prey selection can also be accounted for by both nesting and home-range habitat. Van Eeden et al., (2017) demonstrated that habitat type was an important factor in the description of prey species between eagle pairs, and this may well be the basis of prey selection for the martial eagles in this study too. Nesting and home range habitat types may also come into play when describing niche overlap, in itself an important descriptor of diet (Gaston & Spicer, 2001). Understanding the processes by which age cohorts within a species fit themselves into existing territories and home ranges is still a central puzzle and is important to understand if biodiversity is to be maintained and nurtured (Marks & Doremus, 1988; Miranda, et al., 2018). Niche overlap can reveal the effects of competition (inter-cohort, sex based, breeding versus non-breeding) and disturbance within any community (Mason et al., 2011). In my calculations I found thatPR1 and PR2 had a 70% niche overlap, with the much higher overlap being between the males of the pairs. Interestingly, these pairs were nested the furthest apart but in comparable habitat types. A high niche overlap was also seen between PR5-F and PR4-F (95%). These pairs nested the closest together, with only a maximum of 7.47km between the nests. It is clear that an abundant, easy to access food source (domestic poultry) collapses the food-niche hypothesis and all diet differences and sexual predation preferences disappear, to the point of ignoring other food sources almost entirely. These inter-nesting distances however, do reflect those found in studies regarding the martial eagle in Hwange NP in and elsewhere in South Africa (Steyn 1982; Tarboton & Allan 1984; Hustler & Howells 1987; Boshoff 1993; Ferguson-lees& Christie 2001). As would be expected, the nests are much closer than the nests found in arid . These inter-nesting distances may also reflect the availability of nesting trees in the Greater Mara (primarily grassland) ecosystem (Björklund et al., 2017).

The Mara-Serengeti ecosystem provides critical habitat for raptors and thus is an important geographic area in which to implement conservation action, especially population monitoring. Studies of protected, buffered and cultivated areas in have shown that the numbers are raptors are declining in the face of fast human growth and habitat change, avian-wildlife conflicts (especially from birds on the edge of protected areas) and/or traditional belief systems contributing to the hunting of these avian apex predators (Thiollay, 2006, 2007).Habitat loss, rampant in Kenya and evident in the Mara, affects prey species first (Lamprey & Reid, 2004; Li et al., 2020; Løvschal, et al., 2017), thus management of the martial eagle should focus on their habitat and accompanying prey base. Further studies on adult survival and turnover, breeding success and nesting frequency in protected and unprotected regions and the relative proportions of prey taxa that make up their diets would ensure long-term sustainability and viability of the species in this important ecosystem.

Conclusion

The nest-cam method has provided an overview of the composition and relative importance of prey in the diet of the martial eagles and chicks in this study area(Lewis et al., 2004). The observed species composition is also consistent with previous data collected from studies that looked at prey remains at the nest, where gamebirds and medium-sized mammals are by far the dominant prey for martial eagles nesting in protected areas (Boshoff & Palmer, 1980; Boshoff, et al., 1990; Cloete, 2013). The analyses of the image frames have also allowed me to investigate other important aspects such as parental roles and timelines in prey delivery, prey presentation at the nest and which parent is the main nest-custodian. Healthy prey populations are a critical step towards the mitigation of these human-avian predator conflicts, which will in turn contribute to the conservation of martial eagles.

Ethics Statement: The data used for this study were collected by a field team that works with and in fact created, the Mara Raptor Project, headed by Stratton Hatfield. The collection of this data did not require the capture, handling or killing of any and, although nest-cams were mounted while the nestlings were in the nest, this was done by experienced personnel and neither the chicks nor the nests were touched in the mounting. There appeared to be no camera effect on eagle nest success and/or on predation of the chick.

Acknowledgements

Thanks very much to Stratton Hatfield for trusting me with data that he collected alongside doing a PhD of another topic in the same region on the same species and with some of the same eagle pairs studied here. Thanks also to Simon Morgan and Jordana Meyer, who both took time from their commitments to read and comment on drafts and helping me in formulating thoughts clearly. Finally thanks must also go to Rida Israr, who took time from her busy schedule to double check my statistical testing and to Larry Greenberg, my supervisor, who took time to comprehensively annotate all drafts for repair and alteration – without him I could not have turned in such a paper.

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