Interview with Ralph Buij about the Grasshopper Buzzard

Ralph Buij (1976) is a Dutch biologist who obtained his MSc at the University of Utrecht in 2000.  His thesis subject was the behavioural ecology of the Sumatran orangutan. Following further wildlife studies and work in South Africa and Gabon, Ralph took over the coordination of the University of Leiden’s research programme at the Centre for Environmental and Development Studies in far northern Cameroon.  While in that position from 2006-2010, he carried out the field work for his PhD thesis, which led to the successful defence in January 2013 of ‘Raptors in changing West African Savannas.  The impact of anthropogenic land transformation on populations of Palearctic and Afrotropical raptors in northern Cameroon’.   One very commendable aspect of the thesis is that both Afro-tropical and Palearctic raptor species were studied.  Key species reported on include Pallid Harrier, Grasshopper Buzzard, African Swallow-tailed Kite and Dark Chanting Goshawk.”  Ralph’s wife Barbara Croes is co-author on four of the chapters.

Joost Brouwer

1) What is known about the current status of the Grasshopper Buzzard in Africa?

The Grasshopper Buzzard is found in a savanna belt south of the Sahara, between Senegal and Ethiopia. Some parts of the breeding range are as narrow as 400 km wide, and Grasshopper Buzzards venture south of the equator only in east Africa and during the non-breeding season. Little is known about the abundance of this raptor in countries that cover extensive areas within the range (Sudan, Nigeria, Mali, Chad), but the Grasshopper Buzzard is among the most common raptors in the well-studied areas of the distribution range. In our study area in northern Cameroon, which encompassed the breeding and non-breeding range, circa 1 out of every 10 raptors recorded along road transects was a Grasshopper Buzzard. We counted averagely 30 individuals/100 km in the low-lying grasslands of the Lake Chad Basin, where productive and partly flooded grasslands produce an abundance of prey. Sclerocarya birrea woodlands on higher ground support high breeding densities. Only Black Kite (“Yellow-billed Kite”) and Hooded Vulture were more commonly encountered in northern Cameroon.

2) How has the population developed during the last decades?
Populations appear to have decreased the past forty years in both western and east Africa. The savannas in large part of the distribution range are under pressure from some of the highest human population densities on the continent. In the cultivated areas of central West Africa, J-M Thiollay counted fewer than half the numbers along transects in 2003 compared to 1969. But population trends are tricky to evaluate in such a mobile species and numbers may vary quite considerably in any area within periods of weeks or even days. It would be very useful to have longer-term monitoring programs in place, with regular surveys, to evaluate current population trends of this and other raptors that depend on the arid sub-Saharan savannas.

3) Is there a difference between protected and non-protected areas?

It all depends on the extent of land clearance for cultivation, because breeding density decreases with extensive tree clearance and expanding cultivation. Population declines appear to have been less severe inside protected areas. We found that breeding Grasshopper Buzzard adapted quite well to moderately cultivated landscapes in northern Cameroon. For example, we found no significant difference in reproductive output between pairs breeding in protected and non-protected areas. Grasshopper Buzzards breeding in agricultural habitat experienced lower predation rates and some accepted heavily pruned trees for breeding as shown on the photo. Some prey animals, such as reptiles, are more easily accessible in transformed habitats which may compensate for a decrease in the abundance of other prey populations.

4) What is the preferred habitat of the Grasshopper Buzzard?

This depends on the time of the year. They use open woodlands in Sudano-Sahelian savannas for breeding at the transition of the dry and wet seasons and migrate northwards into Sahelian grasslands and thornbush after breeding. They subsequently move southwards again into denser Guinea savanna woodlands in western Africa. Grasshopper Buzzards can be quite common in cultivated habitats even when breeding and when they exploit alate termites and ants after rains.

5) What is known about movements of adult and immature birds?

Both vacate the breeding area soon after breeding- when rains stimulate grass growth and rapidly reduce prey accessibility – and move north to exploit a flush of insects with the rains. There is a shift in the start of the rainy season in western Africa, with rains starting later at higher latitudes, so Grasshopper Buzzards sort of ride a wave of rains and an abundance of insects to northern latitudes. The entire population that moved northwards in July-August, gradually returns southwards into the Sudano-Guinea savannas when the rains have stopped, following increasing prey availability as a result of fires and grazing. The timing and extent of these movements have been well described by Jean-Marc Thiollay, as has their relationship with insect availability. In a way Grasshopper Buzzards and African Swallow-tailed Kite replicate movements by Palearctic migratory raptors, but at a smaller scale. Grasshopper Buzzard populations largely remain south of the main winter range of the Palearctic migrants, which also shifts southward over the course of the dry season. When Grasshopper Buzzards move north to breed in the Sudano-Sahelian woodlands, most Palearctic migrants have already departed to breeding grounds north of the Sahara.

6) What is the preferred prey of Grasshopper Buzzards?

Grasshopper buzzards are primarily grasshopper specialists during the non-breeding season. They consume a range of insects, mostly grasshoppers and beetles, also scorpions and sunspiders when breeding, but their breeding season diet is dominated by reptiles in terms of biomass. Other vertebrates such as frogs, rodents, and birds are also regularly taken during this time.

7) What is known about the conservation status of the Grasshopper Buzzards prey species?

Although small vertebrates and invertebrates that feature on the breeding season diet decline with severe grazing and land transformation, Grasshopper Buzzards are opportunists and may switch to other prey to accommodate such changes. In general, their dependence on small prey makes Grasshopper Buzzards much less vulnerable to prey depletion compared to the larger raptors, which compete with humans for preferred “bushmeat” prey (gamebirds, squirrels, hedgehogs, monitor lizards, etc).

8 ) What is known about the size of the required territory and home range for a pair of Grasshopper Buzzards?

We found that densities were generally high with up to 3.3 nests per square km and inter-nest distances < 100 m in high-quality habitat. Home ranges greatly overlap and birds regularly pass over neighboring territories on foraging flights. It would be nice to tag a few to get better information on range size and movements, also from different areas in the distribution range.

9) Is there competition with other raptors for nesting places or for food?

They breed alongside a number of other small to medium-sized raptors such as African Swallow-tailed Kites, Yellow-billed Kites, Gabar Goshawks, Dark-chanting Goshawk, etc. and most importantly in terms of numbers, other Grasshopper Buzzards. Frequent intraspecific interactions in high-density areas may lower reproductive output, but competition for food is probably limited during the rains when small prey is abundant. Apart from competitive interaction with similarly-sized raptors, direct predation of adults or their offspring by larger raptors may take a heavy toll during the breeding season. Our studies showed that the canopy cover above the nest was positively related to nest success and the number of fledglings, suggesting that concealment of nests lowers predation rates by other raptors. Over the course of the breeding season, Grasshopper Buzzards experience an influx of migratory raptors (Red-necked Buzzard, Wahlberg’ Eagle) capable of killing adults and nestlings. Pairs will fiercely attack passing large raptors and crows, and pairs may join to form a strike force. I once saw a juvenile African Hawk-Eagle tailed by three loudly alarming Grasshopper Buzzard pairs as it flew over their territories. Apart from raptors, nocturnal carnivores also take a toll on nestlings and breeding adults. When mammalian predators are sighted during the day they are also vigorously attacked – we once saw a Serval being attacked by a pair of Grasshopper Buzzards who took turns dive-bombing the cat. In the end the Serval made a run for it.

10) How many eggs do Grasshopper Buzzards lay?

The clutch size is 1-3, with averagely 2 eggs laid in Cameroon.

11) What is known about the breeding success and survival rates of Grasshopper Buzzards?

Not much for such a common raptor in its breeding range. Nest success in Cameroon was around 40%, twice as high as in African Swallow-tailed Kites, another intra-African migrant that breeds in the same habitat during the same time. So far, no work has been done on fledgling survival rates and this will be an important next step. We do have evidence that fledgling condition is compromised in human-transformed vs. natural habitat, and it would be interesting to know whether this affects their survival. Reproductive success may be comparable in natural and transformed habitats but if fledglings have a lower survival rate due to depressed body condition at fledgling, long-term breeding output may still be lower in man-modified habitat. Given the positive relationship between rainfall, food supply, and reproductive output, much may depend on the duration and extent of rains. Some (not all) climate models show that the Sahel is likely to experience a drought period and rains will become more local and erratic. Survival and long-term reproductive output may drop considerably under drought condition and this needs more study.

12) What gaps in the knowledge about the Grasshopper Buzzard do exist and where should research focus in the future?

I mentioned a few gaps above. It would be very interesting to further examine the relationship between climate conditions and survival rates and reproductive output. We need to assess what factors determine clutch abandonment, whether birds have the ability to re-nest after nest failure, possibly at higher latitudes, and how this influences reproductive output. Also, very little is known about breeding densities outside of Cameroon, mostly because much of the breeding range is in areas little visited by ornithologists. There have been apparent reductions in the number of non-breeding visitors to Kenya and Tanzania, which might be linked to declines further north. The timing and extent of seasonal movements is insufficiently known, particularly in the eastern parts of the distribution range. Finally, locust control operations have the potential to depress this important resource in the Sahel and more studies are needed to investigate and mitigate its impact on these and other insectivorous migratory raptors.

13) What are the main threats for the species in Africa?

Like other wildlife, it is most affected by increasingly extensive land-use change by rapidly growing human populations, notably conversion of woodlands into cultivated areas with few trees, and heavy grazing pressure. People may also directly impact breeding populations by harvesting nestlings. We worked in an area where the vast majority of the Muslim population would not eat raptors because of religious conviction, but found that some people with animist and Christian beliefs regularly consumed raptor nestlings.

14) What can and must be done to secure the survival of the Grasshopper Buzzard?

Any measure to minimize the effects of human population growth on the landscape would benefit raptors in western Africa. In most areas, the lack of financial means for investments to improve agricultural yields (e.g. fertilizer) results in rapid soil denudation and loss of natural habitat from destructive slash-and-burn activities. Investments in improved agricultural techniques would benefit people and wildlife. As long as such developments remain localized and few, agro-bushlands are becoming increasingly impoverished and over-utilized. This will affect raptors as well as people depending on the bush for wood, thatch, food, grazing, etc. Grasshopper Buzzards use native trees in croplands for breeding, but many trees are logged or their large side-branches cut, among others to prevent Red-billed Quelea from establishing breeding colonies in them. Queleas can be an important agricultural pest species in this region, and people have limited means of stopping them, apart from using handheld ropes when a flock lands in their fields. In some areas reforestation projects have been initiated but these often use exotic tree species, such as Neem, which are rarely used as nest trees by Grasshopper Buzzards. These trees are valued be local populations because of the medicinal properties of various parts of the trees, but they are ecologically of little value.

15) Are there any conservation projects for the Grasshopper Buzzard?

None that I know of. Any project focusing on proper agricultural intensification practices with patches of bushland protected from heavy exploitation would also be beneficial to Grasshopper Buzzards.

16) How do you see the future of the Grasshopper Buzzard?

Let’s be optimistic and say that populations may remain stable in the short term in some areas, but the long-term outlook is bleak. Despite still being among the commonest raptors in the region, it is endemic to a region that has seen a crash of raptor populations in only 40 years. Given the predictions of human population growth, and irrespective of the potentially negative effect of climate change, breeding densities and reproductive output will decline further with expansion of agriculture and vegetation clearance. True, other raptors such as larger eagles and vultures are likely to vanish from the region before Grasshopper Buzzards do. Some have already disappeared from vast areas of their former range; Secretary Bird, Martial and Long-crested Eagles, while the large vultures are on the brink of disappearing from many countries in western Africa, if they have not already been “functionally extirpated”. Similar trends in the region have been noted in other apex predators, such as lions, cheetahs, wild dogs. Relationships between park size, human populations and wildlife extinctions inside parks are telling and predict that only very few parks in the region are probably large enough to sustain intact predator populations. In the absence of substantial investments in national park management capacity, western Africa will be the first region where high-profile wildlife species including raptors disappear, even from national park strongholds. In contrast to the larger raptors, Grasshopper Buzzards are less sensitive the human exploitation and likely to persist in parks and agro-ecosystems, but developments in agriculture will determine at what level of their former population size.

17) What was your most amazing experience with the Grasshopper Buzzard?

This is not a fierce hunter, like some of the large eagles or accipiters portrayed here. Still, it has all features of an opportunistic hunter of agile prey, catching grasshoppers in the air and even birds. I recall one situation when I as standing at the edge of a sorghum field, planning to check a nest in an isolated marula tree. While scanning the surroundings for potential nest predators I spotted a Grasshopper Buzzard in the top of another tree 60 m from me. I continued on my way towards the nest but after having walked several meters, I suddenly heard a hard whooshing sound as if something had been thrown at high speed into the foliage of a nearby tree. I looked up and saw the Grasshopper Buzzard hanging upside down in the tree, only 4 meters from where I was standing, clasping a 60-cm snake in its talons. The bird must have seen the snake move as I approached the tree. A struggle followed and I could see the tenacious battle, the buzzard not wanting to let go of such a prize even with the snake coiled around its body and the branches. The bird appeared to be unaffected by my presence, focusing all its attention on the snake. Eventually the snake gave way and the Grasshopper Buzzard flew off with its prey toward the nests, where she started feeding the nestlings. A memorable experience, I was thrilled to see the birds’ determination at such close range, somehow testimony to the resilience of these raptors in an increasingly humanized landscape.