Mistletoe, carobs and birds work together in Nigeria’s forest ecology

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Mistletoes are found in a wide range of forest ecosystems. As pests, they form a fascinating group of plants. They derive their nutrition from host plants and are ecosystem engineers, having an impact throughout food chains.

They affect the population dynamics, diversity and distribution of other plants as well as invertebrates, birds and mammals. Their wide geographic distribution and long, unique flowering and fruiting periods make them an attractive resource for wildlife. The fruits and nectar are food for birds, which also nest and roost on the plant, providing pollination and seed dispersal services in the process.

In West Africa, mistletoes are found on many native trees and several economically important tree crops. These hosts include shea, neem, sweet orange, cocoa, rubber and African carob.

African carob (Parkia biglobosa) is considered an important tree crop, used for medicinal and food purposes. Trees also play a valuable role in nutrient cycling by fixing atmospheric nitrogen in soils. They are susceptible to mistletoe infection and agroforestry managers usually eradicate the parasitic plant.

But if mistletoes provide food and shelter to species that are particularly important in an ecosystem, removing them might not be a good strategy.

So we investigated an aspect of the ecological benefits of mistletoe that has not been well studied. We have studied how birds use the mistletoes that grow on P.biglobosa in Amurum Forest Reserve, Nigeria, through its mosaic of habitats.

We recorded all bird visits to trees with mistletoe: when they visited, how long they spent in the trees, and how they behaved. As predicted, Tapinanthus dodoneifolius mistletoe on P.biglobosa were an important provider of food and shelter for birds. Moreover, the ecological role of this mistletoe on P.biglobosa in times of food shortage, especially during the dry season, appears important.

This broader understanding of the importance and ecology of mistletoe could inform action in African carob forest management and conservation.

Our research

We conducted our study in the Amurum Forest Reserve in Jos, Plateau State, central Nigeria. The reserve has three main habitat types, which differ in plant species. It has about 278 species of birds, 31% of the total recorded in Nigeria. This makes it one of Nigeria’s biodiversity hotspots.

Some plant species, including P.biglobosa, in the reserve host mistletoes, attached to their stem as parasites. Carob trees in the study area are infected by three species of mistletoe: Tapinanthus dodoneifolius, T. bangwensis and T. sesselifolius.

Only T. dodoneifolius was fruiting during our study, so we only observed birds visiting this species.

Amurum Forest Reserve had a relatively high density of mistletoe infected species. P.biglobosa trees. Of 663 trees, 398 (60%) were parasitized by T. dodoneifolius gui and 265 (40%) were not. Ninety-four (14.2%) of the total number of trees were recorded in the rocky habitat, with 49 infected and 45 uninfected. Seventy-one (10.7%) of the total were in gallery forest, with 59 infected and 12 uninfected. We recorded 498 (75.1%) of the total in the savannah, with 290 infected and 208 uninfected.

In 432 hours of observations, we recorded 725 individual birds, comprising 71 species, and belonging to 31 families and four orders, visiting both carob trees and their associates. T. dodoneifolius Mistletoe. Fruit eaters, insect eaters, nectar eaters, and omnivores have all visited mistletoe flowers or fruits on carob trees. A total of 352 individual bird visits (of 54 species) were recorded directly on the mistletoes.

The rate of mistletoe infection on the trees in our study did not differ significantly between habitat types. This suggests that the probability of infection does not depend on habitat type but may be related to host plant quality, host availability, and bird behavior.

Use of mistletoe by birds on carob trees

Our results support the host quality hypothesis: mistletoes favor nitrogen-fixing plants and legumes as hosts.

Bird species in our study had similar odds of accessing all habitat types. Therefore, they could move seeds from one habitat to another to an available host. This supports a higher number of birds and increases the chance that mistletoe and host plant fruit will be dispersed.

The number of mistletoes on the host plant also determines birds’ preferences for particular trees (measured as time spent by birds on plants in a tree), as has been found in other studies. Birds were attracted to a dense accumulation of berries T. dodoneifolius mistletoe on the host and tended to spend a lot of time feeding on it, improving dispersal. Mistletoes do not all produce fruit or ripen at the same time. Fruit dispersers therefore find their reward in fruit available year-round in some species or in times of general food scarcity.

We observed that the height of the host tree and the number of mistletoes it contained influenced bird activity. In addition to eating fruit, we also saw birds roosting, pecking, and feeding on insects, seeds, leaves, and nectar on the mistletoe and host. This benefits the bird, the mistletoe and the host.

Implications of our findings

Our study supported the idea we started with – that T. dodoneifolius mistletoes on locust beans are a keystone producer, based on bird species use and attendance. Keystone producers are species that have a significant impact or influence on the ecosystem. These mistletoes on the trees seem to play an important role in times of food scarcity, especially during the dry season. These are important resources for the birds of the reserve.

Understanding such relationships can help identify critical resources and potential keystone species to inform conservation planning. Reforestation programs should consider the parasitic relationship between mistletoes and their hosts and their ecological benefits for bird diversity, fruit dispersal and pollination, and ultimately ecosystem stability.

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