Recent studies have highlighted the vulnerability of hornbills breeding in hot, arid environments, raising concern about the species’ persistence with climate change. Hornbills are, however, a widespread avian family found in various climates in Africa and Asia. In this study, we investigated the factors impacting the breeding phenology of three sympatric African hornbill species in a semi-arid environment. We found that rainfall was associated with breeding initiation and breeding success in all three species (African grey hornbill Lophoceros nasutus, Southern yellow-billed hornbill Tockus leucomelas, and Southern red-billed hornbill Tockus rufirostris). Breeding success and chick body mass change of African grey hornbills and Southern yellow-billed hornbills, but not Southern red-billed hornbills, were negatively impacted by high air temperatures during the breeding season. This study shows that Southern red-billed hornbills were more successful at producing offspring compared to African grey hornbills and Southern yellow-billed hornbills, which was likely due to their later breeding initiation compared to the other two species. Future changes in rainfall patterns may cause the African grey hornbills and Southern yellow-billed hornbills to delay breeding activities. Delayed breeding could result in a greater overlap of the nesting period of the three species, which would, in turn, increase the competition for food and suitable nesting sites. This study confirms that also in semi-arid areas, climate change has the potential to affect the breeding success of hornbills.

Animal movement is mainly determined by spatial and temporal changes in resource availability. For wetland specialists, the seasonal availability of surface water may be a major determinant of their movement patterns. This study is the first to examine the movements of Shoebills ( Balaeniceps rex ), an iconic and vulnerable bird species. Using GPS transmitters deployed on six immature and one adult Shoebills over a 5-year period, during which four immatures matured into adults, we analyse their home ranges and distances moved in the Bangweulu Wetlands, Zambia. We relate their movements at the start of the rainy season (October to December) to changes in Normalized Difference Water Index (NDWI), a proxy for surface water. We show that Shoebills stay in the Bangweulu Wetlands all year round, moving less than 3 km per day on 81% of days. However, average annual home ranges were large, with high individual variability, but were similar between age classes. Immature and adult Shoebills responded differently to changes in surface water; sites that adults abandoned became drier, while sites abandoned by immatures became wetter. However, there were no differences in NDWI of areas used by Shoebills before abandonment and newly selected sites, suggesting that Shoebills select areas with similar surface water. We hypothesise that the different responses to changes in surface water by immature and adult Shoebills are related to age-specific optimal foraging conditions and fishing techniques. Our study highlights the need to understand the movements of Shoebills throughout their life cycle to design successful conservation actions for this emblematic, yet poorly known, species.

1. The behaviour of individuals affect their distributions and is therefore fundamental in determining ecological patterns. While, the direct observation of behaviour is often limited due to logistical constraints, collection of movement data has been greatly facilitated through the development of bio-logging. Movement data obtained through tracking instrumentation may potentially constitute a relevant proxy to infer behaviour. 2. To infer behaviour from movement data is a key focus within the "movement ecology" discipline. Statistical learning constitutes a number of methods that can be used to assess the link between given variables from a fully informed training dataset and then predict the values on a non-informed variable. We chose the random forest algorithm for its high prediction accuracy and its ease of implementation. The strength of random forest partly lies in its ability to handle a very large number of variables. Our methodology is accordingly based on the derivation of multiple predictor variables from movement data over various temporal scales, to capture as much information as possible from changes and variations in movement. 3. The methodology is described in four steps, using examples on foraging seabirds and fishing vessels for illustration. The models showed very high prediction accuracy (92%-97%), thereby confirming the influence of behaviour on movement decisions and demonstrating the ability to derive multiple variables from movement data to predict behaviour with random forests. 4. The codes developed for this methodology are published in the "M2B" (Movement to Behaviour) R package, available at https://CRAN.R-project.org/package=m2b. They can be used and adapted to datasets where movement was sampled from a wide range of taxa, sampling schemes or tracking devices. Observations are needed for a subset of the data, but once the model is trained, it can be used on any dataset with similar movement data.

Cape gannet Morus capensis chicks depend entirely on fish prey and metabolic water for water requirements during development. Water loss through evaporative cooling due to heat stress is substantial. We measured water flux and field metabolic rates (FMR) of Cape gannet chicks and adults to determine if gannets developed water saving strategies. The water economy index (WEI, gkJ(-1)) decreased with chick age according to the model WEI=0.676 - 0.272xlog(10)(t), indicating that water efficiency increased with age. At fledging, the WEI of chicks was at the level expected of adult desert birds. Desert birds maintain a low WEI by also having a low FMR, whereas Cape gannet chicks have FMR comparable to other seabird species' nestling requirements. We propose that maintaining low WEI is adaptive for Cape gannets because (1) chicks need to balance water loss through evaporative cooling, (2) fledglings need to overcome a period of up to a week when they cannot ingest any water and (3) adults spend extended periods in the breeding colony during which water can become a limiting factor. Understanding the physiological mechanism of maintaining low WEI will become increasingly important with future rising temperatures.

During four years 646 breeding Cape gannets (Morus capensis) at two breeding colonies were equipped with GPS-loggers to obtain insight in how foraging behaviour of gannets varied between colonies and whether it was predictive for the “health status” of these colonies. To study the association between foraging tracks and breeding success we also collected data on chick growth. Foraging behaviour of gannets from Malgas Island (South Africa) varied considerably during the breeding season; average trip durations could double between weeks. At Ichaboe Island (Namibia) foraging behaviour varied less, but the gannets made 2.3 h longer trips and had a larger foraging range than the gannets from Malgas. Gannets scavenging for fishery discards made shorter foraging trips than birds foraging for live prey (22.3 vs. 27.3 h respectively), during which they spent less time flying. Scavenging occurred more on Malgas. Chicks from Ichaboe were growing faster and had higher survival rates, possibly associated with the higher proportion of live prey in their diet. The fraction flown during foraging trips was positively associated with chick growth in the colony. Likely this relationship was mediated through diet, as gannets that made longer trips were more likely to return with (good quality) live prey. The fact that predation on chicks in the colony can be substantial and that overwinter mortality may vary a lot can explain why we could not confirm an earlier described relationship between parental foraging behaviour and colony status. The study of parental behaviour is important to explain chick growth, a component of colony health status, but inadequate to predict overall colony health status in Cape gannets.

Life history theory predicts a trade-off between current and future reproduction, such that long-lived species should not increase their reproductive effort at a cost to their own survival. In species with long term pair bonds and bi-parental care, each parent must balance its reproductive investment against that of its partner. While the effects of “handicapping” studies on the focal individual are sometimes difficult to interpret, they are a powerful approach for investigating compensatory responses of the partner. In the present experiment, we manipulated flying ability of one parent in long-lived Cape gannets (Morus capensis), thereby indirectly increasing the demands on reproductive effort of the unmanipulated partner. Handicapped birds doubled their foraging trip duration and reduced nest attendance. Their partners showed behavioural compensation via increased nest attendance for chicks younger than 30 days and increased foraging trip frequency for older chicks. The behavioural responses of partners did not fully compensate for the reduced care of handicapped adults. For manipulated nests, overall foraging trip frequency was 21% lower, chicks were left unattended at 5 days younger, and their growth and survival was reduced compared to control nests. Handicapped adults lost 10% of their body mass during the experiment, but their partners showed no decrease in body mass. We observed no differences in survival between handicapped birds, their partners or controls. Our results show that long-lived Cape gannets can increase current reproductive effort when needed, without negative effects on body condition or survival. The reduced care of one parent was partly compensated for by its partner, and remaining costs were borne by the chick.

Most seabirds are very noisy at their breeding colonies, when aggregated in high densities. Calls are used for individual recognition and also emitted during agonistic interactions. When at sea, many seabirds aggregate over patchily distributed resources and may benefit from foraging in groups. Because these aggregations are so common, it raises the question of whether seabirds use acoustic communication when foraging at sea? We deployed video-cameras with built in microphones on 36 Cape gannets (Morus capensis) during the breeding season of 2010–2011 at Bird Island (Algoa Bay, South Africa) to study their foraging behaviour and vocal activity at sea. Group formation was derived from the camera footage. During ~42 h, calls were recorded on 72 occasions from 16 birds. Vocalization exclusively took place in the presence of conspecifics and mostly in feeding aggregations (81% of the vocalizations). From the observation of the behaviours of birds associated with the emission of calls, we suggest that the calls were emitted to avoid collisions between birds. Our observations show that at least some seabirds use acoustic communication when foraging at sea. These findings open up new perspectives for research on seabirds foraging ecology and their interactions at sea.

Shoebills (Balaeniceps rex) are endemic to large, well-vegetated wetlands in central-eastern Africa. Populations are believed to be declining throughout their range and knowledge about their ecology, behaviour and distribution is vital for their effective conservation. In this study we quantified and explored Shoebill foraging behaviour across habitat types and seasons through behavioural observations in the Bangweulu Wetlands, Zambia. Behaviours associated with foraging were standing, walking and flying. Shoebills spent 85% of their time engaged in low-energy activities, mainly by standing still and preening. They caught on average one prey every 8.3 h and catfish Clarias spp. were the most common prey caught (71% of prey in 170.1 h observed). Despite small sample sizes (n = 17.7 h during the breeding season), we found an indication that the proportion of successful strikes was higher during the breeding season (five of seven strikes successful) compared to non-breeding (16 of 70 strikes successful). This study provides useful information for effective conservation management, by showing the importance of catfish as prey for Bangweulu Shoebills, the possible increased prey capture during the breeding season, and indicating the importance of the two habitat types: floating vegetation and flooded grassland (capture rates 0.10 and 0.29 prey h(-1), respectively).

We believe the two resident birds occupying the roosting nest had evicted the two intruders which evidently attempted to share this nest.

Shoebills (Balaeniceps rex) breed in central-eastern Africa with a world population of only 5,000-8,000 individuals. To provide protection to this threatened species, conservationists need a better understanding about Shoebill foraging and breeding ecology, their habitat use and their distribution. For this study, nest attendance and prey provisioning were recorded with nest cameras for Shoebills in the Bangweulu Wetlands in Zambia in 2012 and 2013. Chick growth and breeding success were monitored at the same time. Parental attendance was constant in the first 40 days of chick rearing, with attending parents only leaving the nest briefly to collect water for cooling the chicks or to collect material to maintain the nest. Attendance decreased as chicks aged, but prey provisioning remained constant throughout the nestling stage at 1.2 deliveries per day. Feeding peaked during the early and late morning. Chick growth rates were as expected given the size of the species, and chicks reached a fledging mass of approximately 5.7 kg. During 2011, breeding success was particularly low (20%, n = 10 nests) due to high levels of human disturbance, with chicks being removed from nests. Parents fledged 0.89 chicks per nest (n = 11 nests) when nests were actively protected from human disturbance and theft in 2012-2013. These findings could be useful for formulating guidelines for sustainable tourism to minimize disturbance and optimize breeding success in Shoebill populations.

The Cape gannet Morus capensis, a large fish-eating seabird, is endemic to southern Africa. To study the energetics of nestling growth, we used the doubly labeled water technique to measure field metabolic rate (FMR) of nestlings, from hatchings to large partly feathered chicks (n = 17) at Malgas Island, Saldanha Bay, South Africa. At the same time, the growth rate of a large sample of chicks was measured (n = 338). These data, together with literature values on resting metabolic rate and body composition, were used to construct and partition the nestling energy budget. Nestling FMR (kJ d(-1)) increased with body mass according to FMR = 1.23m(0.923), r(2) = 0.944. Mass-specific FMR (FMRratio; kJ d(-1) g(-3/4)) was independent of chick age (r(2) = 0.20, P > 0.05); mean mass-specific FMR was 4.11 ± 1.28, n = 17. Peak daily-metabolized energy (DME), which represents the maximum rate at which parents must supply their nestlings, occurred at age 71 d and was 2,141 kJ d(-1). Between the ages 51 and 92 d (43% of the fledging period), the DME of Cape gannet chicks was equal to or surpassed 90% of adult FMR at the nest. Energy demand during this period of peak DME represented 58% of the total metabolized energy, which was estimated at 150.1 MJ for an average chick during a 97-d period, from hatching to fledging. Sensitivity analysis of the energy budget indicated that the model was robust; the biggest source of error (±15%) was for the mass-FMR equation used in the model.

The cameras were programmed to take a photograph each time the sensor detected movement and the batteries lasted for about a week. Only a few other species than Shoebills were observed near the nests. On two occasions we saw a Sitatunga ...

The study of ecological and behavioral processes has been revolutionized in the last two decades with the rapid development of biologging-science. Recently, using image-capturing devices, some pilot studies demonstrated the potential of understanding marine vertebrate movement patterns in relation to their proximate, as opposed to remote sensed environmental contexts. Here, using miniaturized video cameras and GPS tracking recorders simultaneously, we show for the first time that information on the immediate visual surroundings of a foraging seabird, the Cape gannet, is fundamental in understanding the origins of its movement patterns. We found that movement patterns were related to specific stimuli which were mostly other predators such as gannets, dolphins or fishing boats. Contrary to a widely accepted idea, our data suggest that foraging seabirds are not directly looking for prey. Instead, they search for indicators of the presence of prey, the latter being targeted at the very last moment and at a very small scale. We demonstrate that movement patterns of foraging seabirds can be heavily driven by processes unobservable with conventional methodology. Except perhaps for large scale processes, local-enhancement seems to be the only ruling mechanism; this has profounds implications for ecosystem-based management of marine areas.

Seabirds forage in a highly dynamic environment and prey on fish schools that are patchily distributed. Colonially breeding seabirds regularly commute back and forth from their colony to foraging areas and need to acquire information on the location of food before and/or during each foraging trip. The use of conspecifics as cues to locate prey has long been debated, and although the hypothesis was backed up by modeling studies, observations have been contradictory. We deployed GPS devices coupled with micro video cameras on Cape Gannets to observe the social context of foraging seabirds and the influence of conspecifics on the movement of individuals. The Cape Gannets reached their first patch using a succession of flights interrupted by stops on the water, during which the birds were mainly preening. During flight, the birds reacted to conspecifics by changing direction, either flying in the opposite direction of conspecifics that were flying toward the colony or following conspecifics outward. The time to reach the first patch was significantly reduced (by half) when the birds reacted to conspecifics in these different ways, compared with the birds that did not react. The use of conspecifics flying toward the colony to find food is consistent with the hypothesis that colonies can act as a focal place for information transfer, with foragers updating their flying direction when they detect conspecifics flying toward the colony. The fine-scale reaction of seabirds toward each other at sea, and the associated improved foraging efficiency, as well as the division of trips into a succession of flights, constitute elements that indicate the existence and the use of a structured network among foraging Cape Gannets.

Seabirds foraging on pelagic fish develop behavioral strategies specifically adapted to locate inconspicuous prey that are aggregated in spatially dynamic patches. In the marine environment, they may use various mechanisms to detect cues of prey availability. The aggregation of predators at a patch of food is a particularly obvious cue to locate prey, a mechanism known as local enhancement. Pioneering studies described the formation of foraging groups at sea, showing that seabirds are attracted to feeding conspecifics. Improved foraging success due to local enhancement has been suggested from modeling studies, but no direct validation of these results exists. We deployed video cameras concomitantly with GPS loggers on Cape gannets to study the behavioral responses of equipped birds to the aggregation of predators at food patches. We showed that the reaction distances of equipped birds increased with the size of an aggregation, demonstrating that predator aggregations enhance food detectability for foragers. For small aggregations (<50 gannets), reaction distances were mostly less than 10 km, and they increased up to almost 40 km for larger aggregations (100–150 gannets). In addition, we showed that the number and frequency of dives increased with the number of conspecifics aggregated, up to a threshold. The predator aggregations on a patch of food could, therefore, not only inform about the presence of prey but also entail information about foraging conditions. From direct observations on the various components involved, our study provides justification of the use and advantages of local enhancement in foraging seabirds.

Oceanic structures such as mesoscale fronts may become hotspots of biological activity through concentration and enrichment processes. These fronts generally attract fish and may therefore be targeted by marine top-predators. In the southern Benguela upwelling system, such fronts might be used as environmental cues by foraging seabirds. In this study we analyzed high-frequency foraging tracks (GPS, 1 s sampling) of Cape gannets Morus capensis from two colonies located on the west and east coast of South Africa in relation to mesoscale fronts detected on daily high-resolution chlorophyll-a maps (MODIS, 1 km). We tested the association of (i) searching behavior and (ii) diving activity of foraging birds with mesoscale fronts. We found that Cape gannets shift from transiting to area-restricted search mode (ARS) at a distance from fronts ranging between 2 and 11 km (median is 6.7 km). This suggests that Cape gannets may be able to sense fronts (smell or vision) or other predators, and that such detection triggers an intensified investigation of their surroundings (i.e. ARS). Also we found that diving probability increases near fronts in 11 out of 20 tracks investigated (55%), suggesting that Cape gannets substantially use fronts for feeding; in the remaining cases (45%), birds may have used other cues for feeding including fishing vessels, particularly for gannets breeding on the west coast. We demonstrated in this study that oceanographic structures such as mesoscale fronts are important environmental cues used by a foraging seabird within the rich waters of an upwelling system. There is now need for further investigations on how Cape gannets actually detect these fronts.

Using a multi-disciplinary approach, we evaluated the potential consequences of long-term contrasting prey availability on the condition Cape gannets Morus capensis. We compared breeding adults from a decreasing colony on Malgas Island off the west coast of South Africa, where the abundance of small pelagic fish has decreased, with an increasing colony on Bird Island off the south coast, where pelagic fish are more abundant. We investigated (1) pelagic fish density using data from a hydro-acoustic survey, (2) gannet diet (stomach content analyses, fatty acid and stable isotope analyses), (3) gannet foraging effort and at-sea feeding areas (nest attendance patterns, GPS-tracking and blood haematocrit), (4) chick growth rates, and (5) adult body condition (morphometric measurements and breast muscle thickness). Our data confirmed contrasting prey availability between colonies, although pelagic fish were more abundant on the west coast than in previous years. Gannets exhibit dietary plasticity, feeding on pelagic fish and trawler discards, but favour natural prey when available. Stomach content samples showed that gannets from both islands mainly ate natural prey in 2009, but there were differences in their stable isotope and fatty acid signatures, supporting evidence of long-term diet differences. Nevertheless, chick growth rates and adult body condition were similar at both colonies, which was surprising for breeding adults from the west coast colony that had been feeding extensively on energy-poor fishery waste for several years. Breeding gannets' behavioural flexibility seems to have succeeded in maintaining body condition. However, this might have long-term costs, as adult survival at Malgas Island has decreased in recent years. Population decreases at this colony are exacerbated by low juvenile survival and perhaps differential recruitment to Bird Island. Higher foraging effort by adult breeding on the large colony of Bird Island compared to birds from the west coast, despite greater pelagic fish abundance on the south coast, probably suggests a greater intra-specific competition there. Monitoring of population trends, population health indices and foraging behaviour, as well as prey availability is necessary to better understand the mechanisms underlying the population trends.

A recent decline in population numbers of Cape gannets (Morus capensis) breeding off the west coast of South Africa coincided with decreased availability of lipid-rich fish prey: anchovy (Engraulis encrasicolus) and sardine (Sardinops sagax). Seabirds can use fishery discards as an alternative, but the quality of this food in the Benguela ecosystem is lower than that of their natural prey species. We consider whether chick growth and survival during chick rearing co-vary with the periods of high and low availability of their lipid-rich prey species and whether fishery discards would be an alternative. The proportion of anchovy and sardine in the diet was between 66 and 84% in the years 1986-1988, but just 16-35% from 2004 to 2006. Months with large proportions of anchovy and sardine in the diet were associated with faster chick growth. No association between the proportion of fishery discards in the diet and chick growth was found. The patterns are consistent with the notion that a distributional shift of anchovy and sardine decreased their contribution to the diet of Cape gannets and slowed chick growth along with lessening chick survival at the breeding colony. The reduced survival may partially explain the decline in numbers of Cape gannets breeding in the southern Benguela.

Life-history theory predicts a trade-off between current and future reproduction, such that long-lived species should not increase their reproductive effort (RE) at a cost to their own survival. In species with long-term pair bonds and biparental care, each parent must balance its reproductive investment against that of its partner. Although the effects of "handicapping" studies on the focal individual are sometimes difficult to interpret, they are a powerful approach for investigating compensatory responses of the partner. In the present experiment, we manipulated flying ability of one parent in long-lived Cape gannets (Morus capensis), thereby indirectly increasing the demands on RE of the unmanipulated partner. Handicapped birds doubled their foraging trip duration and reduced nest attendance. Their partners showed behavioral compensation via increased nest attendance for chicks younger than 30 days and increased foraging trip frequency for older chicks. The behavioral responses of partners did not fully compensate for the reduced care of handicapped adults. For manipulated nests, overall foraging trip frequency was 21% lower, chicks were left unattended at 5 days younger, and their growth and survival was reduced compared with control nests. Handicapped adults lost 10% of their body mass during the experiment, but their partners showed no decrease in body mass. Our results show that long-lived Cape gannets can increase current RE when needed, without negative effects on body condition or survival. The reduced care of one parent was partly compensated for by its partner, and remaining costs were borne by the chick.