You know what they say about blue feet
The obvious thing about a blue-footed booby is, of course, its feet. Whilst the rest of the bird is relatively simple and dour, those cerulean feet are bright and eye-catching. I have previously discussed why male birds adopt bright and distinctive ornaments to prove their health and worth in the pursuit of female. Yet, in the case of this booby, both sexes have these flashy ornaments. Well, the argument follows that an individual should compete for a mate when that mate is the limiting factor, i.e. when the mate invests a lot of energy in offspring so cannot reproduce as often. For boobies, and a few other species, just as males compete for females, so females compete for males because the males too invest a lot in the offspring. Essentially this is mutual sexual selection and it is responsible for many of the ornaments found in monomorphic species. Pairs of blue-footed boobies engage in foot-waving dances where both sexes show off their bright, blue feet as an indicator of health and well-being.
The blue footed booby is a member of the Sulidae which also includes gannets (Morus spp.). I had thought that boobies and gannets were very similar but for their colours and distribution but measuring the family members revealed gannets to be far larger. Gannets are famous for packing on to rocky islands where they compete in huge colonies for space and food. I have seen a gannet colony from afar, both off the coast of Pembrokeshire and adjacent to the Channel Island Alderney. What I didn’t realise was that any gannets I have seen cruising up and down the southwest coast are actually members of one of those two colonies on far-reaching foraging trips. Their ability to traverse huge distances in the search of food makes them robust to local fish depletion. Gannets are famous for their ability to plunge into the water from a great height to grab unsuspecting fish from their shoals. This ability has produced a skull built to absorb shock and internal nostrils to prevent a nose full of sea water.
Day 22: European shag – Phalacrocorax aristotelis
Crest the wave Together, shags and cormorants comprise the Phalacrocoracidae. Comorants are a staple of any rocky coastal community where they are often seen perched on the rocks closest to the water. In Britain we have two Phalacrocorax species, the European shag and the cormorant (P. carbo). One might ask what the difference is (and one might get a witty response) but actually it’s a useful question because the two species are not worlds apart. There are clear aesthetic differences with shags being much smaller. Shags are black to metallic green all over except for their bright yellow gapes whilst cormorants tend to be browner with a white cheek patch. The shag is notable for its crest, a great quiff protruding above the. However these visual differences are not the interesting answer. The intriguing question is how two similar species can co-exist.
The theory goes that two very similar species which share the same home (are sympatric) cannot coexist indefinitely. Either one (the superior competitor) out-competes the other or the species change so that their niches do not overlap as much. The fact that two species of a similar nature do coexist on some shores means that their niches are not (entirely) the same. In the case of shags and cormorants, any birder will know that shags are most often found on rocky shores whereas cormorants are found more in bays, lagoons, estuaries, rivers and inland water. This niche differentiation allows them to occupy habitats in different places however they do overlap in some coastal areas. In this case it is the foraging strategy that differs as shags tend to dive deeper for but for pelagic fish in the water column whereas cormorants dive in shallow waters taking fish from the seabed.. Thus both species exploit different resources and so do not encroach on each other’s niche. We leave the
Pelecaniformes now, passing the unusual darters (Anhinga), cormorant like birds with serpentine necks. You will have notice and absence of pelicans on the list. All pelicans are in the museums large collection so they will wait for another day.
Day 23: Lappet-faced vulture – Torgos tracheliotus
Top of the pecking order
The lappet-faced vulture is one of a dozen scavenging raptors (Aegypinae) famed for their unsavoury reputation for devouring carcasses. Though perhaps not beautiful to behold they are very impressive birds. This species is one of the largest with a colossal wingspan of up to 2.9 m. To see this flying must be like watching two barn doors flying through the air. I have only seen Old World vultures once, two griffon vultures (Gyps fulvus) gliding through the Pyrenees. These birds were huge and awe-inspring yet smaller in comparison to the lappet-face. On the plains of Africa, smaller vulture species such as white-backed vulture (Gyps africanus) spot dead wildebeest and zebra from miles away and crowd towards the food source all around.
However once these vultures touch-down next to the carcass they must wait their turn. First the animals’ killer must take its fill. Once the lion or jaguar has departed, scavenging hyaena and jackals move in to fight over the flesh. All the while the white-backs watch on, trying now and then to dart in and seize a scrap. Yet even when the mammals have departed, the white-backs must still wait for it is the turn of the lappet-faces. Though there are few of them in comparison to the white-backs they are far larger and see-off any infringement from the smaller species. However the larger species does provide a service for the smaller, tearing up the toughest bits of the carcass. In the vulture world, lapped-faces are top dog and will not be moved by the lesser species surrounding them.
Today we began to measure the Accipitriformes (‘sparrowhawk-shape’), a large group of raptorial birds. Traditionally this group has undergone a lot of taxonomic changes due to the evolution of ‘birds of prey’. Firstly it was realised long ago that owls were separate from other birds of prey in their own order, the Strigiformes. The canonical raptors where then housed in the Falconiformes which included vultures, eagles, hawks and falcons. Since the 1980s genetic studies have started to turn up unusual results regarding the group. The New World Vultures were placed in their own family, the Cathartidae, and these were believed by some to be unrelated to other raptors and often placed with storks! The second change was that falcons now seemed to be unrelated, closer kin to parrots! The recently resolved taxonomy has removed some of the ambiguity. The Cathartidae are indeed a separate family from other raptors but they share a common, raptorial ancestor however the falcons are separate and distantly related keeping their order name and leaving the rest of the raptors now named for the genus Accipiter.
The Accipitriformes are thus composed of the New World vultures, the secretary bird (Sagitariidae), the ospreys (Pandionidae) and the true raptors (Aquilidae). Most raptors are included in that last family which is split into many subfamilies: elanid kites (Elaninae), honey buzzards (Perninae) true kites (Milvinae), Old World vultures (Aegypinae), sea eagles (Haliaetinae), harriers (Circinae), sparrowhawks/goshawks (Accipitrinae), snake-eagles (Circaetinae), buzzards/true hawks (Buteoninae), true eagles (Aquiilinae) and harpy eagles (Harpiinae). I apologise for the list but I wanted the reader to appreciate the stunning diversity of the raptors and this can act as a reference point for future discussion.
Day 24: Little sparrowhawk – Accipiter minullus
Underestimate at your own risk
From one of the largest to the smallest and from the ridiculous to the sublime we reach this tiny bird of prey. My obsession for the superlative meant that I chose the little as my focal species. I like looking at the extremes in a group because by looking at them you get an idea of every possibility in between. Additionally you catch yourself exclaiming ‘it’s so cute!’ or ‘it’s so huge!’. It was an interesting day as in the morning I measured the largest of the Accipitridae: the cinereaous vulture weighing up to 11.5 kg and with a wingspan of up to 3.1 m. By comparison, I finished the day with the smallest species, the little sparrowhawk which weighs 85 g and has a wingspan of as little as 39 cm! The vulture thus weighs 135 times more and its wingpan is eight times greater. To the vulture, the sparrowhawk would seem a tiny irritating fly!
It is at this point that we acknowledge that size isn't everything especially when considering the foraging strategy of the vultures compared to sparrowhawks. Both Old World Vultures and the unrelated New World vultures include the largest raptors on earth and yet their diet is largely carrion based. If vultures ever do catch live prey it is generally small in comparison. Behind the vultures in size are eagles from a few genera including Steller’s sea eagle (Haliaeetus pelagicus), martial eagle (Ploemaetus bellicosus), wedge-tailed eagle (Aquila audax), harpy eagle (Harpia harpyja) and Philippine eagle (Pithecophaga jefferyi). Together these apex predators can seize anything from large fish to howler monkeys.
I highlight the capabilities of large accipitrids to then make the case for the sparrowhawks. Sparrowhawks are famed for their ability to catch relatively large prey. Often garden reports provide photos of sparrowhawks wrestling with woodpigeons or magpies, birds which weigh at least 50% more, if not 3 times as much! That would be like a sea eagle taking a large swan or something even heavier. So you have to give it to these little balls of fury that they know how to hunt!
