This dainty looking little blue-grey bird holds the title of being the only exclusive North American passerine, or songbird, and the only predatory one too! They have blue grey feathers, black and white barred breasts and bellies and a distinctive hooked beak. It is well known for its unusual way of catching prey; swooping down from a great height and impaling the unfortunate animal on a thorn, branch or even barbed wire, another example of smart birds utilizing human features in their landscape. Unfortunately, although the shrike was once abundant throughout America, in recent years there have been significant declines in their numbers, prompting the IUCN to list them as near threatened, and research is ongoing to figure out the reasons for these declines and the best way to tackle them.
Natural History and Evolution
The Loggerhead Shrike is a passerine bird hailing from the genus Lanidae, of which there are 26 species around the globe. The very earliest passerine birds evolved in Gondwana, the super continent that existed around 550 million years ago and incorporated present day South America, Africa, Arabia, Madagascar, India, Australia and Antarctica. When the continent began to split up in the Early Jurassic period (around 180 million years ago), the ancestors of the songbirds we see today began to diverge into different species, although none of these species ended up in what is now South America or Australia. These birds first lived in Africa and Eurasia and arrived in North America later in the Pleistocene era across what is now the Bering strait, a common route many animals took; in fact many scientists believe it was the path humans from Asia to North America, on foot during the last ice age when the strait was frozen over.
There are 2 species of shrike in North America, the Great Grey Shrike (Lanius excubitor) and the Loggerhead Shrike (Lanius ludovicianus), of which there are 12 recognised subspecies. Many of these species are very similar in appearance, but there are some slight differences between some.
- In the Eastern USA, the birds have pale grey rumps.
- In the Northern and Western USA, they have white rumps.
- In Southern California, the birds have all over darker colouring.
- Off the coast of Southern California on the Island of San Clemente, there is a subspecies here that is the darkest feathered of all the subspecies, and due to precipitous population decline is considered to be endangered.
Adult Loggerhead Shrike from Southern California (image from allaboutbirds.org)
The endangered San Clemente subspecies of Loggerhead Shrike (image from allaboutbirds.org)
Habitat and Ecology
The Loggerhead Shrike is a widespread breeder across the United States and has some populations in Mexico and parts of Canada. Populations in the South are resident all year round, whereas those in the North are migratory from early spring onwards. They occupy numerous ecosystems, including sage steppe, prairie, desert scrub, pastures and pine savannahs. It is a grassland bird needing wide open areas interspersed with shrubs or low trees. The birds use vegetation to perch and hunt from, and they especially need branches to impale their food. Like many other grassland birds, this species is facing serious pressure from loss of suitable habitat and the degradation of grassland ecosystems, leading to a steady but constant decline in numbers since the 1960s.
Butcher bird: not just a name
The genus name Lanidae is derived from the latin word for butcher, which is apt given this birds unique predatory behaviour. Although shrikes are insectivorous, they will also eat mice, amphibians, reptiles and small birds and given their small size, they’ve had to get pretty creative with how they get such a big meal. The shrikes use a perch, whether it’s a branch or a telephone wire, to scout their habitat, then burst into a sudden rapid decline to catch their prey. Once they’ve caught their dinner, they use twigs to impale their prey and hold the animal in place while they use their perfectly adapted hooked beak to take chunks off it; not the nicest table manners for such a dinky, fluffy bird! There is also some research to support that they impale their prey as a kind of food storage, a particularly grizzly type of pantry! This behaviour is almost certainly an adaptation to their small size; insects can be caught on the wing, but a much larger reptile or amphibian is going to take a little more effort. It may be a slightly disturbing sight to see small creatures stuck like Halloween decorations on branches and barbed wire, but the butcher bird can eat a far more filling meal than many other similar sized birds thanks to this feeding strategy. Their beak is perfectly adapted to this behaviour; on the upper edge is a row of tomial teeth, small pointy projections that are likely used by the shrike during the tackling of their prey to bite down on the nape of the neck and paralyse them, a strategy seen in falcons too. Small and cute the shrike may be, but it’s a fierce predator. You don’t want to be a hapless frog when the butcher bird is about!
The Loggerhead shrike engaging in its famous impaling behaviour. (Image from animalspot.net)
Behavioural studies of impaling in the butcher bird reveal that it appears to be an inherent behaviour, as adults both in the wild and captivity have never been seen demonstrating this to their young. Birds raised in the absence of impaling devices like twigs never show impaling behaviour, even when they are shown other individuals doing it. Researchers think that it is trial and error learning that leads to impaling, and there is a critical period twenty to seventy days after hatching when impaling must be practiced, otherwise the shrike will never learn to do it.
A species in decline: but why?
Despite the fact that declines in Loggerhead Shrike populations have been known about since the 1960’s, no one is entirely sure of the reason why this species is suffering such losses when it was once so widespread. It is now listed as endangered in fourteen states and in Canada, with the main declines occurring in the eastern and mid-western United States.
One of the most popular theories is land use change and habitat loss. Huge swathes of prime Loggerhead habitat have been lost to extensive deforestation and agricultural expansion, with changes from grassland and small farms interspersed with vegetation for perching and impaling to huge intensive farms with few trees and shrubs contributing to serious losses. When studying habitat usage by shrikes, researchers found that many areas no longer inhabited by shrikes still have vegetation for perches and impaling posts, so why aren’t the shrikes there? This has suggested that perhaps the habitat requirements for shrikes are more complicated than initially thought. Not only are resident shrikes struggling with habitat loss, but migrating birds are facing issues in their wintering lands, with poor habitat there too, driving competition with other shrikes and other resident species, decreasing reproductive fitness and pushing even more populations into decline. Increased use of pesticides, which have timed with the beginning of the declines, car collisions and predation by cats have also been hypothesised as reasons for the loss of the Shrike across America.
On San Clemente Island off the coast of California, the shrike subspecies endemic there, Lanius ludovicianus mearnsi, is now considered endangered, primarily due to significant land use change on the island throughout the 20th century. The situation with this subspecies has become so dire that there is a captive breeding programme ongoing with the intent to release birds back into the wild, although there are concerns about genetic swamping, which occurs when the unique genes held by one subspecies become lost through interbreeding with other subspecies.
How to halt the decline?
Despite the alarming population trend seen in the loggerhead shrike, there is hope for its future. The species has a potentially very high reproductive rate, and so if adequate habitat and conditions can be increased, the species stands a good chance of bouncing back. There is fortunately some legal clout behind shrike conservation, with Canada, North America and Mexico all protecting the species under the Migratory Birds Convention Act, with Canada listing the loggerhead shrike under their Species At Risk Act and engaging in a breeding programme that has produced 400 juveniles between 2001 and 2010. In 2013 the North American Loggerhead Shrike Working group was set up, developing a standardized monitoring and banding programme, with different coloured plastic bands indicating different home regions, and carrying out multiple surveys and research projects to improve understanding of the forces driving decline. They locate prime breeding areas, carry out feather sampling for genetic studies to identify how well-connected populations are and monitor breeding rates and habitat usage. In 2015, the group set up the ‘Shrike Force’, teams of community scientists across America that volunteer to undertake surveys to locate breeding and wintering grounds and conduct regular monitoring of the banded birds.
The Smithsonian Conservation Biology Institute are also contributing to the fight against Loggerhead declines, partnering with the Canadian breeding programme to improve reproduction rates and release more birds into the wild. They are also using Geographic Information Systems (GIS) to map shrike populations and to determine their habitat preferences, all vital information that can further our understanding of why this unique little bird is disappearing.
Conservation Organizations, tips and heroes!
- As mentioned above, the Loggerhead Shrike Working Group is the main conservation organisation acting on behalf of this species. If you live in North America in Shrike habitat, you can volunteer as part of the Shrike Force or just keep an eye out for banded birds and food caches; watch out for those impaled little critters!
- If you own or manage land in the US, you can craft perfect shrike habitat by leaving thorny shrubs and trees (hawthorn and red cedar are particular favourites). Leaving hedgerows between fields can create perfect nesting habitat. Helping shrikes also helps other grassland birds like the Eastern Meadowlark, Upland Sandpiper and the Short-Eared Owl.
- More tips and advice can be found in the 2015 Loggerhead Shrike Landowners Guide on the Working groups’ website at https://loggerheadshrike.org/stewardship.
References
Chabot, A.A. (2011) ‘The impact of migration on the evolution and conservation of an endemic North American passerine: Loggerhead Shrike (Lanius ludovicianus), Biology, p 1-188
Craig, R.B. (1978) ‘An analysis of the predatory behaviour of the Loggerhead Shrike’ Ornithology, 95(2), pp 221-234
Ericson, P.PG. Irestedt, M. and Johansson, U.S. (2003) ‘Evolution, biogeography, and patterns of diversification in passerine birds.’ Journal of Avian Biology, 34(1), pp 3-15
Eseley, J.D. and Bollinger, E.K. (2001) ‘Habitat selection and reproductive success of Loggerhead Shrikes in Northwest Missouri: a hierarchical approach.’
Froehly, J. Tegeler, A.K. and Jachowski, D.S. (2020) ‘Nest site selection by Loggerhead Shrike (Lanis ludovicianus) in a fragmented landscape’ The Wilson Journal of Ornithology, 132(1)
https://www.allaboutbirds.org/news/
https://www.iucnredlist.org/species/22705042/179538598
https://wildlifepreservation.ca/
Michaels, H.L. and Cully, J.F. (1998) ‘Landscape and fine scale habitat associations of the Loggerhead Shrike’ The Wilson Bulletin, 110(4), pp 474-482
Patten, M.A. and Campbell, K.F. (2008) ‘Typological thinking and the conservation of subspecies: the case of the Sane Clemente Island Loggerhead Shrike’ Diversity and Distributions, 6(4), pp 177-188
Smith, S.M. (1972) ‘The ontogeny of impaling behaviour in the loggerhead shrike, Lanius ludovicianus’ Behaviour, 42(3/4), pp 232-247
Vallianatos, M. and Lougheed, S.C. (2002) ‘Conservation genetics of the Loggerhead Shrike (Lanius ludovicianus) in central and eastern North America.’ Conservation Genetics, 3, pp 1-13
