Gritting greylag geese

Birds that feed on fibrous or hard food of vegetable origin often swallow sand or small stones ('grit'). Grit accumulates in the gizzard or crop, and together with the muscular action of the crop it helps macerate their food facilitating digestion and increasing food processing rate. The limited size of the gizzard means that herbivorous birds need to spend time just processing food, waiting until the gizzard empties, before another foraging bout. Grit can be ingested accidentally with the food or purposefully, by visiting places where it is easy to find. Wintering flocks of Greylag goose in Doñana National Park (Spain) visit sand dunes to ingest sand, and their crop can hold up to 10 g of sand.  Birds can adjust the amount of grit to their diet and in turn, crops containing more grit become more muscular, flexibly responding to the demands of different coarseness or amount of fibre in the diet.
 While watching the flock of wintering geese in my local park, I noticed them stopping in a bare area. First I thought they were feeding on the small tufts of grass there, but when I looked closer I realised they were ingesting grit. They spent a few minutes doing this, and then moved onto the grass to feed. The distinctive individual with a white head (above) serves as an identifier for this flock. I have seen him or her both at East Park and Pearson Park.

A pair gritting together.

Here is a short video of the behaviour:

More information
Amat, J. A., & Varo, N. (2008). Grit ingestion and size-related consumption of tubers by Graylag Geese. Waterbirds, 31(1), 133-137. here.

VerCauteren, K. C., Lavelle, M. J., & Shively, K. J. (2003). Characteristics of grit in Canada goose gizzards. Wildlife Society Bulletin, 265-269. Here.

Broken Wing

This has been an unusual year for Canada Goose in the park. Usually, a flock visits during the winter, roosting elsewhere and returning every morning to enjoy the bread and food given by people. Some time during last winter, one of the geese got injured, its right wing hanging a bit loose on the side (I first noticed it the 16th of January, the photo above is from the 16th of March). The injury, at the base of the wing, prevented it from flying, and it must have happened in the park, maybe due to a collision with a tree branch or a fight with a dog. The bird seemed content, fed well and recovered enough for the injury to be almost unnoticeable. But when the flock decided it was time to depart for the breeding grounds, at mid February, the lame goose stayed behind. All through the summer it has been alone in the park, joining the mallards during feeding time, and probably roosting on the little island at night. I felt for him as geese are such sociable birds.

Part of the Canada Flock returning from the roost in the morning

 The flock of Canada Geese returned last week. I searched for the lame one in the pond, but failed to spot him, it must have mingled with the rest of the geese. I wished I had been there to watch his reaction to, first, the distant honks of the approaching flock, and then to the geese themselves once they landed. Then a couple of days ago, early in the morning, I spotted him with two others, just before most of the flock returned. Again, today, the goose was with a female before the main flock returned. They followed each other closely, like a pair of geese would do. Could it be that this was/is his partner? Geese form strong partnerships and bond through the year, and for many years if not for life. They also recognise many individuals in their flock, including their past offspring. The female goose is actually staying to roost with the lame goose at night, instead of following the flock. Maybe when the migratory urge kicks in spring she will leave with the flock, but maybe not.

The lame goose in the background, with a partner on the 30th of September

My peak count per visit graph for Canada Goose in Pearson Park. If you try you can see a tiny green bar between week 8 and week 39, corresponding to the lame goose. Created with BirdTrack.

Canada Geese taking off decisions

This morning, the 60 strong flock of Canada Geese that seemed to have roosted in the park were restless. There were continuous loud grunts and honks and, after a crescendo in which more and more individuals joined in the calling, part of the flock took off in a coordinated way. The vocalising geese were making a decision, with individuals deciding to join or not a party leading the departure, maybe to quieter feeding grounds. It is unclear if the individuals felt hungry or if the several dog walkers had made then nervous (or both!).
  Flocking birds have to travel together to stay in a group to search for new feeding or roosting patches, to avoid predation or to migrate. When the individuals differ in their motivations to move away (some might be hungrier than others, for example), there might be a period in which an a consensus is reached about leaving or staying involving communication of the individuals intentions. An individual that is not hungry might change its mind and join in if most of the flock appear willing to move, so as not to become isolated.
  Dennis Raveling, in a paper in 1969, reported on the behaviour before flock taking off in Canada Geese. He observed a large flock in their natural range, in which 77 geese had been marked and radio tracked, including 10 families. Flock departure was preceded by a ceremony, with the neck stretched, there are quick head tossing movements with the bill pointing up and repeatedly, and the white head patch conspicuously displayed - communicating an intention to fly. Geese often spread and flap their wings and start to walk in the intended direction of flight for a few steps (this video illustrate this behavior). Ganders (adult male geese) were more successful at recruiting his family than any other family members, as a shorted time elapsed from his initiation of head-tossing until the family took flight, although all family members initiated head tossing at some point. In a couple of occasions when an excited immature took flight but the rest of the family did not follow, it flew in a circle and returned with the family shortly.
 Other than the cohesive function of the head-toss ceremony for family members, group vocalisations and wing flapping serves to synchronise the whole flock. The coordination of the flock during take off included the presence of an invisible 'starting line': individuals run until they arrived at the same position at which the individual before them had just taken off (instead of taking off where they were). Raveling hypothesized that the contrast between the white tail coverts and the black tail served as a signal to optimise the position of individuals during flight, quite important in such large birds. Families tended to keep together during flight and their vocalisations then changed from grunting to a more trumpet-like honking.

More information

Dennis G. Raveling (1969). Preflight and Flight Behavior of Canada Geese The Auk, 86, 671-681 DOI: 10.2307/4083454