Diet specialization in an insular population of coastal Peregrine Falcons

Individual diet specialization is known to occur in populations of generalist predators, where specific individuals develop specialist feeding strategies. Diet specialization has been reported in many raptor species, and it may be an important driver of intraspecific population structure. Here, we quantify the diet of five breeding pairs of Peregrine Falcons Falco peregrinus from an offshore island determined from prey remains collected over four breeding seasons. Three prey species accounted for 69.8 % of total prey frequency, with Manx Shearwater Puffinus puffinus the primary prey accounting for 47.3 % by frequency and 40.8 % by biomass. Herring Gull Larus argentatus was the second most important prey species by frequency (13.8 %) and biomass (29.8 %) followed by Domestic Pigeon Columba livia (frequency = 8.7 %, biomass = 7.0 %). Predation frequency on specific prey groups varied substantially between breeding pairs and months. Two pairs specialized on Manx Shearwater, one pair specialized on Herring Gull and Manx Shearwater, with the remaining two pairs having a relatively generalist diet of Manx Shearwaters, Domestic Pigeon and small passerines. Predation on Manx Shearwaters increased throughout the breeding season with a peak in total diet frequency of 63.8 % in July, with a concurrent decrease in Herring Gull predation frequency. Higher percentage of Manx Shearwater in the diet was able to explain 87 % of the variation in a narrower dietary breadth for the Peregrine pairs. Our results suggest individual diet specialization may be important for understanding population density in insular raptor populations.

A case report of biochemistry and serum amyloid A in a moribund free-ranging Baltic herring gull (Larus argentatus) with necrotic wing fracture

An adult herring gull (Larus argentatus) found lethargic and moribund showed an open fracture of the right radius and ulna with necrosis of the surrounding tissue. Hematologic testing and plasma biochemical analysis revealed elevated creatinine kinase consistent with traumatic muscle damage in addition to hyperuricemia, hyperkalaemia, and hyperphosphatemia consistent with renal insufficiency. Increase in the acute phase protein Serum Amyloid A indicate a high degree of inflammation supported by leucocytosis, heterophilia, and hypoglycaemia pointing towards septicaemia. This case provides knowledge about Serum Amyloid A in gulls, and how bone fracture and secondary infection may affect gull blood haematology and biochemistry.

Nest sanitation behavior does not increase the likelihood of parasitic egg rejection in herring gulls

Birds’ behavioral response to brood parasitism can be influenced not only by evolution but also by context and individual experience. This could include nest sanitation, in which birds remove debris from their nests. Ultimately, nest sanitation behavior might be an evolutionary precursor to the rejection of parasitic eggs. Proximately, the context or experience of performing nest sanitation behavior might increase the detection or prime the removal of parasitic eggs, but evidence to date is limited. We tested incubation-stage nests of herring gulls Larus argentatus to ask whether nest sanitation increased parasitic egg rejection. In an initial set of 160 single-object experiments, small, red, blocky objects were usually rejected (18 of 20 nests), whereas life-sized, 3 D-printed herring gull eggs were not rejected whether red (0 of 20) or the olive-tan base color of herring gull eggs (0 of 20). Next, we simultaneously presented a red, 3 D-printed gull egg and a small, red block. These nests exhibited frequent nest sanitation (small, red block removed at 40 of 48 nests), but egg rejection remained uncommon (5 of those 40) and not significantly different from control nests (5 of 49) which received the parasitic egg but not the priming object. Thus, performance of nest sanitation did not shape individuals’ responses to parasitism. Interestingly, parents were more likely to reject the parasitic egg when they were present as we approached the nest to add the experimental objects. Depending on the underlying mechanism, this could also be a case of experience creating variation in responses to parasitism.