Conserve Wildlife Blog

Posts Tagged ‘shoals’

Scarcity and Abundant – Shorebirds Near the Finish Line on the Delaware Bay

Wednesday, May 31st, 2017

By Dr. Larry Niles, LJ Niles Associates, LLC

Our latest catch of red knots and ruddy turnstones two days ago (May 27) suggests 2017 to be one of the most challenging years for our 20 years of work on Delaware Bay. It challenged the birds for certain.

For example, as of two days ago (May 27), the average weights of red knots remain mired in the mid 160’s when it should be in the 180-gram range. This seems a minor difference but to red knots it means a flight through the cold and often inhospitable north country of Canada and dropping out of the sky never to be seen again or landing and never attempting to breed. We really don’t know for sure what happens to ill-prepared shorebirds, except they are less likely to be seen ever again. In 2017 most birds will be ill prepared.

This histogram of the red knot catch made on May 27, 2017 shows the range of weights and the number of birds in each weight category. The average of 168 is far lower than the 180-gram threshold necessary for a successful flight to the Arctic.

This season also challenged our understanding because it lies so far outside the norm. To be sure the cause of this dramatic scarcity of horseshoe crab eggs springs from the cold weather this May. We started with a good crab spawn in the first week of May, when water temperatures rose somewhat faster than normal, a consequence no doubt of one of the warmest winters on record. Then cold and wet weather dogged the Bayshore until the day of this post. Today, temperatures will rise no higher than 70 degrees Fahrenheit and the prospects for warmer weather are unlikely for the rest of the week. The cold air temperatures forced down the bay temperature in the second week and although it has gradually improved it is still low by normal standards.

The Delaware Bay water temperature as measured by the bour off Lewis Delaware. The Bay warmed early until the second week of May when cold weather chilled the Bay.

All of this led to generally diminished horseshoe crab eggs especially on the beaches, the mainstay of most stopovers of the past. This year crabs mostly spawned in the creek mouth and outer creeks shoals, mostly spurred to spawn by tidal waters warmed by the movement in and out of the small estuarine systems. Water moves in with the tide and out again to the creek mouths twice a day warming the shoals.

The Importance of Tidal Creek Mouths and Shoals

A shoal at the mouth of BayCove creek and the crab spawn on Reed creek.

The creeks also accumulate sand leaving them loose and perfect for crab spawning. Even in good years, egg densities in the creeks top all beaches, no matter where they occur. The sands of the shoals loosen by the waves of the Bay and release more buried eggs than those buried in the beaches, making more available to the birds. The creek mouths on the Cape May peninsula from Green Creek to Moores Creek saved the birds from an even worse fate this year and the best were those that benefited from the restoration of Reeds, Cooks, Kimbles and Pierce Point Beaches. As it happens a major portion of the Bay’s knots stayed in this area throughout the entire month but flying widely in search of pockets of good spawning in other places. This year Norbury’s in the south and Goshen in the north stood out, and extended the core stopover area.

Horseshoe crabs breeding at Reeds South shoal.

Spawning Starts Again

Then in the last three days all changed. The new moon tides, reaching around 8 feet for four nights in a row, spurred spawning despite the relatively cool water. Today, May 29, the crabs shifted into high gear.

It takes a lot of crabs breeding to bring eggs to the surface on the beaches, there must be enough breeding for one crab to dig up the eggs of another. For the first time, this occurred in the last few night and we finally saw green eggs on the sand. A welcoming sight for the birds, who could barely stand still and gobble up the fat producing eggs. With most of these Arctic nesting shorebirds remaining in the Bay and apparently feeding right into the night, they still might reach the fat gain finish line and only lose a few days reaching the Arctic. The next few days will tell.

Horseshoe crab eggs litter the surface of North Reeds Beach.

A close up of the same beach. The immense number of eggs on the surface of the beach is in part due to the number of crabs spawning and the wave action of the Bay.

Shorebirds and Gulls feeding near dark in the intertidal flats and creek shoals of Reeds, Cooks, Kimbles and Pierce Point Beaches.

Can they though? A good question and just one of the many that have challenged our team’s knowledge of this well-known stopover. With literally centuries of combined experience (many of our team, including this author, are long in the tooth as the Brits would say) we still kept guessing what would happen next throughout the season. Would the birds suffer mighty declines as a consequence of the generally diminished spawn of horseshoe crabs?  Or will they build weight in time to get to the Arctic in good condition? This is usually the central question.

Why Are There Fewer Knots?

An equally intriguing question, however, is why have red knot numbers in Delaware Bay declined this year? We estimate shorebird numbers in two ways, direct observation by aerial and ground counts and a statistically derived estimate based on the resighting of birds flagged with unique IDs. Our aerial and ground counts tell us how one year compares to another because we have been doing shorebirds counts by airplane, boat and on the ground since 1981. This year the number fell dramatically.

Guy Morrison, Christian Friis and Joe Smith survey shorebirds by airplane near Egg Island Point.

At the start of our project on Delaware Bay in 1986, we had nearly 100,000 knots on the Bay and nearly 1.5 million shorebirds of all species. The number of knots declined to around 15,000 in the mid-2000’s, then jumped to over 24,000 over the last four years. This year our best estimate is around 17,969, a 5,000-bird decline. Why did this happen?

One must always consider the possibility of a large group of birds dying. But this is not likely.

More likely, some portion of the knot flock came to the Bay, and on finding too few eggs or too much competition, moved on to better places. The ones moving on could have been the short distance migrants, those who spent their winter in Southeast US or the Caribbean. These birds travel a shorter distance and so have a longer time and lower energy needs than those that winter in South America. These long-distance migrants would have a very difficult time gaining weight on anything other than crab eggs (I explained this in a previous post). There are two reasons to believe the short distance birds moved on from the Bay this year.

The first is the discovery of birds banded in Delaware Bay this year and reported elsewhere. I reported on Mark Faherty’s Ebird report of a knot he saw in Cape Cod, that was flagged by the Delaware Bay Shorebird Team on May 16, 2017. The second line of evidence is the 1,300 birds seen by our team feeding on a 10-mile stretch of the Atlantic Coast marsh from Cape May to Stone Harbor. Play this out over the entire coast of New Jersey and other places with sand and marsh, like Cape Cod, and one could easily imagine 5,000 knots using other places.

About 200 knots feeding and roosting on the inter-tidal shoal of Hereford Inlet on the Atlantic coast.

But this reduction in population also suggests an explanation for the sudden rise in numbers found in 2013. Did the restoration of habitat on the Delaware Bay coast bring back knots that once used the Bay but stopped because of the lack of available eggs? In other words, did the increase in numbers seen in the Bay reflect a return of birds and not a population increase? This year’s loss may simply be a result of those returning birds, leaving once again.

Let’s hope so. At any rate, eggs are now available to all birds in the Bay and we should start seeing them leave for the Arctic. Let’s hope for that too.

Dr. Larry Niles has led efforts to protect red knots and horseshoe crabs for over 30 years.

LEARN MORE

 

Tags: , , , , , , , , , , , , , , , , , ,
Posted in Birds, Education, Events, Get Involved, Habitat Restoration, horseshoe crabs, Outdoor Recreation, Shorebirds, Volunteer Programs, Wildlife News, Wildlife Protection | Comments Off on Scarcity and Abundant – Shorebirds Near the Finish Line on the Delaware Bay

In Dangerous Territory on the Delaware Bay

Wednesday, May 24th, 2017

By Dr. Larry Niles, LJ Niles Associates, LLC

Four days ago, the shorebirds of Delaware Bay could look forward to a bright future. But in the last week their chances for survival and good production have diminished. In fact, they are as dismal as the cold drizzle pockmarking the murky water in front of our house on Reeds Beach.

The following two graphs tell the story. We captured red knots on May 12 and 16 that showed a normal, although not spectacular progression. Then we made a catch of knots on the 19th and again today on the 23rd, and in total they gained only 2 grams of fat per day. With an average weight of 144 grams at this late date and only 7 days to go before they must leave for the Arctic, their future looks bleak. If current conditions hold, the knots will suffer their worst year in 14 years. Turnstones fared no better gaining less than a gram per day on average.

The graph plots all the average weights of all the catches of red knot our team has made since 1997. The average weight of our catch on May 23 suggests trouble is brewing for these birds.

 

The graph plots all the average weights of all the catches of ruddy turnstones our team has made since 1997. The average weight of our catch on May 22 suggest trouble for both species.

So why this dismal report? Several factors are at work that were covered in my last post. The water temperature of the bay has only just exceeded the threshold for horseshoe crabs to start breeding in earnest. But the nights are cold and the water temperature remains cold. Last night was the first good crab spawn since the birds arrived and it was lackluster. Although there is some spawning in the creek mouth shoals and the lower beaches near Norburys Landing and Villas, our most productive beaches remain nearly devoid of crabs and crab eggs.

The second problem is still a mystery. At this stage only about half of the red knots have found their way into the bay. Weather patterns in the southern US could have been blocking migration for the last 5 days because adverse winds, poor visibility and rain impedes birds progress and could stop northward movement. The conditions have finally let up, so it possible a new cohort of birds might arrive any day. If so they will face a true food fight with many birds already here and desperate for eggs.

Laughing Gulls, Red Knots, Ruddy Turnstones, Sanderlings and Semipalmated Sandpipers struggle to find horseshoe crab eggs on the shoals of South Reeds Creek. Eggs are scarce because cool water temperatures prevent crab spawning.

However, it may not be the adverse weather but choice that is keeping the population down. Today we learned of a red knot banded on May 16 this year by our counterparts in Delaware that was resighted in Cape Cod by Mark Faherty, the senior scientist for Massachusetts Audubon in Cape Cod. In other words, red knots and other shorebirds are coming to the bay finding too little food or too much competition for the food now available and choose to move on. This is very possible for the short distance migrants because they arrive earlier and have less weight to gain before leaving for the Arctic. Knots wintering in Tierra del Fuego, arrive later and in much worse condition, often times lose muscle mass to get here. They cannot recover that loss and still gain an extra 80 grams on their normal diet of mussels and clams.

We tried to test this second possibility today (May 23) after our red knot catch this morning. Humphrey Sitters, Amanda Dey and I surveyed the intertidal mud flats of the Atlantic Coast from Cape May to Stone Harbor looking closely at the mussel beds. We know that every year red knots, especially short distance birds, use mussels and to some extent clams, rather than come to the bay and feast on horseshoe crab eggs – simply because they can. We found 1700 knots, so it possible even more are spread out further up and down the coast.

In the end, it may turn out to be both explanations. The short distance knots are using the Atlantic Coast and the long-distance birds have yet to arrive. One should remember that the knot is federally listed in both Canada and the US primarily because of the dramatic declines in the long-distance winters. There is still a small window for a successful outcome. The next few days will tell the full story.

Dr. Larry Niles has led efforts to protect red knots and horseshoe crabs for over 30 years.

LEARN MORE

 

Tags: , , , , , , , , , , , , , , , , , , ,
Posted in Birds, Education, Get Involved, Habitat Restoration, Outdoor Recreation, Shorebirds, Volunteer Programs, Wildlife News, Wildlife Protection | Comments Off on In Dangerous Territory on the Delaware Bay

The Importance of water temperatures, windstorms and shoals on the Delaware Bay

Friday, May 19th, 2017

By Dr. Larry Niles, LJ Niles Associates LLC

As we begin our field work on Delaware Bay shorebirds, our 21st season, oddly enough we are once again faced with extraordinary circumstances. As usual, the birds, after various flight of up to 6 days of nonstop flying, arrive in emaciated conditions. For example, in one catch this week we caught several red knots at around 86 grams far lower than normal weight of 130 grams. Putting that into perspective, a woman of 145 pounds would tip the scale at 93 pounds while a male of 175 pounds at 113 pounds! In other words, these birds are desperate to feed on the only prey on which they can build weight fast, the eggs of Delaware Bay horseshoe crabs.

But the various impacts of climate change and destructive forces of sea level rise, storm surge and out of normal weather patterns can wreak havoc on the timing of the horseshoe crab spawn. It messes with the heating and cooling of the bay and when combined with the normal variation one expects in an estuarine system, it creates almost unpredictable consequences.

Adding more uncertainty to this mix is the ongoing harvest of crabs for bait and the irresponsible bleeding by international medical companies. Both kill hundreds of thousands of crabs every year while doing nothing to create new crabs. Their combined impact has put the brakes on any recovery of the population after they both nearly mortally wounded the Bay population in the 1990’s and early 2000’s. Higher numbers of crabs would overcome a lot of early season uncertainty; lower numbers exacerbate them.

And thus, the story of this early part of the shorebird stopover. It starts with the odd weather this April and May. Can everyone remember how warm the weather of this winter? The map below is a reminder that it was one of the warmest on record. The figure below that shows how the Bay’s water warmed early reaching the threshold temperature for horseshoe crab breeding by early May. We trapped sanderling in the first week and were surprised to see a truly great crab spawn on May 4. Thank God for that.

The bays water temperature as measured at the Lewis DE buoy, increased earlier than normal until the first week of May. By that time it reached the threshold for horseshoe crab spawning. But by the second week it plunged as a consequence of the cooler than normal weather.

By the second week of May and yesterday (May 16) temperatures plunged in horseshoe crab world. We generally consider water temperature of near 59 degrees necessary for crabs to spawn in great numbers. We reached 62 degrees on May 4, then it went down to 58 degrees, lingering there for five crucial days.

At the same time, we suffered brutal westerly winds. Wind from this direction gins up waves on Delaware Bay that crash against many of the important crab spawning beaches. Crabs don’t spawn in waves.

Westerly winds turn the Delaware Bay into a tumult of breaking waves because of its relative shallow depth. Horseshoe crabs won’t breed in breaking waves

And just as the first flush of shorebirds came to the Bay, over 5,000 red knots on the New Jersey side, all the spawning shut down. All tried desperately to find enough horseshoe crab eggs to regain lost weight and begin the process of doubling their body weight.

Fortunately, breaking waves and cold water will prevent crabs from spawning on the beaches but not in the intertidal creeks. One of the key features of the New Jersey bayshore are its abundant tidal creeks. Most drain only tidal watersheds, draining and filling marshes twice every day. Naturally they build sand shoals because sand moves around the Bay generally in a south to north direction along the Cape May peninsula. When sand encounters the currents of the creeks, it settles forming shoals.

A small creek just north of Dennis Creek on Delaware Bay. The tidal creek mostly drain tidal marsh, the daily ebb and flow warming the waters making crab spawning possible when the bay waters are too cold

These shoals support most shorebirds during these early days. This is so because the intertidal flow of water into the marsh and out again warms the water that flows over the shoals. The shoals themselves are practically paradise for breeding crabs because of the loosely consolidated and large grain sand. They breed with abandon laying eggs in the shifting sands that brings many of the eggs to the surface where shorebirds can prey upon them. And they do.

This diagram by Joe Smith shows how the creeks of Delaware Bay create superior spawning and shorebird foraging habitat. Sand movement on the Cape May section of the bay moves northward because of tidal currents. This moves sand from south to north. When the American Littoral Society and CWF placed sand on Pierces, Kimbles and Cooks beaches, some part moved northward to the adjacent beaches. Ultimately it ended up on south Reeds making it a great spawning site. But on the way the sand falls out of the current and settles on the creek shoals. These shoals are large grain sand, loosely consolidated, making them perfect for crab spawning. At the same time the shoals shift exposing eggs to the sea, thus making them available to the birds. This is why the shoals are among the most important habitat on the bay.

This is what happens in the early days of this season. It was nip and tuck for most of the scientists, not knowing if the shoal resources would hold up to an ever-growing number of shorebirds arriving in desperate condition.

But today (May 19) we enjoyed warmth with the promise of the season back on track.

In the last 5 days, we were able capture enough knots, turnstones and sanderlings to track conditions and add new flags to the population for a later determination of population size. Despite adversity, so far so good. The data for each species is below.

Dr. Larry Niles has led efforts to protect red knots and horseshoe crabs for over 30 years.

LEARN MORE

 

Tags: , , , , , , , , , , , , , , , , ,
Posted in Birds, Education, Get Involved, Habitat Restoration, Outdoor Recreation, Shorebirds, Volunteer Programs, Wildlife News, Wildlife Protection | Comments Off on The Importance of water temperatures, windstorms and shoals on the Delaware Bay